Challenge

• Increase the cutting capability of work over systems to cut larger sizes of coil tubing for thro’ riser well intervention operation

Solution

• En-Tervene; the development of a ram valve that provides the cutting and sealing performance of a drilling BOP in a compact external envelope for deployment with a sub-sea thro’ riser work over system.

Benefits

• Significant improvement in the reliability and operating capability of sub-sea work over well controls valves, combining intensified closure force through the ram linkage mechanism to increase the shear capability with pressure energised sealing technology for optimum sealing characteristics.

Operating challenges

• Many of the fields developed with sub-sea production systems now require intervention operations, the requirement for and difficulty of these operations being increased by the complexity of reservoirs and the nature of the wells with long horizontal producing sections that often require the use of compressively stiff and larger sizes of coil tubing for remedial operations or the deployment of intervention tooling.
• The critical function when deploying this equipment in a sub-sea environment is the ability of the sub-sea work-over system to cut the intervention string and isolate the well. Current sub-sea work over systems are generally designed for deployment within a marine riser and BOP stack with the use of ball valves as the primary cutting and sealing device. The use of a ball valve to provide a cutting function is unique to this type of application and the incapability of the ball valve to cut larger sizes of coil tubing and reliably seal the well often restricts the use of the coil tubing as an intervention medium.

Solution

• Conventional BOP systems feature horizontally opposed rams, hydraulically actuated by pistons mounted on the axis of the ram. This design whilst offering increased operating integrity over ball valves requires a considerable external envelope that precludes the use of this technology in a thro' riser application.
• The En-Tervene ram was conceived to provide ram technology with the advantages of enhanced operating and sealing integrity with an external envelope that can be deployed within the constraints of a marine riser and BOP.

Development

• The expansion of the initial concept was to provide the cutting performance, reliability and ruggedness of conventional BOP in a dimensional envelope suitable for sub-sea thro' riser applications. The development program conducted in conjunction with a major oil company consisted of the design and manufacture of a series of prototypes to initially establish the operating characteristics of the technology and progressively refine the design to meet or exceed relevant industry standards for performance and reliability.

Operation Mechanism

• On a conventional BOP, large opposing horizontally mounted cylindrical actuators are connected to the rams via straight axial stem. On En-Tervene a vertically mounted actuator is connected to the rams via a pin jointed high efficiency linkage mechanism. This reconfiguration offers a unique set of benefits, the most obvious of these is compact size of the diametric envelope that enables the system to be used in sub-sea thro' riser or surface applications where vertical access to the well is restrictive. In a conventional BOP, force created by the internal bore pressure acts on the end of the actuator stems, whereby in certain failure modes the BOP will fail in the open position. In comparison, the vertical actuator of the En-Tervene valve is balanced to the internal bore pressure ensuring that the same failure modes would not suffer from the same tendency to move to the open position.
• The use of a pin jointed link mechanism to transmit the vertical force of the actuator to the horizontal force on the ram system is extremely efficient and minimises the frictional losses within the system whilst intensifying the force delivered to the ram to provide the optimum force required for obstruction cutting. A further benefit emerges from the configuration of the vertical actuator, when closure of the rams is initiated in a flowing well, the rams as they are closing create an orifice and as a consequence of this a pressure drop develops across the rams whereby the higher upstream pressure assists in the ram closure. This characteristic distinguishes En-Tervene from other well control technology that have a limited capacity to close against well flow, instead stalling in a partially closed position.
• A further important aspect of the En-Tervene design is the ability of the mechanism to withstand the entrainment of debris, exceeding the debris tolerance of valve systems specifically designed with this in mind.

Applications

• The En-Tervene ram valve is available for a wide range of applications in sub-sea thro' riser, open water and surface well intervention operations from lubricator and sub-sea test tree valves to BOP applications for coil tubing and drilling operations.