This topic will demonstrate you how to determine accumulator bottles required for Koomey Unit (Accumulator Unit) in order to close the surface BOP stack.
This is a specification of Accumulator (Koomey) Unit.
Accumulator 3,000 psi system
Volume each bottle is 10 gallon.
Pre charge pressure is 1,000 psi.
Minimum operating pressure is 1,200 psi (200 psi over pre charge pressure)
Usable fluid per gallon is 5 gallon.
Safety factor require is 50 %. This safety factor may be different depending on each company’s requirement.
BOP Stack and HCR’s as listed below:
|Equipment||Gallon to open||Gallon to close|
|Upper Pipe Rams||3.0||3.5|
|Blind Shear Rams||3.5||4.0|
|Lower Pipe Rams||3.0||3.5|
Please follow the steps below for calculation
1. Determine total volume require to close all of equipment
Volume = 4.5+3.5+4+3.5+0.5+0.5 = 16.5 gallon
2. Volume accounted for safety factor
Volume = 16.5 x 1.5 = 24.75 gallon
3. Determine numbers of accumulator bottles required to meet volume determined in step#2
Number of bottles = volume ÷ usable fluid per bottle
Number of bottles =24.75 ÷ 5 = 4.95 so you round it up to 5 bottles
In order to close all BOP as per requirement without any assistance of electric and pneumatic pumps, you need to have a total of 5 accumulator bottles.
You will see that based on the calculation above, determining required Koomey bottles is quite straight forward. Thing to remember is that you must use closing volume not opening volume. I see many people using the wrong figures. Even though it may not have big impact on the final result, you need to select the right figures for calculation. Moreover, the safety factor may be different based on the regulations of your working area or your company policy.
Reference books: Well Control Books