Investigation of gas flow in shale gas reservoirs in the transition regime

Shale and tight gas reservoirs consist of porous structure with diameter of pores in the range of some mm to μm. In these scales, pores diameter become comparable to the gas mean free path. Flow in such structures fail often in the transition and slip flow regime. Standard continuum fluid method such as the Navier-Stokes-Fourrier set of equations fails to describe flows of these regimes. Kinetic theory such as the Boltzmann equation must be adopted. Here, we present a Direct Simulation Monte Carlo study of a 3D porous structure in an unlimited parallel simulation and we describe the gas properties. The three-dimensional geometry was obtained using a microcomputed-tomography (micro CT) scanner with a resolution in the scale of some μm. We present results at different Knudsen numbers and compare them with other continuum methods. In addition the method is also examined in convectional gas reservoirs and compared with unconventional one. Our findings demonstrate that significant differences appear in gas properties depending on the method that it's been used and the Knudsen number. In lower Knudsen number the methods show similarities, while in transition and slip flow regime different results between Navier-Stokes-Fourrier and Direct Simulation Monte Carlo have been gained.