The Federal Government of Nigeria in a bid to promote indigenous companies participation in the oil and gas sector, and to grow the nation’s production capacity passed legislation in 1999 to foster the exploitation of Marginal Oil Fields (MOFs). MOF is one that is considered non – commercial as a result of strategic business development philosophy of the operator, often times large oil companies. Reservoir management is central to the effective exploitation of any hydrocarbon asset; this dependence is heightened for an undeveloped marginal field. There is no ‘one-size fits all’ approach to reservoir management; this paper reviews some techniques adopted by Midwestern Oil and Gas Ltd in the development of the Umusadege marginal field.
These techniques fall under three categories: (I) subsurface study (II) well placement and spacing, (III) integrated surface production and optimization, in accordance with regulatory practices.
The previously acquired 3-D seismic data was reprocessed and interpretation of reservoir heterogeneities within the Umusadege field concessionary boundary carried out form the basis of the initial field development plan. To optimize reservoir drainage, the general principles of non-interference well spacing were employed, and advanced well placement technology was deployed to guarantee optimum well placement within the reservoir for effective and efficient drainage.
Subsequently, 14 vertical wells and 4 horizontal wells were drilled to effectively optimize recovery from the field. Prior to bringing these wells on-stream, clean-up and Maximum Efficiency Rate (MER) tests were conducted to determine the optimum choke settings, GOR and water cut limits for all wells. An integrated approach encompassing choke sizing, gas and water production management, vessel and line sizing were implemented on the Umusadege field to maintain and optimize recovery. Crude custody transfer measurements and export were enabled by an optimized Group Gathering Facility (GGF).The above techniques combining new technologies, traditional reservoir and production strategies led to the successful development of the Umusadege field; increasing daily oil production from 2,000 bbls/d from the first well re-entry to approximately 30,000 bbls/day over a 7-year period. This case study proves that with the correct implementation of the key elements of reservoir management the value of any hydrocarbon asset can be maximized in a cost effective, safe and environmentally friendly manner.