Thermal Breakthrough Research Articles

Well spacing of the doublet at the Huangtsuishan geothermal site, Taiwan

The issue of thermal breakthrough is often encountered in the extraction of geothermal fluids with reinjection. This study analyzes the minimum safe distance between doublet wells that will maintain thermal productivity under various conditions at the Huangtsuishan geothermal site. A conceptual model is constructed and hypothetical exploitation scenarios are explored. The results show that a distance of 300 m is required to avoid a thermal break in 80 years with 120 tons/hour pumped and 90 % reinjected at the Huangtsuishan Geothermal site. A regression formula was provided as a guideline for the minimum required doublet distance for various pumping rates.

The influence of reinjection and hydrogeological parameters on thermal energy storage in brine aquifer

When brine aquifer is used as thermal energy storage medium, pore structure and permeability of brine aquifer may change owing to the difference of salinity and temperature between the reinjected water and underground. Consequently, heat transfer characteristics and thermal energy storage performance in brine aquifer may vary correspondingly. In present work, heat transfer in brine aquifer is investigated, which considers the effect of reinjected water salinity, temperature, effective porosity and hydraulic gradient. Based on the temperature variation of pumping water, thermal energy storage efficiencies are analyzed under different conditions. The results indicate that the heat transferred from reinjection well to pumping well decreases with the reduction of reinjected water salinity, temperature difference and effective porosity of brine aquifer. The occurrence of thermal breakthrough delays when reinjected water salinity and effective porosity reduce, while thermal breakthrough is almost unaffected by reinjected water temperature and hydraulic gradient. The effective porosity of brine aquifer has the greatest influence on performance of thermal energy storage. When effective porosity of brine aquifer increases from 0.33 to 0.43, cold storage efficiency and heat storage efficiency decreases about 56.56% and 40%, respectively. Reducing reinjected water salinity and hydraulic gradient result in the increase of thermal energy storage efficiency. Reinjected water temperature has opposite effect on heat and cold energy storage efficiency. Sensitivity analysis indicates that the sensitivity of heat energy storage efficiency to considered parameters is greater than that of cold energy storage efficiency does.

Effects of lateral-well geometries on multilateral-well EGS performance based on a thermal-hydraulic-mechanical coupling model

Our previous study (Song et al., 2018) presented a novel enhanced geothermal system (EGS) with multilateral wells to exploit geothermal energy, and illustrated that the multilateral-well EGS had a better heat extraction performance than conventional double-well EGS. However, to further improve the heat extraction performance of the multilateral-well EGS, the effects of lateral-well geometries on multilateral-well performance should be studied and the geometrical parameters should be optimized. In this paper, we use a thermal-hydraulic-mechanical (THM) coupling model with a complex discrete fracture network (DFN) to investigate the influences of lateral-well geometrical parameters on the multilateral-well EGS performance. The lateral-well geometrical parameters include the lateral-well length, number, spacing and diameter. The results indicate that the longer lateral well and larger well spacing are beneficial for enhancing the multilateral-well EGS performance. In terms of better heat extraction performance and lower pressure impedance, the 400 m well spacing is the optimizing value under the fracture density of 0.067 m−1. The lateral-well number has a complicated effect on the heat extraction process. A large number of lateral wells can improve swept volume and reduce pressure impedance, but simultaneously connect more fractures and accelerate thermal breakthrough. Therefore, the lateral-well number should be optimized according to the specific DFN and under the DFN in this paper, 6 lateral wells are the best for the multilateral-well EGS performance. When there is a rotation angle between injection and production lateral wells, it can postpone the thermal breakthrough and be beneficial for heat extraction. The influence of the lateral-well diameter on the EGS performance can be ignored. The results of this study provide good guidance for the lateral-well design of the multilateral-well EGS.

