The paper presents a new technique designed to control unwanted water production in open-hole sections of horizontal production wells targeting carbonate reservoirs. It consists in water shut-off treatments with coiled tubing conducted through a supplementary horizontal hole drilled below and parallel to the main horizontal (water producing) wellbore to form a rigid water barrier using polyaluminumchloride and polyacrylamide. These water shut-off stages are also discussed in this paper.
The existing geological model presents a typical Bashkirian reservoir production zone. It was used to create a three-dimensional numerical flow model, which not only contained geological model parameters but also described in situ fluid dynamics. For the purposes of reservoir simulation study, the main horizontal wellbore located in the upper portion of the production zone was as summed to be 324 m long, while the length of the supplementary wellbore located in the water-oil zone was assumed to be 375 m. Over the course of reservoir simulation, it was taken into account that tracer (water shut-off composition) injection resulted in relative permeability changes in the order of 0.1 to 1 times depending on tracer concentration. This is attributable to water phase mobility changes. If no tracer is presenting model grid blocks, water phase mobility does not change. Otherwise, if a grid block is filled with tracer, particularly in the vicinity of the supplementary wellbore, water phase mobility reduces 10 times. Simulation data on tracer distribution in situ are reviewed for three simulation cases: 1) perforations around the horizontal wellbore – tracer distribution while flowing towards the production well is negligible; 2) water shut-off treatments in the upper portion of the horizontal wellbore – tracer covers a larger reservoir area compared to the previous case; 3) water shut-off treatments in the upper and side portion of the horizontal wellbore – reservoir coverage with tracer (water shut-off composition) is much more considerable compared to the previous cases. According to reservoir simulations conducted to study water-oil ratio versus tracer injection rate, the optimal injection rate for the tracer is within 0.5-1 m3/d. Numerical studies suggest that natural fracture network should also be considered during treatments. Economic assessment of further Bashkirian reservoir production performance using horizontal wells and tracer injection from the existing well is favorable.
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