Doctor of Philosophy (PhD)
Downhole water sink (DWS) technology is an alternative to conventional limited-entry completions to control water production in wells with bottom water drive. DWS wells comprise two completions: the bottom completion produces water and keeps the top completion open to oil inflow. The system performance depends on careful manipulation of the top and bottom rates to maximize oil productivity and produce oil-free water from the bottom completion. Conventional nodal analysis cannot provide a solution for DWS wells because the critical rates for water coning change with water drainage rate. A reservoir simulator is used to model two-phase flow to the dual completions. Suites of related simulations are created and managed using algorithms to generate inflow performance relationships and build accompanying tubing performance models. A nodal analysis approach for dual completed wells is proposed. The approach identifies the operational range of top and bottom rates with water coning at the top completion and oil-free water production at the bottom completion subject to a range of practical operational constraints such as maximum drawdown. Because the operational range changes in time, optimization methods must evaluate the dynamic performance and maximize the well's discounted revenue by appropriately scheduling the best top and bottom production rates. New successive nodal analysis and stepwise optimization methods evaluate the best performance for a given moment and time increment. This localized strategy is compared with two algorithms that optimize the entire production schedule globally rather than sequentially - a conjugate gradient method (CGM) and a hybrid CGM-polytope method. Operating strategy can be optimized to maximize oil production early in wells' life using water drainage. Hybrid optimization (global search) finds the best solutions, but demands considerable computation. Stepwise (localized) optimization technique perform nearly as well for rate scheduling, final recovery, well life, and cumulative water production, and these methods are significantly more efficient computationally compared to the hybrid method. All the optimization methods analyzed in this study (static, stepwise, and global strategies) suggest that better well productivity can be achieved by maintaining low water saturation around the producing completion with DWS completions.
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Arslan, Ozan, "Optimal operating strategy for wells with downhole water sink completions to control water production and improve performance" (2005). LSU Doctoral Dissertations. 4049.