Cementing Best Practice Jorge Sierra

Table of Contents Introduction

Engineering and Planning Job Procedures Plug Cementing

Squeeze Cementing

Contractor Requirements

Cementing Best Practices

Table of Contents

Table of Contents Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tips for Using This Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reminders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Time-Saving Navigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1 2 2 2

Introduction

Engineering and Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Engineering and Planning

Mud Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Drilling Fluid Conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pipe Movement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pipe Centralization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Spacers and Flushes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Operational Priorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Job Volume Excess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Flow Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Downhole Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Centralizers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Wiper Plugs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Shoe Joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Considerations for Liner Jobs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Cement Design Priorities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Priority No. 1—Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Priority No. 2—Pump Time (Thickening Time) . . . . . . . . . . . . . . . . . . . . . . . . 9 Priority No. 3—Mixability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Priority No. 4—Rheology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Priority No. 5—Fluid Loss Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Priority No. 6—Compressive Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Priority No. 7—Free Fluid and Settling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Cement Slurry Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Evaluation of Cementing Job Proposal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Data Review and Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Review of Cement Job Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Interpretation of “Pilot” Test Results and Laboratory Reports . . . . . . . . . . . 12

Job Procedures Plug Cementing Squeeze Cementing

Job Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14


14 15 15 15 16 17 17 17 18 19 21


Monitoring and Recording . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prejob Preparations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Design Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Equipment / Materials Verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wellbore Circulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pumping Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pressure Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mixing and Pumping Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shallow Water Flow Cementing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Wait on Cement (WOC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

ii

Table of Contents Plug Cementing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 22 22 22 23 24 25 25 26 26 27

Table of Contents Introduction

Engineering and Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Plug Length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Volumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Slurry Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Spacers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Slurry Displacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical Tools for Supporting Cement Plugs . . . . . . . . . . . . . . . . . . . . . Waiting On Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Job Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Squeeze Cementing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 29 29 30 30 32 32 34 34 35


Engineering and Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slurry Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Washes and Spacers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prejob Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Job Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bradenhead Cement Squeeze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bull Head Cement Squeeze . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Job Procedures

Contractor Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 37 38 39 40 40 41 42 43 45 45 48 50 53 56

Plug Cementing Squeeze Cementing

Cement Job Planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Job Mobilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Job Implementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cementing Recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reporting Responsibilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Designs for “Pilot Testing” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Laboratory Testing Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . On-Location Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Bulk Blending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Load-Out for Land Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Loadout for Offshore Operations . . . . . . . . . . . . . . . . . . . . . . . . . . Prejob Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Job Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .



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Introduction

Introduction

Promoting Best Practices is an ongoing effort throughout Unocal drilling operations. Given the wide variety of cementing operations going on throughout the Unocal drilling world, it is hoped that a collective sharing of Best Practices will help all areas obtain competent and economical cement jobs. Visit the Casing, Liner Running and Cementing Network LiveLink site to view the network’s charter, goals, and members’ names and contact information. Access the Toolbox section for engineering tools, calculation worksheets, and detailed job examples.

Job Procedures

Visit the Engineering Network LiveLink site now by clicking on this text link.


This document is a guide for planning and executing cementing operations for worldwide operations. It is realized that, in some well situations, the preferred Best Practice may not achieve the best results. Every cement job should be designed for the wellbore characteristics and the cementing objectives desired.

Introduction

The purpose of this document is to teach and promote a “Best Practices” philosophy throughout the Unocal Global Drilling Community. Unocal spends millions of dollars each year on cementing operations. Poor planning and operational execution not only can lead to cement failure but can result in the loss of hydrocarbon recovery from the wellbore.

Table of Contents

Purpose

Plug Cementing Squeeze Cementing Contractor Requirements


11

Introduction

Tips for Using This Document This document is divided into seven main categories: Table of Contents Introduction Engineering and Planning

• Table of Contents • Introduction • Engineering and Planning • Job Procedures • Plug Cementing • Squeeze Cementing • Contractor Requirements “Engineering and Planning” and “Job Procedures” cover all the basics involved in planning and executing a primary cementing job. “Plug Cementing” and “Squeeze Cementing,” as the names suggest, contain information specific to these techniques.“Contractor Requirements” provides information about contractors’ responsibilities in ensuring the job is carried out as planned.

Reminders Job Procedures

In many of the sections, you will find white text in the blue column at the left of the page, topped with an orange bar. These comments are emphasized to indicate their importance in the success of the job.

Time-Saving Navigation

Table of Contents

The Table of Contents allows you to view the subtopics discussed within each major section. To navigate to a particular topic, just click on the entry.

The blue and orange tabs at the right of each page offer quick navigation to any major section of the document, including the Table of Contents, from any page in the document.


Where Am I?

The title of the section you are viewing is always located in the upper right hand corner of the page, in the same color as its corresponding tab.


Squeeze Cementing

Colored Tabs

Plug Cementing

This document is easily navigated from either the Table of Contents or the color tabs located at the right side of every page.

22


Engineering and Planning The first step in Engineering and Planning for cementing is to identify the purpose of the cementing operation. Once the purpose is clearly defined, the wellbore conditions and casing design must be evaluated to determine the cement placement, hydrostatic constraints, and volumes. The cementing contractor must be involved in this stage, as detailed in the Contractor Requirements section of this document.


Application of the following guidelines for mud removal, cement and spacer design, in conjunction with a cementing software program, will enhance the displacement process and improve the probability of successful primary cementing. Cementing software can be used to help determine the optimum displacement parameters and safe operating equivalent circulating densities (ECD).

Introduction

Primary cement job failures are predominately due to a breakdown in the “displacement process,” which leads to channeling of the cement through the drilling fluid.

Table of Contents

The cementing contractor’s role begins with the Engineering and Planning stage, and his work will parallel that of the Drilling Engineer. For details, see the Contractor Requirements section.

Mud removal is best achieved through proper drilling fluid conditioning, pipe rotation or reciprocation, pipe centralization, and the use of properly designed spacers and flushes.

Job Procedures

Mud Removal

Drilling Fluid Conditioning

Pipe Movement


33


Pipe rotation or reciprocation before and during cementing helps break up gelled, stationary pockets of drilling fluid and loosens cuttings trapped in the gelled drilling fluid. Pipe movement allows high displacement efficiency at lower pump rates because it helps to keep the drilling fluid flowing. If the pipe is poorly centralized, pipe movement can compensate by changing the flow path through the casing and allowing the slurry to circulate completely around the casing. The industry does not specify a minimum requirement for pipe movement, however it acknowledges that even a small amount of movement will enhance the displacement process.

Squeeze Cementing

The condition of the drilling fluid is one of the most important variables in achieving good displacement during a cement job. Regaining and maintaining good mobility is the key. An easily displaced drilling fluid will have low gel strengths and low fluid loss. Pockets of gelled fluid, which commonly exist following the drilling of a wellbore, make displacement difficult and must be broken apart.

Plug Cementing

The condition of the drilling fluid is one of the most important variables in achieving good displacement during a cement job.


Table of Contents

In some instances, pipe movement is not recommended. For example, when equivalent circulating density and fracture pressure are very similar, or shallow gas or water influx is critical, moving the pipe can induce surge and swab pressures that could promote pipe sticking and surface casing-head pressure. The use of mechanical devices, such as some models of liner hangers, may also prevent casing movement. All of these factors must be considered when designing the displacement program.

Pipe Centralization Drilling fluid displacement is best achieved when annular tolerances are approximately 1.5 to 2 in. Centralization of very small annuli is very difficult, and pipe movement and displacement rates may be severely restricted. Very large annuli may require extreme displacement rates to generate enough flow energy to remove the drilling fluid and cuttings.

To improve centralization of the casing, adhere to the following guidelines:

•

Run a centralizer calculation program and reference well deviation surveys to determine the number of centralizers necessary to achieve the recommended standoff and their ideal placement.

•

For liner jobs, include centralizers in the lap area to aid in the displacement of cement all around the casing perimeter either in the primary cement job or subsequent squeeze job.

•

For highly deviated wells in which cuttings beds are likely, place the centralizer on the lower joints to hold the landing shoe off of the bottom of the wellbore. This design will allow cuttings to pass underneath and help eliminate any snowplowing effect.

44


Use cementing simulator runs to determine the standoff necessary to achieve complete flow around the casing.

Squeeze Cementing


•

Plug Cementing

Good pipe standoff ensures uniform flow around the casing and helps equalize the force that the flowing spacer and cement exerts around the casing, increasing drilling fluid removal. In a deviated wellbore, standoff is even more critical to prevent a solids bed from accumulating on the low side of the annulus. The industry benchmark for standoff is approximately 70%, however the preferred standoff for a given well should be developed from computer modeling and will vary with well conditions.

Job Procedures

The industry benchmark for standoff is approximately 70%.


Centralizing the casing by placing mechanical centralizers across the intervals to be isolated is critical for effectively displacing the drilling fluid and placing cement all around the casing. In poorly centralized casing, cement will bypass the drilling fluid by following the path of least resistance; as a result, the cement travels down the wide side of the annulus, leaving drilling fluid in the narrow side.

Introduction

Drilling fluid displacement is best achieved when annular tolerances are approximately 1.5 to 2 in.

Engineering and Planning Spacers and Flushes

Parameters governing a spacer’s effectiveness include flow rate, contact time, and fluid properties. To achieve maximum drilling fluid displacement, adhere to the following guidelines:


Density

Set spacer density 0.5 to 1.0 ppg above the drilling fluid weight and at least 0.5 ppg less than the cement slurry density. In situations that require the difference between cement weight and drilling fluid weight to be less than 1.0 ppg, design the spacer density to be mid-way between the two densities.

Job Procedures

Provide a contact time and volume of spacer that will provide optimum amount of drilling fluid removal.

Introduction

Spacers and flushes are effective displacement aids because they separate unlike fluids such as cement and drilling fluid, and enhance the removal of gelled drilling fluid, allowing a better cement bond. Spacers can be designed to serve various needs. For example, weighted spacers can help with well control, and reactive spacers can provide increased drilling fluid-removal benefits. Compatibility of the drilling fluid/spacer as well as the compatibility of the spacer/cement slurry is of prime importance. Application of the compatibility procedures as outlined in the API SPEC RP10B, 22nd Edition, December 1997 is highly recommended.

Table of Contents

Compatibility of the drilling fluid/spacer as well as the compatibility of the spacer/cement slurry is of prime importance.

