Comprehensive Reservoir Evaluation of Coal-Rock Gas Based on Geologic and Engineering Integrated Model: A Case Study in the Eastern Ordos Basin

Coal-rock gas (CRG) resources are abundant and have broad development prospects, a geologic-engineering integrated modeling methods for comprehensive reservoir evaluation is extremely important for high efficient CRG development, while there is few studies reported on the CRG modeling and reservoir evaluation process. Therefore, in present study, with the fine characterization of CRG reservoir and the analysis of the main controlling factors of gas enrichment, a systematic process of building geologic-engineering integrated geological model and comprehensive reservoir evaluation is provided for the Carboniferous Benxi Formation in the eastern Ordos Basin. The results indicate that, there is a zonal distribution characteristic in plane, and its burial depth, metamorphic grade, local positive structure, fracture development degree, and roof lithology type are the main controlling factors affecting the gas enrichment. Based on that, total gas content model was built by neural network algorithm with lab test data. Absorbed gas content model, free gas content model, Young’s modulus model and Poisson’s ratio model was built by combination method of sequential indication and co-variation. In-situ stress model was built based on DEN model, Young’s modulus model and Poisson’s ratio model. A large scale fracture model was built by ant tracking of three dimensional seismic data and a small scale fracture was built with the resistivity image interpret data. Sweet spots of coalbed methane reservoirs were identified with optimized integrated criteria, based on above-mentioned high-precision models. The study results provided references for the comprehensive reservoir evaluation of deep coalbed methane in this area and similar areas.