Riser Recoil Analysis Report for Acme Drillship

GEI-RRA1100

June 8, 2010

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Riser Recoil Analysis Report for Acme Drillship GEI Document GEI-RRA1100 Revision 00 June 8, 2010 Prepared for

Acme Corp. By

Groves Engineering, Inc.

Riser Recoil Analysis Report for Acme Drillship Revision 00 Prepared by Groves Engineering, Inc.

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Document Information Prepared For: Acme Corp.

123 Main Street, Suite 1

City, State, Zip

Prepared By: Groves Engineering, Inc.

2755 NW Crossing Drive, #233

Bend, Oregon, 97701

Document Title: Riser Recoil Analysis for Acme Drillship Document Description: Emergency disconnect, parted riser, and recoil control algorithm analysis for the Acme Drillship in 7150 ft. and 1000 ft of water. Initial Document Date: May 25, 2010

Revision Date: May 25, 2010

Revision Number: 00

GEI Document Number: GEI-RRA1100 Project Engineer: Josh Groves Engineering Manager, GEI

Supervising Engineer: Frank Groves President, GEI

Revision Notes Revision Number:

Revised By:

Notes:

About Groves Engineering, Inc. Frank Groves has almost four decades of advanced offshore engineering experience, having focused on the hydraulic and mechanical design of riser anti-recoil systems. Josh Groves has over 10 years of experience in control system engineering, specializing in hardware and software development. GEI is based out of Bend, Oregon and can be found on the web at www.grovesengineering.com.


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Table of Contents 1

INTRODUCTION ..................................................................................................................................................................... 4

2

OBJECTIVE............................................................................................................................................................................. 5

3

SCOPE OF REPORT NOTIFICATION.......................................................................................................................................... 6

4

ANALYSIS, RESULTS AND DISCUSSION.................................................................................................................................... 7 4.1 PLANNED, EMERGENCY DEEPWATER DISCONNECT IN 7,150 FT OF SEAWATER .......................................................................................... 8 4.1.1 Predicted Sea States (Emergency Disconnect, 7,150 ft) ....................................................................................................... 8 4.1.2 Telescoping Joint Travel and Cylinder Stroke (Emergency Disconnect, 7,150 ft) ................................................................. 9 4.1.3 Riser Configuration and Top Tension per API RP 16Q (Emergency Disconnect, 7,150 ft) .................................................. 10 4.1.4 Tensioner System Design and Setting (Emergency Disconnect, 7,150 ft)........................................................................... 12 4.1.5 Anti-Recoil Control Algorithm (Emergency Disconnect, 7,150 ft)....................................................................................... 13 4.1.6 Simulation Results (Emergency Disconnect, 7,150 ft) ........................................................................................................ 15

5

CONCLUSIONS ..................................................................................................................................................................... 19

6

APPENDIX - RISER CONFIGURATION AND TENSIONS PER API RP 16Q (7,150 FT) ................................................................... 21


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1 Introduction This document presents analyses and discussions based upon the emergency disconnects simulated by Groves Engineering, Inc. (GEI) for Acme Corp. involving the drilling riser and tensioning system of the Acme Drillship. Section 4 of this document presents and discusses the analyses and results for the following Acme Drillship scenario: a planned emergency disconnect occurring in 7,150 ft of seawater. Other items covered in Section 4 include calculated riser top tension, telescoping joint vs. tensioner rod relationship, as well as tensioner system design and setup. Section 5 discusses conclusions of the analysis as well as possible improvements to the existing anti-recoil valves and to their control algorithms. The disconnects have been simulated using the GEI proprietary software, GRASIM (Groves Riser Anti-Recoil Simulation). GRASIM adheres to the guidelines of API RP 16Q wherever applicable. Dividing the riser into constituent parts, GRASIM analyzes the riser from the load ring and outer barrel of the TJ down to the LMRP. The analysis accounts for complex effects such as the viscous drag of the seawater external to the riser and LMRP and the viscous drag of the mud internal to the riser, the spring rates and buoyancies of the riser sections and the interaction of the load ring with the TJ outer barrel. For the Acme Drillship, the tensioning system consists of the load ring, tensioner cylinders, control valve, local accumulators (high and low pressure sides), piping between the cylinder and control valve and between the control valve and accumulator, compressibility of the compensator fluid, length and diameter of the air line connecting the local, high pressure accumulator to the air banks and volume of the air banks. As the LMRP clearance over bottom and telescoping joint clashing are key considerations in riser recoil analysis, both the rig’s heave amplitude and period of motion are critical. The nature of the recoil is affected by the event’s occurrence point in the heave cycle. Therefore, the disconnect analysis is performed at eight, evenly distributed points throughout one heave cycle of the rig. The vessel motion is simulated as a sinusoidal heave wave with the period and amplitude of the heave wave derived from the vessel RAOs and significant heave information provided by the rig owner/operator. The emergency disconnect is examined for the event occurrence at various points along the heave cycle. Forces, pressures, flows, accelerations, velocities, positions, etc., are calculated for very small time intervals and, thus, the program proceeds in time in an iterative manner.