Contact Time

Provide a contact time and volume of spacer that will provide optimum amount of drilling fluid removal. Typically 8 to 10 minutes contact time or 1,000 feet of annular space are adequate. Rheology

Spacer must be fully compatible with drilling fluid and cement. Contact with drilling fluid must not result in flocculation, settling, or excessive rheology. Contact with cement must not decrease pump time. Stability

Spacer must remain stable with no excessive settling or separation. For all liner and tieback jobs, the spacer must be tested by “hot-rolling” at circulating temperature. Wettability

When an oil-based or synthetic-based drilling fluid is in the hole, the spacer must also be capable of converting the pipe and hole to a “water wet” condition.


55


For all liner and tieback jobs, the spacer must be tested by “hot-rolling” at circulating temperature.

Compatibility

Squeeze Cementing

Spacer must be fully compatible with drilling fluid and cement.

Plug Cementing

Design spacer rheology that will provide turbulent flow where hole geometry allows. Turbulent flow of spacer is required on all liner jobs.


Operational Priorities

Job Volume Excess

Introduction

Unless caliper data is available or excess volume is otherwise specified, use the recommended percentages in the following table to calculate cement slurry volume requirements across an open hole. Calculations of Volume Excess Depth (ft)

% Excess with Oil-Based Mud

0 to 4,000

100

50

4,000 to 8,000

75

25

8,000 to 10,000

50

15

10,000 to 18,000

35

15

Greater than 18,000

25

15


% Excess with Water-Based Mud


•

Design spacer to be in turbulent flow as it rounds the shoe and passes the sections to be isolated.

•

Mix and pump cement as fast as density control, pumping equipment, material supply, and wellbore conditions allow.

66


To maximize displacement, adhere to the following guidelines:

Squeeze Cementing

Cement flow is characterized by three flow rate regimes: turbulent flow, laminar flow, and plug flow. High-energy displacement rates are most effective in ensuring good displacement. Turbulent flow conditions are desirable, but are not required. When turbulent flow is not a viable option for a formation, use the highest pump rate that is feasible for the wellbore conditions. The best results are obtained when the spacer and/or cement is pumped at maximum energy, the spacer or flush is appropriately designed to remove the drilling fluid, and a good competent cement is used.

Plug Cementing

Flow Rate

Job Procedures

For cementing operations on offshore wells that use subsea housing, try to plan the well’s programs so that cement returns are not transported through the subsea housing. In such cases, the surface casing is usually cemented only to 500 ft above the conductor shoe. The presence of cement in the recesses of subsea housing can cause great difficulty in setting subsequent hangers or packoffs.

High-energy displacement rates are most effective in ensuring good displacement.

Table of Contents

Determining how the cement will be placed in the hole is as important as the design of the cement itself. This section discusses the operational factors that should be determined in planning a successful job.

Engineering and Planning •

Displace at high rates (8 bbl/min and higher) without exceeding the formation breakdown pressure.

Choose all downhole equipment for fit, operation, and proper installation.

Table of Contents

Downhole Equipment Choose all downhole equipment (float collars, shoes, guide shoes, centralizers, liner hanger systems, and wiper plugs) for fit, operation, and proper installation.

Determine which type of centralizer is best for a particular application by evaluating the centralizer’s suitability for the specific application, its ability to mitigate exposure for problems in the running of casing due to its design, and to provide centralization cost-effectively.

•

Select appropriate centralizer types, stop rings, and casing connections to minimize the risk of centralizers sliding and stacking-out. Bowspring-type centralizers provide an acceptable balance between cost and standoff for most standard cementing operations.

•

For highly deviated wellbores, evaluate the use of double bowspring or solid body centralizers to centralize the casing and to maintain or improve running force requirements. Tight clearances and holes drilled with bicenter bits may require the use of bow spring centralizer subs.

Wiper Plugs Top and bottom cement plugs are recommended for every primary cementing job, when possible. The bottom plug minimizes contamination of the cement as it is pumped. The top plug prevents contamination of the cement slurry by the displacement fluid and provides a positive indication that the cement has been displaced. Use composite body plugs that are easy to drill out with PDC bits.

Squeeze Cementing

Top and bottom cement plugs are recommended for every primary cementing job, when possible.

Plug Cementing

If centralizers are at risk of becoming smashed when running through existing liner tops or downhole components such as wellhead housings, choose a durable centralizer such as solid integral centralizer subs that can withstand these conditions.

Job Procedures

•


Bowspring-type centralizers provide an acceptable balance between cost and standoff for most standard cementing operations.

•

Introduction

Centralizers



77

Engineering and Planning Shoe Joint A shoe joint is recommended for all primary casing/liner jobs. The length of the shoe joint will vary. The absolute minimum length is one joint of pipe. If a bottom plug is not required, a minimum of two joints are required. Recommended Shoe Joint Lengths No. of Pipe Joints

> 18 5/8

Tag in

> 13 3/8

2 joints

> 9 5/8

3 joints

> 7 5/8

6 joints

Introduction

Casing Size (in.)

Table of Contents

A shoe joint is recommended for all primary casing/liner jobs.

Considerations for Liner Jobs

•

On all liner float shoes, verify that holes exist on the side of the float shoe, allowing circulation and preventing a hydraulic lockup in the event that the liner hanger fails and the liner lands on the bottom of the hole.

•

Use or design autofill float equipment that can be activated without setting the liner hanger, should a well control condition arise while going in hole.

•

Design liner hanger systems with a tieback sleeve length that allows the bottom of the tieback stem to be partially stung into the tieback sleeve when cementing the tieback casing. This will enhance the process of slacking off the tieback casing after the cement job has been completed. Buckling of the lower portion of the tieback casing after cementing can make it difficult to stab the tieback stem into place.

•

For ultradeep liners on directional wells with relatively high torque and drag, use a pressure-indicating method to verify that a liner is released from the running tool. The actual liner weight may be small in comparison to the drag forces, making it difficult to determine if the liner is actually released.

Plug Cementing

Ensure that the liner hanger set pressures are well above the circulation pressures that could be required while running the liner to prevent premature setting of the liner hanger.

Job Procedures Squeeze Cementing Contractor Requirements


•


A liner hanger must be designed for the combined loading of the liner weight to be hung off and the mud weight differential on the slip area to avoid exceeding the elastic limit on the ID of the casing in which the slips are engaged.

88


Cement Design Priorities

Cement slurry density must be within range to maintain well control. If hole conditions allow, cement slurry density should be a minimum of 1.0 ppg greater than drilling fluid weight and 0.5 ppg greater than the spacer weight.

Priority No. 2—Pump Time (Thickening Time) The pump time should include the estimated job time plus a safety factor. The safety factor must be based on wellbore parameters, operational objectives and limitations, and the accuracy of expected temperatures to which the cement slurry will be exposed during the cementing process as compared to the laboratory testing conditions. Keep the following in mind when specifying and evaluating thickening time: The first sack or leading edge of the cement is exposed to different temperature conditions and will require a different placement time than the last sack of cement.

•

Consider the total placement time for the lead slurry (mixing and pumping of lead + mixing and pumping of tail + displacement).

For surface and intermediate strings where cement placement is relatively easy and minimal WOC is the objective, allow a 1-hr safety factor.

•

For HPHT liner cementing where cement placement is critical, allow a minimum safety factor of 2 hours or 50% of the calculated job time, whichever is greater.

Priority No. 3—Mixability

Priority No. 4—Rheology The cement slurry must be pumpable, and the cement slurry rheological properties must allow effective placement, with a PV and YP as low as possible, but higher than that of spacer or drilling fluid.


99


Cement must be easy to mix at the cementing unit in order to achieve density control at a mixing rate that allows cement slurry placement within the available pump time.

Squeeze Cementing

•

Plug Cementing

Recommended Safety Factors

Job Procedures

•


The pump time should include the estimated job time plus a safety factor.

Priority No. 1—Density

Introduction

Cement slurry density must be within range to maintain well control.

Table of Contents

A slurry design must address a broad assortment of well conditions and wellcontrol parameters. To maximize the performance of a slurry, adhere to these seven guidelines, listed in the order of importance:

Engineering and Planning Priority No. 5—Fluid Loss Control Design fluid loss control to specification. Excessive loss of fluid from the cement slurry has negative impact on other slurry properties.

Priority No. 6—Compressive Strength

Priority No. 7—Free Fluid and Settling Cement slurry must remain stable (free water within specification and no significant settling or separation) while fluid. Design and test for given hole conditions, i.e. for directional well test at appropriate angle.


Cement Slurry Specifications Slurry Properties

Conductor and Surface Casings

Intermediate Casings and Drilling Liners

Production Deep Casings and Production Liners Liners and for Gas Control

Job Procedures

+ 1 ppg > drilling fluid density

Density

< Equivalent Circulating Density (ECD) to fracture formation Thickening Time

Job time plus at least one hour for safety factor For production casings or for gas control, the TT chart should display a right angle set (transition from 40 to 100 Bc in less than 15 minutes) < 0.5 %

0%

0%

Fluid Loss

NA

< 250

< 100

< 50

Rheol. (PV)

< 150

< 150

< 100

< 100

Rheol. (YP)

< 50

< 40

< 25

< 20

Comp. Strength WOC (hr to 500 psi)

< 12

<8

<8

<8

24-hr Comp. Strength (psi)

1,000

2,000

2,000

2,000


< 1.0%

Squeeze Cementing

Free Water

Plug Cementing


Introduction

The goal is to achieve rapid compressive strength development after placement. The minimum requirement is a WOC time (time to achieve 500 psi) of less than 12 hours and 24-hr strength greater than 1,000 psi.

Table of Contents

The minimum requirement is a WOC time of less than 12 hours.

1010


Evaluation of Cementing Job Proposal

Data Review and Verification

• • •

hole and pipe sizes hole and pipe weights annular, hole, and pipe volumes

Caution—Do not proceed unless these data are confirmed. 2. Review the BHST and BHCT; if any deviation or uncertainty exists, investigate further. 3. Review the Cement Slurry Formulation to verify that it matches the slurries tested in the laboratory.

•

a. Check inputted values.

Plug Cementing

Mix Water—Use this value to calculate the volume of water needed for the job. • Density—Mix the cement slurry to this value • Yield—Use this value to calculate the number of “sacks” required for the job. 5. Review the Cement Job Simulation as follows:

Job Procedures

4. Read the Density, Yield and Mix Water requirement.


Do not proceed until well data have been confirmed.

