Temperature Of Injected Fluid Research Articles

Parameter optimization of hot dry rock heat extraction based on discrete element crack network model

Hot-dry-rock (HDR) has long been considered a potential exploitable energy source due to its high energy content, cleanliness, and abundant reserves. However, HDR typically resides in ultra-deep strata with high temperatures and pressures, which makes its extraction a highly complex thermal-hydrological-mechanical (THM) coupling. In this paper, the THM coupling relationship in the geothermal extraction is clarified. It establishes a dynamic porosity and permeability model and creates a pair-well geothermal extraction model. The investigation focuses on understanding the influence of the pressure difference between pair-wells, number of cracks, and injection temperature on the heat extraction temperature, permeability ratio, geothermal reservoir reduction rate, and heat extraction temperature. The research findings indicate the following: (1) Increasing the inter-well pressure difference from 2 to 10 MPa reduces the extraction temperature from 155 to 138 °C. However, the thermal reservoir permeability ratio increases from 1.07 to 1.35. Consequently, the extraction efficiency rises from 6.2 to 12.4 MW. (2) The number of cracks from 200 to 400 led to a decrease in extraction temperature from 160 to 115 °C. However, the thermal reservoir permeability ratio increases from 1.12 to 1.35. In the first 8 years of extraction, the thermal pumping power of 400 cracks exceeded 200 cracks, but later this trend reversed. (3) Elevating the injection temperature from 20 to 60 °C increases the extraction temperature from 142 to 158 °C while reducing the permeability ratio from 1.28 to 1.20. Consequently, the extraction power decreases from 8 to 6 MW. (4) The inter-well pressure difference has the greatest impact on the decrease in extraction temperature, whereas the number of cracks has the greatest impact on the increase in permeability ratio. Injection temperature has the most significant impact on extraction power. This study reveals that increasing the pressure difference between wells, increasing the number of cracks, and lowering the injection fluid temperature will enhance geothermal extraction power. These findings provide valuable insights for geothermal development.

Investigation of thermal cooling effect of long-term circulation in Raft River enhanced geothermal system

The Raft River Enhanced Geothermal System (EGS) demonstration project incorporated three hydraulic stimulations in well RRG-9 ST1 to improve geothermal production. This study investigated the injectivity index (injection rate divided by injection pressure) increase during long-term injection into RRG-9-ST1 after the stimulations from the perspective of thermoelasticity. We have used a one-dimensional approximate solution to estimate the injectivity/aperture change due to thermal cooling. The inferred aperture change vs. square root of time falls along a linear trend. The thermal coefficient (a combination of rock thermal properties, rock initial temperature, and injected fluid temperature) back-calculated by fitting the field injection data is in the same order of magnitude as the value directly calculated from these parameters. We have conducted fully-coupled thermal-hydro-mechanical modeling to simulate long-term circulation (cold water injection). The simulated injectivity index increased by 1.7 × 10−8 m3/(Pa·s) after 272 days of cold-water injection, similar to the field data, which increased by 2.5 × 10−8 m3/(Pa·s). Both the trend and the magnitude of the simulated injectivity change match with the field data recorded at Raft River. The injectivity index increased faster at the beginning and then the rate of increase became smaller with time. The injectivity index increase is hypothesized to be the result of fracture aperture increase due to cooling effects. The simulated fracture aperture at the injection well increased by 0.64 mm, and the simulated maximum fracture aperture increased by 1.93 mm. The trend of the simulated aperture change also matches the value interpreted from the field data using the 1D approximate solutions. The study suggests that cooling is the major reason for the injectivity increase at Raft River EGS during the long-term injection. More broadly, cold water injection could serve as a method to increase the injectivity in other settings after high-volume and high rate/pressure hydraulic stimulation

Development status and research recommendations for thermal extraction technology in deep hot dry rock reservoirs

AbstractBased on a comprehensive review of domestic and foreign literature, this article discusses the technical difficulties and development status of enhanced geothermal system (EGS) concerning the thermal energy extraction of deep hot dry rock (HDR) reservoirs and proposes suggestions for the research focus of numerical simulation of HDR reservoir stimulation. Additionally, it summarizes the existing methods and mainstream working fluids for HDR reservoir stimulation. The article emphasizes the significance of factors such as well location, production well depth, artificial fracture orientation, and complexity in optimizing the thermal production efficiency of the EGS. Furthermore, this article delves into a detailed discussion on the influence of fracture spacing, fracture permeability, fracture length, fluid injection rate, and injected fluid temperature on the performance of the EGS. In light of the thermo‐hydro‐mechanical coupling challenges associated with high‐temperature reservoirs, it is suggested that future research efforts should focus on investigating the impact of thermo‐induced stresses on the stability of the artificial fracture network within the EGS during long‐term (>30 years) circulation of hot and cold fluids.

