Review of multi-scale and multi-physical simulation technologies for shale and tight gas reservoirs

This paper provides a comprehensive literature review on the simulation techniques being developed in recent years for describing unique flow behaviors in shale and tight gas reservoirs. The advances in modeling gas flow and transport mechanisms during the primary and enhanced gas recovery processes are reviewed in detail. The capabilities of reservoir simulation tools are discussed in terms of mathematical treatment (finite difference, finite element, explicit/implicit scheme, sequentially and fully coupled schemes), fluid flow characteristics (Darcy and non-Darcy flow, desorption, Klinkenberg effect and gas slip flow, transitional flow, Knudsen diffusion), reservoir rock properties (pore size distribution, fractures, geomechanics), multidisciplinary coupling scheme (THM, THC, THMC), modeling scale, and computational efficiency. For pore-scale modeling of gas flow and transport in unconventional reservoir rocks, the numerical methods for generating pore network models and the procedure for constructing real 3D digital rocks are first explained. Then, the network modeling methods used for simulating slip and transitional flows in pore networks are introduced and compared. After that, existing lattice-Boltzmann models developed for slip flow simulation are illustrated. Along with the explanation, pros and cons of the models for pore-scale modeling have been identified. Overall, dwelling on the concerns and challenges in shale and tight gas reservoir simulation, current status, progress and bottlenecks of numerical simulation technologies are discussed and perspectives on future development of unconventional gas reservoir simulators are proposed.