Chapter 3 - Perforating Methods

3. PERFORATING METHODS

TUNIO, May' 2011,,, Courtesy AP Aung

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LESSON OUTCOMES At the end of this chapter, students should be able to: – Describe the options, advantages and disadvantages for perforating oil and gas wells. – Describing an outline strategy to complete a well as part of a completion operation. – Understand the importance of charge design and factors influencing performance. TUNIO, May' 2011,,, Courtesy AP Aung

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CHAPTER OUTLINE • Perforation Techniques • Candidate Selection


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INTRODUCTION Needs of perforating… • To provide the communication path between the wellbore and all desired zones • To evaluate and optimize production rate/injectivity as well as oil and gas recovery from each zone Perforating… • produce holes through the wall of the casing, the cement sheath and penetrate into the formation TUNIO, May' 2011,,, Courtesy AP Aung

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INTRODUCTION

• History:  1910

: Used mechanical perforators Blade or wheel knife to open hole in the casing.  1948 : Through-tubing perforating (underbalanced perforating) TUNIO, May' 2011,,, Courtesy(TCP) AP Aung  1975 : Tubing Conveyed perforating 5

INTRODUCTION

 1980 : Start to produce fractures from burst of pressure developed from gun detonation.  1993 : wells.

Tubing Conveyed Perforation (TCP), succeed in commercial TUNIO, May' 2011,,, Courtesy AP Aung

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INTRODUCTION Causes for poor perforation 1. Lack of understanding of requirements for optimum perforating 2. Inadequate gun clearance 3. Selecting perforating guns or charges on the basis of surface penetration tests 4. Awarding perforating jobs on the basis of price rather than job quality


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Types of Perforators Two(2) Types of Perforators 1. Bullet perforators 2. Jet perforators


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Types of Perforators 1. Bullet perforators • • •

Bullet perforator is multi-barreled firearm designed for being lowered into a well Electrically fired from surface controls. Perforating of the casing, cement and formation is accomplished by bullets or high velocity projectiles


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Types of Perforators THREE(3) ways of firing: 1. Selective firing of one bullet at a time 2. Selective firing of independent groups of bullets 3. Simultaneously firing of all bullets


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Types of Perforators Availability: • • •

A number of bullet types Bullet guns for use in all sizes of casing from a number of service companies Velocity of bullet = 3300 ft/sec


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Types of Perforators

• • • •

When gun clearance > 0.5 in, velocity and energy drop When clearance = 1 in., 25% penetration loss than at 0.5 in. clearance When gun clearance = 2, penetration loss is 30 % than at 0.5 in. clearance When gun clearance = 0, penetration increases about 15% over 0.5 in. clearance


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Types of Perforators 2. Jet perforators •

The use of shaped explosive charges to create perforation tunnels. The explosive charge produces an extremely high-pressure jet that penetrates the casing or liner to shoot into the reservoir formation.

•

The shaped charges are contained in a perforating gun assembly that can be conveyed on wireline, tubing or coiled tubing, depending on the application and the wellbore conditions. TUNIO, May' 2011,,, Courtesy AP Aung

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Characteristics and Performance of Jet Perforator Basic jet perforator consists of: • • • •

A primacord / primer The main explosive charge A conical liner A charge case or container


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Jet perforating process using a solid metal liner

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Characteristics and Performance of Jet Perforator Process of Jet Perforating • An electrically fired detonator starts a chain reaction which successively detonates • the primacord • High velocity booster in the charge • Finally, the main explosive


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Process of Jet Perforating • High pressure generated by the explosive causes the metal in the charge liner to flow, separating the inner and outer layers of the liner. • Continued pressure buildup on the liner causes a needle like high speed jet of fine particles to spew from the cone at a speed of about 20,000 ft/sec at its tip with a pressure this point estimated to be 10 million psi.


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Characteristics and Performance of Jet Perforator Factors on which Properties and extent of the crushed zone depends: • Size of perforation charge • Casing wall thickness and strength • Cement sheath thickness and strength • Grain composition, size and shape of the formation rock • Stress conditions in the near wellbore region • Closeness of nearest perforations in the same vertical plane. TUNIO, May' 2011,,, Courtesy AP Aung

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Characteristics and Performance of Jet Perforator Factors Influencing Charge Performance are as follows: • • • • •

Penetration length Perforation diameter Perforation hole volume Impact on casing integrity Perforation flow performance TUNIO, May' 2011,,, Courtesy AP Aung

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Characteristics and Performance of Jet Perforator Parameters which may influence the physical performance of the jet perforator • Gun Size/Explosive Charge Size – The size of the perforating gun will dictate the maximum explosive load which can be accommodated in the charges.


