Quantitative characterization of the effect of geomechanical coupling on solute transport and permeability evolution in fractured rocks is an open problem in geologic carbon sequestration, groundwater contaminant remediation, enhanced oil recovery, and tracer-based reservoir surveillance. Despite recent advances in modeling flow and geomechanics coupling, a holistic approach to capturing the synergy between fluid flow, solute transport, induced stresses, and fracture mechanics is lacking. This study investigates the rich interplay between these processes by proposing a novel computational framework to solve the coupled flow, transport, geomechanics, and fracture mechanics problem. Embedded Discrete Fracture Modeling (EDFM) is used to model the flow and transport processes in fractured porous media while an improved Bandis model is employed to capture the fracture-mechanical response to flow-induced stress perturbations. The role of transport-geomechanics coupling in modulating the spreading and miscibility of a solute slug during viscously unstable flows is examined. We examine how flow-transport coupling, parameterized through the solute viscosity contrast and the fracture permeability, influences the stress state and fracture stability in the domain. A case study, inspired by a huff-n-puff tracer flowback study, is conducted to investigate the applicability of the proposed framework in the field. A sensitivity analysis is performed to evaluate the dependence of global transport characteristics, permeability evolution, and fracture stability on parameters dictating the strength of coupling between geomechanics, flow, and transport.

1. Introduction

Applications of fluid injection into naturally or hydraulically fractured reservoirs are evident in many engineering disciplines: carbon sequestration (Iding and Ringrose, 2010), contaminant tracking (Sahimi, 2011), tracer surveillance (Warner et al., 2014), and enhanced oil recovery (EOR) (Jimenez et al., 2016). In those practical scenarios, it is important to characterize how well the injectant mixes with the in-situ fluid and the spatial coverage of the resultant mixing zone. This is critical in dictating the success of the injection operation, i.e. delivering costly injectant to sweet spots to attain optimal miscibility (EOR), ensuring permanence and security of storage/disposal (carbon sequestration), or tracking the spatial and temporal distributions of tracer particles (contaminant tracking). The geologic formations are often geomechanically sensitive because of the presence of discontinuities (i.e. joints, faults, or fractures) and the heterogeneity in consolidation environment. Therefore, there is a need to integrate geomechanical coupling in transport modeling to examine the extent of impact of stress-activated processes on macroscopic transport metrics (Tran and Jha, 2018).

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