Numerical modeling of thermal breakthrough induced by geothermal production in fractured granite

It is well known that the complicated channeling of fluid flow and heat transfer is strongly related with the intricate natural fracture system. However, it is still challenging to set up the fracture network model which is strong heterogeneous. Compared with other methods (e.g. equivalent continuum model (ECM), discrete fracture model (DFM), and ECM-DFM), the fracture flow module in the COMSOL Multiphysics simulator is powerful in definition of fractures as the inner flow boundary existing in the porous media. Thus it is selected to simulate the fluid flow and heat transfer in the geothermal-developed fractured granite of Sanguliu area located at Liaodong Peninsula, Eastern China. The natural faults/fractures based on field investigation combined with the discrete fracture network (DFN) generated by the MATLAB are used to represent the two-dimensional geological model. Numerical results show that early thermal breakthrough occurs at the production well caused by quick flow of cold water along the highly connected fractures. Suitable hydraulic fracturing treatments with proper injection rates, locations, etc. can efficiently hinder the thermal breakthrough time in the natural fracture system. Large well spacing helps the long-term operation of geothermal production, but it is highly dependent on the geometrical morphology of the fracture network. The enhancement of reservoir properties at the near-well regions can also increase the geothermal production efficiency. The results in this study can provide references to achieve a sustainable geothermal exploitation in fractured granitic geothermal reservoirs or hot dry rocks at depth.

Study on the effect of well layout schemes and fracture parameters on the heat extraction performance of enhanced geothermal system in fractured reservoir

Well layout and fracture network in the enhanced geothermal system (EGS) jointly determine the fluid flow path, affecting the fluid flow and heat transfer process. It is necessary to investigate the optimal well layout and fracture parameter to get an efficient EGS. In this paper, the combination of multi-well layout and fracturing technology is conceptualized, a thermal-hydraulic coupling model is established to study the heat extraction performance under various multi-well layout schemes and fracture networks. Results show that the heat extraction ratio of Case 1 is highest, which is the optimal well layout under the research conditions. The fracture aperture is negatively correlated with heat extraction ratio. A higher fracture aperture is more likely to cause a short circuit and thermal breakthrough. The heat extraction ratio increases with the fracture length, while the growth rate decreases with the fracture length. Increasing the fracture number can improve the heat extraction performance to some extent, but excessive fractures can be counterproductive because they aggravate the interference among fractures. Under the research conditions, the preferable fracture aperture, length and number are 0.05 mm, 140 m and 114, respectively. This paper provides some reasonable suggestions for improving heat extraction performance from the perspectives of well layout and fracture network.

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.

Modeling study of deep direct use geothermal on the West Virginia university campus-morgantown, WV

To reduce the geothermal exploration risk, a feasibility study is performed for a deep direct-use (DDU) system proposed at the West Virginia University (WVU) Morgantown campus. This study applies numerical simulations to investigate reservoir impedance and thermal production. Because of the great depth of the geothermal reservoir, few data are available to characterize reservoir features and properties. As a result, the study focuses on the following three aspects: 1. model choice for predicting reservoir impedance and thermal breakthrough: after investigating three potential models (one single permeability model and two dual permeability models) for flow through fractured rock, it is decided only the single permeability model is needed; 2. well placement (horizontal vs. vertical) options: horizontal well placement seems to be more robust to heterogeneity and the impedance is more acceptable; 3. Prediction uncertainty: the most influential parameters are identified using a First-Order-Second-Moment uncertainty propagation analysis, and the uncertain range of the model predictions is estimated by performing a Monte Carlo simulation. Heterogeneity has a large impact on the prediction, therefore, heterogeneity is included in the predictive model and uncertainty analysis. The numerical model results and uncertainty analysis will be used for further economic studies.

A new well pattern of cluster-layout for deep geothermal reservoirs: Case study from the Dezhou geothermal field, China

A well pattern of cluster-layout is proposed to reduce the risk of thermal breakthrough at production wells, as well as to improve the convenience of surface management. Its performance in the heterogeneous porous geothermal reservoir models based on the Dezhou geothermal field, China is systematically examined using the coupled thermal-hydraulic numerical modeling. In order to compare the performance of different well patterns, three assessment parameters including thermal breakthrough time and water table of production wells and recovery efficiency of geothermal energy in the licensed region are defined. The results showed that the well pattern of cluster-layout has the higher recovery efficiency of geothermal energy compared with other well patterns of tramrail-layout and checkers-board-layout for most simulations. Effects of anisotropy and correlation length of reservoir permeability on the performance of different well patterns are examined. Flow channeling appears along the direction of high permeability, and thus the injection-production direction should avoid to be parallel with that direction. With increasing correlation length, the possibility of flow channels appearing in the licensed region increases and the fate of production wells declines. When the difference of correlation lengths between different directions increases, the induced anisotropy of reservoir permeability increases but the recovery efficiency decreases.