A new semi-analytical model for studying the performance of deep U-shaped borehole heat exchangers

In deep geothermal exploitations, the U-shaped borehole heat exchanger (UBHE) has a longer fluid retention time and a larger contact area with the formation. In order to improve the utilization efficiency of geothermal energy, it is becoming increasingly important to accurately evaluate the performance of the deep UBHEs. In this study, the authors develop a new semi-analytical model for characterizing the heat transfer behavior of the deep UBHE geothermal system. In this developed model, the temperature change within the wellbore is numerically simulated by the finite difference method, whereas the temperature change between the formation and the wellbore is analytically simulated by the Green's-function. Besides, the non-uniform heat flux distribution along the horizontal section is considered to characterize three-dimensional heat transfer behaviors. By means of this model, the influences of developing strategies and well configurations on the outlet temperature and total thermal power are investigated. The calculation results indicate that the traditional assumption of uniform temperature along the horizontal section can induce significant errors in evaluating the performance of the UBHE geothermal systems; the horizontal section length is more conducive to improving the extraction performance in a shallower geothermal formation, and a longer horizontal section leads to a higher outlet fluid temperature, together with a larger total thermal power; a higher injection rate, as well as a lower injection fluid temperature, is more favorable for improving the total thermal power; an insulation casing with a length equaling the depth of injection point can lead to the maximum thermal power of the UBHE geothermal system.

Performance evaluation of enhanced geothermal systems with intermittent thermal extraction for sustainable energy production

Efficient extraction of thermal energy from deep geothermal reservoirs using Enhanced Geothermal Systems (EGS) is fundamental for sustainable clean energy generation. This study presents the Intermittent Thermal Extraction (ITE) method, addressing thermal breakthrough challenges encountered during continuous thermal extraction (CTE) within EGS reservoirs. Employing a thermal-hydraulic coupled approach and discrete fracture network modeling, the ITE process for EGS reservoirs is assessed, omitting considerations of stress-induced deformation. The research evaluates the ITE and CTE methods within a typical high-temperature geothermal reservoir in the Himalayan geothermal belt. Analysis includes variations in reservoir temperatures and pressures, alongside an examination of rock matrix permeability and injection fluid temperature impacts on EGS thermal extraction performance. Results demonstrate the ITE method's efficacy in prolonging the EGS reservoir lifespan by preventing thermal breakthroughs and maintaining pressure equilibrium. Under studied conditions, ITE extends the EGS reservoir lifespan by a minimum of 17.7 years, amplifying clean power generation by 13.1% compared to CTE. Additionally, ITE implementation substantially reduces greenhouse gas emissions by an estimated 1.46–5.03 million tons. The rock matrix permeability and injection fluid temperature significantly affect the EGS thermal extraction performance when the fracture aperture is constant. These findings highlight the ITE method's potential to optimize thermal extraction from EGS reservoirs, particularly in remote regions. This study contributes essential insights into advancing geothermal energy extraction techniques, emphasizing ITE as a promising approach for sustainable energy production.

The thermal-fluid-mechanical (TFM) coupling method based on discrete element method (DEM) and the application of CO2 fracturing analysis

Due to the challenges of the complex temperature, fluid and mechanical coupling phenomenon during CO2 fracturing, a new thermal-fluid-mechanical (TFM) coupling method is proposed by using PFC2D fish code. This method utilizes the PFC2D fish code and combines the heat transfer difference algorithm with Cundall's fluid-mechanical coupling algorithm to establish a TFM model for CO2 fracturing. Subsequently, the validation of the TFM coupling model is conducted using the analytical solution provided by the plane strain Khristianovic Geertsma-de Klerk (KGD) model. The reservoir temperature variation, pore pressure and crack propagation are studied considering many involved factors, such as injection fluid temperature, injection flow rate, in-situ stress and formation temperature. Crack number and length would increase with the increasing temperature difference between fracturing CO2 and reservoir temperature. The breakdown pressure reduces when there are large injection flow rate or temperature differences between fracturing CO2 and reservoir temperature, which can be optimized in the CO2 fracturing operation. Even CO2 fracturing could create complex fracture network, we must pay attention to the in-situ stress distribution and injection flow rate. Our simulation suggests that pore pressure and heat could prevent the fracture from initiating and propagating in the direction of the minimum principal stress, and the temperature influencing has contributed to the extra pressure increment in the pore domain, which could not be ignored in CO2 fracturing. From the above research, it is expected to offer a novel method to simulate the complex TFM coupling phenomenon and enhance our understanding of CO2 fracturing.

Shear instability in geothermal fields under hydromechanical feedback

A recent trend in improving the seismic safety and economic efficiency of enhanced geothermal systems in deep rock formation has led to an interest in the underlying mechanisms of shear stimulation. This contribution investigates the formation of shear localization patterns around an injection hole in deep geothermal reservoirs considering thermo-hydro-mechanical coupled processes. The constitutive formulation treats the target rock layer as an elasto-visco-plastic material with an Arrhenius dependence taking into account the effect of pore fluid pressure. Considering the thermal pressurization effect resulting from frictional heating, the role of system heterogeneity and the influence of injected fluid temperature are investigated. The findings of this study indicate that a deeper layer and a hotter injection would favor localized shear deformation around a deep borehole and hence an effective network of fluid pathways.

Utilizations of reaction exothermic heat to compensate the cost of the permanent CO2 sequestration through the geological mineral CO2 carbonation

Many climate change events drive global efforts on CO2 sequestration to reach carbon neutrality. With the help of chemical processes, the novel “geological mineral CO2 carbonation” procedure makes it possible to sequester CO2 quickly and then store it permanently as stable carbonates. The exothermic nature of the mineral carbonation reaction can potentially compensate for the energy consumption during CO2 sequestration. This study mainly addresses a two-dimensional model of the geological mineral CO2 carbonation (herein, the geological formation of peridotite), by which the effects of temperature conditions on the reaction rate and the quantity of the sequestrated CO2 and exothermic heat energy are discussed. Results reveal a typical case of the average temperature elevation of peridotite by over 55 °C (reaching 240 °C) after 2 years. Peridotite's average CO2 sequestration rate in this typical case can achieve 132.62 kg/(year·m³). By changing the injected fluid temperature and the initial peridotite temperature to 110–150 °C, the average CO2 sequestration rate can be increased by 33–43%, obtaining a temperature greater than 150 °C. This heat production from the geological mineral CO2 carbonation can profitably compensate for the energy consumption in the Carbon Capture, Utilization, and Storage projects via the geological mineral CO2 carbonation.

Geothermal energy extraction from abandoned oil and gas wells using mono and hybrid nanofluids

The present study aims to analyze the thermal performance of the water-based nanofluids inside the wellbore heat exchangers to extract the geothermal energy from abandoned oil and gas wells (AOGW). Consequently, the study has considered Al2O3/water, Cu/water and CuO/water nanofluids as well as the Al2O3–Cu/water hybrid nanofluid with various particle volume concentrations ranging from 1% to 4% inside the coaxial wellbore heat exchanger (CWHE). For this purpose, a conjugate heat transfer module with a well-known k-epsilon (k-ε) turbulent model of COMSOL Multi-physics has been employed to simulate the fluid flow and heat transfer of the CWHE installed in AOGWs. Additionally, a sensitivity analysis has also been performed to determine the impact of individual operational parameters such as injection fluid mass flow rate and temperature on the system's thermal performance. It has been noted that the outlet fluid temperature enhanced by 25% with the addition of 4% of Cu nanoparticles to the water. Moreover, the maximum coefficient of performance of CWHE has been observed around 1.83 using Cu/water nanofluid with 4% volumetric fractions at an injection fluid temperature of 20 °C and a mass flow rate of 5 kg/s. Finally, the Cu/water nanofluid provided the best thermal performance followed by Al2O3-Cu /water, CuO/water and Al2O3/water nanofluids. It is expected that the findings of this study could motivate the researchers to work on the potential application of nanofluids/hybrid nanofluids to extract geothermal energy from AOGWs.

