Hot Dry Rock Resources Research Articles

Investigation on the effect of the relative position between fracture and injection-production well on thermal extraction performance

The development of hot dry rock (HDR) resources is mainly through hydraulic fracturing to build fracture in low permeability high-temperature rock to form working fluid flow channels. The control mechanism of thermal transfer and conversion process in fracture system is the key to influence thermal extraction effect. In this paper, a temperature-hydraulic-mechanical (THM) coupling model of fractured rock mass is established considering the temperature variation of rock elastic modulus and Poisson's ratio. The dynamic changes of fracture aperture and permeability are investigated. Taking fractured HDR reservoir as a case study, the depletion thermal extraction process of dual-well enhanced geothermal system (EGS) is simulated, the spatial-temporal evolution of multi-field are analyzed. The results show that the cold front of the horizontal and vertical single fracture model advance in an oval shape and a rectangle shape, respectively. Over 30 years, the horizontal fracture aperture typically changes by a factor ranging from 1.02 to 1.12, permeability typically changes by a factor ranging from 5 to 15. The vertical fracture aperture typically changes by a factor ranging from 1.02 to 1.14, permeability typically changes by a factor ranging from 10 to 25.

A true triaxial experiment investigation of the mechanical and deformation failure behaviors of flawed granite after exposure to high-temperature treatment

Understanding the mechanical and deformation failure behaviors of heated flawed granite under true triaxial stresses is of great significance for evaluating the wellbore stability in developing hot dry rock resources. In this study, true triaxial experiments are conducted on flawed granite specimens of a varying flaw overlapping length lfo with and without high temperature (HT) treatment, with the emphases on the crack development under true triaxial stresses and its correlations with the strength, plastic anisotropy and failure forecast. Investigations demonstrate that HT, σ2 (intermediate principal stress) and lfo, significantly affect the mechanical properties of flawed granite. Due to strong 3D confinement, the loop crack, the secondary transverse crack and the far-field crack are frequently induced in flawed granite, unlike experiments of uniaxial, biaxial and conventional triaxial compression. When increasing lfo, the rock bridge undergoes the stress amplification which tendentiously drives the internal crack coalescence and typically causes a reduced strength. The PSIRs (Plastic Strain Increments Ratios) analysis, first extended to the true-triaxial experimental data, reveals that the 3D stress-induced extensional/shear fracturing from the flaw tips in σ2-direction is the mechanism of the plastic anisotropy generated. Besides, an attempt to anticipate the failure time in the framework of the time‐reversed Omori’s law suggests a poor predictability by using the acoustic emission but a higher-quality forecast (being more precise and less biased) by using the dissipated energy.

Prediction of geothermal temperature field by multi-attribute neural network

Hot dry rock (HDR) resources are gaining increasing attention as a significant renewable resource due to their low carbon footprint and stable nature. When assessing the potential of a conventional geothermal resource, a temperature field distribution is a crucial factor. However, the available geostatistical and numerical simulations methods are often influenced by data coverage and human factors. In this study, the Convolution Block Attention Module (CBAM) and Bottleneck Architecture were integrated into UNet (CBAM-B-UNet) for simulating the geothermal temperature field. The proposed CBAM-B-UNet takes in a geological model containing parameters such as density, thermal conductivity, and specific heat capacity as input, and it simulates the temperature field by dynamically blending these multiple parameters through the neural network. The bottleneck architectures and CBAM can reduce the computational cost while ensuring accuracy in the simulation. The CBAM-B-UNet was trained using thousands of geological models with various real structures and their corresponding temperature fields. The method’s applicability was verified by employing a complex geological model of hot dry rock. In the final analysis, the simulated temperature field results are compared with the theoretical steady-state crustal ground temperature model of Gonghe Basin. The results indicated a small error between them, further validating the method's superiority. During the temperature field simulation, the thermal evolution law of a symmetrical cooling front formed by low thermal conductivity and high specific heat capacity in the center of the fault zone and on both sides of granite was revealed. The temperature gradually decreases from the center towards the edges.

