A 3D hybrid DFPM-DFM Model for gas production from fractured shale reservoirs

Hydraulic fracturing as a key technology has been applied to improve gas productivity from shale reservoirs. Both induced hydraulic fractures (HFs) and inherent natural fractures (NFs) delineate a shale reservoir into matrix and fracture domains. Accurate characterizations of matrix and fracture are critical in evaluating gas production. In this work, an in-house built 3D discrete fracture model (DFM) was proposed to explicitly represent the distribution of the NFs network. Gas flow in shale matrix containing multiscale pores in inorganic matters (IOM) and organic matters (OM) was represented by a dual-fractal permeability model (DFPM). Consequentially, a hybrid DFPM–DFM model was proposed to couple gas flow and geomechanics the model was solved by commercial software based on the finite element method. The proposed model was verified using field data from a shale reservoir. The model was further employed to investigate the impacts of fractally-distributed pore size and fracture attributes on the evolutions of permeability and the associated gas production. The results showed that the fractally distributed pore size of IOM accounts for the diverse profiles of permeability evolution that exhibits a downward trend before rebounding. The impacts of pore diameter and tortuosity index on cumulative gas production were quantitatively analysed. We also highlighted the remarkable effects of fracture patterns (fracture connectivity, aperture and number) on cumulative gas production. This work provides a framework to explore the multiscale structural heterogeneities on hydrocarbon recovery and shale deformation.