Marine drilling riser
MARINE DRILLING RISER (EN: water trap column, water separator column; DE: Wasserabscheider, Erdolfeldwasserabscheider; FR: colonne de separation d'eau; ES: columna separadora de agua; RU: водоотделяющая колонна) is the element of the underwater wellhead equipment of the borehole, which element is serving for the connection of the underwater mouth of the borehole with the rotary table of the drilling installation of the watercraft (platform, vessel). The marine drilling riser isolates from the stratum of the water the tools and the drill string, which is directed into the mouth of the borehole, and permits us to conduct the marine drilling with the closed-loop circulation of the drilling fluid.
The marine drilling riser comprises the individual links of the pipes with the diameter of 400-600 millimetres and more, with the length of 8-12 metres, with the locking connections. During the displacements of the watercraft, the marine drilling riser experiences the tensile, compressive, and bending forces (the total tensile forces reach 160-200 tonnes). The strength of the marine drilling riser is ensured using the sliding telescopic devices, using the tensioning hydraulic devices, and using the ball joint assembly. The telescopic connection, which is compensating the change of the length of the marine drilling riser, represents by itself two pipes, which are inserted one into another, and which are sealed using the special sealing ring. The external pipe of the telescopic compensator is connected using the coupling with the last section of the marine drilling riser, and is pulled up with the help of the four ropes of the system for the tensioning. The internal pipe is hang to the girders of the rotary table, and there is placed on the upper end of this pipe the funnel with the nozzle for the delivery of the drilling fluid into the system for the purification.
The hydraulic device is installed onto the deck, and comprises the hydraulic cylinders, which are built into the polyspast system, on the account of which the stroke of the rope, which is creating the constant tensile forces within the marine drilling riser, independently of the pitching of the watercraft, is increased by 4 times. The free end of the rope, through the system of the blocks, is attached to the external pipe of the telescopic connection, and thus is pulling the marine drilling riser. The tensioner with the usage of the ropes can transmit the force of up to 45 tonnes each, with the length of the stroke of the rope of 15 metres.
The lower part of the marine drilling riser is the connecting element, which comprises the ball joint for the compensation of the angular deviations of the marine drilling riser, and the block of the preventers of the equipment for the prevention of the blowout, with the couplings for the connection of the marine drilling riser with the wellhead. Along the entire length, they equip the marine drilling risers with the additional pipeline of the small diameter for the plugging of the borehole, and also with the multi-channel hoses for the operational control over the work of the underwater wellhead equipment (the remote opening and closing of the rams of the preventers, and of the hydraulic coupling of the ball joint). The length of the marine drilling riser is determined by the depth of the water at the point of the drilling.
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