Characterizing thermo-hydro-mechanical behavior of rock using a grain interface-based discrete element model (GIB-DEM)

Understanding the meso-structure evolution and macro-mechanical property changes in rocks under thermo-hydro-mechanical (THM) treatment is crucial for advancing and managing deep geological projects. However, due to complex discontinuity networks in rocks, achieving an accurate characterization that quantitatively correlates the micro-macro mechanical behaviors under THM conditions remains challenging. This study introduces a groundbreaking multi-scale analysis method called the grain interface-based discrete element model (GIB-DEM) to tackle this issue. By utilizing digital imaging processing (DIP) and meso-mechanical measurements, the GIB-DEM directly determines the meso-mechanical parameters of bonds, eliminating the need for complex calibration found in traditional methods. After validating the GIB-DEM through experimental and numerical Brazilian Splitting tests, we investigate the macro- mechanical behaviors of rock under different THM conditions. Our results indicate that the increase in the tensile strength at 75 °C is attributed to the tensile strength increase of quartz grain interfaces. The development of micro-cracks on the interfaces of feldspar and feldspar-quartz accounts for the decrease in tensile strength of rock under thermal and hydraulic treatment. Overall, this pioneering research provides valuable insights for optimizing Enhanced Geothermal System (EGS) projects and effectively managing Hot Dry Rock (HDR) resources.

Study on the Meso-Failure Mechanism of Granite under Real-Time High Temperature by Numerical Simulation

In the development of geothermal resources in hot dry rocks, deep underground rock masses are typically subjected to real-time high-temperature environments. High temperatures alter the physical and mechanical properties of the rocks, directly affecting the safe and efficient utilization of hot dry rock resources. Therefore, a grain-based model (GBM) of particle flow code (PFC) was constructed based on uniaxial compression tests, and the model was verified according to macroscopic mechanical parameters and damage modes, in order to carry out the simulation study of the uniaxial compression of granite and explore the meso-failure mechanism of granite under real-time high temperature. The relationships between stress–strain curves and crack derivation, the evolution of microcracks, and the characteristics of acoustic emission activity and energy changes at different temperatures were investigated in conjunction with the results of laboratory tests. The results show that crack development, acoustic emission activity, and energy evolution during uniaxial compression include four main stages: initial compression, elasticity, plastic strengthening, and post-peak damage. The failure of granite is primarily controlled by mica and feldspar. During loading, intergranular tensile cracks first emerge within the granite, followed by intragranular tensile cracks, with shear cracks appearing last. As the temperature increases, the total number of microcracks continuously rises, the frequency of acoustic emission events increases, and both dissipated energy and boundary energy gradually decrease, showing an upward trend in the energy dissipation ratio, indicating an increase in thermal damage due to high temperatures. At 400 °C, the rate of microcrack formation increases significantly, with intergranular and intragranular cracks starting to coalesce into macroscopic cracks that extend outward. In the post-peak stage, the phenomenon of multiple peaks in acoustic emission events begins to appear. At 600 °C, the rate of microcrack formation reaches its maximum, with cracks extending throughout the sample to form a network of fractures, resulting in the granite exhibiting ductile failure characteristics.

A Method for Determining Target Areas of Hot Dry Rock Resources: A Case Study in Continental China

Geothermal resources have been recognized as important sources of clean renewable energy. The exploration, development, and utilization of geothermal resources, especially hot dry rock (HDR) resources, are highly important for achieving peak carbon and carbon neutrality. However, there is no comprehensive evaluation method for determining HDR target areas, and the evaluation scale and application disciplines are relatively simplistic. In this paper, we sought to optimize the identification of HDR target areas through a multiscale and multidisciplinary method and formed a set of generalized and demonstrative processes to guide the exploration of HDR resources. Through practical application to the Gonghe Basin and the Zhangzhou Basin, it was found that the comprehensive geothermal conditions of the Gonghe Basin are superior to those of the Zhangzhou Basin, and the geothermal reservoir depth, geothermal reservoir temperature, geothermal gradient, and heat flow are the four most important factors affecting hot dry rock geothermal resources. Using this method, the prioritization of target areas changes from a qualitative study to a quantitative and semiquantitative study, increasing the specificity and reliability of the decision-making process.