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2 Objective The primary goals of the analyses presented herein are: A. Determine the top tension requirements per API RP 16Q for the Acme Drillship given various operational scenarios

B. Determine acceptable control criteria to be used with the Acme Drillship’s riser anti-recoil control system with consideration for clashing of the telescoping joint (TJ), jump-out of the outer barrel from the load ring, as well as the lower marine riser package’s (LMRP) clearance over the lower blow-out preventer (BOP) stack. The customer has prescribed that GEI optimize the anti-recoil control algorithm for an emergency disconnect event for the heaviest riser weight scenario. Then, this same algorithm will be applied to the lightest riser weight scenario and the disconnect event will again be analyzed. GEI shall assess whether multiple anti-recoil control curves are required by the Acme Drillship.


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3 Scope of Report Notification The results and recommendations of this report apply solely to the test cases as described in specific detail in this document. Groves Engineering, Inc. has relied upon the accuracy of information provided by the customer to generate this report and shall not be held responsible for inaccuracies in this information. The results and recommendations of this report exclude any consideration for the yielding of materials, failure modes of the riser and riser tensioning system, and regional or international laws that may be applicable to the design or operation of the drilling equipment. Groves Engineering, Inc. does not intend to imply any guarantee or warranty with the contents of this report, and the results and recommendations contained herein are only to be viewed as academic and informational in nature.


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4 Analysis, Results and Discussion In this section, summaries will be presented for the following recoil events that were modeled by GEI: •

Planned, emergency deepwater disconnect, 7,150 ft of seawater

For the test case above, the following information will be discussed: •

Predicted sea states

•

Telescoping joint travel and cylinder stroke

•

Riser configuration, mud attributes, and top tension requirements per API RP 16Q

•

Tensioner system design and setting

•

Key output from simulation, including LMRP and telescoping joint clearances


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4.1 Planned, Emergency Deepwater Disconnect in 7,150 ft of Seawater This section discusses the riser and tensioning system arrangement, along with the GRASIM simulation results, for a planned, emergency deepwater disconnect in 7,150 ft of seawater for the Acme Drillship. This disconnect occurs by way of a planned disconnect of the LMRP from the lower BOP.

4.1.1

Predicted Sea States (Emergency Disconnect, 7,150 ft)

The owner/operator of the Acme Drilling Rig provided the following information regarding the rig heave amplitude and period to be used for the emergency disconnect analyses. The following values have been used in this simulation:

WAVE PERIOD 11.2 seconds

HEAVE AMPLITUDE 47 inches

HEAVE PERIOD 11.7 seconds

Table 1 Customer-Supplied Rig Heave Values Used in Analyses


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Telescoping Joint Travel and Cylinder Stroke (Emergency Disconnect, 7,150 ft)

Tensioner Cylinder vs. Telescoping Joint Stroke 0 9

Over-stroke of tensioner cylinder (9 in)

0

Riser recoil control region (110 in) 119

250

444

Rig heave amplitude for typical operational conditions (58 in)