Introduction

1. Check the accuracy of Subject, Field, Well and Rig entries. Well data include the following:

Table of Contents

Evaluation and quality control of the service company’s job plan, simulator runs, slurry design, and laboratory test results is necessary to ensure that the cement slurry design fits the planned operation.

b. Review the following data output against the job plan. Squeeze Cementing

• pumping rates • ECDs • placement pressure at the pump • spacer contact time c. Change planned pumping rates as necessary.


6. Review the centralization program, taking note of • •


centralizer placement and type minimum standoff across zones of interest

1111

Engineering and Planning Review of Cement Job Simulation Although gas flow may not be apparent at the surface, it may occur between zones, damaging the cement job and eventually leading to casing pressure at the surface. A cementing simulator program can be used to determine the gas flow potential for any primary cement job, and to identify possible solutions that are tailored to the severity of the possible gas flow.

Table of Contents

Run the simulator to test equivalent circulating densities (ECD), flow regime of the different fluids, required rheological properties of the fluids, maximum pumping rates, centralizer standoff requirement, displacement efficiency, anticipated pumping pressures at surface, pressure to shear or bump plugs, BHCT, etc. Using this tool will aid in job design and will help identify any potential problems with the design.

Introduction

1. Check cement slurry formulation for the following information:

Job Procedures

• Cement type • Additive types and concentrations • Water source and concentration 2. Check cement slurry “pilot” test results against specifications as listed in the following table.


Interpretation of “Pilot” Test Results and Laboratory Reports



1212


Slurry Property

Task Check test value.

Thickening Time

Check times and test temperature.

—

Table of Contents

Density

Notes Test temperature must be at BHCT.

—

Check time reported vs. times read from chart.

—

Fluid Loss

Check value and test temperature.

Test temperature must be at BHCT.

Rheology

Check PV, YP and test temperature.

PV and YP must be reported.


Attach strip chart for the thickening time test.

Introduction

Time must be within the specified range. Use 70 Bc for liner and narrow clearance jobs. Use 100 Bc for surface and intermediate jobs.

Compressive Strength

Check the time for WOC Test temperature must be (500-psi) and check 24-hr at the requested value. strength.

Free Water

Check value and test temperature.

Job Procedures

Test temperature must be at BHCT, 194F maximum.

Test temperature must be at BHCT.



1313

Job Procedures

Job Procedures

Use the following checklist to ensure that all pertinent job data is captured at the appropriate time as each job is executed. Prejob Preparations

Loading of wiper plugs or darts All volume calculations Circulation of hole till clean


• • •

Pumping Operations



Pressure testing Start and stop of each fluid pumped Pumping rates for each fluid Any pumping rate changes Any pressure changes Volume of spacer pumped Dropping any plug, dart or ball Start of cement slurry mixing Cement slurry density Mix water volume Start of displacement Surface pressures Displacement rate Landing of plugs Pressure to release liner wiper plugs Pressure to bump top plug Reverse circulation Total displacement Job time Returns Any shutdown Safety issues or incidents

Job Procedures

• • • • • • • • • • • • • • • • • • • • • •

Introduction

Monitoring and Recording

Table of Contents

This section contains basic procedures for every step of a job, from prejob preparations to pumping and displacement. Throughout each phase, it is very important to monitor and record various measurements, times, and events. This information allows the job to be tracked as it is carried out, and is invaluable in troubleshooting an unexpected problem.

1414

Job Procedures

Prejob Preparations Cement Design Verification Table of Contents

1. Verify that the following cement design and test conditions coincide with current well conditions. a. BHCT and BHST b. Thickening time and job time

Introduction

c. WOC time 2. Verify the following calculations. a. Volumes for all fluids to be pumped


b. Hole and pipe volumes c. Total displacement volume to bump plugs and correction factor as applicable d. Pressure to bump plug

3. Review the cement job simulator. 4. Review pumping rates for wash/spacer, cement slurry and displacement.

Job Procedures

e. Volume to catch liner wiper plugs, and displacement volume from that point

5. Review pumping pressures expected during the job. Plug Cementing

6. Review ECD’s at shoe and zones of interest. 7. Review the returns expected during the job.

Equipment / Materials Verification 1. Check the bulk tanks for proper contents.

3. Check operational features, ensure that the float backpressure valve is operational, and that the plugs are of the correct type and fit.


4. Check wiper plugs, the bottom plug (hollow), and the top plug (solid). 5. Witness the loading of plugs. 6. Confirm the delivery rates for water and mud. 7. Confirm what type of displacement fluid will be used and the parties responsible for routing and pumping downhole.


Squeeze Cementing

2. Confirm that all equipment (include a complete list) is on location and in good working condition.

1515

Job Procedures 8. Confirm that all density devices have been calibrated properly with fresh water.

1. Clean and stabilize the wellbore by circulating during wiper trips, before and after logging.

Table of Contents

Wellbore Circulation

2. Run the casing at a controlled rate, and circulate drilling fluid at intervals.

3. Condition the drilling fluid until drilling fluid properties are optimized (PV < 15; YP < 10).

Introduction

If there is known potential for lost circulation, run the casing at less than 1 minute per stand.

4. Move the pipe via reciprocation or rotation during conditioning.

Total conditioning time is determined by drilling fluid properties and the circulatable hole volume.


5. Circulate the wellbore until clean, using a minimum of two bottoms-up.

Job Procedures Plug Cementing Squeeze Cementing Contractor Requirements


1616

Job Procedures

Pumping Operations Pressure Testing 2. If running two bottom plugs, load the first bottom plug into the casing at this time.

Introduction

3. Connect (reconnect) the cement head. The bottom and top plugs should have already been loaded during prejob preparations.

Table of Contents

1. Pump wash or spacer to the cement head.

4. Clear the rig floor and the area surrounding the lines. 5. Pressure-test the lines as follows: a. Increase pressure to a predetermined level.


b. Hold the pressure for 5 min. c. Release the pressure.

Mixing and Pumping Cement

Job Procedures

1. Drop the bottom plug (the first one, if using two). 2. Pump the wash or spacer. Standard pumping rates are 6 to 8 bbl/min. Caution—Never open the cement head once pumping has begun. 3. Drop the second bottom plug (if running two bottom plugs).

5. Measure the mix water for the cement slurry through the displacement tanks and record the measurement.

Plug Cementing

4. Start to mix and pump the cement slurry. The standard pump rate is 5 to 8 bbl/min, depending upon the specific job.

6. Control the density within 0.2 lb/gal accuracy throughout the job.

8. Confirm slurry density by monitoring the pressure (downhole) readings of the densitometer.


9. Continue to mix and pump cement. Important—Never compromise slurry density to maintain the scheduled pump rate.


Squeeze Cementing

7. Check the cement slurry density with a pressurized balance to calibrate the densitometer.

1717

Job Procedures Caution—Near the end of the job, bulk delivery may decline. Never sacrifice density control to use up the cement. If the designed density cannot be maintained, discontinue cement slurry mixing.

11.Displace the top plug out of the cementing head with minimal down time.

Table of Contents

10.After the cement is pumped, drop the top plug.

12.Do not open the cementing head to drop the top plug. Introduction

13.Begin displacement.

Displacement Measure the displacement volume with the cementing unit displacement tanks or rig pumps. DO NOT use a “barrel counter.”


1. Maximize displacement with a pump rate of 8 to 12 bbl/min. Limit the rate only if necessary to prevent excessive ECD’s. 2. Maximize the pump rate as spacer passes zones of interest. 3. Begin decreasing the pump rate as the final displacement volume nears.

Job Procedures

4. Displace to bump the top plug at 1 to 2 bbl/min. Never overdisplace. 5. After displacement is completed and the plug has been bumped, relieve surface pressure and check for flowback. Important—Do not hold pressure inside the pipe unless operations will be compromised by flowback.



1818

Job Procedures

Shallow Water Flow Cementing

a stab-in float shoe

•

one joint with two bow-spring centralizers

•

one bow-spring centralizer per joint to the drive pipe

•

one centralizer per joint between casing and casing

To cement casing in a shallow-water-flow formation, use the following procedure.


1. Drill the conductor hole section with MWD so that sand depths are known.

Introduction

•

Table of Contents

Consider the following standard shoe track, centralizer, and wiper plug requirements for use in shallow water flow cementing:

2. Set the conductor casing above potentially flowing sands. 3. Cement the conductor pipe, using centralizers, etc. to achieve complete coverage.

5. Once the casing point is reached, pump out of hole with kill-weight mud that has low gel strength (i.e. yield point of 8 to 10 lbf/100 ft2, 10 ft, 10 in. and 30 in. gels flat and < 25 lbf/100 ft2).

Job Procedures

4. Drill with controlled drilling fluid.

6. After pulling out of hole before running casing, observe for flow. Plug Cementing

If flowing, increase the mud weight in the hole. Caution—Conducting a cement job with the well in flowing condition will most likely result in channeling, causing the job to be unsuccessful. 7. Run the casing, maintaining kill-weight mud in the hole at all times.

9. Before running in hole, displace the drillpipe and casing below with the same mud weight as that in the hole.

11.Pump the required spacer system weighted to a density between that of the mud in the hole and that of the lead cement slurry.


1919


10.Circulate in hole and fill the drillpipe with the same mud weight as that in the hole.

Squeeze Cementing

8. Design a program to eliminate seawater in the drillpipe and casing below the stinger.

Job Procedures 12.Run the designated cement system with a foamed lead slurry (1.0 ppg heavier than the drilling mud) and a non-foamed tail slurry. Table of Contents

13.Pump the cement and allow it to set to 500-psi compressive strength before drilling out. See API RP 65 for further recommendations.

Introduction Engineering and Planning Job Procedures Plug Cementing Squeeze Cementing Contractor Requirements


2020

Job Procedures

Wait on Cement (WOC)

To maximize the efficiency of WOC, adhere to the following guidelines. Know the well conditions before, during, and after the cement job.

•

Know the WOC (500-psi time) for the cement slurries pumped.

•

Never allow the well to be underbalanced during WOC.

•

Minimize WOC by using the correct cement systems that develop strength quickly after placement.

•

WOC cannot be accurately determined from thickening time alone.

•

In some areas, regulations specify minimum WOC times that may exceed, and thus supercede, these guidelines.

•

During the WOC period, perform operations that can help minimize the time and cost of WOC, such as

Plug Cementing

Pick up drillpipe for the next hole section. Run any required surveys. Clean up the mud by circulating it over shakers. Rigup equipment that may be required for the next hole section.