Failure mechanism of hot dry rock under the coupling effect of thermal cycling and direct shear loading path

Inducing shear failure in reservoir rocks is a critical strategy for enhancing hot dry rock resource exploitation, as it promotes the development of an extensive fracture network. In this study, granite was subjected to direct shear tests under three distinct temperatures and five thermal cycling treatments. Utilizing acoustic emission (AE) and digital image correlation (DIC) techniques, the shear failure traits and the evolutionary patterns of cracks in granite under diverse thermal cycling treatments were probed. Experimental results reveal that the direct shear strength of granite initially decreases, subsequently rebounds with increasing thermal cycles, and exhibits a steady decrease with temperature increase. Effects of thermal shock provoke a surge in AE counts and energy during the initial half of the shearing process, steering the failure mode of the samples from brittle to plastic. Furthermore, the macro crack morphology changes from a singular shear crack to a pair of parallel shear cracks, becoming intricately complex at elevated temperatures (600 °C). Additionally, the initiation of the main shear crack in granite consistently manifests a mixed tensile-shear failure, with the proportion of shear action displaying a positive correlation with temperature. In contrast, the proximal secondary cracks are purely tension-initiated. Finally, a competitive mechanism between rock strengthening and weakening induced by thermal cycles treatment was proposed to explain the remarkable rebound in direct shear strength following thermal cycling treatment. The current work provides insights for the mechanism of shear failure in rocks under different thermal cycling conditions in geothermal reservoir stimulation.

Phase-field cohesive zone modeling of hydro-thermally induced fracture in hot dry rock during liquid nitrogen fracturing

Liquid nitrogen (LN2) fracturing is regarded as a viable alternative for the efficient development of hot dry rock (HDR) resources due to its main advantage in producing complex fracture networks and lowering breakdown pressure. However, the fracturing mechanisms and major factors controlling the LN2 fracturing efficiency are still poorly understood. A thermo-hydro-mechanical-damage (THMD) coupling model is proposed to study the fracture initiation/propagation behavior of LN2 fracturing under various fracturing parameters and reservoir conditions based on a phase-field cohesive zone method (PF-CZM). The characteristic differences between LN2 and water fracturing are compared. Results indicate that the tensile stress of LN2 fracturing is concentrated at the tip of fractures. When the HDR reservoirs are undertaken lower stress level with higher initial rock temperature, the damage ratio can be enhanced. Young's modulus and thermal expansion coefficient are the key petrophysical and mechanical properties affecting the LN2 fracturing performance. The optimal pressurization rate is 0.2 MPa/s. It indicated that a balanced contribution of thermal stress and fluid pressure is crucial to the bifurcation of major fracture and forming complex fracture networks. The major findings of the study are expected to provide theoretical guidance and computational simulation basis for the LN2 fracturing on HDR reservoirs.

A multi-objective optimization and multi-attribute decision-making analysis for technical-thermodynamic-economic evaluation considering the rock damage on production performance of hot dry rock geothermal resources

In the long-term mining of geothermal resources in hot dry rock (HDR), the change of thermal stress and pore pressure will increase fracture conductivity evolution, further improving production performance. The optimization and decision-making of the development scheme based on the impact of damage from fractures have yet to be reported. The damage to fractures is essential in designing and adjusting geothermal resource development schemes, particularly in selecting optimal schemes. Therefore, the production performances of HDR resources under different parameters are analyzed to establish a database. Then, minimizing flow resistance, maximizing net power, and maximizing economic benefits are set as optimization goals. Various injection-mining parameters and fracture characteristics are treated as decision variables. Multi-objective optimization and multi-attribute decision analysis is conducted to obtain optimal schemes. Finally, optimal schemes are evaluated and compared, considering damage and non-damage scenarios. Results show that the NSGA-II algorithm is more suitable for optimizing geothermal development questions. Net power and economic benefits of the optimal scheme considering damage increase by 45.84 % and 21.35 % compared to the control scheme with damage. For the non-damage scenario, the above values increased by 31.55 % and 5.15 %, respectively. Compared to not considering the damage, higher mass flow and well spacing of optimal scheme can be selected for the case when damaged. Moreover, the parametric design of the optimal scheme becomes more conservative as the production cycle increases.

