Well control equipment falls into five basic working pressure classifications:·13,800 kPa (2000 psi) WP,·20,700 kPa (3000 psi) WP,·34,500 kPa (5000 psi) WP,·69,000 kPa (10,000 psi) WP,·103,500 kPa (15,000 psi) WP.
The BOP stack rating of used BOP"s (> 5 years old) should be at least 10% higher than the maximum expected surface pressure that could be encountered during drilling and workover operations. The safety margin may become less than 10%, depending on condition and age of the BOP stack. Higher rated BOP stacks need only to comply with the recommended configuration for the required working pressure classification.
General considerations for selecting well control equipment
The following considerations should be made when selecting well control equipment:
- the equipment shall be selected to withstand the maximum anticipated surface pressures;
- the blowout preventer stack shall consist of remotely controlled equipment capable of closing in the well with or without the pipe in the hole;
- welded, flanged, or hub connections are mandatory on all pressure systems above 2000 psi as apposed to threaded connections;
- in some areas, well control equipment suitable for sour service may be required; in such cases the complete high pressure BOP system should consist of metallic materials resistant to sulphide stress cracking. (Well Control Planning H2S)
- dedicated kill lines must not be smaller than 2" nominal and shall be fitted with two valves and an NRV. Choke lines must not be smaller than 3" through bore and are to be connected with two valves to the BOP stack of which the outer valve shall be hydraulically operated. When dual purpose kill- and choke lines are employed, both lines must not be smaller than 3" through bore and the outer valve of each line shall be hydraulically operated.
- during drilling and workover operations, blind/shear rams shall be provided in the BOP stack. The blind/shear rams shall always be capable of shearing the drillpipe/tubing in use under no-load conditions and subsequently provide a proper seal.
- closing systems of surface BOP"s should be capable of closing each ram preventer within 30 seconds; the closing time should not exceed 30 seconds for annular preventers smaller than 20" and 45 seconds for annular preventers of 20" and larger (see also API RP53);
- closing systems of subsea BOP"s should be capable of closing each ram preventer within 45 seconds. Closing time should not exceed 60 seconds for annular preventers (see also API RP53);
- all master and remote operating panel handles should, at all times, be in the full open or closed position, and be free to move into either position, i.e. the shear ram operating handles should not be locked;
- all spare operating lines and connections which are not used in the system should be properly blocked off with blind plugs at the hydraulic operating unit;
- all four way valves should be either in the fully open or fully closed position, as required; they should not be left in the blocked or centre position.
Last Updated on Thursday, 30 June 2011 07:52