Flow mechanisms are complex in the tight shale porous matrix due to the multi-physics affecting fluid flow: the geomechanical effect, slip flow/diffusion and adsorption/desorption. The multi-physics make it difficult to obtain a deep understanding of flow mechanisms and production process of shale gas reservoirs. Ignoring any physics might lead to misleading prediction or misunderstanding of shale gas production behaviors. In this work, a set of realistic experimental data of the Marcellus shale and the Eagle Ford shale are used to obtain pressure-dependent shale gas permeability considering separate and combined effects of theses multi-physics. These data include gas permeability under a series of pore pressures and in-situ stress, and methane adsorption isotherms under laboratory temperatures. This work proposes a methodology to clearly describe shale gas permeability evolution during shale gas production. Based on our results, the geomechanical effect (increasing in-situ stress) is the dominating factor influencing gas apparent permeability, and the significance of slip flow and diffusion is highlighted under low pressures, and it even overwhelms that of the geomechanical effect and adsorption at a turning pressure point when gas apparent permeability begins to increases.
Despite the rapid growth of non-fossil fuels, fossil energy still is expected to account for 78% of the global energy consumption in 2040 (IEA 2016). Fossil fuel might still be the dominating energy supply because of its large amount (Jin et al. 2014; Sonnenberg et al. 2011; Jin and Sonnenberg 2013). Natural gas is probably the most promising fossil fuel and shale gas is a major component of natural gas supplies. Horizontal drilling and multi-stage hydraulic fractured wells provide great momentum for shale gas production (Theloy et al. 2013). However, the production mechanisms are not well understood due to the complex non-Darcy flow behaviors in the porous and fractured reservoirs (Wu 2015).