BLOW OUT PREVENTERS AND BOREHOLE PRESSURISATION SYSTEMS
GEOTHERMAL AND COAL SEAM METHANE TOOLS
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Equipment
In 1994 Sigra built a borehole pressurisation tool. This device was designed to maintain pressure in a horizontal hole whilst open hole drilling took place. The tool contained a rotary seal, a pressure relief valve, a blow out preventer and a chip sampling system. The pressure relief valve was capable of passing drilling cuttings up to 6 mm diameter and maintaining a back pressure up to 7 MPa (1000 psi). The chip sampler was designed to gather coal chips under pressure so that their sorption pressure and gas content could be determined on a regular basis without the need to resort to coring. The borehole pressurisation tool performed well in trials but never became a commercial success. It did however serve as a basis for designs to come. It is described in the report Borehole Pressurisation System (ACARP Project C3072).
Sigra then designed and constructed a blow out preventer system for use with SIMCAS in geothermal conditions at Lihir mine. This system is designed to permit sub-horizontal drainage drilling through a cemented well head with SIMCAS.
Two blowout preventers are incorporated in the system. An outer BOP between the well head to the casing and an inner one between the casing and the drill rods. Drilling takes place with a hammer and eccentric bit at the end of the drill rods and the casing is simultaneously pushed into the hole. In the event of a blowout occurring both blowout preventers are closed down and steam is diverted through a tee in the well head. The rods and hammer are then withdrawn through the inner blow out preventer. The rods are then fitted with a casing plug and run to the bottom of the casing. The casing plug is then mechanically locked and sealed in the casing. The rods are disconnected and withdrawn through the casing and inner BOP. The inner BOP is then removed and the casing can be pulled through the outer BOP leaving the hole free of casing. The valve in the well head can then be closed and the outer BOP recovered. This sequence of operation is shown in drawings D16 to D18 (below).
Since this development Sigra have designed a BOP system for coal seam methane coring. The sequence of operations for this is shown in drawings D19 to D22 (below)
Recently Sigra has designed a wireline coring system for operating in an active geothermal system. This permits the core to be cut in a controlled pressure environment without the use of weighted muds. The core is then retrieved and depressurised. A seal is run into the outer core barrel and another rod can be added to the drill string. The seal is then retrieved and the inner core barrel can be run and another core cut and retrieved by the same process.
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Research and Development
Sigra is prepared to innovate and design to meet client's specific BOP needs.