Job Procedures

• • • •


Know the WOC (500-psi time) for the cement slurries pumped.

•

Introduction

For a cement slurry, WOC is the time necessary for the cement to solidify and attain a compressive strength of 500 psi. This is most effiiciently determined through laboratory testing with a UCA, which plots strength development vs. time.

Table of Contents

For operations, waiting on cement (WOC) is the waiting time required after cementing in order to safely remove well control equipment or to allow the well to be underbalanced.

Squeeze Cementing Contractor Requirements


2121

Plug Cementing

Plug Cementing

Placement Use a small workstring to balance cement plugs for optimal displacement. The length of the tail pipe must be at least equal to the plug length with tubing in place. Tubing vs. Drillpipe

Plug Length Assume that the top and bottom 100 ft of cement will be contaminated with spacer.


2222


A diverter sub can improve the success of cement plug setting by directing the flow and preventing the jetting of cement downhole. Use a distribution (diverter) tool to direct flow up the annulus, such as a bull plug with four to eight small (approximately 1-in.) horizontal side holes greater than the flow area of tailpipe and at 90-degree phasing. If a wiper plug catcher is used, place it below the holes.

Squeeze Cementing

Diverter Sub

Plug Cementing

Run the tail pipe to the planned bottom of plug depth. Tubing diameters of 2 7/8 in. should be used in slim holes of 8 1/2 in. or less; 3 1/2-in. tubing should be used for larger hole sizes. Tubing is preferred over drillpipe in plug jobs because the displacement of the tubing reduces swabbing and reduces the weight of pipe to be pulled. For 17 ½-in. or larger open plugs, this is not critical and thus, they can be set using drillpipe. Coupling OD’s of the tubing should be minimized. If no tubing is available, 3 ½-in. drillpipe may be used. If a stinger is to be run through open hole or in casing after a milling operation, break circulation every 5 to 10 stands to prevent plugging of the stinger.

Job Procedures

Tubing diameters of 2 7/8 in. should be used in slim holes of 8 1/2 in. or less; 3 1/2in. tubing should be used for larger hole sizes.


Plan a plug job based on hole conditions to pull out of cement. Many methods are available and consideration should be given to prevention of contamination, risk exposure, environmental spill considerations, etc. The well depth, the mud type, and many other factors will determine which procedure should be used.

Introduction


Table of Contents

Plug cementing is the process of placing a column of cement in casing or an openhole to isolate or “plug” a section of the wellbore. This best practice provides important guidelines that must be considered when designing a plug job, as well as a detailed procedure for carrying out a plug cementing operation to ensure proper placement of the plug and adequate zonal isolation.

Plug Cementing

Cement plugs set across perforations should be set from 100 ft below the perforations to 200 feet above the perforations.

Table of Contents

If large quantities of cement are observed above the top of cement when circulating the well clean, channeling has likely occurred, and the area contaminated by the spacer will be larger than normal. This will increase the risk for failing to tag the plug and/or for obtaining a pressure test.

Recommended plug lengths are as follows:

For recovery of oil-based and synthetic-based mud, 1,500-ft abandonment plugs have been set in 12 ¼-in. open holes with thickening times exceeding 10 hr.

•

In 8 1/2-in. and smaller open holes, plugs of up to 800 ft have been set and successfully tagged to ensure a minimum volume criterion is met.

•

Plugs in extended reach wells are special cases and where plug setting depth exceeds 14,500 feet and hole angle exceeds 45°, plug length should be 600 to 750 ft, with 300 ft of contamination allowance on top of the plug.

Plug Cementing

Caution—Minimize your risk by making sure plug lengths are adequate. Drilling out excess cement is normally far less expensive than setting a second balance plug to accomplish required objectives. No cement plug of less than 20 bbl should be set through drillpipe for a 6-in. or larger open hole. Caution—If there is a risk of lost circulation, do not place more than two plugs in a row without waiting the time required for the first plug to attain 500-psi compressive strength.

Whenever possible, use a caliper log to determine the cement volumes and to help determine where to set a plug. Setting a plug in a section of the hole that is near gauge will increase the chances for success.


If no caliper is available, refer to the following table for recommended percentages of excess volume.

Squeeze Cementing

Cement Volumes


Job Procedures

•


Plugs of 300 to 600 ft have been used for 8 ½-in. to 36-in. open holes for abandonment, suspension and sidetracking in wells that are less than 14,500 ft deep and have less than a 45° inclination.

Introduction

Minimize your risk by making sure plug lengths are adequate. Never use a cement plug of less than 20 bbl set through a drillpipe for a 6-in. or larger open hole.

•

2323

Plug Cementing Calculation of Volume Excess % Excess (Water-Based Mud)

% Excess (Synthetic-Based Mud)

30 to 36

200

—

24 to 30

100

—

14 3/4 to 17 1/2

50

20

12 1/4

30

20

6 to 8 1/2

30

20

Table of Contents

Hole Size (in.)

Introduction

Always consider the particular area and hole conditions such as sloughing shales or losses when determining the actual excess to be used.

Cement Slurry Design


Temperature Make sure the BHST and BHCT are accurate for proper job design.

Make sure the BHST and BHCT are accurate for proper job design. Select the temperature for your design on the basis of deviation, operation, and local experience.

Job Procedures

Wherever hole angle exceeds 60°, perform a temperature simulation. In water depths exceeding 1,500 ft, predict cooling in the riser. Allow some safety margin for slurry test temperatures; if no local expertise is available, allow a 10°F margin.

Plug Cementing

Slurry Properties

For kick-off plugs, the density of the slurry is important for rapid, high strength development.

For Class H cement, use 17.0 to 17.2 ppg densities.

For Class G cement, use 16.2 to 16.5 ppg densities.

•

For Class H cement, use 17.0 to 17.2 ppg densities.

•

Add a dispersant and/or retarder as needed to densify and to provide the required pump time.

Plug and abandonment plugs and squeeze plugs are generally designed at normal density for the cement available, but may be adjusted for specific well conditions. Dispersants and retarders are the most common additives used. A fluid loss control additive may also be required for some open hole and squeeze operations.

2424



•

Squeeze Cementing

For Class G cement, use 16.2 to 16.5 ppg densities.

Plug Cementing Fluid loss is required in plugs set across permeable formations; a fluid loss less than 150 ml is adequate for abandonment / suspension plugs. However, squeeze slurries should have less than 75 ml.

For all cement plugs that are to be spotted and balanced, the required thickening time is based on the calculation: 40 Bc time (in the lab report) must be greater than or equal to job pump time + time to pull out of plug + 1 hr (safety factor).

Introduction

40 Bc time (in the lab report) must be greater than or equal to job pump time + time to pull out of plug + 1 hr (safety factor).

Calculated pump time is based on time cement is moving, and does not include static time. The recommended pulling rate is 30 to 50 ft/min.


Spacers Separate mud and cement with adequate spacer/wash. For sea-water mud, pump water as a spacer/wash.

•

For synthetic-based mud, pump a weighted chemical wash system or spacer system to displace mud and provide a water-wet surface for bonding.

The volume of spacer/wash ahead of the cement should equal 500 ft of annular fill.

•

The volume of spacer/wash behind the cement should be calculated to balance.

•

Always calculate the loss in hydrostatic pressure ahead of a cement plug.

Plug Cementing

•

Job Procedures

•

Calculate the volumes of spacer/wash as follows.

Squeeze Cementing

Cement Slurry Displacement Use a cement unit to displace the cement slurry to ensure accurate control over displacement volume.

When an indicator sub is not used, a slight under-displacement, typically 1 to 3 bbl, is recommended in order to pull dry. For deep plugs, the average pipe ID should be determined to ensure a correct displacement volume.

2525


The displacement can be accurately determined with an indicator sub, usually positioned in the drillpipe above the balance point. The tool used will provide a positive indication of displacement volume when it makes contact with the plug catcher sub.


Table of Contents

Thickening Time

Plug Cementing Mechanical Tools for Supporting Cement Plugs

Introduction

Inflatable packers and mechanical bridge plugs are not suitable for use in open holes.

Waiting On Cement


Plugs should not be tagged until they have at least 1,000-psi compressive strength. A total of 1,500-psi compressive strength is required for pressuretesting the plug. Kick-off plugs require a compressive strength of 3,000 psi.

Table of Contents

Mechanical tools should be used only where necessary. Setting a reactive pill may be more economical and easier, if support is necessary. The simplest tool is a small sub run on the end of the tubing stinger that holds a short “umbrella” like tool. When a ball is dropped, the umbrella extrudes and then springs open to an approximate 20-in.diameter. This tool can be run in open hole and casing. In casing, inflatable packers or mechanical bridge plugs set on wireline can be used.

Kick-off plugs require a compressive strength of 3,000 psi. Deep kick-off plugs (placed at depths of 10,000 ft or more) across hard formations will require 4,000-psi compressive strength.

Job Procedures

Compressive strength should be determined at a temperature mid-way between static temperature and the temperature used for designing the pumping time, unless more precise values are available.



2626

Plug Cementing

Job Procedure 1. Make sure the stinger is run at least 300 feet below the plug-setting depth. Table of Contents

Note—In an openhole situation, consider jetting across the interval. 2. Pull back to plug-setting depth, condition the mud, and circulate the annulus clean a minimum of one bottoms-up while moving pipe.

4. Pump cement.


a. Check the density using a pressurized mud balance.

Introduction

3. Pump 500 ft (up to 50 bbl) of spacer/wash ahead of cement. As in primary cementing, the weight of the spacer/wash should be halfway between mud weight and cement weight.

b. Control the mixing rate at 2 to 4 bbl/min. c. If the cement is mixed with a jet mixer, dump the first quantities of cement overboard until a consistent slurry is obtained. d. If a batch mixer is used, disregard Step 4c.

•

8. Pull out of the plug at a controlled rate (approximately 25 stands/hour) to prevent swabbing and contamination.


2727


Note—For ultradeep jobs, a ball catcher sub and wiper plugs may be required to effectively verify displacement.

Squeeze Cementing

For hole sizes less than 12 1/4-in, pump at 2 bbl/min for the last 20 bbl. • For hole sizes greater than 12 1/4-in, pump at 3 bbl/min for the last 40 bbl. 7. Under-displace by 1 to 3 bbl, excluding the volume of surface lines, unless using a latchdown sub, to ensure the plug is not contaminated and that the pipe pulls dry.

