Flow Dynamics and Pore Scale Physics in Unconventional Shale Reservoirs Available to Purchase

This paper sheds a new light on the physics of flow and the relevant hydrocarbon recovery mechanisms from liquid-rich shale reservoirs. Spatial confinement in tiny pores affects the phase behavior, fluid properties and flow behavior as a result of the pore proximity. Specifically, it is theorized that the phase behavior, capillary pressure and relative permeability are influenced by confinement effects in small scale pores of nanometer size. The phase envelope in nanopores will shift to a point where many reservoir hydrocarbon mixtures are in supercritical state. Also, interfacial tension is reduced due to confinement effects causing a reduction in capillary pressure. By the same token, the relative permeability will be modified in the nanopores and mesopores because of lower capillary pressure as well as the shift in phase envelope. In mesopores, the favorable phase envelope shift, capillary pressure, and relative permeability are assumed to have intermediate effects (i.e., the mid-confined effects). The macropores on the other hand have no pore proximity effects and will behave similar to the conventional pores with no shift in phase behavior, capillary pressure, and relative permeability. The multiphase mass transfer and flow in the above pore scales is of great interest to understand production mechanism of liquid-rich shale reservoirs. In this paper we constructed several flow models to assess the viability of pore confinement concepts. The focus will be deciphering the phase behavior, capillary pressure, and relative permeability effects in nano, meso, and macropores. We evaluate these effects using hierarchy of subdomains which are based on shale pore size distribution. Their effects are captured using dual permeability model with detailed logarithmic spaced local grid refinement (LS-LGR) with the following allocation: 20% confined, 30% mid-confined, and 50% unconfined pore regions. We applied the model to Eagle Ford shale reservoir dew-point and bubble-point fluid systems. For the dew-point system, inclusion of shifted phase envelope in several matrix allocated subdomains promotes slight oil production while keeping total gas produced the same. For the bubble-point system, inclusion of shifted phase envelope promotes more oil production and lowers the onset of gas evolution. Capillary pressure and relative permeability confinement effects have marginal impact on incremental hydrocarbon recovery during primary production; however, these effects are expected to be significant during secondary and tertiary production scenarios.