The Study of Porous TH Model of CO2-EGS in ChingHsui, ILan Assessment

本研究之目的為探討以超臨界二氧化碳（supercritical CO2）為取熱流體之二氧化碳增強型地熱系統（CO2-EGS）開發之可行性並預估其取熱產能以活化暫停開發之地熱井。為此，本研究以紅柴林2號井（HCL-2）與結元井（JY-1）為基礎，使用有限元素分析法建立了結合裂隙網路（fracture network）、孔隙熱傳與達西流（Darcy’s law）的孔隙-熱-水模型（porous-thermal-hydraulic model），並探討了儲集層於不同注入條件下的溫度變化趨勢及CO2-EGS之總產能。<br>由本研究可知當注入質量流率愈大，注入井底溫度變化大，生產井產出溫度愈高，使得EGS總產能愈高；大的注入質量流率可有效降低工作流體沿生產井流出時的溫降；然注入流體溫度對儲集層溫度分布幾乎沒有影響，生產井溫度對之亦較不敏感。在本研究中，CO2-EGS在注入質量流率為4 ton/hr與0.0005 ton/hr之條件比較發現，生產井口溫度增加約21.5%；溫降降低約16.96%，僅為約0.04%；總產能由23.6 kW增加到219 MW。而流量為4 ton/hr之比產能為571.4 kJ/kg，相較0.0005 ton/hr之比產能增加約11.8%。<br>未來本研究可結合更進一步之現地示蹤劑試驗數據做產能預估，評估以此二井為基礎建立CO2-EGS之產能與效益，可為活化已暫停開發之地熱井做出貢獻。The re-utilization and activation of the abandon geothermal well was an economic concept for increasing the geothermal potential. The purpose of this study was to evaluate the feasibility of CO2 enhanced geothermal systems (CO2-EGS) based on the geothermal well HCL-2 and JY-1 and to estimate their capacity. A porous-fracture thermal-hydraulic model combined the fracture network, porous heat transfer model and Darcy's Law was established by finite element analysis. The temperature variation of the reservoir under different injected conditions and the total geothermal capacity of CO2-EGS are discussed. <br>The results show that the higher the mass flow rate of injection, the higher the outer temperature of the production well, the higher the total EGS capacity. The temperature difference of the production well decreased as the injected mass flow rate increased. The reservoir temperature distribution could be affected by the injected fluid temperature slightly. In this study, the temperature of the production wellhead of CO2-EGS increased about 21.5% when the injected mass flow rate was from 0.0005 ton/hr to 4 ton/hr. The specific capacity increased about 11.8%. <br>In future, this study can be combined with further in-situ tracer test data to estimate the capacity realistically, which can contribute to the activation of the abandon geothermal wells.

Cryogenic liquid nitrogen stimulation-induced cracking in gas-enriched shale reservoirs: A numerical investigation

Cryogenic shock-induced brittle cracking has promising application prospects in reservoir stimulation. In this paper, a fully coupled thermo-hydro-mechanical (T-H-M) model combined with the statistical meso-damage theory is proposed to investigate the trans-scale progressive cracking process of shale gas reservoirs stimulated by liquid nitrogen (LN2). In this theoretical framework, shale meso-heterogeneity in both thermo-mechanical and hydraulic properties is characterized by two independent statistical distribution functions; temperature-dependent rock properties and temperature- and pressure-dependent fluid thermodynamic properties are described using some experimental and theoretical formulas. The numerical model is implemented in a finite element context and subsequently validated against existing classical coupling results. Numerical results demonstrate that LN2 fracturing accompanied by the unique cryogenic shock effect leads to a complex cracking process involving multiple-point fracture initiation, asymmetric macrofracture propagation, and primary fracture bifurcation. Sensitivity analysis indicates that approximately equidistant or equilength radial fractures may be generated at a lower stress difference, lower permeability, or higher elastic modulus; both fracture initiation pressure and induced fracture morphology are more sensitive to injected fluid temperature relative to initial reservoir temperature; a larger thermal expansion coefficient is beneficial for inducing more fractures, but not applicable to the thermal conductivity. Preferable candidates for LN2 stimulation to generate multiple fractures in shale reservoirs are recommended. It is also found that compared with H2O and supercritical CO2, fracturing using LN2 can generate fractures with lower initiation pressure and greater complexity. Preliminary results confirm the potential of using LN2 fracturing to improve the stimulation effect of shale reservoirs.

