Geothermal Energy Extraction Research Articles

Prediction of new vortices in single-phase nanofluid due to dipole interaction

Magnetic field effects are encountered in many engineering applications which include but are not limited to metal casting, nuclear reactor coolers, and geothermal energy extraction. On the other hand, due to their outstanding thermal performance, nanofluids have been successful in obtaining acceptability as per the new generation of heat transfer fluids in automotive cooling devices, in heat exchangers, and building heating. Therefore, this research is carried out to understand how the nanofluid flow in a cavity is affected by a magnetic field (due to a dipole placed nearby). The single-phase model is employed for modeling the nanofluid, whereas the governing partial differential equations are solved numerically. The dipole may give rise to the new vortices in the flow near its location while enhancing Nusselt number. The Reynolds number reduces Nusselt number along the lower wall while affecting the strength of vortices near the dipole location. Increasing the strength of the dipole results in distorting the symmetry of streamlines by first enhancing the size of the lower vortex; some vortices near dipole also join and merge. Further, the magnetic field makes the temperature field nonsymmetric and shifts the zone of higher temperature gradient around the location of a dipole. The presence of dipole is more effective for skin friction compared with the Nusselt number.

A COUPLING ANALYSIS FOR HEAT TRANSFER AND WATER FLOW IN A FRACTAL ROUGH FRACTURE OF GEOTHERMAL RESERVOIRS

The coupling of heat transfer and water flow in rock fractures is a key issue to geothermal energy extraction. However, this coupling in a rough fracture has not been well studied so far. This paper will study this coupling in a rock fracture with different roughness. First, multi-scale and self-affine rough fracture are constructed through the Weierstrass–Mandelbrot function and embedded into a rock block. Its single scale trend line is also derived. Second, a roughness factor is proposed based on the standard deviation of each segment from the trend line and introduced into the governing equation of fracture flow. After coupling with heat transfer and matrix deformation, a thermal-hydro-mechanical (THM) coupling model is formulated for a rough fracture flow. Third, an analytical solution is derived through the Laplace transform and Stehfest method and used for the validation of this THM coupling model. Finally, the effects of fracture roughness and matrix deformation on heat transfer and fracture flow are numerically investigated. The simulation results indicate that the rock fracture with lower fractal dimension has higher heat transfer efficiency. The effect of fracture roughness on heat transfer is much greater than that of aperture variation induced by the shrinkage of rock matrix.

Poroelastic Solution for the Nonlinear Injectivity of Subsurface Rocks With Strain‐Induced Permeability Variations

AbstractFluid injection in porous rock occurs in a variety of hydrogeological operations including wastewater disposal, CO2 sequestration, enhanced oil recovery, and geothermal energy extraction. Influx of fluid into the host rock is usually accompanied by induced permeability enhancement due to increased pore fluid pressure and consequent dilation of the pore volume. The effect would, in turn, enhance the well injectivity index. This paper presents an analytical solution to the nonlinear problem of underground fluid injection in a disk‐shaped reservoir while accounting for the induced permeability enhancement. The host rock permeability is considered to depend on the rock total stress and pore fluid pressure. For this purpose, the rock stress is formulated as a nonlocal function of disturbances in the pore fluid pressure using the fundamental solution for a nucleus of strain in an elastic half space. Alongside, the nonlinear fluid transport equation that incorporates stress‐sensitive rock permeability is analytically solved using a perturbation technique. The good match with finite difference solution to the same problem verifies the validity and accuracy of the perturbation solution. Parametric study on a test case problem is conducted to examine the influence of different parameters on well injectivity. Findings reveal the higher vulnerability of shallower host reservoirs to stress‐induced permeability variations. The effect of rock poroelastic properties on fluid transport process is discussed.

Performance analysis of a cascade PCM heat exchanger and two-phase closed thermosiphon: A case study of geothermal district heating system

In this paper, a geothermal energy extraction system has been designed based on a two-phase closed thermosiphon, cascade phase change material heat exchanger, and an organic Rankin cycle. The proposed system is thermodynamically analyzed for supplying power and heat to a selected hotel in Sarein city in Iran. In the first step, the optimum diameter of the two-phase closed thermosiphon, according to the average yearly energy consumption rate (3100kW), is obtained. A two-level cascade heat exchanger with a storage medium of phase change materials is used to supply the building's energy consumptions. For the summertime, only the first level of the heat exchanger is operating to drive the ORC unit with two turbines for power generation. The second turbine output power is transmitted to the upper grid. On the other hand, in the wintertime, since the heating demands dominated, besides the first level of the heat exchanger, the second level of the heat exchanger is operated to supply the heating demand. Based on the thermodynamic analysis, employing phase change materials in the heat exchanger is an effective method for reducing overall exergy destruction, and consequently, increasing system efficiency. The energy and exergy efficiency is more favorable in terms of the application of PCM in the heat exchanger.

Acoustic emission uncovers thermal damage evolution of rock

The thermal damage evolution of rock closely relates to many important scientific and engineering problems, such as the mechanisms of earthquake and the effective extraction of deep geothermal energy. However, there is lack of rational thermal damage evolution model, and the mechanisms of thermal damage are still unclear especially during cooling. By use of a specially designed acoustic emission (AE) test system, we explored the thermal damage evaluation in a rock and established a thermal damage evolution model which takes into account both heating and cooling processes. The mechanisms of rock damage caused by heating and cooling were analyzed by using a lattice spring model, and two different microstructural explanations were found, i.e. heterogeneous microstructure and microdefect structure. The damage evolution model can be used for more accurate modeling of these problems which involve rock thermal damage, such as induced seismic activity during deep geothermal exploration.

Increased Power Generation due to Exothermic Water Exsolution in CO2 Plume Geothermal (CPG) Power Plants

A direct CO2-Plume Geothermal (CPG) system is a novel technology that uses captured and geologically stored CO2 as the subsurface working fluid in sedimentary basin reservoirs to extract geothermal energy. In such a CPG system, the CO2 that enters the production well is likely saturated with H2O from the geothermal reservoir. However, direct CPG models thus far have only considered energy production via pure (i.e. dry) CO2 in the production well and its direct conversion in power generation equipment. Therefore, we analyze here, how the wellhead fluid pressure, temperature, liquid water fraction, and the resultant CPG turbine power output are impacted by the production of CO2 saturated with H2O for reservoir depths ranging from 2.5 km to 5.0 km and geothermal temperature gradients between 20 °C/km and 50 °C/km. We demonstrate that the H2O in solution is exothermically exsolved in the vertical well, increasing the fluid temperature relative to dry CO2, resulting in the production of liquid H2O at the wellhead. The increased wellhead fluid temperature increases the turbine power output on average by 15% to 25% and up to a maximum of 41%, when the water enthalpy of exsolution is considered and the water is (conservatively) removed before the turbine, which decreases the fluid mass flow rate through the turbine and thus power output. We show that the enthalpy of exsolution and the CO2-H2O solution density are fundamental components in the calculation of CPG power generation and thus should not be neglected or substituted with the properties of dry CO2.

Effect of temperature and confining pressure on the evolution of hydraulic and heat transfer properties of geothermal fracture in granite

The hydraulic and heat transfer properties of artificial fracture networks are key to the efficiency of energy production from geothermal reservoirs. To date, no conclusive view exists of the evolution in fracture permeability and heat transfer coefficient when arbitrary stresses and temperatures are applied. This work examines the evolution of hydraulic and heat transfer properties during simulated geothermal energy extraction using a novel fluid flow-through test device accommodating large single artificial fractures in granite. Experiments are conducted in two contrasting modalities: at constant temperature with increasing confining pressures, and at constant confining pressure with increasing temperature. At constant temperature, as the confining pressure increases from 4 to 20 MPa, both hydraulic and heat transfer properties decrease, with permeability decreases by 46–63% and heat transfer coefficient decreases by 13–67%. Permeability decreases by 28–37% as temperature increases at constant confining pressure larger than 10 MPa, but permeability may first decrease and then increase at low constant confining pressure of 5 MPa. As the temperature increases from 100 to 200 °C at constant confining pressures, heat transfer coefficient increases by 25–45%. Results show that confining pressure impacts hydraulic properties more strongly than heat transfer properties, while reservoir temperature affects the heat transfer properties more strongly than hydraulic properties. These new findings on the evolution of permeability and heat transfer rate for different paths of temperature and confining pressure are critically important to the understanding of heat production from real geothermal reservoirs.

Exergy analysis of heat extraction from hot dry rock by enclosed Water recycling in a horizontal Well

In this paper, a novel mathematical model for the heat extraction process from hot dry rocks (HDRs) by enclosed water recycling in a horizontal well is established, on a basis of which a series of exergy analyses are conducted. The pressure and temperature distributions in the wellbore and the exergy extracted under different working conditions are calculated. Eight factors are specifically studied to evaluate their effects on the accumulated exergy of the produced hot water. It is found that the accumulated exergy first gradually increases but decreases subsequently with the water rising flow rate. The accumulated exergy is noticed to increase obviously with the increase of the length for the horizontal section, temperature of the HDR, thermal conductivity of the HDR, and diameter of the casing. The temperature distributions in the HDR around the wellbore are analyzed at different time. More specifically, the temperature drop of the HDR gradually spreads to far area of the wellbore with the continuous extraction of geothermal energy. The temperature of the rock around the wellbore decreases by increasing the injection rate. A higher HDR thermal conductivity leads to a quick heat transfer from the remote to near wellbore area. The exergy analyses in this study provide strong theoretical supports to utilize the HDR heat extraction.

Combining natural gas recovery and CO2-based geothermal energy extraction for electric power generation

We investigate the potential for extracting heat from produced natural gas and utilizing supercritical carbon dioxide (CO2) as a working fluid for the dual purpose of enhancing gas recovery (EGR) and extracting geothermal energy (CO2-Plume Geothermal – CPG) from deep natural gas reservoirs for electric power generation, while ultimately storing all of the subsurface-injected CO2. Thus, the approach constitutes a CO2 capture double-utilization and storage (CCUUS) system. The synergies achieved by the above combinations include shared infrastructure and subsurface working fluid. We integrate the reservoir processes with the wellbore and surface power-generation systems such that the combined system’s power output can be optimized. Using the subsurface fluid flow and heat transport simulation code TOUGH2, coupled to a wellbore heat-transfer model, we set up an anticlinal natural gas reservoir model and assess the technical feasibility of the proposed system. The simulations show that the injection of CO2 for natural gas recovery and for the establishment of a CO2 plume (necessary for CPG) can be conveniently combined. During the CPG stage, following EGR, a CO2-circulation mass flowrate of 110 kg/s results in a maximum net power output of 2 MWe for this initial, conceptual, small system, which is scalable. After a decade, the net power decreases when thermal breakthrough occurs at the production wells. The results confirm that the combined system can improve the gas field’s overall energy production, enable CO2 sequestration, and extend the useful lifetime of the gas field. Hence, deep (partially depleted) natural gas reservoirs appear to constitute ideal sites for the deployment of not only geologic CO2 storage but also CPG.

Thermal and Thermoelectric Generation Using Geothermal Energy Extraction Through Cogeneration System

The manuscript has focused on the evaluation of the improvement of energy efficiency in using geothermal energy for heat and electricity generation through additional thermoelectric production to conventional heat transfer processes. The proposed system uses Peltier rings made up of a serial and parallel Peltier cells grouping, as part of the upward and downward ducts that connect the geothermal heat exchanger and the surface heating system. The new system can improve performance related to conventional operating mode. As thermoelectric generation does not reduce working fluid temperature significantly, available heating power is preserved, thus improving overall efficiency. The new system operates, therefore, under cogeneration mode, being consistent with energy efficiency principles, which ensures an improvement of system performance related to conventional operating mode. Tested thermodynamic efficiency has been around 50%, which is a very good value if compared to conventional thermal systems. Global efficiency, including mechanical aspects, is reduced to 21.5%, which is comparable to current overall efficiencies of conventional systems. This efficiency is, however, improved up to 26%, if thermoelectric conversion is produced. The system operates at its higher efficiency mode in cold climates where thermoelectric conversion is more effective. Keywords: Cogeneration, efficiency improvement, geothermal energy, thermoelectric conversion Cite this Article Carlos Armenta Deu, Leticia Bottazzi Thermal and Thermoelectric Generation Using Geothermal Energy Extraction Through Cogeneration System Journal of Alternate Energy Sources & Technologies.2020 ; 11(1): 58-71 p.

Hydraulic Fracturing Experiment Investigation for the Application of Geothermal Energy Extraction.

