Characterisation and analysis of non-linear seepage in different regions of deep shale-gas reservoirs

To investigate the seepage characteristics of deep shale gas reservoirs, considering their complex pore and fracture networks (including both natural and artificial fractures), nonlinear seepage experiments were conducted on three rock samples. Combined with micro-nano CT technology, these experiments analyzed how changes in effective stress and production pressure differential jointly affect reservoir seepage, providing insights into seepage patterns under extraction conditions. The results indicate: (1) The seepage characteristics of the without fractures and fracture systems are consistent; permeability is inversely proportional to effective stress and directly proportional to the pressure gradient. (2) Fracture aperture and morphology significantly affect the stress sensitivity of the reservoir. Under an effective stress of 50 MPa, the permeability damage relationships are: fracture system (90%) > microfractures (70%) > natural bedding (55%). (3) The more developed the fractures, the lower the initiation pressure gradient, with the fracture system at 0.0018 MPa/m, microfractures at 0.0382 MPa/m, and natural bedding at 0.0525 MPa/m. (4) At an effective stress of 20 MPa and a pressure gradient of 1 MPa/m, the seepage capacity of the without fractures system (average 3.522×10 -4 mD) is significantly lower than that of the fracture system (0.775 mD).Under effective stress, the average pore and throat damage in the without fractures system is 19.01% and 18.32%, respectively, while in the fracture system, it is 26.27% and 23.16%. This study, through a combination of physical experiments and numerical modeling, provides experimental support for the study of seepage patterns in shale gas reservoirs.