Factors affecting the efficiency of closed-loop geothermal wells

Geothermal energy has a promising prospect of becoming a feasible source of clean energy in the future. However, conventional open-loop geothermal systems need continuous water circulation, which limits their application in dry areas. On the other hand, long-term fluid injection into the reservoir may cause issues such as seismicity. To overcome these shortcomings, closed-loop geothermal systems are not requiring water withdrawal or water injection. However, the mechanism controlling the efficiency of closed-loop systems has not been well analyzed. To resolve the issue, a systematic study was conducted on factors affecting production efficiency of a closed-loop geothermal well. First, a coupled three-dimensional model was established, which was then validated against experimental results available in the literature. Using this model, the effects of several critical design factors were investigated quantitatively. These factors include cement thermal conductivity, cement thickness, fluid circulation rate, injected fluid temperature, heat capacity of circulating fluid, heat exchanger height, and tubing outer diameter. Our simulation results indicate that increasing the cement thermal conductivity enhances both produced fluid temperature and thermal power. The effect of cement thickness is correlated with the value of its thermal conductivity. As the circulation rate increases, the temperature of produced fluid decreases while thermal power increases asymptotically. Using a circulating fluid with high heat capacity would result in higher thermal power. A large heat exchanger height would boost both the production temperature and thermal power significantly. Finally, a dimensionless analysis was conducted, through which two dimensionless numbers were derived to integrate the effects of different factors. By comparison analysis, the accuracy of the dimensionless numbers was validated. Also, the impact of the dimensionless numbers on dimensionless produced fluid temperature was determined. With the dimensionless numbers, the effects of different individual factors can be evaluated comprehensively, which brings convenience to parameter design. The potential applications of the derived dimensionless numbers in parameter design of closed-loop systems were discussed. Results and conclusions obtained in this paper may provide a reference for optimally designing closed-loop systems.

Heat extraction performance evaluation of U-shaped well geothermal production system under different well-layout parameters and engineering schemes

The U-shaped well geothermal production system is proposed on the basis of abandoned oil wells which can achieve the non-interference conversion of “heat extraction without water”. Compared with the fracturing enhanced geothermal system, the U-shaped well system is more stable and more achievable. However, there is no comprehensive parametric study of the heat extraction performance of U-shaped well geothermal production system. In this paper, the thermal-hydraulic model of U-shaped geothermal production system is established based on the abandoned oil well. The temporal and spatial evolution of temperature field is analyzed, radiation range of the temperature drop is calculated, the effects of well-layout parameters on heat extraction performance are investigated. For well-layout parameters, the optimal horizontal section length is 1500m, the optimal insulation material length is 1000m. For the engineering parameters, the optimal injection rate is 1500m3/d and the optimal injection fluid temperature is 288.15K to obtain a higher heat extraction power. The discontinuous mode can sustainably guarantee better heat extraction performance compared with continuous mode. These findings can provide some reasonable suggestions for the deep geothermal development.

The Numerical Simulation of Heat and Mass Transfer on Geothermal System-A Case Study in Laoling Area, Shandong, China

Geothermal resources have become increasingly attractive and promising because of their abundant resource base and environmental protection, especially for hydrothermal resources, which are widely developed for heating in winter. It is indicated that numerical simulation is an important tool for high efficiency geothermal system development. Compared with other methods, numerical simulation is a more comprehensive, scientific, and effective method in the evaluation of recoverable resources and the formulation of development plans. However, there are some problems in the existing software, such as deviation in physical property calculation, incomplete multifields coupling, and poor applicability for low-permeability reservoir and large-scale models. Therefore, based on the optimized multiphysics coupling mathematical model and MPI architecture, a simulator for a multiphysics-coupling geothermal system (SMG) was developed by Sinopec. A case study in the Laoling area, Shandong, China was primarily conducted by using geothermal software SMG, where the effect of well spacing and injection fluid temperature on the production was illustrated. Moreover, a geothermal recoverable resources evaluation method based on numerical simulation is proposed and used for the evaluation of regional geothermal dynamic recoverable resources in Laoling.

