Abstract: Integrating and Optimizing A Reservoir Development Plan: Usari Field Development Project

Smith III, L.; J. Mohammed and W.B. Odufisan - Mobil Producing, Nigeria

The Usari field with 1.1 Billion barrels (STOIIP) is located in OML 70, 25 kilometers offshore, in 65 feet of water southwest of Qua lboe Terminal in Akwa lbom State, Nigeria (Fig. 1). The main Usari structure is an annealment phase anticline on the down-thrown side of a major down-to-the-south growth fault and is cut by several small faults and a large down-to-the-north antithetic fault. Petrophysical evaluation indicates porosities and oil saturations ranges from 25-38% and 49-89%, respectively. The API gravity ranges from 18 - 44 degrees.

The three formations; the Benin, Agbada, and Akata typical of the Niger Delta Province are present in the Usari field. The Agbada formation in this area is subdivided into three members; the Biafra, Rubble Beds (Disturbed Biafra), and the Qua-lboe Shale in younging order. The member of interest in the Usari field area is the Biafra as it contains all of the known hydrocarbon reservoirs in the field. The structural setting and stratigraphic relationship across this part of the field is illustrated in Figure 2. The Akata formation is made of deeply buried shale of very high temperature and pressure, which is widely believed to be the source of petroleum generation in Niger Delta Province.

The field was discovered in 1964 with the Usari-Ol wildcat well and was later appraised with wells Usari-02 through 06. In early 1995, the Usari field was re-mapped based on new 3-D seismic data. This new interpretation provided the basis for drilling two additional appraisal wells. The field was then re-evaluated using available RFT, core data, logs and seismic that clearly indicated as many as twenty-eight (28) reservoirs. In late 1996, development of the field was recommended based on favorable economic indicators.

The development project involved the drilling of six wells; three conventionals, and three horizontals, which provided initial drainage points in the 434 MMB P+P STOIIP from the Usari intermediate reservoirs. The horizontal wells were preceded with pilot holes which helped determine the lateral continuity of each reservoir, confirm lithology and sand facies at the target locations and refine the structural configuration prior to drilling the horizontal sections.

Due to the large numbers of stacked reservoirs, fluid contacts, fluid types, reservoir distributions and other challenges, the optimized development of this field required tremendous integration and team work. After addressing the benefits and concerns of drilling, completions, reservoir management and a technical computing strategy, the first phase of development exceeded expectations and resulted in 308 Million barrels of P1 (STOIIP) uplift and 60 TBD producibility.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil