Subsea Development of Okwori and Nda Oil Fields, Niger Delta

Summary Addax Petroleum's operated Okwori oil field, offshore Nigeria, illustrated the benefits of reviving shelved projects, because of an insufficient return on investment using more traditional approaches, by applying more recent technical and contractual solutions. The Okwori project demonstrated the feasibility of developing small and geologically complex offshore oil fields in medium water depth of 440 ft with subsea technologies traditionally used for large fields. In the subsurface, the Okwori wells combined multiple selective completions hydraulically controlled from the surface with expandable sand screens as the downhole sand exclusion solution. This combination of equipment in subsea wells used to fully develop a small offshore oil field marked another technological first in Nigeria. Far away from pre-existing facilities and with less than 50 million bbl of median technical reserves at the time of project sanction, the Okwori oilfield development went a step further than the more usual subsea tieback to a pre-existing offshore production facility. The Okwori development plan was based on horizontal subsea trees flowing to a leased spread-moored floating production storage and offloading (FPSO) vessel by means of (6-in.) flexible subsea flowlines and risers. The Okwori leased production facilities had a built-in capability for additional tiebacks such as the Nda oil field, whose development was completed in October 2006, or for later redeployment in other parts of the acreage depending on further exploration and appraisal drilling. A review of the field operations to date highlighted a steep learning curve in the formulation of completion design, completion fluids, stimulation, downhole sand exclusion systems, and bean-up/bean-down procedures.