Telescoping Joint Stroke

177

110

Cylinder Stroke

4.1.2

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168 Tidal variations, stretch in riser and other variations (73 in) 241 Allowable increase in tensioner stroke due to offset (194 in) 435 Rig heave amplitude for severe operational conditions (96 in)

540

531 Excess telescoping joint stroke (165 in) 696

Full Cylinder Stroke

Nominal Space-Out

Clashing of TJ

(Fully Collapsed)

168 in 9 in 531 in 177 in 540 in (Fully Extended)

Figure 1 Telescoping Joint vs. Cylinder Stroke (7,150 ft)


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Riser Configuration and Top Tension per API RP 16Q (Emergency Disconnect, 7,150 ft)

It should be noted that the minimum tension (Tmin) as calculated by way of API RP 16Q and referred to in this document represents the sum of the upward forces exerted by all tensioner pistons on the load ring, measured parallel to the stoke path of each piston, with the weight of load ring then subtracted from this sum. Tmin = ( Fpiston * N ) – Wload ring Minimum top tension as calculated per API RP 16Q: Tmin TSRmin

= Minimum Top Tension

= TSRmin * N / [ Rf * ( N - n ) ]

= Minimum Load Ring Tension

= Ws * fwt - Bn * fbt + Ai * [ dm * Hm - dw * Hw ]

Ws

= Submerged Riser Weight

Hm

= Drilling Fluid Column

fwt

= Submerged Weight Tolerance Factor

dw

= Sea Water Weight Density

Bn

= Net Lift of Buoyancy Material

Hw

= Sea Water Column

fbt

= Buoyancy Loss and Tolerance Factor

N

= Number of Tensioners Supporting Riser

Ai

= Internal Cross-Sectional Area of Riser including fluid lines

n

= Number of Tensioners Subject to Sudden Failure

dm

= Drilling Fluid Weight Density

Rf

= Reduction Factor Relating Vertical Tension at Load Ring to Tensioners

A detailed account of the API 16Q calculations for minimum top tension requirements can be found in the Appendix, Section 6. The below summary tables capture key results of the calculations. Since inaccuracies in riser and LMRP weights significantly affect the results of the recoil analysis, all recoil scenarios were simulated for both upper and lower limit weight estimates. Utilizing the convention of API RP 16Q, the upper limit was derived by applying a factor of 0.98 to the nominal lift on the riser and LMRP, and a factor of 1.05 was applied to the nominal steel weight. The lower limit was then calculated, per the customer’s recommendation, by applying a factor of 1.00 to the nominal lift on the riser and LMRP, and a factor of


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1.00 was applied to the nominal steel weight (i.e. the lower weight limit equals the nominal weight and buoyancy). Table 2 through Table 3 below show the weights that were used in the riser recoil analysis.

Steel Weight Penalty Factor Buoyancy Module Penalty Factor

1 1

RISER AND LMRP WEIGHTS LENGTH QUANTITY PER OF SECTIONS SECTION IN GROUP (ft) 35.4 1 Telescoping Joint, Above Water 42.0 1 Telescoping Joint, Below Water Pup Joint 30ft 30.0 3 Pup Joint 5ft 5.0 2 Slick Joint (0.875" wall) 80.0 5 Bouyancy Joint 5,000ft 80.0 50 Bouyancy Joint 7,500ft 80.0 27 Bouyancy Joint 9,500ft 80.0 0 Slick Joint (0.75" wall) 80.0 5 Riser Adaptor 12.6 1 LMRP 43.3 1 TOTALS 95 SECTION GROUP DESCRIPTION

GROUP LIFT FORCE GROUP DRY GROUP WETOF SUBMERGED WEIGHT, W/O WEIGHT, W/O BUOY MODULES BUOY MODULES BUOY MODULES (lbs) (lbs) (lbs) 50874 50874 0 29986 26070 0 58971 51269 2130 11374 9889 202 164065 142638 10965 1681400 1461809 1394750 907956 789377 716796 0 0 0 149320 129819 10890 13589 11814 0 262300 228044 0 3329835 2901603 2135733

GROUP WEIGHT (lbs) 50874 26070 49139 9687 131673 67059 72581 0 118929 11814 228044 765870

