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BOP testing
A BOP test is a sequence of pressure tests of portions of the well control equipment, until the entire well control system is tested. Tests can be either offline (not part of the critical path of well construction activities) or online (a so-called "flat line" activity that is part of the critical path). The cost for online testing is the time required for this activity multiplied by the full spread day rate of all the time-based drilling contracts.
BOP test necessity
At the most basic level, Blow Out Preventer (BOP) systems must be maintained and inspected to ensure that the equipment will function properly. Regulators, operators and drilling contractors have put in place the requirement to test BOP systems as a method of inspection and assurance. BOP testing is a process safety critical step in the drilling, completion, workover, and plug and abandonment (P&A) phases of well operations.
BOP test plan
BOP testing consists of several pressure tests with different valve "line ups" in order to test all the components of the BOP system. Careful planning is required to ensure all components are tested, and in a minimum number of pressure tests in order to ensure efficient execution of drilling operations.
Pressure decay lead testing method
BOP testing employs a pressure decay leak testing method. Well control equipment is pressurized to a predetermined target, the pressurized volume is isolated from the pump by means of a valve, and pressure is observed. The test is deemed to have "passed" if the steady state pressure decline rate is less than a specified rate for a given period of time: otherwise, the test is deemed to have "failed" (example criterion: 3 psi/min for 5 minutes with a maximum pressure drop of less than 5%).
One shortcoming of the pressure decay leak testing method is that it is an indirect leak flow measurement. Any correlation between the leak flow rate (e.g. cc/min) and pressure decay (e.g. psi/min) must be performed with the same volume and fluid compressibility. The consequence is that a small volume test, for example a stump test, and a large volume test, say a subsea BOP testing through the choke line, will have different leak flow rates for the same pressure decline rates (likewise two different sized test volumes will have different pressure decline rates for the same leak flow rate). A similar phenomenon occurs when tests are conducted on systems with different fluid compressibility, for example when a different amount of air is trapped in a system of the same volume.
Typically, a "one size fits all" pressure decline criterion is specified for all tests regardless of the volume or fluid compressibility.
See also
A description of Digital BOP testing.