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Characteristics and Performance of Jet Perforator Perforation Charge Arrangement • The orientation of perforations defined as the angular phasing can be: – 0° , 1800 or in-line firing which can provide the minimum clearance for all perforations – 45° to 120° phasing which provides the nearest approximation to radial flow


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Characteristics and Performance of Jet Perforator


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Characteristics and Performance of Jet Perforator

Perforation shot density: Example of 4 shots/foot in line firing and 90o phasing TUNIO, May' 2011,,, Courtesy AP Aung

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Assessment of Jet Perforator Performance • Penetration prediction for formation rocks


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Perforating Gun Systems Whether the gun will be run on: – wire line – or be conveyed on tubing or a drill string. Whether perforating will be conducted prior to, or after mechanical completion of the well.


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Optional technique for perforating TUNIO, May' 2011,,, Courtesy AP Aung

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Comparison of the Bullet and Jet Perforators Jet perforation is superior to bullets • in dense formations • for penetration of multiple casing strings


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Comparison of the Bullet and Jet Perforators

In softer targets, • Bullets lose velocity when gun clearance >0.5 in. • Often use in a unconsolidated formations • Cheaper to use, rarely been used today • Bullets plug the end of the flow channel

TUNIO, May' 2011

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Comparison of the Bullet and Jet Perforators Bottom-hole temperature limitation • Jet perforating .... Up to 400 °F • Bullet perforating ..Less than 275°


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Equipment Comparisons

Jet 1.

Deeper penetration in hard rocks and multiple casing strings.

2.

Minimum burring of casing wall.

3.

Minimum cement shattering.

4.

Available for use in permanent type completions

5.

Higher temperature range. TUNIO, May' 2011,,, Courtesy AP Aung

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Equipment Comparisons Bullet 1.

Deeper penetration in soft and medium.

2.

Maximum fracturing of cement and soft rocks.

3.

Completely selective firing available.

4.

Controllable penetration available by using different bullet.

5.

High powered, large diameter gun available

6.

Generally cheaper, due to lower cost per shot. TUNIO, May' 2011,,, Courtesy AP Aung

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Candidate Selection 1.

Perforating Sandstone Wells

a. Perforate all wells in clean, non-damaging fluids normally NaCl, KCl, oil, or Nitrogen. b.

Guns and completion systems should be designed to match given well conditions.

c.

All sandstone wells should be perforated with a standard casing gun, through-tubing gun, or a tubing-conveyed gun. TUNIO, May' 2011,,, Courtesy AP Aung

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Candidate Selection d. Sandstone wells should not be perforated in acids because of severe emulsion problems and formation damage. e. Selection of perforators should not be based alone in cement and/or sand stone. It may lead to poor quality penetrations. Ability to readily clean-out and flow through the formation and perforation tunnel must be the basic criteria for perforator selection.


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Candidate Selection 2. Perforating Carbonate Wells a. Perforate in clean fluid, water or oil with a pressure differential into well bore. b. In limestone, chalk, or dolomite wells, it may be desirable to perforate in HCl or Acetic acid with a differential pressure of 200 t0 500 psi. Perforating in acid is especially beneficial if the well is to be fractured.


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2. Perforating Carbonate Wells c.

If a carbonate well is perforated in Acetic acid, this acid should remain under some differential pressure into the formation for 8 to 12 hours to allow time for dissolution of carbonates with Acetic acid.


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Candidate Selection

3. Perforating in oil, water, or acid below a higher weight mud column is not satisfactory and is not recommended.


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Candidate Selection 4. When perforating in mud or other fluids containing fines, it should be recognized that: a. It is impossible to remove mud of silt plugs from all perforations by back flowing or swabbing. b. Mud or silt plugs are not readily removed from perforations with acid or other chemicals unless each perforation is fractured with ball sealers.


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Candidate Selection 5. Drilling mud and completion fluid containing appreciable fines should not be allowed to enter perforations through out the life of the well. Water containing fines or dirty oil may be very damaging due to perforation plugging and plugging of formation pores with solids for a greater distance from the well bore.


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Thank You…


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Chapter 3 - Perforating Methods

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