Evaluation of geothermal development considering proppant embedment in hydraulic fractures

Conductivity in hydraulic fractures embedded with proppants has a great impact on the efficiency of geothermal development in an enhanced geothermal system. This study explores the effects of proppants and hydraulic fracture arrangement on the efficiency of geothermal development by developing a thermo-hydro-mechanical coupled model. The evolution of the fracture aperture is captured based on the Hertz contact theory and the Kozeny-Carman equation. The finite element method (FEM) is used to analyse the mechanical behaviour of the fractured system. The thermo-hydro circulated process is investigated using the unified pipe-network method (UPM). In the simulation of a doublet system embedded with propped hydraulic fractures, the increase of proppant distribution density enhances the net heat-extraction rate and reduces the thermal breakthrough time and accumulated thermal energy. The influence of reservoir properties on the heat production is further investigated. In the designing of the hydraulic stimulation, both the increase of the propped hydraulic fracture number (at least two hydraulic fractures) and the spacing promote the efficiency of geothermal development, however, the cost of the field design should be considered for optimization.

Measurement of competitive $$\text {CO}_{2}$$ and $$\text {H}_{2}\text {O}$$ adsorption on zeolite 13X for post-combustion $$\text {CO}_{2}$$ capture

The adsorption isotherms of water on Zeochem zeolite 13X were measured from 22 to 100 $$^{\circ }\text {C}$$ and 0 to $$2.1\times 10^{-2}$$ bar using volumetry and gravimetry. The equilibrium data was fit to a dual-site Langmuir isotherm. A series of single component H2O dynamic column breakthrough experiments were measured on zeolite 13X at $$ 22\,^{\circ }\text {C}$$ and 0.97 bar. These breakthrough experiments were modeled and simulated with our built in-house adsorption simulator. The simulator predicted composition and thermal breakthrough behavior well for all single component experiments. Competitive $$\text {CO}_{2}$$ / $$\text {H}_{2}\text {O}$$ breakthrough experiments were then performed at $$ 22\,^{\circ }\text {C}$$ and 0.99 bar. The collected equilibrium data showed up to a 98% loading reduction for $$\text {CO}_{2}$$ (compared to the single component loading) for $$\approx $$ 74.4% RH while $$\text {H}_{2}\text {O}$$ showed no reduction compared to its single component loading. The binary equilibrium isotherms were described by an explicit water-loading adjusted dual-site Langmuir isotherm.

Heat production from lab-scale enhanced geothermal systems in granite and gabbro

Lab-scale cold water circulation test results and analysis are presented as a proxy for field-scale heat mining in enhanced/engineered geothermal systems. The cold water circulation tests were conducted in hydraulically stimulated igneous rock blocks heated to a uniform temperature. The test blocks had a five-spot system with one injection well at the center and four producers drilled about 9 cm away from it. Two kinds of igneous rocks (granite and gabbro) with different permeability were tested. Due to the heterogeneity of the rock and the notch at the injection well, different fracture geometries with different number of producers connected by the hydraulic fracture were obtained. The circulation tests illustrate for the first time a number of interesting phenomena in a laboratory setting. The great potential of geothermal energy has been demonstrated by nearly 50W of power produced by the cold water flowing through a hydraulic fracture in a mini-EGS reservoir, yielding a good heat extraction percentage of 6.24%~7.85% after 2000 ml of cold water injection. Also, the cooling effect on the injection pressure and thus the fracture aperture has been clearly observed in the experiments i.e., with continued cold water injection the pressure drops, indicating fracture aperture increase due to thermal stress. In addition, reservoir growth during circulation has been observed based on the AE record and production data. Production well competition has also been observed when multiple producers were connected to the injection well by the induced hydraulic fracture, emphasizing the necessity of proper field management to maximize heat production. The test result indicates that a more “complex” flow path enhances heat production, and early thermal breakthrough and undesirable fracture propagation can be avoided by close monitoring of AE, pressure, and production responses.

