THM Induced Fluid Flux with Conductive-Convective Heat Transfer Around a Borehole in Naturally Fractured Media

Abstract For underground storage and sequestration design, studies on wellbore responses of injecting CO2/CH4/H2 into and producing it from naturally fractured media (NFM) are important for examining project efficiency, safety, and economic evaluations. A coupled formulation was developed using a dual-porosity model to simulate a coupled thermal-hydraulic-mechanical (THM) responses in an NFM with a two-phase Darcy's type fluid flow. Considering the conductive heat flow in low-permeability NFM (LPNFM) and conductive-convective energy transport in high-permeability naturally fractured media (HPNFM), analytical solutions of THM responses in the vicinity of a borehole, subject to a Cauchy-type thermal-hydraulic (TH) boundary condition and [1] non-hydrostatic loading at the wellbore and in the far field, are generated. A local thermal equilibrium (LTE) conditions over the bulk fissured medium is considered. The Laplace transform technique was applied, and semi-analytical solutions for the fluid pressures, temperature changes, and induced effective stresses in each system were developed. The results of the induced and total pressures/temperatures are generated, which are critical for wellbore integrity, capacity, and efficiency design, and the latter are critical for TH property determination, particularly when a supercritical state is surpassed. Affected by fluid mobility, temperature perturbation may significantly differ between the two media owing to a higher hydraulic flux in the HPNFM, in which convective energy transport is dominant. Subsequently, the thermally induced hydraulic-mechanical(HM) responses vary, and implications for the sequestration of CO2 and characteristics of the supercritical state of carbon dioxide, for example, for injectivity evaluation, estimating CH4 storage capacity and post-production, and performing enhanced geothermal system (EGS) design, are discussed.