Optimization of Well Performance in a Selective Subsea Sand-Control Completion, Offshore Nigeria

Abstract

Developing the Okwori field (offshore Nigeria) required the combination of several recent technological advances. The subsea development targeted multiple oil-bearing zones in all wells with the requirement that each zone could be operated independently. Expandable sand-screen (ESS) strings were deployed within casing for up to four zones to prevent sand production from unconsolidated-sandstone reservoirs. Independent control of all zones was made possible by use of remotely operated surface-controlled sliding-sleeve units [(ROSS) trademark of Weatherford U.K.]Losses experienced after perforating required the use of losscontrol material (LCM) for well control. Initial LCM formulation appeared to yield formation damage. A special effort ensued to design optimal LCM pills to meet project requirements. This paper presents the completion issues associated with the project, the optimization of the LCM pills, and the design and placement aspect of the remedial treatment associated with this type of completion. The evolution of the completion efficiency for each zone throughout the learning curve is presented and discussed.