Pore network extraction for shale gas flow in nanoporous media

• Published in: Marine and petroleum geology Vol. 126; p. 104896
• Main Authors: Yi, Zhixing, Hu, Shouzhi, Wu, Songtao, Ma, Jingsheng, Gao, Jian, Yuan, Yahui
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-04-2021
• Subjects: Apparent permeability; Apparent pore network; Intrinsic pore network; Shale gas; Intrinsic pore network; Apparent pore network; Apparent permeability; Shale gas
• ISSN: 0264-8172; 1873-4073
• DOI: 10.1016/j.marpetgeo.2020.104896

Most of pore network models were originally designed for conventional porous media (e.g. sandstone), where pore size is at micron-scale and the dominant flow is Darcy-flow. However, those models could be inapplicable for shale (a typical unconventional porous media), since plenty of nanopores exist therein and therefore the non-Darcy effects can no longer be ignored. In this contribution, the details of shale gas flow were analyzed, and it was found that flow resistance could be misestimated by previous models. For this reason, we propose a pore network model that takes into account the influences of non-Darcy effects on pore structure. In the model, pore/throat radius and throat length are not constant but change with pressure, which is distinguishable from previous models where parameters are independent of pressure. The proposed model and previous models are defined as apparent pore network (APN) and intrinsic pore network (IPN), respectively. A shale sample, imaged by focused ion beam-scanning electron microscope, was used to extract APN and IPN, and then, their network structures were compared in the terms of throat length and throat radius. Under different pressure conditions (ranging from 0.1 MPa to 48 MPa) and image resolutions (5 nm, 10 nm, 20 nm, 50 nm, and 100 nm), shale gas flow was simulated through APN and IPN, respectively. Numerical results show that apparent permeability is likely to be erroneously predicted by IPN, while APN provides a relatively reasonable solution.
•A new method, aimed at extracting pore network from shale matrix for studying shale gas flow, is presented.•The non-Darcy effects are suggested to be incorporated into pore structure.•The presented model is promising to be a reasonable alternative for apparent permeability prediction.