A major operator manages multiple, multiwell deep water projects in West Africa. For two such projects in Congo and Nigeria, it was determined that sand control was necessary and a stand-alone screen (SAS) completion was an efficient and cost-effective means for providing sand control for the majority of wells in both projects. This paper describes a new and unique feature of the SAS completion, called the Dual-Isolation Assembly (DIA), which addresses many challenges, and its application in Nigeria on the Egina Project.

Standard SAS completions incorporate a circulation path down the workstring, through the float shoe, and back to surface through the workstring by casing annulus for circulation, pressure maintenance, and removal of the filter cake at the operation's conclusion. The capability to wash down through the toe of the system while running in the well requires washpipe seals inside the float shoe, which incorporates spring-loaded valves that open during pumping, but close when pumping stops. In addition to the wash-down capability, the washpipe incorporates a shifter for closing an uphole isolation valve with the ability to reopen the valve, if necessary.

For an injector well, the flow path into the formation is through the sand-control screens and float shoe from the inside. The path is the opposite for a producer well, which flows from the formation to inside the screen while the float shoe is closed. Because of the different natures of the flow paths, the float shoe is continuously exercised in an injector well as a result of injection fluid starts and stops. During injection, if the opening pressure of the float shoe spring is exceeded, it could stay open over time, causing loss of integrity of the float shoe. When pumping stops, the flow path into the screen through the float shoe could heave formation particles back into the wellbore, as a result of the reservoir being energized upon injection shutdown. The DIA provides secondary and permanent isolation of the float shoe, as requested by the operator, and is capable of shifting a barrier isolation valve installed in the lower completion to comply with the operator's barrier policy for deepwater wells. The DIA and lower completion design allows the operator to safely place a filter-cake breaker treatment in the open hole after setting a lower completion packer.

In addition to fulfilling the requirements of these SAS completions, the DIA design addresses other potential challenges, such as hydraulic locks and any potential swabbing while manipulating the service tools. This paper describes the evolution of the DIA design and full QA/QC and operational procedures, which led to the successful deployment and excellent functionality of the DIA in 12 completions run to date in Nigeria.

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