Plug Cementing

6. Displace at a maximum rate (limited by ECD) to improve gelled mud removal; then reduce the displacement rate according to the following guidelines:

Job Procedures

5. Pump a volume of spacer/wash behind the cement to balance the spacer ahead of cement. Rotate pipe (approximately 20 rpm) to improve cement displacement into the annulus in deviated wells.

Plug Cementing

Note—Step 9 below does not pertain to intermediate plugs set in series. 9. If ECD’s allow reverse circulation, pull back to approximately 500 ft above the top of any cement plug that is not to be tagged, otherwise go to the TOC; then, reverse circulate clean. Caution—Reverse circulation can only take place if the ECD would not induce losses.

a. Flush the pipe clean. b. Displace 150% of the pipe’s contents at maximum rate.

10.When going in hole to tag a cement plug, start washing down and rotating pipe at the previous depth of last bottoms-up circulation or 500 to 1,000 ft above the calculated top of cement.

Caution—Do not run back into a cement plug with the stinger until the cement has set. When the plug has been tagged, do not run back into the cement without circulation.

Squeeze Cementing

Do not run back into a cement plug with the stinger until the cement has set. When the plug has been tagged, do not run back into the cement without circulation.

Plug Cementing

Where a plug is being tagged with a kick-off assembly, use minimum flow rates.

Job Procedures

c. Drop a dart or pump 50 bbl of 50 pp. Nutplug in active mud to clean pipe of cement rings. In the latter case, the size of openings in diverter tool needs to be considered.


If reverse circulation is not possible due to losses or differential sticking, perform the following steps before POOH:

Introduction

Reverse circulation can only take place if the ECD would not induce losses.

Caution—Minimize any unnecessary time from shutdown to pullout. The thickening time estimate is based on moving cement; once the cement is static, this time allowance is reduced. Table of Contents

Minimize any unnecessary time from shutdown to pullout. The thickening time estimate is based on moving cement. Once the cement is static, this time allowance is reduced.



2828

Squeeze Cementing

Squeeze Cementing

Before a squeeze cement job is designed, it is important to identify the objectives to be met and to perform a risk analysis.

Introduction


Table of Contents

Squeeze cementing is the process of placing cement into a confined area with hydraulic pressure. Often this cementing process does not attempt to “squeeze” or dehydrate the slurry at all but to place high quality, noncontaminated cement in the proper location to provide isolation or achieve other objectives.

Some of the more common objectives include:

•

Add to the height of the cement column in place to produce upper zones.

•

Eliminate water from above, below, or within the hydrocarbon zone.

•

Reduce the producing gas:oil ratio.

•

Repair a casing leak.

•

Seal the annulus of a liner top or casing shoe.

•

Plug all, or part, of one or more zones in a multi-zone injector or production well.

Plug Cementing

A risk analysis should include:

•

Pore, fracture and planned squeeze pressures.

•

Work-string and displacement accuracies.

•

U-tube effect, hydrostatic pressure, and location of cement.

•

Casing condition, especially for old wells.

•

Ability to contend with unexpected events.

•

Worst-case pressures for circulating out.


Well control considerations.

Squeeze Cementing

•

Placement There are two basic squeezing techniques: the Bradenhead squeeze and the Bull Head squeeze.


Job Procedures

Repair a failed primary cement job.


•

2929

Squeeze Cementing

For squeeze jobs in which the operator plans to “squeeze” away the cement into the formation, the total slurry volume should equal the amount to be squeezed, so that only a minimal volume of excess cement will have to be circulated out.

The properties of the cement slurry must be tailored according to the characteristics of the formation to be squeezed and the technique that will be used. Low-pressure squeezes do not exceed formation fracture pressures. They are recommended for depleted wells with low bottomhole pressures and for squeezing existing voids in any well where cement is not desired within the formation. High-pressure squeezes have no pressure limitations other than that of the casing or tubing. Final squeeze pressure is either the maximum that can be


3030


The properties of the cement slurry must be tailored according to the characteristics of the formation to be squeezed and the technique that will be used.

Squeeze Cementing

Slurry Design

Plug Cementing

For squeeze cement jobs in which the cement is to be held in place, a total slurry volume of approximately four times the volume of casing below the work string is recommended. This should represent 60 to 80% of the work string volume.

Job Procedures

The volume of slurry depends on the length of interval to be cemented, the pipe size, placement technique, formation characteristics, and the amount of excess slurry desired. Formation characteristics are especially important. To accurately calculate the cement slurry volume required, the job designer must know the fracture pressure of the formation, the permeability of the selected zone, and whether or not the zone(s) are fractured.


Cement Volume

Introduction

“Bull Head” or “Non-Bradenhead” is the technique whereby the cement is pumped down tubing or drillpipe and the wellhead annulus simultaneously. The preferred method is to design a placement schedule that allows at least half of the slurry to be pumped into the formation and leaves the remainder of the slurry in the tubing or casing. When the Bull Head technique is used with a packer, slurry can be placed with greater precision and higher injection pressures can be run.

Table of Contents

“Bradenhead” is the technique whereby the cement slurry is pumped down tubing or drillpipe and circulated to the surface. Once the cement is spotted or balanced, the tubing is pulled above the cement, the blowout preventers are closed, and the slurry is pumped into the target zone. No packer is required, and the hesitation squeeze method is often used. The Bradenhead squeeze is recommended when the casing can withstand the pressure and the target zone is effectively isolated.

Squeeze Cementing obtained or a predetermined value based on experience and calculations. Depending on the type of squeeze job performed and operational objectives, the formation fracture pressure may or may not be exceeded.

Fluid loss is extremely important when a low-pressure squeeze is used against high-permeability zones. If fluid loss is too low, it will leave non-dehydrated cement in the perforations, which could be removed during reversing or when a negative differential pressure is created. Excess fluid loss could allow premature dehydration of a slurry to the extent that a zone is not completely covered. Optimum fluid loss varies with the permeability of the zones.

•

For a low-pressure squeeze in a high-permeability formation, use a slurry with fluid loss of 50 to 100 ml/30 min.

•

For a high-pressure squeeze, use a slurry with fluid loss of 200 to 500 ml/ 30 min.

•

Use a slurry with high fluid loss for fast cake buildup in a fracture. A fluid loss of 300 to 800 ml/30min at 1,000-psi differential pressure is recommended.

•

In a fractured limestone or dolomite, the addition of a lost circulation material may help form a bridge on the formation to prevent cement dehydration.

Slurries with a low yield point, or thin slurries, are preferred for most squeeze jobs. Thin slurries can flow into narrow cracks or channels. Thick slurries are more useful when cementing large voids.

Plug Cementing

Dispersion

Job Procedures

For a low-pressure squeeze in a low-permeability formation, use a slurry with fluid loss of 100 to 200 ml/30 min.


•

Introduction

Fluid loss is extremely important when a low-pressure squeeze is used against highpermeability zones.

Table of Contents

Fluid Loss Control

Thickening Time

Cements with high compressive strength may be desirable, but compressive strength should not be the primary concern. Normally, the dehydrated cake of slurries made with cements of moderate compressive strength will attain the compressive strength necessary to accomplish the job and in a shorter time than that required for cements with high compressive strengths.


3131


Compressive Strength

Squeeze Cementing

Accelerators and retarders are used as necessary to overcome the effects of depth, temperature, and squeeze technique on the slurry’s thickening time. The thickening time must be sufficient to mix the slurry, pump the slurry, pull the workstring, reverse any excess slurry, and squeeze the slurry away.

Squeeze Cementing Washes and Spacers As in primary cementing, washes and spacers are normally recommended for two reasons: to clean the perforation and surrounding voids of mud so that the cement can get to the formation face and dehydrate properly

•

to prevent contamination of the cement slurry Introduction

Prejob Considerations

•

Plan a pump-in test to determine the injection rate.

•

Reduce the risk for cement contamination by using spacers, plugs, excess cement or other tools.

•

Estimate the fracture gradient at depth.

•

Estimate the pressure differential between the fracture gradient and the mud weight at depth.

•

Help prevent flowback due to the U-tube effect by planning procedures to hold the cement in place and eliminate the risk of cement being where it is not wanted.

•

Calculate what the hydrostatic pressures will be once cement is in place and determine whether or not over-displacement will occur. A water column may need to be included in displacement pumping schedule for well to remain static once cement is in place. (This is especially important if squeezing is being performed due to the loss of returns or when the liner laps right at the fracture gradient.)

•

Plan displacement procedures to help compensate for the U-tube effect that can occur when mixing heavy cements slurries relative to light mud weights. For example, when mixing 300 sk (63 bbl) of 15.6 ppg cement slurry on a well with 12.0 ppg mud and a 5-in. drillpipe, the level in the drillpipe will fall 18.8 bbl. You will recover 18.8 bbl more volume from the annulus while mixing cement since it is being slugged. The cement is 18.8 bbl ahead of surface displacement volumes in the drillpipe.

•

Make calculations to set the bottom of the drillpipe or work string off bottom by 15 to 20% of work string volume below the drillpipe.

3232


Always perform a preliminary prejob analysis and calculations to assure the planned procedure fits actual hole conditions. All pressures, volumes, pumping times, injection rates, and fracture gradients must be within acceptable limits.

Squeeze Cementing

•

Plug Cementing


Plan the job in detail with the service contractor to define the objectives and operational procedures and pressures.

Job Procedures

Help prevent flowback due to the U-tube effect by planning procedures to hold the cement in place and eliminate the risk of cement being where it is not wanted.

•


Always perform a preliminary prejob analysis and calculations to assure the planned procedure fits actual hole conditions.

Table of Contents

•

Squeeze Cementing

•

Determine the expected worst-case pressure to reverse out.

•

Plan to test the casing with worst-case pressure to reverse out excess cement or develop a contingency plan that can be used if reversing out is not practical.

•

Establish a plan for circulating out cement. Never circulate out cement the long way if it cannot be reversed. Leaving cement on the inside of a work string is not advised, but a cemented-up work string on the rig’s pipe rack is better than cementing up a drillstring in an active well that’s being drilled.

•

When unexpected problems arise in performing a squeeze cementing job (mechanical failure of equipment, losing track of cement displacement, pressure loss indicating a possible washout, etc.), reverse out the cement and start over.

Job Procedures

In planning cement squeeze jobs, always allow for a 10% error in displacements based on the volume of the work string, unless some mechanical devices are used to calculate displacements more accurately.


When unexpected problems arise in performing a squeeze cementing job, reverse out the cement and start over.

•

Introduction

Never circulate out cement the long way if it cannot be reversed.