Numerical modelling of the cooling effect in geothermal reservoirs induced by injection of CO2 and cooled geothermal water

The utilization of geothermal energy can reduce CO2 emissions into the atmosphere. The reinjection of cooled return water from a geothermal field by a closed loop system is an important strategy for maintaining the reservoir pressure and prolonging the depletion of the geothermal reservoir by avoiding problems, e.g., water level drawdown, ground subsidence, and thermal pollution. However, the drawdown of water injectivity affected by physical and chemical clogging may occur in sandstone aquifers, and the reservoir temperature may be strongly affected by the reinjection of large amounts of cooled geothermal water, thus resulting in early thermal breakthrough at production wells and a decrease in production efficiency. In addition to the injection of cooled geothermal water, the injection of CO2 can be used to maintain the reservoir pressure and increase the injectivity of the reservoir by enhancing water–rock interactions. However, the thermal breakthrough and cooling effect of the geothermal reservoir may become complex when both CO2 and cooled geothermal water are injected into aquifers. In this paper, a simplified small-scale multilayered geological model is established based on a low-medium geothermal reservoir in Binhai district, Tianjin. The ECO2N module of the TOUGH2MP simulator is used to numerically simulate temperature and pressure responses in the geothermal reservoir while considering different treatment strategies (e.g., injection rates, temperatures, well locations, etc.). The simulation results show that a high injection pressure of CO2 greatly shortens the CO2 and thermal breakthrough at the production well. A much lower CO2 injection pressure is helpful for prolonging hot water production by maintaining the reservoir pressure and eliminating the cooling effect surrounding the production wells. Both pilot-scale and commercial-scale cooled water reinjection rates are considered. When the water production rate is low (2 kg/s), the temperature decrease at the production well is negligible at a distance of 500 m between two wells. However, when both the production and reinjection rates of cooled return water are increased to 100 m3/h, the temperature decrease in the production well exceeds 10 °C after 50 years of operation.

Injection strategies in an enhanced geothermal system based on discrete fractures model

In this investigation, injection and recovery strategies are studied in order to improve the performance of an Enhanced Geothermal System with multiple fractures. The three-dimensional heterogeneous reservoir intercepted by three inclined discrete fractures is modeled under transient conditions with the finite element method. Numerical results show that the produced fluid temperature and the extracted heat are affected, the fluid flows through preferred paths and the premature thermal breakthrough is avoided. The produced fluid temperature increases slowly the first 9.8 – 20.1 years according to the considered scenario and decreases with the production time. Under the conditions in this paper, the best performance is obtained by injecting the fluid in the fourth layer of the reservoir over 100 m. For a volumetric flow rate of 150 l/s and a fluid injection temperature of 60 °C, a better option is obtained for an average electrical power of 9.66MWe and the reservoir flow impedance is 0.222 MPa/(kg/s). The average production temperature after 40 years of operation time is 166 °C, it is thus reduced by 1.13%, which is acceptable. The sensitivity analysis of fracturing parameters indicates that the increasing of the fracture aperture leads to the decrease of the effective electric power.

A numerical sensitivity study of how permeability, porosity, geological structure, and hydraulic gradient control the lifetime of a geothermal reservoir

Abstract. Geothermal energy is an important and sustainable resource that has more potential than is currently utilized. Whether or not a deep geothermal resource can be exploited, mostly depends on, besides temperature, the utilizable reservoir volume over time, which in turn largely depends on petrophysical parameters. We show, using over 1000 (n=1027) 4-D finite-element models of a simple geothermal doublet, that the lifetime of a reservoir is a complex function of its geological parameters, their heterogeneity, and the background hydraulic gradient (BHG). In our models, we test the effects of porosity, permeability, and BHG in an isotropic medium. Furthermore, we simulate the effect of permeability contrast and anisotropy induced by layering, fractures, and a fault. We quantify the lifetime of the reservoir by measuring the time to thermal breakthrough, i.e. how many years pass before the temperature of the produced fluid falls below the 100 ∘C threshold. The results of our sensitivity study attest to the positive effect of high porosity; however, high permeability and BHG can combine to outperform the former. Particular configurations of all the parameters can cause either early thermal breakthrough or extreme longevity of the reservoir. For example, the presence of high-permeability fractures, e.g. in a fault damage zone, can provide initially high yields, but it channels fluid flow and therefore dramatically restricts the exploitable reservoir volume. We demonstrate that the magnitude and orientation of the BHG, provided permeability is sufficiently high, are the prime parameters that affect the lifetime of a reservoir. Our numerical experiments show also that BHGs (low and high) can be outperformed by comparatively small variations in permeability contrast (103) and fracture-induced permeability anisotropy (101) that thus strongly affect the performance of geothermal reservoirs.