Table 2 Nominal/Low Limit Riser and LMRP Weights (7,150 ft)

Steel Weight Penalty Factor Buoyancy Module Penalty Factor

1.05 0.98

RISER AND LMRP WEIGHTS LENGTH QUANTITY PER OF SECTIONS SECTION IN GROUP (ft) Telescoping Joint, Above Water 35.4 1 Telescoping Joint, Below Water 42.0 1 Pup Joint 30ft 30.0 3 Pup Joint 5ft 5.0 2 Slick Joint (0.875" wall) 80.0 5 Bouyancy Joint 5,000ft 80.0 50 Bouyancy Joint 7,500ft 80.0 27 Bouyancy Joint 9,500ft 80.0 0 Slick Joint (0.75" wall) 80.0 5 Riser Adaptor 12.6 1 LMRP 43.3 1 TOTALS 95 SECTION GROUP DESCRIPTION

GROUP DRY GROUP WETGROUP LIFT FORCE WEIGHT, W/O WEIGHT, W/O OF SUBMERGED BUOY MODULES BUOY MODULES BUOY MODULES (lbs) (lbs) (lbs) 53418 53418 0 31485 27373 0 61920 53833 2087 11943 10383 198 172268 149770 10746 1765470 1534900 1366855 953354 828846 702460 0 0 0 156786 136310 10672 14268 12405 0 275415 239446 0 3496327 3046683 2093018

Table 3 High Limit Riser and LMRP Weights (7,150 ft)


GROUP WEIGHT (lbs) 53418 27373 51745 10185 139024 168045 126386 0 125638 12405 239446 953664

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Tensioner System Design and Setting (Emergency Disconnect, 7,150 ft)

For the Acme Drillship riser tensioning system, one tensioner consists of a direct-acting tensioner rod and cylinder applying an upward force on the load ring. The hydraulic fluid in the cylinder is pressurized by an accumulator that, in turn, is pressurized by a common air bottle bank. An Olmsted Co. anti-recoil control valve lies in the fluid pathway between the accumulator and the tensioner cylinder. See Figure 2 below for a qualitative depiction of the tensioning system layout.

Accumulator (Qty 6)

Common Air Bottle Bank (Qty 1)

Direct Tensioner (Qty 6)

Olmsted AntiRecoil Valve (Qty 6) Figure 2 Qualitative Layout of Riser Tensioning System

The required top tension as discussed in Section 4.1.3 determines the necessary pressure settings for the riser tensioning system. The relationship of the cylinder to telescoping joint stroke is depicted in Figure 1. Based upon these values and the information provided by the rig owner/operator regarding the characteristics of tensioning system, the following values have been used for this analysis. Note, the values in Table 4 correspond to a nominal, calm sea state.


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Description

Units

Value

Description

Units

Value

Ambient Temperature

rankine

540

Area of Line, Cyl to Accum

In^2

7.07

Number of Tensioners

(no units)

6

CV of Valve (Fully Open)

(no units)

305

Bulk Modulus of Hydraulic Fluid

psi

250,000

Total Accumulator Volume

In^3

102,942

Total Rod Stroke

inches

540

Initial Pressure in Accum

psi

2,119

Rod Weight

lbs

6357

Initial Air Volume in Accum

ft^3

41.1

Rod-Side Cylinder Area

In^2

181

Length of Line, Accum to Bank

inches

167

Initial Pressure in Cylinder

psi

2,119

Area of Line, Accum to Bank

In^2

7.07

Initial Rod Stroke-Out

inches

168

Total Volume of Air Bank

ft^3

2079

Length of Line, Cyl to Accum

inches

167

Initial Pressure in Air Bank

psi

2119

Table 4 Tensioning System Characteristics (7,150 ft, 17.2 ppg)

4.1.5

Anti-Recoil Control Algorithm (Emergency Disconnect, 7,150 ft)

