Fluid flow through porous sandstone with overprinting and intersecting geological structures of various types

Abstract

AbstractIt is well established that compaction bands (CBs), joints and faults are often present in the same rock volume in the Jurassic aeolian Aztec Sandstone, exposed in the Valley of Fire State Park, Nevada, USA. Because the permeability of CBs can be one or more orders of magnitude less than the matrix permeability, and joint permeability, depending on its aperture, can be several orders of magnitude greater than matrix permeability, the combined effect of these structures on subsurface flow can be complex and substantial. In this study, we investigate the effects of a variety of intersecting geological structures on fluid flow. This is accomplished by performing two- (2D) and three-dimensional (3D) permeability upscaling and waterflood simulations over areas/volumes populated by hydraulically interacting geological features. The regions considered are approximately the size of typical grid blocks used for reservoir or aquifer flow simulations, so the results are of practical interest. The systems studied include models with two sets of vertical CBs intersecting at various angles, an inclined CB set intersecting a vertical CB set, a joint set intersecting a CB set at various angles, and a small fault and its damage zone overprinting a CB set. Our numerical results quantify the impact of these composite structures on subsurface flow and show, for example, that the intersection angle of two sets of structures can have a considerable effect on the upscaled directional permeability. In addition, waterflood simulations demonstrate that the efficiency of oil recovery can be significantly impacted by the direction of flow relative to the orientation of intersecting geological structures.