Pore-scale imaging and lattice Boltzmann modeling of single- and multi-phase flow in fractured and mixed-wet permeable media

Three investigations of pore-scale single-phase and multiphase flow in fractured porous media and mixed-wet porous media are presented here. With an emphasis on validating and utilizing lattice Boltzmann models in conjunction with x-ray computed microtomography.;The objective of the first study is to investigate fracture flow characteristics at the pore-scale, and evaluate the influence of the adjacent permeable matrix on the fracture’s permeability. We use X-ray computed microtomography to produce three-dimensional images of a fracture in a permeable medium. These images are processed and directly translated into lattices for single-phase lattice Boltzmann simulations. Three flow simulations are presented for the imaged volume, a simulation of the pore space, the fracture alone and the matrix alone. We show that the fracture permeability increases by a factor of 15.1 due to bypassing of fracture choke points through the matrix pore space. In addition, pore-scale matrix velocities were found to follow a logarithmic function of the distance from the fracture. Finally, our results are compared against previously proposed methods of estimating fracture permeability from fracture roughness, tortuosity, aperture distribution and matrix permeability.;In the second study we present a pore-scale study of relative permeability dependence on the strength of wettability of homogenous-wet porous media, as well as the dependence of relative permeability on the distribution and severity of wettability alteration of porous media to a mixed-wet state. A Shan-Chen type multicomponent multiphase lattice Boltzmann model is employed to determine pore-scale fluid distributions and relative permeability. Mixed-wet states are created—after pre-simulation of homogeneous-wet porous medium—by altering the wettability of solid surfaces in contact with the non-wetting phase. To ensure accurate representation of fluid-solid interfacial areas we compare LB simulation results to experimental measurements of interfacial fluid-fluid and fluid-solid areas determined by x-ray computed microtomography imaging of water and oil distributions in bead packs (Landry et al. 2011). The LB simulations are found to match experimental trends observed for fluid-fluid and fluid-solid interfacial area-saturation relationships. The relative permeability of both fluids in the homogenous-wet porous media is found to decrease with a decreasing contact angle. This is attributed to the increasing disconnection of the non-wetting phase and increased fluid-solid interfacial area of the wetting phase. The relative permeability of both fluids in the altered mixed-wet porous media is found to decrease. However the significance of the decrease is dependent on the connectivity of the unaltered solid surfaces, with less dependence on the severity of alteration.;In the third study we present sequential x-ray computed microtomography (CMT) images of matrix drainage in a fractured sintered glass granule pack. Sequential imaging captured the capillary-dominated migration of the non-wetting phase front from the fracture to the matrix in a brine-surfactant-Decane system. The sintered glass granule pack was designed to have minimal pore space beyond the resolution of CMT imaging, so that the pore space of the matrix connected to the fracture could be captured in its entirety. The segmented image of the pore space was then directly translated to a lattice to simulate the transfer of fluids between the fracture and the matrix using lattice Boltzmann (LB) modeling. This provided us an opportunity to validate the modeling technique against experimental images at the pore-scale. Although the surfactant was found to alter the wettability of the originally weakly oil-wet glass to water-wet, the fracture-matrix fluid transfer is found to be a drainage process, showing little to no counter-current migration of the oil-phase. The LB simulations were found to closely match experimental rates of fracture-matrix fluid transfer, equilibrium saturation, irreducible wetting phase saturation and fluid distributions.