A primary objective of this analysis is the determination of the control algorithm for the rig’s riser anti-recoil system. Based upon the customer’s direction, an anti-recoil control algorithm shall be optimized to minimize telescoping joint clashing as well as outer barrel/load ring jump-out. The scenario that results in the closest proximity for telescoping joint clashing, referred to Test Case 1, occurs when the top tension is at its maximum and the riser and LMRP weights are at their low weight extreme. Based upon the customer’s description of the anti-recoil control system aboard the Acme Drillship, GEI is providing coefficients for a 5th-order polynomial that dictates the relationship of the valve CV to the tensioner position, along with boundary conditions for the control curve. The polynomial is of the structure: CV = A * CYLPOSITION ^ 5 + B * CYLPOSITION ^ 4 + C * CYLPOSITION ^ 3 + D * CYLPOSITION ^ 2 + E * CYLPOSITION + F It has been assumed that one second before the disconnect event, the control system will begin shifting the anti-recoil valve to the position as calculated by the polynomial and its boundary conditions. Thus, when the disconnect event occurs, the control valve will be fully throttled to the CV as dictated by the curve. The control curve recommended below has been optimized to minimize telescoping joint clashing and outer barrel/load ring jump-out, while maximizing LMRP clearance, for Test Case 1 as explored by GEI.


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Coefficient A Coefficient B Coefficient C Coefficient D Coefficient E Coefficient F Cylinder Stroke-Out for CV=0 Cylinder Stoke-Out for Full CV

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-1.19E-10 8.71E-08 -2.07E-05 4.05E-03 -7.35E-02 -3.31E-10 20 400

Table 5 5th-Order Polynomial Coefficients and Boundary Conditions for Anti-Recoil Valve Control Curve

Table 6 Anti-Recoil Valve Control Curve


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Simulation Results (Emergency Disconnect, 7,150 ft)

There are two primary concerns for emergency disconnect event which occurs at the LMRP/BOP interface: the LMRP’s clearance over the BOP during subsequent downward heave cycles of the rig and the clashing that can occur if the telescoping joint runs out of travel. A secondary point of interest is the jump-out which can occur at the outer barrel/load ring interface when the upward rate of travel of the riser exceeds that of the tensioner pistons. Though GEI has analyzed the disconnect event for varying riser weights, top tensions, mud weights, and telescoping joint space-outs, the two most extreme scenarios present the greatest opportunity for unfavorable outcomes. The scenario that results in the closest proximity for telescoping joint clashing, referred to Test Case 1, occurs when the top tension is at its maximum and the riser and LMRP weights are at their low weight extremes. Also, the rig is considered to be off location, exposed to larger significant waves, and the telescoping joint is at its minimum allowable nominal space-out. Table 6 below summarizes the key settings for Test Case 1.

Item Description Nominal Top Tension Riser and LMRP Total Wet Weight Mud Weight Rig Heave Range Rig Heave Period Nominal Telescoping Joint Space-Out

Units lbs lbs ppg inches seconds inches

Value 2,259,000 775,103 17.2 94.0 11.7 168.0

Table 7 Key Settings for Test Case 1: Testing Exposure to Telescoping Joint Clashing

The affect of the disconnect event on the ACME Drillship’s riser and LMRP was analyzed at eight points evenly spaced over one rig heave cycle. Table 8 below presents key results of the analyses while Figure 3 shows the outcome in graphical form. It should be observed that no modification of the control curve could fully remove the potential for jump-out, the slight parting of the load ring from the telescoping joint outer barrel. Though the jump-out is small (1.6 inches at its maximum), GEI is not prepared to make any comments on how this jump-out will influence the anti-recoil control system overall and what will occur when the riser goes into compression.


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June 8, 2010

Item Description Closest Proximity of Telescoping Joint to Clashing Closest Proximity of LMRP to BOP Clashing Maximum Jump-Out from Load Ring Average 95%-Full-Recoil Time

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Units inches inches inches seconds

Value 16.1 97.2 1.6 17.8

Table 8 Key Results of Test Case 1: Testing Exposure to Telescoping Joint Clashing

Figure 3 Test Case 1 Results: Testing Exposure to Telescoping Joint Clashing


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The scenario that corresponds to the closest proximity for LMRP/BOP clashing, referred to Test Case 2, occurs when the top tension is at its minimum and the riser and LMRP weights are at their high weight extremes. Also, the rig is considered to be off location, exposed to larger significant waves, and the telescoping joint is at its minimum allowable nominal space-out. Table 7 below summarizes the key settings for Test Case 2. Recall, per the customer’s recommendation, GEI has applied the anti-recoil control algorithm developed for Test Case 1 to Test Case 2.

