Coupled THM formulation and wellbore analytical solution in naturally fractured media during injection/production

Abstract

The heat extraction efficiency, storage, and safety of carbon dioxide (CO2) sequestration and methane (CH4) injection/post-production in naturally fractured formations have attracted significant interest. However, these studies require the examination of complex thermal-hydraulic-mechanical (THM) interacting processes, which include muti-discipline coupling and phase changes. Energy transfer mechanisms and thermally induced hydraulic and mechanical responses are critical for energy extraction efficiency , surface design optimization, and safety evaluation. The THM response in the wellbore, where fluids are injected and circulated, provides key information for design evaluation. A fully coupled formulation was developed based on a dual-porosity model to simulate the THM responses of a wellbore in naturally fractured aquifers under non-isothermal, two-phase fluid flow, and non-hydrostatic loading conditions. Local thermal non-equilibrium (LTNE) conditions are imposed for energy transportation between the fracture and matrix systems in the fissured porous solid skeleton. Different physical parameters reflecting various rock types and fracture characteristics are defined for the corresponding THM behavior models. Analytical solutions for the temperature perturbation and pressure changes in single-phase fluid flow in the vicinity of a wellbore in fissured media are developed to simulate the injection and production processes. Simulating a non-isothermal fluid circulation problem along a wellbore, an newly proposed mixed Type I (Dirichlet) and II (Neumann) boundary condition is imposed to study the heat exchange efficiency between wellbore fluid and the fissured NFM. The analytical solution has the advantages of being simple, explicitly possessing direct physical parameters, and serving as a tool for validating numerical solutions. The impacts of the newly proposed boundary condition on the near-well responses and THM results from the newly developed solution may be used to simulate the injectivity, storage capacity, reproduction, and design of supercritical carbon (scCO2) and CH4 are discussed.