A coupled thermal-hydraulic-mechanical modeling and evaluation of geothermal extraction in the enhanced geothermal system based on analytic hierarchy process and fuzzy comprehensive evaluation

In the paper, the thermal-hydraulic-mechanical (THM) coupling model is improved by considering more factors, and a comprehensive evaluation method is proposed to optimize the heat extraction way. The thermal extraction characteristics in the Enhanced Geothermal System (EGS) and their influence factors were modeled by several researchers, and various evaluation and optimization methods were established. However, by comparing various thermal-hydraulic-mechanical (THM) models, we find that these factors of THM models are not considered comprehensively, and current EGS evaluation focuses on the individual index, the multi-objective evaluation index system of EGS has not been proposed, and a comprehensive evaluation system considering multiple indexes has not been established yet. In this study, a thermal-hydraulic-mechanical coupling model, considering matrix, fractures and changes in physical parameters of rock and fluid, was established for optimizing the EGS. The evaluation index system, including the operation life, the thermal breakthrough time, the average heat production rate, the total heat recovery factor and the re-injection factor, were presented. And the comprehensive optimization method based on analytic hierarchy process (AHP) and fuzzy comprehensive evaluation (FCE) of EGS were proposed. The model is verified by two analytical solutions. Moreover, the model was solved by finite element method (FEM) to optimize various programs of developing the EGS. In this paper, the performances of different geothermal extraction methods are compared and the different extraction parameters are optimized. The results show that the optimized geothermal mining method has better effect than that before optimization. The orthogonal test shows the optimal case of 5 fractures, the fracture permeability of 10D, the well spacing is 400 m and the production pressure draw-down of 20 MPa. The research results provide an accurate and effective method to optimize the development mode of geothermal resources, which is conductive to improve the geothermal energy efficiency.

Numerical Investigation of Techno-Economic Multiobjective Optimization of Geothermal Water Reservoir Development: A Case Study of China

Renewable geothermal utilization is a significant approach for residential heating with two principal modes, direct geothermal district heating systems (DGDHSs) and indirect geothermal district heating systems (IGDHSs). The key principle of geothermal development design is to prevent premature thermal breakthrough, which could result in low efficiency of geothermal heating systems. In this paper, a new approach considering building heating demand, geothermal water resource protection, and optimal economic benefits is presented systematically. The results simulated by OGS software show that well spacing, reinjection temperature, and production rate are the most significant parameters affecting thermal breakthrough in geothermal reservoirs. In addition, production rate and reinjection temperature have a huge effect on the payback period of investment. Comparing IGDHS to DGDHS, the investment in construction of geothermal wells and the annual water consumption decrease by up to 10% and 50%, respectively. Additionally, electricity costs increase by 5% to 30%. The indirect geothermal district heating system with a well spacing of 300 m, a production rate of 100 m3/h, and a reinjection temperature of 301.15 K is much better for this case, both technically and economically. The systematic calculation approach can be reasonably applied to other regions with geothermal energy utilization.

Numerical study on heat extraction performance of multistage fracturing Enhanced Geothermal System

A conceptual Enhanced Geothermal System (EGS) with triplet horizontal well layout is proposed, in which the injection well is flanked by two production wells. The injection well is completed with perforated casing, followed by multistage fracturing with casing packers. Two production wells are drilled through the stimulation zone induced by multistage fracturing and completed openhole to maximize contact with the reservoir. Based on a fully coupled hydrothermal (HT) model accounting for local thermal non-equilibrium (LTNE), sensitivity analysis and optimization for EGS design parameters are conducted. Simulation results show that increasing circulation rate only facilitates the heat extraction rate before thermal breakthrough, but cannot improve the heat extraction performance at the end of EGS operation. Compared with the fracture aperture, the increase in the stimulation zone permeability is more conducive to reducing the injection pressure and increasing the cumulative output thermal power. Insufficient or excessive fracturing stages are detrimental to economic heat extraction. It is found that more uniform flow into each perforation can achieve better thermal sweep efficiency and prevent local thermal breakthrough. The stimulation zone has an optimal reservoir permeability to match the fracture aperture. The optimum number of fracturing segments for a specified wellbore length is obtained. The preferable zone for the production well is between the fracture front and the outermost periphery of the stimulation zone.

