Investigation on Heat Extraction Performance of Fractured Geothermal Reservoir Using Coupled Thermal-Hydraulic-Mechanical Model Based on Equivalent Continuum Method

Abstract

Natural fractures and artificial fractures in a tight rock matrix of an enhanced geothermal system make flow and heat transfer become seriously anisotropic. In this paper, a field-scale fractured heterogeneous geothermal reservoir model is built to study the heat transfer process. Based on an equivalent continuum method and local thermal non-equilibrium model, an equivalent permeability tensor is mapped from discrete fractures and a coupled thermal-hydraulic-mechanical mathematical model is adopted in which logarithmic stress sensitivity model is used to couple effective stress and permeability. From numerical simulation results at different injection rates, the contour results show the heterogeneity of flow, heat transfer and stress sensitivity are dominated by fractures distribution. Temperature contours reveal that the heat convection between water and rock in a fracture is more intense than the heat conduction between rock under different temperatures. The predicted power generation of a geothermal plant reveals the adverse effect on heat conversion efficiency, which is caused by the temperature drop at high injection rates.

Multifracture response to supercritical CO 2 ‐EGS and water‐EGS based on thermo‐hydro‐mechanical coupling method

“…The authors showed that higher heat extraction could be achieved in CO 2 ‐based EGS than water‐based EGS for more substantial formation permeability. The continuum model used by Wang et al assumed fracture properties embedded in the matrix; this fails to mimic a fractured reservoir accurately. Guo et al conducted a performance evaluation of EGS using CO 2 as a working fluid under THM coupling technique.…”

Evaluation methods and influence factors of heat extraction performance in hot dry rock reservoir under multi-field coupling

“…Huang et al (2014) evaluated the production performance of the Songliao Basin through the coupling of reservoir and wellbore, and found that ideal thermal efficiency and total output power could be obtained at the initial stage of operation, but the total output power dropped significantly after 30 years of operation. Wang et al (2019) established a THM coupling mathematical model, studied the flow, stress and temperature of HDR reservoir under different injection flow rates based on the equivalent continuum method, and studied the heat extraction performance of EGS, but there were too few influence factors in the study. Zhou et al (2022) established a THM coupling model for injection and production of HDR and compared the heat extraction performance of water injection development of HDR without considering coupling, partial coupling and full coupling.…”

How Equivalent Are Equivalent Porous Media?

“…Including fractures in numerical thermohydromechanical (THM) models is possible and several approaches have been proposed (e.g., Keilegavlen et al., 2021; Pan et al., 2014; T. Wang et al., 2019; Yao et al., 2018; Zareidarmiyan, Salarirad, et al., 2020). Yet, explicitly accounting for fractures in numerical models of poromechanical problems is a challenging task and often comes at the expenses of a very high computational cost (Lei et al., 2017; McDermott & Kolditz, 2006; Pandey et al., 2017; Salimzadeh et al., 2018; Thomas et al., 2020; Yoshioka et al., 2019).…”