Effects of injection parameters on heat extraction performance of supercritical CO₂ in enhanced geothermal systems

Abstract

Supercritical CO 2 (SCCO 2 ) is considered as a promising alternative heat extraction fluid in the enhanced geothermal system (EGS) which can reduce atmospheric CO 2 emissions and water waste. However, the heat extraction performance of SCCO 2 is greatly affected by its thermophysical properties, which are high sensitivity to temperature/pressure. In this study, by considering the impacts of temperature and pressure on thermophysical properties of SCCO 2 , a thermo-hydro-mechanical coupling numerical model was established to investigate the effects of the initial reservoir temperature as well as the SCCO 2 injection pressure and temperature on heat extraction. The variations of reservoir permeability and mass productivity as well as the net heat extraction rate (HER) were simulated by implementing the model into COMSOL Multiphysics, which showed a good consistency compared with the hightemperature/pressure triaxial seepage experiments. Simulation results indicate that there are three distinct stages in mass productivity including the slow decline stage, the rapid increase stage, and the stabilization stage. Increasing the initial reservoir temperature or the injection temperature will reduce the net HER to varying degrees.Appropriate increase of the injection pressure and injection temperature can extend Stage 2 duration which can subsequently enhance the mass productivity and the net HER. Meanwhile, the higher injection pressure or the lower injection temperature will inhibit heat compensation within rock masses and accelerate the reservoir heat depletion. This study provides guidance for optimizing the injection parameters of CO 2 -EGS and aims to enhance the net HER while ensuring a reasonable reservoir production life. K E Y W O R D S enhanced geothermal system, heat extraction experiment, high temperature/pressure, numerical simulation, supercritical CO 2 How to cite this article: Li P, Wu Y, Liu J-F, et al. Effects of injection parameters on heat extraction performance of supercritical CO 2 in enhanced geothermal systems. Energy Sci Eng. 2019;7:3076-3094. https ://doi.

Numerical Simulation on Heat Recovery Efficiency of Different Working Fluids in High-Temperature Rock Mass

“…It is found that the net heat extracted by CO 2 increases with the increase of injection pressure in the same amount of time. Comparing with the previous experimental research, the results are generally consistent with the experimental results [37]. The increase of gas injection pressure leads to the increase of gas volume flow in unit time and the heat exchange of gas in rock fracture.…”

“…In the process of CO 2 injection heat recovery, the net heat decreases with the increase of initial temperature of rock sample. Comparing with the previous experimental research, the results are generally consistent with the experimental results [37]. Due to the small size of rock sample, the temperature of 8 Geofluids fracture surface decreases rapidly after fluid injection, resulting in the rapid decrease of initial net heat.…”

A Numerical Investigation of the Nonlinear Flow and Heat Transfer Mechanism in Rough Fractured Rock Accounting for Fluid Phase Transition Effects

“…To analyze the relationship between heat transfer conditions and the local roughness of fractures, He et al [17] adopted profile waviness to reflect the local geometric conditions of fractures and recognized that the larger the profile waviness, the smaller the local heat transfer coefficient. Through the study of heat transfer in rough fractures, parameters such as fluid injection velocity, injection temperature, initial temperature of the rock layer, crack width, confinement pressure, and wall roughness all influence the heat transfer mechanisms of fractured reservoirs [18,19]. However, limited by the development of experimental equipment, current research is generally conducted on heat transfer processes at low temperatures with a certain gap from the actual temperatures of HDRs [20,21].…”

Numerical study of enhanced geothermal systems with supercritical CO2 injection considering reservoir changes

“…Results were obtained regarding changes in reservoir temperature and thermal storage lifespan. Li et al 16 developed a three‐field coupled numerical model to investigate the heat transfer characteristics of ScCO 2 in EGS. They performed sensitivity analysis on various parameters and observed that high injection pressure or low injection temperature would impede heat transfer within the rock mass.…”