Plan the displacement volumes necessary to under-displace the leading edge of the cement slurry by 20% and over-displace the tail edge of cement slurry by 10 to 15%. Table of Contents

Allow for a 10% error in displacements based on the volume of the work string, unless some mechanical devices are used to calculate displacements more accurately.

•



3333

Squeeze Cementing

Job Procedures Bradenhead Cement Squeeze

2. Use a cement stinger to place the abandonment plug were possible.

Introduction

3. Place a minimum of 300 to 500 ft of cement slurry on bottom, ensuring that the slurry has a greater density than the mud weight.

Table of Contents

1. Pump 300 ft (up to 30 bbl) of spacer/wash ahead of cement. Pump spacer/ wash behind the cement at a volume calculated to balance.

4. Pull two to three stands above the plug and reverse out the excess. 5. Pump away 1/3 of the cement volume while monitoring for pressure increase as the cement feeds into the formation.


6. Wait for 15 minutes and pump 1/6 of the cement volume – again while monitoring for pressure increase. 7. Again, wait for 15 minutes and then pump 1/6 of the cement volume – while monitoring for pressure increase. 8. Let the well remain static until the cement sets up.

Job Procedures

Hesitation Squeeze Technique

Hesitation Cycle •

When stabilized pressure does not increase, lengthen the hesitation cycle.

•

When stabilized pressure increases, the hesitation cycle can be shortened. Plug Cementing

Pump Cycle Pump at the slowest rate possible.

•

Never pump a predetermined volume of fluid.

•

As pressure increases, continue to pump.

•

When pressure breaks back, drops, or shows any indication of pumping into formation (including gut feeling), STOP pumping.

Squeeze Cementing

•

Potential Squeeze Endpoint


•

When the cement volume in the casing is used, STOP. This is all the squeezing possible for the volume of cement selected. NEVER overflush perforations.

3434


When the cement volume in the casing is used, STOP pumping.

Squeeze Cementing •

Table of Contents

When maximum allowable pressure is attained without significant leak-off, STOP.

When maximum allowable pressure is attained without significant leakoff, STOP. This is all the squeezing possible within the preset pressure limit.

Bull Head Cement Squeeze For best results, use a slurry design with a fluid loss of less than 100 cc/30 min, and perform the following steps:

2. Mix enough cement so that you can squeeze ½ the volume into the formation on the first squeeze. Use excess. 3. Stop and wait 15 minutes; then, pump ½ the remaining volume in the tubing and/or drillpipe while monitoring for a pressure increase.


4. Let the well remain static until the cement sets up. 5. Pull two to three stands above the plug and reverse out the excess. Cement Retainer

Job Procedures

The decision of whether to use a squeeze tool or cement retainer is usually determined by wellbore integrity, as defined by the answers to these questions: Is the well relatively old or new?

•

How recently was the casing tested?

•

Do we know where we are pumping in?

•

What are the wellbore conditions (mud weights and fracture gradients)?


3535

Squeeze Cementing

To use a cement retainer for a squeeze job, set the cement retainer close to the squeeze interval (40 to 60 ft above the interval) to minimize cement contamination. A lesser volume of cement slurry can be used since less contamination will take place below the work string (usually 40 to 50% of the work string volume). The pumping schedule should allow the cement slurry to be underdisplaced by 10% of the work string volume to avoid over-displacement with the excess cement slurry reversed out.

Plug Cementing

•

Squeezing a deep intermediate casing shoe with a low mud-weight may require a very high injection pressure. Very high pressures may also be required to reverse out with a particular work string in certain conditions, which could “junk” the well}.


Introduction

1. Pump adequate wash ahead of the cement to remove mud cake.


Contractor Requirements Included in this section are:

•

instructions for preparing a cementing recommendation

•

procedures for pilot-testing cement designs

•

laboratory test requirements

•

on-location procedures for cement bulk blendng and loadout

•

prejob and job procedures


flowcharts illustrating the roles and responsibilities of various parties during the job planning, mobilization, and implentation

Introduction

•

Table of Contents

The following information is provided to ensure a thorough understanding of the job process as it pertains to both Unocal staff and contractors.



3636


Cement Job Planning

OFFICE

Cement contractor and Unocal Drilling Engineer check if cement job specifications are covered in the Engineering and Planning section of this Best Practices document.

Yes

Job Procedures

Cementing contractor conducts "new" slurry design pilot testing using lab materials.

Plug Cementing

Need a new cement slurry design?


Unocal Drilling Engineer reviews output, verifies input data and updates cementing contractor as appropriate.

LAB Introduction

Cementing contractor conducts cement job simulation, centralizer placement, etc.

Cementing contractor receives and reviews cement job data.

Table of Contents

Unocal Drilling Engineer defines cement job well data and applicable well conditions.

FAIL Simulation OK?

No

Pilot test design check.

Squeeze Cementing

No

PASS Yes



Unocal Drilling Engineer approves simulation output.

Unocal Drilling Engineer approves selected cement slurry design.

3737


Cement Job Mobilization Table of Contents

Unocal Drilling Engineer orders materials / authorizes materials movement.

Introduction

Cementing contractor prepares blending facility and determines volume of bulk blends.

Cementing contractor conducts lab pilot test using actual materials to be used for the job.


Unocal Drilling Engineer and/or Drilling Supervisor checks and approves blending volume. Pilot test results acceptable?

No

Adjust slurry design.

Job Procedures

Cementing contractor blends dry materials. Unocal Drilling Engineer or Supervisor witnesses. Yes

Unocal Drilling Engineer issues bulk blending order.

Plug Cementing

Cementing contractor samples blend and conducts confirmation test to QC blend.

REBLEND

Confirmation test check

FAIL

Squeeze Cementing

Unocal Drilling Engineer approves completion of bulk blending and load out.



Unocal Drilling Engineer or Supervisor provides final well data.

A

3838


Cement Job Implementation Table of Contents

A Introduction

Cementing contractor performs final job calculations.


Unocal Drilling Engineer or Supervisor approves job calculations.

Job Procedures

Cementing contractor conducts all tasks on prejob checklist.

Plug Cementing

Cement job performed.

Squeeze Cementing

Cementing contractor completes post job lab test and job report.



Unocal Drilling Engineer approves job report.

3939


Cementing Recommendation

Contents The Cementing Recommendation should contain the following:

•

cementing operation issues and detailed solutions

•

thickening time requirement for the cement slurry(s)

•

detail of well geometry, including hole, casing, and annular volumes, and pore and fracture pressures

•

required cement slurry volumes

•

BHST and detail on the method of calculation

•

proposed cement and spacer formulations with details as to how they meet the job objectives; this proposal should include the following

•

Important—Always use the standard UNOCAL laboratory report form for submitting laboratory reports. operational details, pump rates for each fluid and shear or bumping pressures for wiper plugs

•

a computer-generated simulation of the cement job(s) that is based on the proposed cement slurries, well information and geometries, with clear and accurate inputs. The output shall include: • •


centralization (centralizer spacing for inputted stand-off, and stand-off for inputted spacing, both in tables and graphs) flow regime of each fluid (for each wellbore geometry based on inputted pump rate and rates for achieving turbulent flow for each fluid

4040


•

Squeeze Cementing

Always use the standard UNOCAL laboratory report form for submitting laboratory reports.

densities, yield and material requirements of the proposed slurries and spacers “pilot” laboratory test results for the cement slurry formulation(s)

Plug Cementing

•

Job Procedures

detailed objectives of the cement job(s)


•

Introduction

The Cementing Coordinator be fully capable of running the simulator, analyzing the output data and making the appropriate job recommendations, and must use standardized software for generating this recommendation.

Table of Contents

The Cementing Coordinator is responsible for preparing a Cementing Recommendation as requested for upcoming wells, and communicating with the UNOCAL Engineer as required to obtain all necessary information for preparation of this document.

Contractor Requirements • •

Important—Well control exceptions must be clearly highlighted and brought to UNOCAL Engineer’s attention. displacement volumes

•

tabular and graph of fluids fill level and placement

•

cost estimates for service and materials

Reporting Responsibilities

Prior to each cementing job the Cementing Coordinator shall update the respective portion of the recommendation. Updates must be referenced to initial recommendation and pertinent lab testing.

Job Procedures

Presentation of this report must include a hard copy and an electronic file in either Microsoft Word or Excel format. Graphs may be generated to supplement the reports.


•

Introduction

Well control exceptions must be clearly highlighted and brought to UNOCAL Engineer’s attention.

Table of Contents

•

U-tube simulation for the cement job under dynamic conditions (tables and graphs of free-fall vs. time) temperature simulation profile of cement slurry temperatures, bottomhole circulating temperatures (BHCT) and a graph of particle temperature profile at depth well security and control (equivalent circulating densities at total depth and at other selected points, graphed against pore and fracture pressures)



4141


Cement Designs for “Pilot Testing”

Conduct all laboratory testing in a timely and accurate manner.

•

Incorporate sufficient lead-time into the testing program so that the designs are ready well in advance.

•

Conduct testing with the representative samples of materials that will be used on the job (bulk plant or rig samples) as appropriate.

•

For liner jobs, isolate critical additives such as retarders.

•

Conduct all laboratory testing in accordance with UNOCAL-designated procedures and report the required test results.

•

Incorporate contingency planning into the testing program, taking into account variations in well parameters that may require adjustments in density or thickening time.

•

Perform compatibility tests between the cement and spacer and between the spacer and drilling fluid for all jobs in which oil-based or syntheticbased drilling fluids are in the hole.

•

For all liner and tieback jobs, test the spacer for stability by “hot-rolling” at circulating temperature.

•

Whenever possible, design the cement job to achieve turbulent flow of the spacer in the open hole.

4242


Important—No cement slurry is considered “approved and finalized” until the UNOCAL Drilling Superintendent or Engineer signs off on it. No slurry design will be sent to the rig without this approval.

Squeeze Cementing

•

Plug Cementing

Use the standard Unocal laboratory report form when submitting laboratory reports.

Job Procedures

•



Clearly reference all “pilot testing” data to the appropriate cementing recommendation with a unique project or “job” number.

Introduction

No slurry design will be sent to the rig without signoff by the UNOCAL Drilling Superintendent or Engineer.

•

Table of Contents

Pilot testing (laboratory testing to develop cement designs that meet the required criteria for the given well parameters) is required for all cementing operations and shall include thickening time, rheologies, free fluid, fluid loss (when fluid loss additive is included in formulation), 24-hour compressive strength and WOC (time to 500 psi) by UCA for tail slurries and kick-off plugs.


