Pore-level modeling of gas-condensate flow in porous media

The objectives of this work are (1) to establish a pore-level model to observe the single-phase non-Darcy flow behavior in the near-wellbore region of high-capacity gas and condensate reservoirs and (2) to develop a mechanistic network model for multiphase flow in gas condensate reservoirs. Pore-scale modeling is a powerful tool that may be used to calculate macroscopic flow properties such as capillary pressure and relative permeability. In addition, pore-scale models provide insights into the accuracy of assumptions in continuum-scale models used in reservoir simulation.; Three structural models of anisotropy are proposed: size-induced, connectivity-induced and spatial correlation-induced. Porous media are represented by network models with pore bodies interconnected by pore throats. Bodies and throats are characterized by their connectivity, shapes, and distributions of radii. Non-Darcy flow is computed in these networks. The tortuosity and porosity of the media are also determined. A tensorial form of the Forchheimer equation is proposed and verified. The non-Darcy term is found to be tensorial and proportional to the square of the superficial velocity at the macroscopic scale. As the pore-scale anisotropic parameter increases, non-Darcy and tortuosity components increase, but the permeability components decrease. An approximate correlation is derived between the non-Darcy coefficient, the permeability, and the tortuosity tensors.; A mechanistic network model for the critical condensate saturation is constructed in which phase trapping and connectivity in the pore comers are examined critically. Pore-level laws are identified from micro-model experiments with near-critical fluids. A non-zero critical condensate saturation can be obtained even in the absence of contact angle hysteresis because of the converging-diverging nature of the throats. The critical saturation at which the condensate flows is found to be a function of pore geometry, water saturation, and interfacial tension (or the Bond number). The modified sphere-pack model underpredicts the critical condensate saturation of typical sandstones. The cubic model adequately predicts the critical saturation and the experimentally observed trends.; The cubic model is used to identify several flow regimes important to gas-condensate flow. The effect of pore structures on gas and condensate relative permeabilities is calculated in the low-capillary number regime and high-capillary number flow regime. The relative permeabilities and non-Darcy coefficients have been computed for the low-condensate-saturation/high-pressure gradient flow regime.