Optimizing heat mining strategies in a fractured geothermal reservoir considering fracture deformation effects

A coupled thermo-hydro model is developed for optimizing heat mining strategies in a fractured geothermal reservoir by incorporating material compressibility and fracture deformation. Governing equations for the three-dimensional fluid flow and heat transmission processes in terms of local thermal non-equilibrium concept are discretized using a unified pipe network method. The influence of fracture deformation on the distribution of fluid temperature is investigated using a near-wellbore reservoir model. The development optimization of a geothermal reservoir at Groβ Schönebeck is performed by evaluating heat production over 60 years. Several strategies are designed that involve changing the arrangement of a new horizontal wellbore and hydraulic stimulations. Simulation results for the different strategies, including the outlet fluid temperature drawdown, thermal breakthrough time, and net heat extraction rate, are analysed. Strategies with poor fracture connections feature relatively low flow rates and accumulated thermal production. Strategy 3 to Strategy 6 greatly improve the accumulated thermal production by enhancing fluid circulation in fracture-connected systems. Heat mining efficiency can be improved if a new wellbore is designed in the high-permeability formation and the discontinuities maintain high hydraulic connectivity for fluid circulation. This study provides a numerical method for optimizing geothermal development strategies in terms of economic benefits.

Experimental investigation of thermal retardation and local thermal non-equilibrium effects on heat transport in highly permeable, porous aquifers

Actively stimulated temperature changes are common in many groundwater applications. A widely used concept to determine water fluxes, mean transit times, and other parameters from heat tracer tests is the use of the thermal retardation factor. Different methods are available to determine the thermal velocity from thermal breakthrough curves (BTCs) depending on the input signal. This study systematically compares these methods and investigates possible local thermal non-equilibrium effects (LTNE) in coupled solute and heat tracer experiments for highly permeable, porous aquifers. One-dimensional column experiments with saturated gravel of grain size 7–15 mm are conducted to compare the measured, effective thermal retardation with the computed thermal retardation predicted by the apparent thermal retardation factor. The results demonstrate that for scenarios with a step input of the heat tracer, the effective thermal retardation for thermal velocities derived by an analytical model, and the mean between injection temperature and initial temperature, can be predicted by the apparent thermal retardation factor. This indicates that possible LTNE effects do not significantly influence the derived velocities within the investigated range of seepage velocity between 5 and 50 md−1. Other methods showed constant deviation from the apparent retardation factor at higher seepage velocities. In scenarios with a finite duration pulse input of the heat tracer, the effective retardation derived by the peak velocity showed deviations from the apparent retardation up to 35% at seepage velocities lower than 10 m d−1. At higher seepage velocities, the peak velocity could be predicted by the apparent retardation factor.

Economic analysis of heating for an enhanced geothermal system based on a simplified model in Yitong Basin, China

AbstractYitong Basin is located in subfrigid zone, and it has a good prospect to use geothermal clean heating. The evaluation of economic efficiency for heating with enhanced geothermal system (EGS) is indispensable. A simplified single‐fracture hydrothermal coupling model with laboratory test is developed in the EGS project to calculate temperature and pressure based on Yitong Basin data. The effects of four factors (K, q, D, and T) on heat production and reservoir characteristics are discussed. The parameters and results of H‐T coupling were applied to economic analysis for heating with EGS from private and social perspectives considering costs and revenues. The results indicate that the combination of laboratory tests (rock physical properties) makes the numerical simulation results more suitable for the study area. The production temperature and heating power will decrease with continuous injection of cold water, and the injection pressure and flow impedance will increase due to the increase in μ/ρ. Four factors (K, q, D, and T) will affect difficulty of fluid injection and reservoir thermal breakthrough, and the high injection rate q may trigger secondary fracturing of reservoir. Heating with EGS in single‐fracture model was uneconomical due to expensive drilling costs. However, heating with EGS can be considered from social perspective based on environment, which can provide advice for decision‐making of the government and business.