Laboratory Testing Requirements Table of Contents

Unless otherwise specified, all laboratory testing of cement slurries for UNOCAL operations must be performed in accordance with the latest revision of API RP10B. The following are the required minimum laboratory testing procedures for cement slurry designs, as applicable. Mixing

Introduction

Mix slurry as per standard API procedure (4000 rpm for 15 seconds and 12000 rpm for 35 seconds). If the slurry contains microspheres, the 12000 rpm requirement may be replaced by 4000 rpm. Density

Measure density with a pressurized mud balance. Engineering and Planning

Free Fluid Test

Follow API RP10B Section 15, with the following exceptions: •

Conditioning in an atmospheric consistometer is acceptable.

•

Time–to-temperature of 6 minutes is not required. Job Procedures

Conduct tests with a heated static period at BHCT or 194°F, whichever is lowest. Place the graduated cylinder at an inclination of 45°. API Static Fluid Loss at BHCTs less than 193°F

API Static Fluid Loss at BHCTs 194°F or Greater

Condition the slurry in a pressurized consistometer at BHCT and pressure. Follow API procedures for heating the fluid loss cell to BHCT and for testing.

Squeeze Cementing

Rheology at 80°F and the lessor of BHCT or 194°F

According to API RP 10B method, include 10-second and 10-minute gel strength values. Thickening Time at BHCT and BHP

4343


Test as per the appropriate API RP 10 B Schedule or as per a calculated temperature and pressure schedule using the equations in sections 9.5.3.2 and 9.5.3.4 through 9.5.3.7 of the API RP 10B. Report the time required to reach 40 Bc, 70 Bc, and 100 Bc.


Plug Cementing

Use an atmospheric consistometer for conditioning, and test at BHCT and 1000 psi.

Contractor Requirements Compressive Strength at BHST and 3000 psi

Table of Contents

Attach documented results of UCA testing required for WOC 500-psi values and UCA charts to the slurry test result sheets. A crush test is required for 12hr or 24-hr compressive strength. Cure and test according to API RP 10B, excluding section 7.6.

Introduction Engineering and Planning Job Procedures Plug Cementing Squeeze Cementing Contractor Requirements


4444


On-Location Procedures

Cement Bulk Blending The following procedure is required for all blended cements containing fluid loss, retarder or silica additives.


Validating Materials

Verify that the following criteria are met for all materials to be blended: Lot numbers of bulk cement and all additives are recorded on the blend sheet.

•

Only one batch number of cement is used per job.

•

This batch number coincides with that used in laboratory testing.

•

Additives are of the same lot or batch number used in laboratory tests.

•

Only one lot number is used per each critical additive, i.e., fluid loss additives, retarders.

Job Procedures

•

Caution—Discard any substandard or suspect material (chunks, lumps, rocks, wet). Calculating Blend Volumes

The UNOCAL Drilling Engineer and Foreman will approve the volume of cement to be blended for the job.


4545


If a UNOCAL representative cannot be present for the blending operation, the bulk plant operator with primary responsibility for the blending operation must verify the blend volumes with the UNOCAL drilling office.

Squeeze Cementing

Discard any substandard or suspect material (chunks, lumps, rocks, wet).

Caution—Never use previously opened sacks.

Plug Cementing

Important—NO exceptions are permitted. Never use previously opened sacks.

Introduction

For smaller jobs (400 sk or less), consider the use of 220-ft3 portable tanks for loading, transporting and pumping the job. This will place the final quality control point at the bulk plant, eliminating the need for quality control checks between the bulk plant and the rig and consequently, the lead time required for those checks.

Table of Contents

The cement bulk blending and loadout procedures that are performed on location are an integral part of quality control, and must be

Contractor Requirements Important—The bulk volume of each batch of cement and additives must not exceed 60% of scale tank capacity. To determine the total volume of cement and additives required:

Table of Contents

The bulk volume of each batch of cement and additives must not exceed 60% of scale tank capacity.

1. Based on total volume of cement blend required, bulk load factor, and blending capacity, determine the batch size and quantity.

Preparing Equipment

1. Verify that the additive scale is clean and operating properly. 2. Check the scale tank balance for proper operation.

4. Check air compressor and/or vacuum system for proper operation, and drain of any moisture.


3. Verify that the scales have been calibrated and certified within the past six months. A certification stamp must be on the scale.

Introduction

2. Use the cement blend formulation to calculate total cement and additives required.

5. Record lot numbers of bulk cement and all additives to be used.

1. Empty, clean, and inspect all blending equipment, including cutting pods, scale tanks, boxing tanks, silos and sampling devices.

Job Procedures

Preparation for Liner Job Blends

2. Open and visually inspect all tanks immediately prior to the job to ensure that they are empty and clean.

4. Follow all appropriate regulations and requirements prior to entry into a tank.

Plug Cementing

3. In addition to blowing down, sweep down and clean out tanks.

5. Check aeration pads for moisture; if wet, blow air through until dry. Squeeze Cementing

6. Inspect air-jets for build-up. Clean or replace jets and rubbers as necessary. 7. Purge, empty, and clean all transfer lines. 8. Clean or replace dust sacks.


Weighing

1. Make sure calibration and certification records for all weighing devices are available. 2. Zero the scale tank prior to the blending operation.


4646

Contractor Requirements 3. Once the scale is zeroed, this same zero point MUST be maintained during the entire blending operation.

1/3 of the cement 1/2 of the additives 1/3 of the cement 1/2 of the additives 1/3 of the cement

Introduction

• • • • •

5. DO NOT exceed 60% capacity of the scale tank.


6. Calculate weights of cement and additives for each step. Double check calculations. 7. Weigh all additives into the bulk tank. Weigh all additives into the bulk tank. Never use the weight indicated on the bag for calculations.

Table of Contents

4. Cement and additives are to be layered into the scale tank in the following order:

Caution—NEVER use the weight indicated on the bag for calculations.

9. Calculate “target” cumulative weight of scale tank at each step.

Job Procedures

8. Take into account bag weight or weight of any other weighing container. Example: For small amounts of additives, the material should be weighed using a clean plastic or steel container (bucket, garbage can, etc.) after adjusting (tarring) the scale for the weight of the container.

10.Record scale tank readings after each step, “actual” cumulative weight.

13.Shake dust socks regularly during the blending operation to minimize accumulation of materials in them.



14.Purge the lines of all material after each transfer of material (cement or additives). Repeat this purging procedure if it is suspected that some of the material is remaining in the line.

Squeeze Cementing

12.For large volume additives such as silica sand, the weigh tank scale may be used to measure the weight of the material. Example: 3700 lbs. silica flour, record current scale tank weight, add 36 sacks of 100 lbs. net (labeled) each, check scale tank weight, weigh out and add any additional silica flour to bring weight added up to 3700 lbs.

Plug Cementing

11.During the weighing process, document and compare the “target” and “actual” cumulative weights after each addition of additives or cement to the blend.

4747

Contractor Requirements Blending

Important—Five complete pneumatic bulk plant transfers are required on all blends. Percolating air through the blend WILL NOT be accepted as a replacement method.

2. Box a minimum of five times. Example: a. scale tank to blend tank


b. blend tank to scale tank c. scale tank to blend tank d. blend tank to scale tank e. scale tank to holding tank, truck or portable tank.

4. Check and record weight of blend each time it comes back into the scale tank.

Plug Cementing

Important—The weight of the material remaining in the scale tank after the transfer must be recorded. This weight will be added to the cumulative weights of the next batch of blended material.

Job Procedures

3. During the last transfer, take bulk blend samples as detailed in the following section on sampling.

The weight of the material remaining in the scale tank after the transfer must be recorded. This weight will be added to the cumulative weights of the next batch of blended material.

Introduction

1. After all cement and additives have been placed in the scale tank, use approximately 30 psi to transfer the material to the blend tank. If extremely light additives are being used (microspheres, silica fume, etc.) the transfer pressure should be reduced to 6 to 8 psi to minimize segregation and losses of these light additives through the vents.

Table of Contents

Five complete pneumatic bulk plant transfers are required on all blends.

Cement Load-Out for Land Operations The bulk plant operator is responsible for visually inspecting through open hatches all transport pods to ensure that they are clean and dry.

Squeeze Cementing

For intermediate and deeper casings, a UNOCAL representative or designated third party inspector is required to inspect tanks prior to loading. 1. Blow or sweep down any residual cement in the pods as necessary.


2. Blow clean all transfer lines. 3. Check the air system and drain any water from the traps. 4. Transfer cement through a weigh tank to determine an accurate weight and volume.


4848

Contractor Requirements Sampling

Always take samples for lab analysis and confirmation testing. A sample MUST be taken for each batch blend when it is transferred from the scale tank to the holding tank prior to load-out. An automatic or manual sampling valve may be used. A pneumatic inline sampler is operated through the complete transfer. A manual 1- or 2-in. valve sampler located on the discharge line, should be opened intermittently throughout the transfer.

Table of Contents

Always take samples for lab analysis and confirmation testing.

Introduction

The minimum total sample quantity is three gallons (three plastic sample bags)—two to send to the lab and one to keep at the bulk plant. To take a sample, perform the following steps:


1. Purge the sample line/valve. 2. Take a sample in a new plastic bag. 3. Force out any excess air. 4. Seal the bag with a wire tie.

5. Label the sample containers and storage tanks with the following information:

Job Procedures

Important—The minimum volume for any single bag is 1 gal.

a. date Plug Cementing

b. formulation c. quantity d. batch number e. bulk plant operator

g. cementing job In some cases sampling should be witnessed by a UNOCAL representative or designated third party inspector.

Bulk blend testing is required for application of dry-blended bulk blends for all casing strings. Bulk blend testing is to include the following, as a minimum:


4949


Bulk Blend Testing

Squeeze Cementing

f. well number

Contractor Requirements thickening time test at BHCT

•

compressive strength test, 24 hr (WOC, if specified) at BHST (and TOL if requested)

•

rheologies at 80oF and BHCT

•

free fluid and solids settling, at temperature

•

fluid loss at BHCT

Table of Contents

•

The Cementing Contractor must not load out a dry cement blend until approved by a UNOCAL representative. Documentation

Job Procedures

The Cementing Contractor must not load out a dry cement blend until approved by a UNOCAL representative.

