Modeling gas inflow for extremely low permeability shale using CFD

Computational fluid dynamics (CFD) has been used to model 2-D well inflow over a range of permeabilities to study the impact of various well completion strategies (Augustine, 2011). Augustine\u27s 2-D model was subsequently extended for 3-D flow by Thepporprapakorn (2013), for gas flow in the permeability range of tight gas (0.01 mD). This work presents a 3-D CFD model of gas inflow valid for extremely low ranges of permeability (0.00001 mD). In extremely low permeability, gas flow is complex and includes flow from fractures, flow through porous media, and diffusive gas transport. Diffusive gas transport is important when strong density and/or temperature gradients are present in the flow systems. The study introduces and applies the concept of three dimensions of extended Navier-Stokes equation (ENSE) to assess the impact of mass diffusive transport in low permeability rock. Two dimensions of ENSE were proposed previously by Rajamani (2013). Core samples from the Huai Hin Lat formation, Thailand, were analyzed for rock properties, geomechanical properties, and used in flow experiments to validate the modeling. CT scans were conducted on multiple planes of core samples, to identify fractures, which were included manually in the CFD modeling. Evaluations of the Huai Hin Lat shale indicate the shale has rock properties comparable to other commercial shales in the United States. Results of the CFD modeling demonstrate a relatively small impact (1%) of including three dimensional ENSE gas flow from extremely low permeability shale. The work provides an assessment of the importance of the diffusive flow contributions, in the range of extremely low permeability. Results of this work are used to inform development of a single 3-D CFD gas flow model that can be used in a parametric study of completion options, over a wide range of reservoir permeability --Abstract, page iii