Book Description

In the Canadian oil and gas industry, heavy oil and unconventional reservoirs play a vital role in sustaining the production of crude oil and face tremendous technical challenges of enhancing recovery while reducing environmental footprints. Among various development technologies, the cold heavy oil production with sand (CHOPS) and hydraulic fracturing techniques have been widely applied in Western Canadian basins to unlock the unconsolidated heavy oil and tight formation reservoirs, respectively. Both technologies are proved to be efficient during the primary production period; however, they suffer sharp production decline and low recovery factor. Moreover, during the enhanced oil recovery (EOR) phase, the existence of wormholes and fractures will cause conformance problems and early polymer injection breakthrough. Therefore, better understanding of the wormholes distributions in CHOPS reservoirs and more reliable description of fractures in tight formations become crucial for Canadian operators to design EOR pilots and operate full field applications. Reservoir characterization and modeling of CHOPS reservoirs with wormholes and fractured tight formations face numerous technical issues due to the existence of wormholes and fractures, which make the system no longer homogeneous and cause more complex problems in fluid flow and solid deformation. The boundary element method (BEM), which has been widely applied to solve for fluid flow and solid deformation problems, however, is limited to homogeneous systems. To inherit the merits of BEM such as near-analytical accuracy and negligible space and time subdivision, this research aims at developing boundary integral approaches, as extensions of BEM, to heterogeneous reservoirs with arbitrary wormhole distributions, realistic fracture morphologies, and variation of geological facies. Moreover, field operators have observed that the in-situ stress state will be altered during hydraulic fracturing with associated stress shadow effects. The depletion-induced stress changes will also cause fracture closure and stress reorientation. Accordingly, the boundary integral approaches are further extended to solve for depletion-induced stress change due to poroelastic and mechanical effects in a heterogeneous reservoir with arbitrary distribution of porosity and permeability. The universal boundary integral approaches, which include the integration of various fundamental solutions along boundaries, have been proposed in this study. The developed boundary integral approaches are benchmarked by comparing with analytical solutions and numerical simulations. Representative cases are also presented to analyze complicated heterogeneous problems. Applications of the universal boundary integral approaches for heterogeneous systems are exemplified in the areas of wormhole coverage estimation, pressure and rate transient analysis of heterogeneous reservoirs, spatial-temporal stress evolution of multi-stage fractured horizontal wells, and evaluation of refracturing upside.