Post on 22-Oct-2014
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Accumulator Sizing
Instructions
DiscussionThe purpose of the accumulator system is to provide closing energy to all members of the blowoutpreventer stack. This is usually done with a hydraulic system designed and built to provide closing power to the equipment in 5 seconds or less to maintain the required pressures as desired.
Usable fluid volume is defined as the volume of fluid recoverable from an accumulator between theaccumulator operating pressure and 200 psi above the precharge pressure. The accumulator operating pressure is the pressure to which accumulators are charged with hydraulic fluid, usually 3000 psi.
to 1000 psi what is the usable fluid volume the accumulator bottle will deliver betwen the operating pressuresof 3000 psi and 1200 psi.
In the following spreadsheets cells with BLUE numbers require input, cells with YELLOW background and RED numbers are calculated values.
In order to calculate usable fluid volumes within accumulators, the ideal gas law formula P1V1 = P2V2 is applied.For example: Assume the total gas volume of the accumulator bottle is 10 gallons. If the bottle is precharged
Solution: Since the gas law formula requires absolute pressures, we must add atmospheric pressure
P3 = 1000 psig + 15 psi (atmospheric)
V3 = 10 gal. (gas volume of Koomey 11 gallon nominal accumulator)
P1 = 3000 psig (system working pressure) + 15 psi (atmospheric)
At a pressure of 3000 psig the gas volume = V2
V1 = P3 * V3 / P1 = 1015 (10) / 3015 = 3.366 gallons (gas)
At a pressure of 1200 psig the gas volume = V2
V2 = P1 * V1 / P2 = 3015 (3.366) / 1215 = 8.352 gallons (gas)
V 1
V 2
V 3
U sab leF lu id
40 ga llons
12 .8 ga llons
F lu id leve l@ 300 ps i
F lu id leve l@ 1200 psi
F lu id leve l@ 1000 psi
4 0 G a llo n s U sa b le F lu id
3 0 0 0 p si sy stem
APEXINDO
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if operating between 3000 psig and 1200 psig.
Subsea StacksFor sizing subsea mounted accumulator bottles, the addtional precharge pressure required to offsetthe hydrostatic head of the seawater column and the effect of subsea temperature should be considered.
The precharge pressure must be increased to compensate for cold water. The temperature compensatedprecharge pressure is calculated from the follwing equation:
Therefore, the usable fluid volume (per bottle) is = (8.352 - 3.366) = 4.986 or » 5 gallons
Temperature compensated Pprech = Original Pprech * (460 + surface Temp oF) / (460 + seabed Temp oF)
Surface BOP Control System Calculation Sheetfor Control Fluid and Minimum Accumulator Volume Requirements
Control Fluid RequirementsType Size Close (gal) Closing Ratio
Annular Preventer #1 13-5/8" 5000 40.99Ram Preventer #1 21.52 10.85Ram Preventer #2 21.52 10.85Ram Preventer #3 21.52 10.85Ram Preventer #4Ram Preventer #5Choke Line HCR Valve 0.78OtherTotal 106.33
Available control fluid volume to close against zero wellbore pressure
3015 psia (usually 3015 psi)
1015 psia (usually 1015 psi)
10 gallons eachNumber of accumulator bottles 24
10 -1) ( 1 - 1015 / 3015 ) = 5.97 gallons
Available accumulator fluid = Number of bottles * Fluid/bottle = 24.0 * 5.97 = 143 gallons
Available control fluid volume to close against full wellbore pressure
Stack Working Pressure (psia) = = 1200 psiaMinimum Ram Preventer closing Ratio
10 -1) { ( 1015 ) - ( 1015 ) = 4.583 gallons1200 3015
Available accumulator fluid = Number of bottles * Fluid/bottle = 24 * 4.58 = 110 gallons
Nominal system Working Pressure (Pwork)
Nominal precharge Pressure (Pprech)
Nominal accumulator bottle volume (Volacc)
Fluid/bottle (Pwork to Pprech) = (Volacc - 1) ( 1 - Pprech / Pwork)
Fluid/bottle (Pwork to Pprech) = (
Pmin =
Fluid/bottle (Pwork to Pmin) = (Volacc - 1) {( Pprech / Pmin) - ( Pprech / Pwork)}
Fluid/bottle (Pwork to Pmin) = (
API 53BOPS system should have sufficient usable Hydraulic fluid volume (with pump inoperative) to close and open one Annular type preventer and all ram-type preventer from a full-openposition against zero wellbore pressure .After closing and opening one Annular and all ramtype preventers the remaining pressure shall be 200 psi above the minimum recommendedpressure.