Item Description Nominal Top Tension Riser and LMRP Total Wet Weight Mud Weight Rig Heave Range Rig Heave Period Nominal Telescoping Joint Space-Out

Units lbs lbs ppg inches seconds inches

Value 1,096,958 953,664 8.55 94.0 11.7 168.0

Table 9 Key Settings for Test Case 2: Testing Exposure to LMRP/BOP Clashing

The affect of the disconnect event on the ACME Drillship’s riser and LMRP was analyzed at eight points evenly spaced over one rig heave cycle. Table 10 below presents key results of the analyses while Figure 4 shows the outcome in graphical form.

Item Description Closest Proximity of Telescoping Joint to Clashing Closest Proximity of LMRP to BOP Clashing Maximum Jump-Out from Load Ring Average 95%-Full-Recoil Time

Units inches inches inches seconds

Value 52.1 0 0 24.6

Table 10 Key Results for Test Case 2: Testing Exposure to LMRP/BOP Clashing


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Figure 4 Test Case 2 Results: Testing Exposure to LMRP/BOP Clashing


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5 Conclusions It is the recommendation of GEI that, in order to account for different mud weights and, thus, top tensions, the Acme Drillship employ more than one anti-recoil control algorithm. An optimized anti-recoil valve control curve was derived by GEI for the 17.2 ppg mud weight scenario, where the only undesirable effect was a small amount of jump-out (1.6 inches) between the outer barrel and the load ring. This same control curve, however, when applied to the 8.55 ppg mud weight scenario resulted in potential LMRP/BOP clashing at significant velocities. GEI recommends that at least two additional anti-recoil valve control curves by used by the Acme Drillship’s control system to accommodate different ranges of mud weights and top tensions. These recommended additional control curves have not been analyzed in this report.


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Appendix Riser Recoil Analysis Report for Acme Drillship GEI Document GEI-RRA1100 Revision 00 June 8, 2010


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6 APPENDIX - Riser Configuration and Tensions per API RP 16Q (7,150 ft) The calculations below are based upon detailed equipment information as provided by the rig owner/operator. The minimum riser top tension calculations have been performed with strict adherence to API RP 16Q, however, high and low top tension limits have been imposed based upon the characteristics of the riser and LMRP. It should be noted that the minimum tension (Tmin) as calculated by way of API RP 16Q and referred to in this document represents the sum of the upward forces exerted by all tensioner pistons on the load ring, measured parallel to the stoke path of each piston, with the weight of load ring then subtracted from this sum.

Information Last Submitted: 6-7-2100 Information Submitted By: John Doe, Acme Drilling and Exploration Co. Information Submitted To: Josh Groves, Groves Engineering, Inc.

TENSION REQUIREMENTS, PER API RP 16Q Tmin = Minimum Top Tension

TSRmin Ws fwt Bn fbt Ai

dm Hm dw Hw N n Rf

= TSRmin * N / [ Rf * ( N - n ) ] = Ws * fwt - Bn * fbt + Ai * [ dm * Hm - dw * Hw ]

= Minimum Load Ring Tension = Submerged Riser Weight = Submerged Weight Tolerance Factor = Net Lift of Bouyancy Material = Bouyancy Loss and Tolerance Factor = Internal Cross-Sectional Area of Riser including fluid lines

FACTORS AND CONSTANTS Steel Wet-Weight Factor Submerged Weight Tol Factor (fwt) Buoyancy Loss and Tol Factor (fbt) Sea Water Density (lbs/ft^3) (dw)

0.8694 1.05 0.98 63.65

Number of Tensioners (N) Tensioners Subject to Failure (n) Tension Reduction Factor (Rf) Elasticity of Steel (psi)

LMRP INFORMATION LMRP Dry Weight (lbs) LMRP Wet-Weight (lbs) LMRP Height Off Sea Floor (ft)

