Simulation and optimization of hydraulic fracturing in shale reservoirs: A case study in the Permian Lucaogou formation, China

Abstract

Long horizontal sections, small well spacings, and dense cutting are the main methods for shale reservoir development. However, there are still significant differences in oil production after large-scale fracturing of horizontal wells due to reservoir heterogeneity. This study presents a fracturing design method based on sweet spot mapping to determine the adaptability of reservoir quality and fracturing scale in order to improve the fracturing effect. First, geomechanics model is constructed utilizing logs and core laboratory tests. Then, comprehensive sweet spot mapping is captured through the two-level fuzzy comprehensive evaluation method, which considered the reservoir physical quality and engineering quality. The sweet spot divides the reservoir into three types: type I (good), type II (moderate), and type III (poor). Finally, fracturing simulation and reservoir numerical simulation are performed to optimize the fracturing parameters for different types of sweet spots. Results show that there is a strong correlation between type I sweet spot and productivity. Increasing drilling rate for type I sweet spot can improve productivity. The 5-year cumulative oil production of segmented way based on sweet spot types is 4005 m3 higher than that of uniform segmented way. Reasonable stage lengths of type I, II, and III sweet spot are 66.67 m, 50 m and 40 m, respectively, and cluster spacing is between 10 m and 12 m. Reasonable single-stage fracturing fluid volume for type I and type II sweet spot is 2200 m3, and type III is 1900 m3. Specifically, the results of applying the optimized parameters to actual well demonstrate that the design scheme has a 5-year cumulative oil production of 7026 m3 and NPV of $1.01 million higher than the actual scheme. This method will be helpful for engineers in developing a reasonable fracturing plan for shale oil in future operations.