API Accumulator requirement
1 times all functions Close and Open
Annular Close/Open 40.99
Ram 1 Close/Open 21.52
Ram 2 Close/Open 21.52
Ram 3 Close/Open 21.52HCR Open/Close 0.78
106.33 GL
Triplex Pump 15HP 3/4 plungger triplex pump Model T
Flow 6.4 GPM
Air Pump Model UA8026-MFlow 4.6 GPM air pump #1
Flow 4.6 GPM air pump #2Total 15.6 GPM
Up to 2000Psi accumulator volume 107 GL
Time 107 / 15.6 = 6.86 mn
Up to 3015 psi (only electric pump) volume 143 GL Volume 143 - 107 = 36 GL to come up to 3015 psi
Additional time 36 / 6.4 = 5.63 mn
Total time 12.48 mn
Surface BOP Control System Calculation Sheetfor Control Fluid and Minimum Accumulator Volume Requirements
Control Fluid RequirementsType Size Close (gal) Closing Ratio
Annular Preventer #1 13-5/8" 5000 35.37Ram Preventer #1 16.5 Ram Preventer #2 Ram Preventer #3 Ram Preventer #4Ram Preventer #5Choke Line HCR Valve 0.6OtherTotal 52.47
Available control fluid volume to close against zero wellbore pressure
3015 psia (usually 3015 psi)
1015 psia (usually 1015 psi)
10 gallons eachNumber of accumulator bottles 14
10 -1) ( 1 - 1015 / 3015 ) = 5.97
Available accumulator fluid = Number of bottles * Fluid/bottle = 14.0 * 5.97 = 83.58
Available control fluid volume to close against full wellbore pressure
Stack Working Pressure (psia) = = 1200 psiaMinimum Ram Preventer closing Ratio
10 -1) { ( 1015 ) - ( 1015 ) = 4.5831200 3015
Available accumulator fluid = Number of bottles * Fluid/bottle = 14 * 4.58 = 64.16
Rig 8 Accumulator remaining pressure after use of 52.47GL requiered by KUFPEC to close BOP will be: 1345 psia
Nominal system Working Pressure (Pwork)
Nominal precharge Pressure (Pprech)
Nominal accumulator bottle volume (Volacc)
Fluid/bottle (Pwork to Pprech) = (Volacc - 1) ( 1 - Pprech / Pwork)
Fluid/bottle (Pwork to Pprech) = (
Pmin =
Fluid/bottle (Pwork to Pmin) = (Volacc - 1) {( Pprech / Pmin) - ( Pprech / Pwork)}
Fluid/bottle (Pwork to Pmin) = (
KUFPEC Accumulator requirement Exibit B section 2-5-14
1.5 times the closing of 1 Annular, 1 Ram and Open 1 HCR
Annular Close 23.58 1.5 35.37Ram Close 11 1.5 16.5HCR Open 0.4 1.5 0.6
52.47 GL
Triplex Pump 15HP 3/4 plungger triplex pump Model T
Flow 6.4 GPM
Air Pump Model UA8026-MFlow 4.6 GPM Air pump # 1
Total 11 GPM
Up to 2000Psi accumulator volume 62.5 GL
Time 62.5 / 11 = 5.68 mn
Up to 3015 psi only electric pump volume 83.6 GL
gallons Volume 83.6 - 62.5 = 21.1 GL to come up to 3015 psi
gallonsAdditional time 21.1 / 6.4 = 3.30 mn
Total time 8.98 mn
gallons
gallons
Rig 8 Accumulator remaining pressure after use of 52.47GL requiered by KUFPEC to close BOP
Subsea BOP Control System Calculation Sheetfor Control Fluid and Minimum Accumulator Volume Requirements
Control Fluid RequirementsType Size Close (gal) Open (gal) Closing Ratio
Annular Preventer #1 88 61(Note the opening and closing volumes of one annular only are required for this calculation.)Ram Preventer #1 17 16Ram Preventer #2 17 16Ram Preventer #3 17 16Ram Preventer #4 17 16Ram Preventer #5Other 1.7Total 157.7 125
Available control fluid volume from subsea accumulators
500 feetSurface Temperature ( ° F) 50 degreesTemperature at Seabed ( ° F) 40 degrees
3000 psia (usually 3015 psi)
1000 psia (usually 1015 psi)
11 gallons each
89 AccumulatorsActual surface precharge pressure required to compensate 1020 psiafor temperature (Pprech)
11 -1) ( 1 - 1223 / 3222.5 ) = 6.21
89 * 6.21 = 552
Stack Working Pressure (psia) = 3000 = 275Minimum Ram Preventer closing Ratio 10.90
or: = 1200 psi
11 -1) { 1222.5 - 1222.5 }1423 3222.5
4.80 gallons
89 * 4.80 = 427
Water depth at which control system will operate (Dw)
Nominal system Working Pressure (Pwork)
Nominal precharge Pressure (Pprech)
Nominal surface accumulator bottle volume (Volacc)
Number of subsea accumulator bottles (Nosubsea)
Fluid/bottle (Pwork to Pprech) = (Volacc - 1) { 1 - (Pprech + .445 * Dw / Pwork + .445 * Dw )}
Fluid/bottle (Pwork to Pprech) = (
Available accumulator fluid (Pwork to Pprech) = Nosubsea * Fluid/bottle =
Pmin is the greater of: Pmin =
Pmin = Pressure to hold c/k valve open at stack working pressure
Fluid/bottle (Pwork to Pmin) = (Volacc - 1) { P prech + .445 * D w - P prech + .445 * D w }
Pmin + .445 * Dw Pwork + .445 * Dw
Fluid/bottle (Pwork to Pmin) = (
Fluid/bottle (Pwork to Pmin) =
Available accumulator fluid (Pwork to Pmin) = Nosubsea * Fluid/bottle =
Total required + 50 % 424.05 Enough Bottles
Subsea BOP Control System Calculation Sheetfor Control Fluid and Minimum Accumulator Volume Requirements
gallons
gallons
psia
gallons
Enough Bottles
BOYEL'S GASS LAW: Formula = (P1*V1)/T1 = (P2*V2)T2 = P3*V3)T3 = etc.Temperature is not taken into considderation
According to API 16 D 2005 version.