6 1 0.9 29000000

= Drilling Fluid Weight Density = Drilling Fluid Column = Sea Water Weight Density = Sea Water Column = Number of Tensioners Supporting Riser = Number of Tensioners Subject to Sudden Failure = Reduction Factor Relating Vertical Tension at Load Ring to Tensioners RISER CROSS-SECTION Main Riser ID Area (ft^2) Choke, Kill, Boost, Hydro ID Area (ft^2) Total Cross-Sectional Area (ft^2) Total Mud Volume in Riser Column (gal)

262300 228044 43.25

1.990 0.271 2.261 120939

RISER SECTIONS LENGTH PER SECTION

SECTION GROUP DESCRIPTION

(ft) Telescoping Joint, Above Water Telescoping Joint, Below Water Pup Joint 30ft Pup Joint 5ft Slick Joint (0.875" wall) Bouyancy Joint 5,000ft Bouyancy Joint 7,500ft Bouyancy Joint 9,500ft Slick Joint (0.75" wall) Riser Adaptor

35.4 42.0 30.0 5.0 80.0 80.0 80.0 80.0 80.0 12.6 TOTALS

SECTION DRY SECTION DRY SECTION WETSECTION LIFT FORCE QUANTITY OF DEPTH AT BASE OF WEIGHT, W/O WEIGHT, W/ WEIGHT, W/O OF SUBMERGED BUOY SECTIONS IN GROUP BUOY MODULES BUOY MODULES BUOY MODULES MODULES GROUP (ft) (lbs) (lbs) (lbs) (lbs) 1 0.0 50874 50874 50874 0 1 42.0 29986 29986 26070 0 3 132.0 19657 21978 17090 710 2 142.0 5687 6124 4944 101 5 542.0 32813 41549 28528 2193 50 4542.0 33628 59318 29236 27895 27 6702.0 33628 60052 29236 26548 0 6702.0 0 0 0 0 5 7102.0 29864 38778 25964 2178 1 7114.6 13589 13589 11814 0 95 7114.6

GROUP LENGTH (ft) 35.4 42.0 90.0 10.0 400.0 4000.0 2160.0 0.0 400.0 12.6 7150.0

GROUP DRY WEIGHT, GROUP DRY GROUP WETGROUP LIFT FORCE W/O BUOY WEIGHT, W/ BUOY WEIGHT, W/O BUOY OF SUBMERGED MODULES MODULES MODULES BUOY MODULES (lbs) (lbs) (lbs) (lbs) 50874 50874 50874 0 29986 29986 26070 0 58971 65934 51269 2130 11374 12248 9889 202 164065 207745 142638 10965 1681400 2965900 1461809 1394750 907956 1621404 789377 716796 0 0 0 0 149320 193890 129819 10890 13589 13589 11814 0 3067535 5161570 2673559 2135733

TENSION CALCULATIONS

Submerged Riser Weight (Ws) Net Lift of Buoyancy Material (Bn) Penalized Riser Weight (Ws * fwt - Bn * fbt)

2673559 2135733 714219

MUD UNIT WEIGHT (ppg)

MINIMUM TENSION LOW LIMIT Min LMRP Overpull, LMRPmin (lbs) Min Load Ring Tension, TSRmin (lbs) Min Tensioners Setting, Tmin (lbs)

45000 987262 1096958

MINIMUM TENSION HIGH LIMIT Riser Coupling Rating (lbs) Tensioner System Limit (lbs) Max Tensioners Setting, Tmin (lbs)

2510000 2950000 2259000

8.55 10.50 15.00 17.20

MIN TENSION AT LOAD RING, TSRmin

MIN TENSIONERS SETTING, Tmin

Ws * fwt - Bn * fbt + Ai * [ dm * Hm - dw * Hw ] (lbs) 724366 960197 1504422 1770488

TSRmin * N / [ Rf * ( N - n ) ] (lbs)


965821 1280263 2005896 2360651

Tmin W/ LIMITS IMPOSED (lbs) 1096958 1280263 2005896 2259000

Riser Recoil Analysis Report for Acme Drillship

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