Blowout Prevention System
Blowout Prevention System is a set of several safety and operation equipment, which usually consist of annular BOP, RAM BOP, accumulator, control panel, gas-mud separator (poor boy degasser), manifolds, high pressure tubes and fitting, which are used during drilling operation.
BOP system is designed and used to prevent uncontrolled release of fluids and liquids by sealing, controlling, and monitoring oil and gas wells. BOP system shall be reliable and operational personnel shall have all necessary training and experience before handling equipment during operation. Formation kicks, which occur during drilling, can lead to catastrophic events. Formation kicks (uncontrolled flow) can occur because of several reasons, such as:
· Fluid column is not maintained with adequate mud density, making the formation pressure more than the hydrostatic pressure. Formation fluids will find a way to the wellbore and kick will occur. In this case well must be secured and killed.
· During trapping, if there is a failure to keep the hole full of mud to maintain adequate hydrostatic head, then hydrostatic pressure will be less than the formation pressure, inducing a kick.
· Swabbing while pulling out of a hole too fast can produce a suction effect resulting in a decrease in the bottom hole pressure large enough to allow formation fluids to enter the wellbore, creating a kick.
· When drilling takes place too fast and into depleted reservoirs without proper reinforcement, it can lead leave cracking on the wall, by this, losing fluids into the formation. This induces a kick.
Well control barriers which are divided into two groups, primary and secondary barriers. Secondary blowout preventer, which is secondary barrier, must be activated immediately when kick is detected. Drilling operator must secure and shut the well for killing operations. Killing operation is conduced by closing one of the BOP by control panels, which are installed in rig floor and Koomey unit. By closing BOP, operator prevents fluids flowing out of the wellbore.
After kick, drilling fluid is pumped downstream and getting returns from the analyst through to the choke line to the choke manifold. Gas-mud separator (Poor Boy Degasser) separates toxic gases, then gas is discharged to the gas flaring unit. When kick is out, well will be shut in.
Kill fluid is used to kill the well by circulating until both the drill pipe and casing pressures reach zero. Kill manifold is used to connect mud pump and the well, through which drilling fluids can be pumped into the well to control a threatened blowout.
When all barriers of blowout prevention system is failed and BOP leaked while circulating the kick out, this could lead to uncontrolled flow of formation fluids and possibly a blowout.
Main components of blowout prevention system:
Annular blowout preventer (Annular BOP) is a special mechanical device used to seal, control, and monitor oil & gas well. Annular BOP is placed on the top of ram preventers. It is called annular due to its structure; it surrounds top of the wellbore in a shape of a ring or an annulus.
Ram blowout preventer (Ram BOP) is a special assembly used during drilling as part of blowout prevention system. The shut-off valves in ram preventers close by forcing or ramming themselves together. Ram BOPs close the well by rams which operate in unison and actuated by hydraulic cylinders. Ram BOP has several types of rams, such as pipe ram, blind ram, shear ram and blind shear ram.
When operating pressure is 2000 psi, BOP stack will at least consist Annular Preventer, Ram Preventers, Drilling Spool. Annular preventer is installed on the top of the wellbore, while Ram preventers are located below the annular preventer. BOP stack for higher pressures have larger structure and more enforced composition.