Summary
The rise in global temperature due to an unceasingly increase in non‐condensable gases (NCG) prompts more development of safe and economical CCUS (Carbon Capture Utilization and Storage) ...technologies. Carbon dioxide (CO2) sequestration with heat mining in deep enhanced geothermal systems (EGSs) is one of the promising methods to reduce CO2 emitted to the atmosphere. In this study, a cyclic alternation of pressures at the injection and production wells is applied in an EGS for heat mining together with CO2 deposit. Simultaneous alternation of the injection and production pressures can significantly increase the amount of CO2 sequestrated compared to applying a fixed pumping or withdrawing pressures at the injector and producer respectively. At the injection well, alternation in pumping pressures at high frequency (small interval of days) increased CO2 sequestration rate. Reducing the pumping frequency resulted in the lowering of the total amount of CO2 sequestrated, lesser than using a fixed pumping pressure. The alternation in pumping frequency has a direct relationship to the CO2 sequestration rate. The frequency of the injection and production pressures refers to the interval in days of the interchange in pressure between high to a low value and vice‐versa. Furthermore, simultaneous alternation of pressures at the injection and production wells respectively (double cyclic method) improved geothermal heat extraction efficiency, thus higher performance for both geothermal and CO2 sequestration projects.
This paper showed that pressure alternation at the injection and/or production well improves the cumulative amounts of CO2 sequestration and heat mining rate. The frequency of pressure variation affects the extent of CO2 deposit. Pressure alternation at higher frequency had more potential in depositing large volumes of CO2 into the geothermal reservoir. Therefore the frequency of pressure alternation at the injector or producer wells is proportional to CO2 sequestration rates.
Summary
Hydraulic‐fracturing treatments have become an essential technology for the development of deep hot dry rocks (HDRs). The deep rock formation often contains natural fractures (NFs) at micro ...and macroscales. In the presence of the NF, the hydraulic‐fracturing process may form a complex fracture network caused by the interaction between hydraulic fractures and NF. In this study, analysis of carbon dioxide (CO2)‐based enhanced geothermal system (EGS) and water‐based EGS in complex fracture network was performed based on the thermo‐hydro‐mechanical (THM) coupling method, with various rock constitutive models. The complexity of the fracture geometry influences the fluid flow path and heat transfer efficiency of the thermal reservoir. Compared with CO2‐based EGS, water‐based EGS had an earlier thermal breakthrough with a rapid decline in production temperature. CO2 can easily gain heat rising its temperature thus reducing the effect of a premature thermal breakthrough. Both CO2‐based EGS and water‐based EGS are affected by in‐situ stress; the increase in stress ratio improved the fracture permeability but resulted in an early cold thermal breakthrough. When the same injection rate is applied to water‐based EGS and CO2‐based EGS, water‐based EGS displayed higher injection pressure buildup. Water‐based EGS had higher reservoir deformation area than CO2‐based EGS, and thermoelastic constitutive model for water‐based EGS showed larger deformed area ratio than thermo‐poroelastic rock model. Furthermore, higher values of rock modulus accelerated the reservoir deformation for water‐based EGS. This study established a novel discussion investigating the performance of CO2‐based EGS and water‐based EGS in a complex fractured reservoir. The findings from this study will help in deepening the understanding of the mechanisms involved when using CO2 or water as a working fluid in EGS.
This paper showed that water‐ based enhanced geothermal system (EGS) had significant injection pressure buildup and higher reservoir deformation due to the flow behavior and properties of water in the thermal reservoir. CO2‐based EGS had a delayed thermal breakthrough than water‐based EGS, CO2 can easily gain heat thus reducing the effect of a premature thermal breakthrough. The thermoelastic or thermo‐poroelastic constitutive models influence the level of simulated results and they should be applied in accordance to the rock mineral constituents.
Carbon dioxide (CO2) sequestration in deep geothermal reservoirs is one of the promising technique to reduce global temperature by decreasing the atmospheric CO2 content. In this study, a cyclic ...pumping technique is proposed and applied in an enhanced geothermal system (EGS) for CO2 sequestration together with heat mining process. Cyclic pumping at higher frequency (small interval of days) can significantly increase the accumulated amount of CO2 sequestrated. Reducing the pumping frequency results to lower amounts of CO2 sequestrated, less than using a fixed pumping pressure. The pumping frequency refers to the number of days between maximum to minimum pressure interchange. Furthermore, compared to a fixed low pumping pressure, a cyclic pumping technique improves geothermal heat extraction ratio, thus higher performance of the EGS.
Abstract
Carbon dioxide (CO
2
) sequestration in deep geothermal reservoirs is one of the promising technique to reduce global temperature by decreasing the atmospheric CO
2
content. In this study, a ...cyclic pumping technique is proposed and applied in an enhanced geothermal system (EGS) for CO
2
sequestration together with heat mining process. Cyclic pumping at higher frequency (small interval of days) can significantly increase the accumulated amount of CO
2
sequestrated. Reducing the pumping frequency results to lower amounts of CO
2
sequestrated, less than using a fixed pumping pressure. The pumping frequency refers to the number of days between maximum to minimum pressure interchange. Furthermore, compared to a fixed low pumping pressure, a cyclic pumping technique improves geothermal heat extraction ratio, thus higher performance of the EGS.
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