As an attractive renewable energy source, deep geothermal energy is increasingly explored. Granite is a typical geothermal reservoir rock type with low permeability, and hydraulic fracturing is a promising reservoir stimulation method which could obviously enhance the reservoir permeability. Previous hydraulic fracturing studies were mostly conducted on artificial samples and small cylindrical granites. The fracturing pressures of artificial samples and small real rock sample were much lower than that of field operation, and it was difficult to observe morphological changes in small rocks. Hence, this paper presents a hydraulic fracturing experimental study on large-scale granite with a sample size of 300 × 300 × 300 mm under high temperatures. Besides, injection flow rate is an important parameter for on-site hydraulic fracturing; previous studies usually only focused on breakdown pressure, and there is a lack of comprehensive analysis about fracturing pressure curves and fracturing characteristics caused by different injection flow rates. This study aims to investigate the influence of injection flow rate on different pressure curve characteristic parameters which are initiation pressure, propagation time, breakdown pressure, postfracturing pressure, fracture geometry, and fracture permeability. The mean injection power was proposed to roughly estimate the fracture total lengths. These results could provide some guidance for field-scale reservoir stimulation and heat extraction efficiency improvement.

Evaluation of flow paths during stimulation in an EGS reservoir using microseismic information

Evaluation of fluid flow behavior is important for understanding various phenomena in a geothermal reservoir. Microseismic monitoring and location can be used to track pore pressure migration to some extent; however, microseismic information cannot directly provide the detail of flow behavior, such as how fluid flow occurs in the reservoir. In this study, we propose a new method to evaluate the entire flow-path system in a fractured reservoir. We first estimate the pore-pressure increase for each microseismic event based on microseismic and in-situ stress information. We extend the discrete pore pressure data to a continuous distribution based on the idea of a main flow pathway and sub flow pathways. We also introduce a honeycomb-shaped flow pathway model, which consists of flow pathways and nodes. Hydraulic parameters are different between different flow pathways. To match observed pore pressures at the nodes, an optimization process is used to adjust the hydraulic parameters for each flow pathway. We get a proxy of the hydraulic conductivity distribution based on the flow pathway model, that can evaluate flow pathways and flow behavior. We apply this method to hydraulic stimulation and microseismic data from the Basel enhanced geothermal system (EGS) project. Our method successfully delineated the main permeable zone and caught the tendency of fluid flow behavior that is also indicated by other microseismic analysis. Our method can catch the qualitative behavior of fluid flow in the geothermal reservoir and can contribute to designing geothermal energy extraction systems and forecasting.

Combination of MRI and SEM to Assess Changes in the Chemical Properties and Permeability of Porous Media due to Barite Precipitation

The understanding of the dissolution and precipitation of minerals and its impact on the transport of fluids in porous media is essential for various subsurface applications, including shale gas production using hydraulic fracturing (“fracking”), CO2 sequestration, or geothermal energy extraction. In this work, we conducted a flow through column experiment to investigate the effect of barite precipitation following the dissolution of celestine and consequential permeability changes. These processes were assessed by a combination of 3D non-invasive magnetic resonance imaging, scanning electron microscopy, and conventional permeability measurements. The formation of barite overgrowths on the surface of celestine manifested in a reduced transverse relaxation time due to its higher magnetic susceptibility compared to the original celestine. Two empirical nuclear magnetic resonance (NMR) porosity–permeability relations could successfully predict the observed changes in permeability by the change in the transverse relaxation times and porosity. Based on the observation that the advancement of the reaction front follows the square root of time, and micro-continuum reactive transport modelling of the solid/fluid interface, it can be inferred that the mineral overgrowth is porous and allows the diffusion of solutes, thus affecting the mineral reactivity in the system. Our current investigation indicates that the porosity of the newly formed precipitate and consequently its diffusion properties depend on the supersaturation in solution that prevails during precipitation.

Thermal and fluid processes in a closed-loop geothermal system using CO2 as a working fluid

A co-axial closed-loop geothermal system is a new method to extract geothermal energy. It uses a continuously closed wellbore and the closed system can avoid many problems of traditional geothermal development methods, such as reservoir blockage and heat transmission fluid leakage. Generally, water as a working fluid will cause a series of problems which are not conducive to the operation and maintenance of the geothermal system. Recently, using CO2 as a working fluid has attracted considerable attention. CO2 has a larger mobility and buoyancy that result from its lower density and viscosity. However, a large flow rate will lead to incomplete heating of the working fluid, which will reduce the thermal performance of the geothermal system. In addition, CO2 has a smaller specific enthalpy, which is not beneficial to the heat extraction of the geothermal system. Therefore, it is necessary to study the advantages and disadvantages of CO2 and water as working fluid. In this work, a wellbore reservoir coupled model is built to simulate the operation fluid flow and thermal processes in a co-axial closed-loop geothermal system. The difference in productivity between water and CO2 as working fluids is investigated. The fluid flow and thermal processes of CO2 and water along the wellbore and the heat-extracting mechanism are analysed. The results show that although CO2 is more efficient, its output temperature is lower than water. Therefore water is still suitable for geothermal reservoirs with lower temperature. The modelling and analysis methods presented here may provide a theoretical reference for the selection of a working fluid in geothermal engineering developments.