Flow and heat transfer of nitrogen during liquid nitrogen fracturing in coalbed methane reservoirs

Liquid nitrogen (LN2) fracturing has the potential to induce complex fracture networks, avoid formation damage, and eliminate water consumption. However, the flow and heat transfer of nitrogen in fractures and its effect on the fracture generation during LN2 fracturing have not been studied, and the fracturing mechanism remains unclear. In this paper, the nitrogen flow during LN2 fracturing in a straight fracture was simulated. First, a 3D unsteady-state fluid flow and heat transfer model for LN2 fracturing in coalbed methane (CBM) reservoir was developed, which considered the phase transition of nitrogen, thermophysical properties variation of coal and the heat transfer between nitrogen and formation. This model was then validated against published analytical solutions. Subsequently, the model was applied to elucidate the phase distribution of nitrogen and its influence on fracture generation. Finally, the factors that affect the flow and heat transfer of nitrogen were analyzed. The results showed that the nitrogen at the fracture tip was in a supercritical state. Thermal stress had minor effects on the propagation of the main fracture. In addition, fracture aperture, injection velocity, reservoir temperature, injection fluid temperature, fracture propagation pressure and coal cleat porosity could affect the effectiveness of LN2 fracturing in a coal seam. The main findings of this study are the keys to the research of liquid nitrogen fracturing mechanisms in CBM reservoirs. • Nitrogen at the fracture tip is in supercritical state during the fracture propagation. • Thermal stress had minor effects on the propagation process of the main fracture. • LN2 injection parameters and coal cleat porosity could affect the heat transfer efficiency in LN2 fracturing in coal seam.

Fluid-CO2 injection impact in a geothermal reservoir: Evaluation with 3-D reactive transport modeling

Geothermal energy is commonly recognized as an environmentally friendly source of energy. However, geothermal fluids have unusually high CO2 content, particularly, in carbonated geothermal reservoirs. An efficient method to mitigate the CO2 emissions of geothermal power plants is to re-inject the captured CO2 with the effluent fluid to mineralize mainly into calcite under reservoir conditions (e.g., reservoir temperatures ranging from 200 to 220 °C). One of the major concerns about the re-injection of the captured CO2 is to predict the geochemical interaction between the injected fluid-CO2 and rock, and the corresponding alterations that occur due to the re-injection in the reservoir parameters. For this study, we have selected one of the largest geothermal fields, which is located in the western part of Turkey. A predictive 3-D reactive transport modeling is carried out using TOUGHREACT v1.2 for potential fluid-CO2 injection into deep metamorphic formation rocks consisting of marble, quartzite, and schist. Each rock type with different mineral constituents is examined in three different scenarios. Moreover, in each scenario, three annual injection rates, 500, 2000, and 4000 tons of CO2 for ten years of continuous injection are tested. The aims of the study are first the evaluation of the dynamic fluid-rock interactions with maximum possible CO2-charged fluid injection and second the identification of the mineralization process. The modeling results indicate that the maximum CO2-charged fluid mixture remains stable as a single-phase in all scenarios. The mineralization process of CO2 in the reservoir is limited due to the different mineral contents of the considered metamorphic rocks and the differences between the CO2 mass fraction of the injected fluid and the reservoir. In addition, the injected fluid temperature, the pH, the convective dispersive fluxes between the wells also affect the chemical process. These results show differences compared to the CarbFix project carried out in basaltic Icelandic geothermal reservoirs where the CO2 mineralization process was successful.

Effect of different exploitation schemes on production performance from the carbonate reservoir: A case study in Xiong'an new area

Operational optimization is the essential factor to maximize the heat production from the thermal reservoir. Well spacing and the arrangement of the production well are the two most pivotal factors for the thermal reservoir which can ensure long-term production at economically acceptable levels. The Xiong'an geothermal area, located in the western margin of the Bohai Bay Basin, is the most developed region of the carbonate stratum and also is one of the areas that have the greatest hydrothermal geothermal resources in China. In this study, based on the temperature data of the carbonate formation and thermosphysical data from the core samples measurement, a three dimensional thermo-hydraulic coupled numerical model was established to assess the geothermal potential of the carbonate reservoir and the effect of different exploitation schemes (mainly involved the injection fluid temperature, injection mass flow rate and lateral well distance) on the thermal reservoir performance was analyzed over a period of 40 years. The effect of permeability heterogeneity on the thermal reservoir performance was also discussed as a case study. The calculation results were then analyzed on the basis of the output temperature decline curves and the cumulative energy production over the entire period from the production well. Among the three important influence factors on the carbonate reservoir performance, the injection temperature has the most significant effect on the energy production rate, followed by the injection mass flow rate and the lateral well spacing.

