A fast method to estimate the correlation between confining stresses andabsolute permeability of propped fractures

Depletion of oil and gas reservoirs during production from fractured wells, or fluid injection through frack-packs may cause significant changes in the effective stress that proppants experience inside the fractures.Previous studies have shown that closure stress may change absolute permeability, however, deriving thisrelationship requires time-consuming and costly experiments that need to be repeated with the change ofproppant or field parameters. Here, we propose a methodology to estimate absolute permeability magnitudesof the propped fracture direction by just using limited knowledge about grains' geometry. In this study,Lattice Boltzmann Methods (LBM) is used to simulate fluid flow to resemble flow in propped fracturesunder reservoir conditions. Due to the large number of particle and complexity of the sitting of proppantparticles next to each other, intensive computational power is required to carry out simulations. Therefore,a parallelized LBM code is utilized to accelerate computations. The three-dimensional granular geometrywas constructed from two-dimensional micro-Computed Tomography images. The geometry was then usedas an input for the finite element analysis to simulate grain deformation/sliding upon applying differentstresses on the samples. The captured deformation of the grains' geometry was then exported to the LBMcode for calculation of permeability. Upon increasing confining stress on the samples, the proppant particlesbegan to deform, slide on each other and the pore network evolved. While the standard API cell measuresonly conductivity changes under different normal stresses, the presented method gives a greater advantageby allowing determination of the simultaneous effect of normal and shear stresses on the components of thepermeability of propped fractures. It is believed that parts of complex fracture networks may experiencesome shear stresses, but these effects could not be measured in the lab easily. Preserving core samples withthe same conditions for a long time is not feasible. Therefore, using LBM, we present a fast and reliablemethod to measure absolute permeability of proppants during flowback and production using limited datain the form of micro-CT images or 3D images of the grains forming proppant packs.