Role of natural fractures characteristics on the performance of hydraulic fracturing for deep energy extraction using discrete fracture network (DFN)

Extraction of geothermal energy, oil and gas, and coalbed methane (CBM) are all constrained by the rock’s permeability. To stimulate the production, hydraulic fracturing has become a routine procedure, which is influenced by many factors especially the pre-existing natural fractures. The natural fractures have various characteristics, such as aperture, persistence, and density, which have different effects on the hydraulic performance. Hence, it is necessary to study the dependence of hydraulic fracturing on natural fracture parameters to improve its effectiveness. In this research, the distribution of natural fracture is generated using the discrete fracture network (DFN) to study these relationships. To verify the accuracy, the numerical model is calibrated at a particular case with observed data and then continued to different fragmentation characteristics. Results show that the hydraulically fractured area has an inverse relationship with the natural fracture aperture. However, the increase of pre-existing fracture persistence first causes the fractured zone to increase but increasing persistence of natural fractures further causes the area to decrease. Parametric study shows that pre-existing natural fractures play a critical role in hydraulic fracturing effectiveness, which ultimately affects the production.

Energy potential of a single-fracture, robust, engineered geothermal system

Engineered Geothermal Systems (EGS) are promising, but high-risk targets for baseline energy generation. Technology breakthrough is needed to lower the high risks from largely unknown geologic variables and the limited control of the coolant flow field underground. A new, robust EGS (REGS) arrangement and creation technology is reviewed featuring innovative fracture opening, stabilization and permeability control. The geometry, aperture support technique and coolant fluid flow isolation system are all robustly planned and created according the inventive concept. The new elements of the REGS technology are (1) the step-by-step creation, control, and tests of hydraulic fracturing to achieve a planar wing fracture or fractures osculating along the well trajectory; (2) fracture stabilization by hardening grouting injection to create a central support island in each planar wing fracture for zonal isolation; and (3) well-fracture-well fluid circulation for geothermal energy extraction from single, or clustered planar fractures as geothermal heat exchangers. The paper reviews ongoing tests to prove the key components of the REGS geologic heat exchanger with stabilized, large fracture aperture and controlled flow zones for minimized opening pressure loss, seismicity and maximized energy extraction. Flow fields and heat transport are reviewed around zonal isolation of fracture flow by a grouted, blocking island for heat exchange. The robustness is reviewed for the step-by-step construction of a REGS. The paper reports new results from using numerical, coolant flow and heat exchange models to demonstrate the geothermal energy potential of a single REGS well drilled in hot, dry rock.

Investigation on fracture creation in hot dry rock geothermal formations of China during hydraulic fracturing

The abundant geothermal energy in hot dry rock (HDR) formations is an attractive renewable energy resource with great potential. China will develop its first HDR geothermal formation in the Gonghe Basin. HDR is a hard and low-permeability granite containing very few fluids. Development requires fluids to cyclically flow between injection and production wells to extract geothermal energy in the artificial heat transfer zone. Hydraulic fracturing is the main technology for creating flow paths. But few studies have investigated fractures in HDR geothermal formations. This paper investigated fractures as flow paths in HDR geothermal formations during hydraulic fracturing. Hydraulic fractures were simulated using a custom true-triaxial hydraulic fracturing test system in a realistic formation environment, in which a scaled wellbore was used that was built in outcrop granite rock from the Gonghe Basin. Fracture creation in granite was investigated via experiments, as well as influence factors, and what experience could be achieved. This study can be used to design and evaluate hydraulic fracturing projects in potential HDR geothermal formations.

