This paper summarizes the strategy adopted in the development of two thin oil rim reservoirs in Okan Field, Offshore Niger Delta, Nigeria. Its objective is to elucidate the strategy, engineering analyses, subsurface assessment and production procedures set in place to optimally develop the reservoirs. Both reservoirs have oil thickness of <30 ft with gas thickness of >100 ft. The adopted development strategy for the two reservoirs involves the drilling of 4 wells, 2 in each reservoir, to drain the remaining oil reserves, prior to gas development. Because of structural and fluid contact uncertainties, soft landing was incorporated into the well designs. Shale-to-shale correlation was used for accurate horizon depth prediction and detailed simulation models with local grid refinements were employed to determine optimum well orientation, landing depth, lateral length and aquifer properties. Details on their use to maximize value are shared. While drilling, Azithrak™, a Baker Hughes tool, was used in geosteering the lateral well section to determine distance of well to nearest conductive zone as part of the oil-water contact tracking. All available data - logs, cuttings, reservoir pressures and production data - was incorporated and used to validate fluid contacts data because of the impact of landing depth relative to the fluid contacts on oil recovery. Simulation results and operational constraints were used to set acceptable production limits to ensure delivery of target reserves. All the four wells have been successfully drilled and completed, with the wells landed successfully within the thin oil column, at the optimized distance from the fluid contacts, with the wells producing at <0.55 percent water cut. Initial production performances of the four wells are in line with static and dynamic assessment forecasts. Lessons learned and challenges encountered during this development are also captured in this paper.
The objective of this paper is to share learnings from the Okan field, highlighting successful strategies adopted to mitigate reservoir and operational decline almost 8 years without producer drilling or major rig workovers. Value gained is quantified to show that over a third of the current Okan production is tied to strategies adopted during the period of interest. Details of the different wellwork methodologies are provided to communicate how value was maximized using minimal cost. Key strategies adopted that have created the Okan success story over the period of interest include the jacket-centric rigless wellwork approach which has resulted in a drop in overall wellwork costs as multiple wells on the same jacket are worked over in one mobilization. The use of interwell gas lift systems for isolated jackets unlocked reserves that would otherwise be uneconomic because of costly pipelay. In addition to enhancing production from wells requiring gas lift, the conversion of idle oil line conversions to gas supply lines for gas lift ensured available facility assets are utilized, bringing pipelay savings as well as production gain. Also, taking full advantage of the Okan Gas Gathering and Compression Platform, production from reservoirs with high GOR has been optimized, resulting in oil and gas gain without routine gas flaring. Challenges encountered and lessons learned are also shared in this paper. As a result of the strategies shared in this paper, the current Okan production is over 30% higher than what it would have been without the deployment of these strategies highlighted. The same strategies can be transferred to other assets to obtain optimum value in these times of low commodity prices.
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