BOP Max Working Pressure 15000 Psi Ram Close 17 Gallon
Pressure pre-charge P1 1000 Psi Ram Open 16 Gallon
Volume pre-charge V1 11 Gallons Ram Close 17 GallonPressure full charge P2 3000 Psi Ram Open 16 GallonVolume full charge V2 (P1*V1)/P2 7.67 Gallons Ram Close 17 Gallon
Pressure Used Charge P3 1376 Psi Ram Open 16 GallonVolume used Charge V3 (P1*V1)/P3 7.99 Gallons Ram Close 17 Gallon
Bottles installed 86 Bottles Ram Open 16 GallonClosure ratio 10.9 to 1 Ann Close 88 Gallon
Pressure rating BOP 15000 Psi Ann Open 61 GallonAnnular size 18-3/4"/10K 1 Failsafe 1.7 Gallon
282.7 TotalNitrogen V2= (P1*V1)/P2 .= 1215*35/3015 3.33 Gallons
Volume Fluid V1-V2 .= D11-F22 7.67 Gallon
Nitrogen V3 (P1*V1)/P3 .= 7.99 Gallon
Volume Fluid Remaining V1 - V3 .= (D12-1)-F25 3.01 Gallon
Usable Fluid .= F24 - F27 4.99 Gallon
424.0 Gallon
Amount of Bottles required 86 Bottles
Conclusion Suffecient Number of Bottles
(D11 * D12) / D11
Vol Pre-Chg - Vol Rem
Full opening of all rams (max 4 rams) + 1 Annular + 1 Failsafe (see BOP Manual)
CALCULATE FUNCTION VOLUME
V
TV TOTAL SYSTEM ACCUMULATOR VOLUME
P1 MAX ACCUMULATOR PRESSUREP2
PCH ACCUMULATOR PRECHARGE
FORMULA
.= Volume Pch
104 10 1000
18.2
Note :- Fill in Yellow boxes
.= TOTAL FUNCTION VOLUME IN GALLONS. ie RAM CLOSE
.=
.=
.= ACCUMULATOR PRESSURE AFTER
.=
.= [P1-P2 / P1 * P2]* PCH *
Onboard volums
No Accumulators
CALCULATE FUNCTION VOLUME Ram closing ratio
Gallons Ram rod Ø
18.214 4.25
153.9 14.2
1040
3000 Ratio
2850 10.9 to 1
1000
Piston Ø
Accumulator Draw Down Test. Date:
Company Well No Ram Size Close Time Volume Open Time Volume PSI
L.P.R Gal GalM.P.R 2 7/8" to 5" VBR's Gal GalU.P.R 5" Gal GalU.P.R 5" Gal GalL.Annular Gal Gal
Failsafes All Gal Gal
Start Pressure in Accumulators. 3000 psi
Start Time End Time
Pipe Size
Final Accumulator Pressure : psi
Time to Pump Accumulators to 3000psi.
Using both electric pumps and air pumps While closing annular and UPR
Using emergency electric pump and air pumps While closing annular and UPR
Final Minimum Acceptable Accumulator Pressure - 1200 psi.After Test.* 1200 psi represents 50% excess Volume required.
Closing / Size requirements.* The closing System must be capable of closing each Ram Preventer within 30 Sec`s* Closing time for Annulars must not exceed 45 Sec`s.
Tool PusherSubSea EngineerCo/Man
5"
18 3/4"
* Accumulator Working Pressure must be 3000 psi
* Precharge Pressure must be 1000 psi
'file:///tt/file_convert/5447330bb1af9f4d3a8b4887/document.xls'#$Draw down test