Geothermal energy potential of Indian oilfields

Geothermal energy is one of the renewable energy sources that have gained extensive recognition as an alternative energy source to fossil fuel energy because of its sustainability and low impact on the environment. However, in spite of the benefits of geothermal energy, drilling costs often hinders the development of geothermal fields for production. The drilling costs can be reduced to a great extent by using the abandoned oil and gas wells, surrounded by hot water, for geothermal resource development. The depth and abundance of abandoned wells in oilfields make them an economically attractive source for geothermal energy. Indian oilfields have several abandoned oil/gas wells and have huge potential for geothermal energy. Such oilfields are discussed in this paper. Geothermal energy resources in the oilfields can be categorized in two categories: (1) High temperature co-produced water—from deep oil/gas wells or from high-temperature shallow formation, thus, heat can be extracted through double-pipe heat exchanger in a single well, (2) Another approach to extract geothermal energy could be in situ combustion of difficult-to-extract hydrocarbons from the formation. In-situ combustion of hydrocarbons produces enormous heat that can be utilized for power generation. A detailed design for the heat recovery from the oil field is also discussed here.

A lattice-Boltzmann study of permeability-porosity relationships and mineral precipitation patterns in fractured porous media

Mineral precipitation can drastically alter a reservoir’s ability to transmit mass and energy during various engineering/natural subsurface processes, such as geothermal energy extraction and geological carbon dioxide sequestration. However, it is still challenging to explain the relationships among permeability, porosity, and precipitation patterns in reservoirs, particularly in fracture-dominated reservoirs. Here, we investigate the pore-scale behavior of single-species mineral precipitation reactions in a fractured porous medium, using a phase field lattice-Boltzmann method. Parallel to the main flow direction, the medium is divided into two halves, one with a low-permeability matrix and one with a high-permeability matrix. Each matrix contains one flow-through and one dead-end fracture. A wide range of species diffusivity and reaction rates is explored to cover regimes from advection- to diffusion-dominated, and from transport- to reaction-limited. By employing the ratio of the Damkohler (Da) and the Peclet (Pe) number, four distinct precipitation patterns can be identified, namely (1) no precipitation (Da/Pe 100), (3) fracture isolation (1 1), and (4) diffusive precipitation (1 < Da/Pe < 100 and Pe < 0.1). Using moment analyses, we discuss in detail the development of the species (i.e., reactant) concentration and mineral precipitation fields for various species transport regimes. Finally, we establish a general relationship among mineral precipitation pattern, porosity, and permeability. Our study provides insights into the feedback loop of fluid flow, species transport, mineral precipitation, pore space geometry changes, and permeability in fractured porous media.

Potential of $$\hbox {CO}_{2}$$ based geothermal energy extraction from hot sedimentary and dry rock reservoirs, and enabling carbon geo-sequestration

Carbon capture and sequestration (CCS) is necessary to mitigate global warming caused by anthropogenic $$\hbox {CO}_{2}$$ emissions in the atmosphere. However, due to very high storage cost, it is difficult to sustain the CCS industry. The hot sedimentary and dry rock reservoirs with very high temperature can support both geothermal energy production, and carbon geosequestration economically, provided the $$\hbox {CO}_{2}$$ is used as a heat-carrying fluid with proper optimization of injection parameters according to reservoir conditions. In this paper we have reviewed past studies discussing the working mechanisms, pressure management strategies and various advantages of energy extraction from hydrothermal reservoirs by $$\hbox {CO}_2$$ plume geothermal technology and hot dry rock— enhanced geothermal system (EGS) technology. Past studies highlighted that due to very high thermal expansivity and mobility, supercritical $$\hbox {CO}_2$$ can produce more heat than water-EGS. For low enthalpy (around 50 $$^\circ$$C) and shallow (0.5–1.5 km) reservoirs, $$\hbox {CO}_2$$ can fetch more heat than water because of higher heat capacity. Other advantages of CCS and EGS are (i) the production of brine or $$\hbox {CO}_2$$ assisting to manage the reservoir pressure and restrict the fluid interference with neighboring reservoirs, (ii) the fluid loss, which is a significant concern in a water-EGS but for $$\hbox {CO}_{2}$$-EGS it is environmentally friendly, and (iii) higher pressure and cold fluid injection induced geological deformation and microseismicity are relatively less for $$\hbox {CO}_2$$-EGS than water-EGS. In this paper, we have also discussed various challenges of $$\hbox {CO}_2$$-EGS to enable CCS in hydrothermal reservoir and hot dry rock system.