The following documentation must be provided directly to the UNOCAL office after completion of every bulk blending operation. quantities and batch/lot numbers of cement and additives

•

copy of laboratory cement slurry formulation sheet

•

weight calculation and recording sheets

•

final quantity and the number of the storage tank into which it was loaded

Preloading

1. Prepare a load ticket detailing type, content, volume, and weight and bulk load factor of each cement or blend to be loaded.

5050


In the event bulk trucks are used to transport the cement blend to the boat dock, a bulk plant operator shall accompany the trucks and uphold responsibilities.

Squeeze Cementing

The bulk plant operator is responsible for loading out cement and must ensure that cement quality is not diminished during or because of this operation. On the rig, the cementer is responsible for the preparation and execution of cement offloading procedures from the boat onto the rig. They must promptly report any problems to UNOCAL.

Plug Cementing

•

Cement Loadout for Offshore Operations



Contractor’s Cementing Supervisor shall monitor bulk blending and coordinate the lab testing.

Introduction

The Cementing Contractor shall ensure that there is sufficient time between field blending and the actual cement job to allow for blending, testing, and when necessary, modifications, re-blending, and re-testing, without jeopardizing the execution of the cement job itself.

Contractor Requirements 2. Prior to loading or inspecting tanks, present a copy of the load ticket to boat captain and discuss which tanks are to be loaded.

4. Verify hose hookup and valve alignment with boat captain or designated representative.

Table of Contents

3. Verify tank volumes and calculate cement volume to be loaded into each tank.

5. Install a rock catcher between bulk facility and boat. Introduction

Boat / Tank Inspection

The bulk plant operator or other approved service company representative must visually inspect all tanks that are to be loaded. Follow all appropriate regulations and requirements prior to entry into a tank. 1. In addition to blowing down the tanks, any tanks containing barite, bentonite, or cement must be swept down and cleaned out. Tanks containing any other type of material require steam or pressure cleaning.

3. Inspect air-jets for cement or other buildup; if found, clean or replace the jets and their rubbers.

Job Procedures

2. Check aeration pads for moisture; if they are wet, blow air through them until they are dry.


The bulk plant operator or other approved service company representative must visually inspect all tanks that are to be loaded.

4. Drain water and moisture from bulk air systems.

6. Pressurize tanks that are to be loaded to 10 psi and check for leaks. 7. Blow down tanks through discharge and hoses that will be used at the rig.

Plug Cementing

5. Blow air through all purge lines until they are dry.

8. Install and seal hatch covers after inspection is completed. Squeeze Cementing

Loading Cement

1. Monitor vent line for overfilling of tanks. Important—Do not change tanks without verifying hose hookup and valve alignment with the boat captain or the designated representative.


5151


2. After loading, request the boat crew to open hatches and verify the amount of cement in each tank, reseal hatch covers, pressure check seal, and then vent pressure.

Contractor Requirements Caution—Leave pressure off tanks until preparing to off-load cement at the rig. Table of Contents

3. Verify that the boat crew caps and stows the cement discharge hoses before getting underway. Offloading Cement at Rig

1. Calculate available rig tank capacities based on bulk load factor of cement to be loaded.

3. Conduct a visual inspection of the rig tanks prior to loading. and make sure that any necessary cleanup or repair operations are witnessed. 4. For a liner job, sweep down the rig tank and completely clean it out prior to loading. Inspect all air pads and jets and replace them as necessary.

6. Install a rock catcher in-line between the boat and the rig tank. The rock catcher should be positioned on the rig.

During the loading, catch two sets of samples by taking two 1-gal samples at the beginning, middle, and end of each tank load for a total of six samples.

Plug Cementing

Rigsite Sampling

Job Procedures

5. Go on board the boat to inspect the air system and to verify the location and type of cement or blend in each tank. Check the hose hookups, valve alignment, and hoses and capped hoses and lines.


2. Meet with the company man to discuss volume calculations for the cement and verify the rig tanks into which cement is to be loaded.

Introduction

The cementer is responsible for overseeing offloading of cement blends onto the rig, including tank inspection, rigging up, volume calculations, and sampling.

Cement Sampling Equipment Squeeze Cementing

For critical jobs, a Gustafson inline sampler is required. If an inline sampler is not available, use a portable cement tank to collect samples as follows:

b. Open the access hatch on the top and open the lower feed line from the bottom of the tank; take three 1-gal samples from each, labeling them as top and bottom.


5252


a. Transfer the loaded cement from the rig tank to a portable cement tank (pod).

Contractor Requirements Labeling Samples

3. Send one set of samples (three cement samples, one mix-water sample, and one drilling fluid sample) to the laboratory and retain the other set on the rig.

Introduction

2. Take two 5-gal samples of mix water and two 2-gal samples of drilling fluid in clean, sealable containers that are labeled with date, rig, and source.

Table of Contents

1. Place the samples of cement blend in the standard sample bags that are prelabeled with the date, job type, formulation, amount, rig tank number, and at what interval the sample was taken during the loading process— beginning, middle, or end.

Prejob Procedures

hole size with caliper data or required excess factor casing length, size, and weight drill pipe length, size, and weight shoe track dimensions required length of tail cement desired top of cement liner hanger configuration any other pertinent information

Plug Cementing

• • • • • • • •

Job Procedures

1. Prior to the cement job, obtain up-to-date well information and cementing objectives from the UNOCAL Drilling Supervisor. This information should include


The cementer is responsible for execution of all on-location procedures, as described below and in the following “Job Procedures” section.

3. Verify equipment and material requirements and confirm that they will be on location for the job.

Squeeze Cementing

2. Conduct a prejob meeting for all service personnel (mud loggers, etc.) to provide information or add value to the process.

4. Review cement and spacer formulations with the cementing coordinator.


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5. Review laboratory test results from the rig samples with the cementing coordinator, paying special attention to the thickening time (available pumping time) and the required WOC (wait on cement time, time to 500psi).

Contractor Requirements 6. Calculate cement volumes in barrels, in cubic feet, and in sacks of cement required for the lead and tail formulations. Include a breakdown of these volumes showing cased hole, open hole, and shoe track volumes.

8. Calculate spacer volumes and material requirements, taking into account available mixing space.

10.Verify that the suction rates required for the job can be achieved with both drilling fluid and water.

12.Develop a pumping schedule based on the cement job simulator output. 13.Determine whether the available pumping time as indicated by the laboratory thickening time test result is sufficient for the planned job.

14.Prepare a job plan that includes the following.

• •


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• •

Squeeze Cementing

•

rig-up procedure safety concerns pressure testing procedure spacer type, density, and volumes to be pumped wiper plugs, dart- or ball-dropping sequence and procedure cement slurry formulation(s) densities and volumes conversion factors for calculating sacks per barrel of slurry and barrels of slurry per barrel of mix water pumping schedule indicating rates, volumes, and times for pumping and displacing each fluid total job time including time to drop plugs and flush lines anticipated job pressures during pumping, shearing or bumping of plugs and darts in-hole hydrostatic pressures of each fluid after placement personnel requirements for the job

Plug Cementing

• • • • • • •

Job Procedures

Note—The cementing contractor’s equipment will be used for all mixing and pumping.


11.Calculate displacement volumes for the casing or liner and drillpipe as required.

Introduction

9. Check the available water supply and verify that sufficient quantities of water will be available for the job.

Table of Contents

7. Calculate the mix water requirement, additive requirements, and the resultant mix fluid volume for both lead and tail cement slurries.

Contractor Requirements • •

contingency plans for the unexpected: liner top packer fails, float equipment fails, loss of returns while going in the hole, etc. WOC criteria prior to rigging down any well-control devices

16.Load the wiper plugs in the presence of the UNOCAL Drilling Supervisor. 17.Review checklists, laboratory test results (available pumping time and WOC time), and job plan with the UNOCAL Drilling Supervisor. 18.Prepare spacer as required and check the weight with a pressurized drilling fluid balance.

Introduction

Load the wiper plugs in the presence of the UNOCAL Drilling Supervisor.

Table of Contents

15.If supplying the wiper plugs and cementing head, verify that the correct equipment is on location and that the cementing head and associated connections have been tested.

Engineering and Planning Job Procedures Plug Cementing Squeeze Cementing Contractor Requirements


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Job Procedure

Maintain an open line of communication to rig floor at all times.

Table of Contents

1. Hold a safety meeting on the rig floor to review the job procedure and address safety concerns. Note—Maintain an open line of communication to rig floor at all times. 2. Pump spacer to break circulation.

Introduction

3. Pressure test the lines and the operating system to a pressure above that expected during the cementing operation. 4. Pressure up the bulk tanks. 5. Pump the job according to the job plan. Note—The cementer is responsible for seeing that wiper plugs darts or balls are released at appropriate times. 6. Use a data acquisition system to record pressure, rate, density and volumes pumped during job.

Job Procedures

7. Manually record the following events during the job. pressure test, psi and time start time for job dropping of any plug, darts or ball start and stop time for each fluid pumped start of displacement landing or shearing of any plug or dart and the observed pressure any unexpected pressure changes and any unscheduled shutdowns top plug bumping pressure and whether or not floats held cement in place

Plug Cementing

8. Count and record the volume of mix water by the number of displacement tank volumes used.

10.Take cement slurry cup samples throughout the job. 11.Take three separate one-gallon mix water samples from the displacement tank and three separate one-gallon dry cement samples from the surge can or a transfer line after the job.


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9. Measure the cement slurry density with a pressurized drilling fluid balance.

Squeeze Cementing

• • • • • • • • •


The cementer is responsible for seeing that wiper plugs darts or balls are released at appropriate times.

Contractor Requirements 12.Label and retain samples for possible laboratory testing until the well is completed. Caution—Do not pump any fluids lighter in weight than the drilling fluid in the hole, unless previously agreed upon by respective parties that a lighterweight spacer or flush is to be used. Do not open the cement head after a cementing fluid (spacer or slurry) has been pumped downhole, until after the job is completed. Introduction

Do not sacrifice cement slurry density for pump rate. Do not over-displace past the calculated displacement plus 50% of the shoe track volume. 13.Prepare a job ticket, a printout of the data acquisition output and chart, and any incident reports, and present them to the UNOCAL Drilling Supervisor.


Do not open the cement head after a cementing fluid has been pumped downhole, until after the job is completed.

Table of Contents

Do not pump any fluids lighter in weight than the drilling fluid in the hole, unless previously agreed upon by respective parties that a lighterweight spacer or flush is to be used.

Do not sacrifice cement slurry density for pump rate.



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Cementing Best Practice Jorge Sierra

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