Technical and economic optimization of marginal mature fields currently becomes a major industry concern: such fields contain considerable amounts of hydrocarbon reserves that could be produced using current technology simplifying lack of pressure support and interference phenomena issues. The total oil recovery factor of depletion drive reservoirs varies from 5 to 30%. This type of reservoir does not initially have a source to maintain pressure: energy is mainly supplied by the release of dissolved gas due to the rapid continuous decrease in pressure and the low compressibility of fluids. Multilateral wells technology accomplished with ESPs is used in our study to mitigate the interference phenomena and provide the strong pressure support to the system- a theoretical marginal reservoir. The major objectives of this work are to design various multilateral alternatives, analyze technical standards and specifications, observe production performance, and judge the designs technically, economically, and based on ethical and environmental codes compliance. Design alternatives of this study contain 2, 4 or 6 fishbone type laterals under 45 or 90 degrees inclination angles. The main horizontal bore is fully cased and cemented, and the branches are fully cased and perforated. All alternatives were accomplished with Electrical Submersible Pumps (ESP) technology. Based on technical performance (Recovery Factors and Cumulative oil production) one design alternative was selected as the best one (2 laterals from 45 degrees group): RF was enhanced from initial 2.6 to 22.6 %. Based on the results of economic evaluation and risk analysis, alternative with dual 2 laterals under 45 degrees inclination demonstrated the best performance. Production performance of marginal field was optimized increasing the RF from primary recovery 2.55 % to 22.63 % after utilization of multilateral well technology combined with ESP-s.

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