The Fracability Estimation with the Digital Rock Simulation Technique for Shale Gas Reservoirs

Abstract Reservoir fracability is an important parameter to predict the potential of complex fracture network creation during hydraulic fracturing for shale gas reservoirs. The selection of a suitable fracability model is beneficial for hydraulic fracturing zones and shale gas production increase. However, it’s tough to determine the critical mechanical parameters for the fracability estimation from traditional core lab tests with limited downhole cores. Moreover, the core samples cannot be applied for repeated tests after compression tests. To offset the limitations, a digital rock simulation technique is proposed. Combined with the results of high solution CT scanning and SEM scanning of shale reservoirs at different scales, a shale digital core including clay, quartz, feldspar, and pyrite is constructed, and then the finite element method is used to simulate rock elastic parameters, and the relative sensitivity of controlling factors of elastic parameters is also determined by principal component classification. The key parameters, such as fracture dip angle, fracture density, bedding density, fracture length, brittle minerals, bedding dip angle, and other influencing factors on the sensitivity of elastic parameters are analyzed. Finally, a fuzzy analytic hierarchy model for the fracability evaluation in Sichuan Basin is established. The results show that the digital core simulation is reliable by analyzing the error between the theoretical value and the experimental value. Through microseismic monitoring and hydraulic fracturing curve verification, the fracability evaluation index established based on digital core simulation is in good agreement with the reservoir stimulated volume, which can guide shale gas reservoirs.