GEI-RRA1100 June 8, 2010 Page 1 of 21 Riser Recoil Analysis Report for Acme Drillship Revision 00 Prepared by Groves Engineering, Inc. R R i i s s e e r r R R e e c c o o i i l l A A n n a a l l y y s s i i s s R R e e p p o o r r t t f f o o r r A A c c m m e e D D r r i i l l l l s s h h i i p p GEI Document GEI-RRA1100 Revision 00 June 8, 2010 Prepared for Acme Corp. By Groves Engineering, Inc.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
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: Revision Date: Revision Number: May 25, 2010 May 25, 2010 00 GEI Document Number: GEI-RRA1100 Project Engineer: Supervising Engineer: Josh Groves Frank Groves Engineering Manager, GEI 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.
4.1.4 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.
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.
Common Air Bottle Bank
(Qty 1)
Olmsted Anti-Recoil Valve
(Qty 6)
Accumulator(Qty 6)
Direct Tensioner
(Qty 6)
GEI-RRA1100 June 8, 2010 Page 13 of 21
Riser Recoil Analysis Report for Acme Drillship
Revision 00 Prepared by Groves Engineering, Inc.
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.
GEI-RRA1100 June 8, 2010 Page 14 of 21
Riser Recoil Analysis Report for Acme Drillship
Revision 00 Prepared by Groves Engineering, Inc.
Coefficient A -1.19E-10 Coefficient B 8.71E-08 Coefficient C -2.07E-05 Coefficient D 4.05E-03 Coefficient E -7.35E-02 Coefficient F -3.31E-10
Cylinder Stroke-Out for CV=0 20 Cylinder Stoke-Out for Full CV 400
Table 5 5th-Order Polynomial Coefficients and Boundary Conditions for Anti-Recoil Valve Control Curve
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 Units Value Nominal Top Tension lbs 2,259,000 Riser and LMRP Total Wet Weight lbs 775,103 Mud Weight ppg 17.2 Rig Heave Range inches 94.0 Rig Heave Period seconds 11.7 Nominal Telescoping Joint Space-Out inches 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.
GEI-RRA1100 June 8, 2010 Page 16 of 21
Riser Recoil Analysis Report for Acme Drillship
Revision 00 Prepared by Groves Engineering, Inc.
Item Description Units Value Closest Proximity of Telescoping Joint to Clashing inches 16.1 Closest Proximity of LMRP to BOP Clashing inches 97.2 Maximum Jump-Out from Load Ring inches 1.6 Average 95%-Full-Recoil Time seconds 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
GEI-RRA1100 June 8, 2010 Page 17 of 21
Riser Recoil Analysis Report for Acme Drillship
Revision 00 Prepared by Groves Engineering, Inc.
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 Units Value Nominal Top Tension lbs 1,096,958 Riser and LMRP Total Wet Weight lbs 953,664 Mud Weight ppg 8.55 Rig Heave Range inches 94.0 Rig Heave Period seconds 11.7 Nominal Telescoping Joint Space-Out inches 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 Units Value Closest Proximity of Telescoping Joint to Clashing inches 52.1 Closest Proximity of LMRP to BOP Clashing inches 0 Maximum Jump-Out from Load Ring inches 0 Average 95%-Full-Recoil Time seconds 24.6
Table 10 Key Results for Test Case 2: Testing Exposure to LMRP/BOP Clashing
GEI-RRA1100 June 8, 2010 Page 18 of 21
Riser Recoil Analysis Report for Acme Drillship
Revision 00 Prepared by Groves Engineering, Inc.
Figure 4 Test Case 2 Results: Testing Exposure to LMRP/BOP Clashing
GEI-RRA1100 June 8, 2010 Page 19 of 21
Riser Recoil Analysis Report for Acme Drillship
Revision 00 Prepared by Groves Engineering, Inc.
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
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.
Tmin dm
TSRmin Hm
Ws dw
fwt Hw
Bn Nfbt nAi Rf
Steel Wet-Weight Factor 0.8694 6 262300 1.990Submerged Weight Tol Factor (fwt) 1.05 1 228044 0.271Buoyancy Loss and Tol Factor (fbt) 0.98 0.9 43.25 2.261Sea Water Density (lbs/ft^3) (dw) 63.65 29000000 120939
LMRP Wet-Weight (lbs)LMRP Height Off Sea Floor (ft)
RISER CROSS-SECTIONMain 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)
LMRP INFORMATIONLMRP Dry Weight (lbs)
= 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
TENSION REQUIREMENTS, PER API RP 16Q
= Submerged Weight Tolerance Factor = Net Lift of Bouyancy Material = Bouyancy Loss and Tolerance Factor = Internal Cross-Sectional Area of Riser including fluid lines
= TSRmin * N / [ Rf * ( N - n ) ] = Ws * fwt - Bn * fbt + Ai * [ dm * Hm - dw * Hw ]
= Minimum Top Tension = Minimum Load Ring Tension = Submerged Riser Weight
= Drilling Fluid Weight Density = Drilling Fluid Column = Sea Water Weight Density
Number of Tensioners (N)
Tension Reduction Factor (Rf)Tensioners Subject to Failure (n)