Design and optimization of multiple wells layout for electricity generation in a multi-fracture enhanced geothermal system

The major challenge in Enhanced Geothermal System is to circulate the injected fluid in most part of the reservoir. One solution to this problem is to create artificial fractures in the reservoir and optimally position multiple injection wells and multiple production wells. The wells layout plays a crucial role and requires investigation. This is the ultimate goal of this paper in order to extract a sufficient amount of energy and allow the fluid to reach a larger volume in the heterogeneous reservoir. The results show that a combination of three injection wells with two production wells provides the best performance. With this well layout, the output electrical power drops from 10.40 to 9.40 MW to 6.84–4.53 MW increasing the injection fluid flow rate in 0.075–0.125 m3/s range because higher the volume flow rate, greater the water losses. The average production temperature after a 40-year period is 164.8 °C and reduced by 3.1%, which is acceptable. The injected fluid temperature and the hydraulic gradient have a low influence on the production temperature evolution and the heat extraction ratio change. Hydraulic gradient influence on the production temperature is noticeable for a hydraulic gradient value greater than 10 mm/m.

Completion Effects on Diagnosing Multistage Facture Treatments with Distributed Temperature Sensing

Summary Distributed temperature sensing (DTS) is a valuable tool to diagnose multistage hydraulic fracture treatments. When a stage interval is shut in, the clusters that take more fluid during pumping warm up more slowly. Therefore, the fluid volume injected into each cluster can be quantitatively interpreted by numerical inversion of the warm-back temperature behavior. This general concept assumes that the different warm-back behavior is controlled by only the injected fluid volume; however, recent observations of DTS data indicate that completion configurations significantly influence the warm-back behavior. This paper investigates the completion effects on the DTS interpretation. In ideal conditions, when a stage is fractured, the upstream stage intervals should show an almost uniform temperature that is close to the injected fluid temperature. This is due to the high fluid velocity of injected fluid in the wellbore, and the upstream intervals have not been perforated (noncommunicating intervals), so the only heat transfer is heat conduction between the wellbore fluid and the surrounding reservoir. But the field DTS data show considerably irregular variations in temperature along the upstream stage intervals. These variations are caused by the completion effects. The nonuniform temperature profile is caused by different heat transfer behavior induced by completion hardware along the production casing string, such as joints, clamps, and blast protectors, and by the sensing cable location in the cement, as well as the cement quality. Because the varying heat transfer behavior impacts the warm-back behavior as well as the temperature profile, the completion effects need to be considered in DTS interpretation. A method of DTS interpretation considering the completion effects to diagnose multistage fracture treatments was developed. Because the heat transfer between a wellbore and a reservoir depends on the overall heat transfer coefficient describing heat conduction through the completion in a forward model, this parameter needs to be tuned all along the wellbore. To calibrate the completion effect, the temperature inversion is conducted using the temperature measured at a stage interval that is upstream of a stage interval currently being treated. Because the interpreted stage interval is not perforated at that time, the thermal behavior at the noncommunicating interval is governed by only the heat conduction through the completion environment. Once the effective values of the overall heat transfer coefficient are estimated along the interpreted stage interval, they can be assumed to be constant physical parameters. Then, the fluid volume distribution is interpreted by using the effective overall heat transfer coefficient profile along each interval. This study provides a field application of the developed interpretation method. The new interpretation method provides more accurate diagnosis of fracture treatments by DTS interpretation.

Production performance of oil shale in-situ conversion with multilateral wells

A novel method using multilateral wells to perform oil shale in-situ conversion process is proposed in this paper. This method constructs radial branches in upper and lower oil shale formation as injection and production wells. Hot fluids are injected from the injection wells, and pyrolyzed oil and gas are extracted by production wells. In this study, a 3D transient model coupling fluid flow, heat transfer and chemical process is established and implemented on COMSOL Multiphysics platform to investigate the oil shale in-situ conversion process. The temperature field, production characteristics and energy performance are characterized. Sensitivity of oil shale properties and operational parameters are analyzed. Influences of multilateral-well arrangements are studied. The simulation results indicate that the products are strongly dependent to oil shale temperature. The specific heat capacity, injection fluid temperature and injection mass flow rate can significantly influence production performance, while thermal conductivity has negligible effect. Multilateral wells with 5 branches, 60° branch angle and 40 m branch length show the best production performance among the computational cases. This study provides comprehensive insights and suggestions for the application of multilateral wells in oil shale in-situ conversion process.