Key Technology of 240°C High-Temperature Drilling Fluid

Hot dry rock (HDR) is a renewable green and clean energy source from the depths of the earth. It has the characteristics of high efficiency, environmental protection, safety, and stability, and is not restricted by seasons and climates. Difficulties in exploration and development include deep burial, formation fragmentation, abnormal pressure, high well temperature gradient, and high hole bottom temperature (usually >200°C), key technical issues such as sticking. This paper analyzes the difficulties of high-temperature resistant drilling fluid in dry hot rock: temperature resistance of treatment agents and systems, foaming, leakage, wellbore instability, and other problems. The optimization and experiment of treatment agents such as loss reducers, high-temperature protective agents, etc., and research on drilling fluid technology resistant to high temperature of 240°C in hot dry rock drilling has been carried out, through the optimization experiment of pulping materials and high temperature treatment agent. The main formula is: 3%-4% Sodium bentonite + 2%-3% HPS + 3%-4% SPNH + 2%-4% GJA + 3%-4% JSJ-1 + 0.5%-1.0% GGDP + 1% GBHJ. The drilling fluid formula has good rheology after hot rolling at 240°C, API filtrate loss<5ml, the viscosity recovery rate is over 90%. It provides effective technical support guarantee for promoting the exploration and development of hot dry rock resources in China.

Study on the heat recovery behavior of horizontal well systems in the Qiabuqia geothermal area of the Gonghe Basin, China

Geothermal energy, as a highly regarded renewable energy source, holds vast potential for widespread applications. However, the methods of geothermal energy extraction need to be optimized and improved according to specific geological conditions. This study aims to provide a multi-level horizontal branch well heat recovery system for the Qiabuqia geothermal field in the Gonghe Basin. To begin, this study systematically investigated the influence of various engineering parameters on production temperature and establishes mathematical models to depict the relationships among these parameters. Subsequently, we unveiled the precise numerical correlation between well length and the limit injection rate, utilizing multiple production indexes to comprehensively characterize the practical production characteristics and effectiveness of the multi-level heat recovery system. Finally, a comprehensive economic evaluation of the system was conducted. The research findings indicate that there exists a linear relationship between production temperature and injection temperature, while a second-order polynomial relationship is observed between production temperature and injection rate, wellbore size, and well length. In single-well heat recovery systems, the ratio of well length to the limit injection rate is 4000, whereas in multi-level branch well system, the limit injection rate is 88 % of that in single-well systems. Furthermore, branch wells located farther from the injection end exhibit greater heat recovery capacity but relatively higher production costs. Nonetheless, overall, the production cost for 1000-m-long branch wells can be reduced to around $0.05 $/kWh, demonstrating significant economic feasibility. These research findings provide momentum for the sustainable development and utilization of hot dry rock resources, simultaneously offering more precise guidance for the design and operation of hot dry rock power generation projects.

Investigating the Formation of Hot-Dry Rock in Gonghe Basin, Qinghai, China

The Gonghe Basin, Qinghai Province, China, has rich geothermal and hot-dry rock resources. Through a magnetotelluric survey line with 400 points, combined with regional geology data, the deep geoelectrical structural background and thermal source mechanisms of the Gonghe Basin were explored. The results showed that (1) a deep structure with high conductivity may exist at a depth of 15 km in the basin, and could be compared to the layer-shaped, low-velocity, high-conductivity structure in the eastern part of the Qinghai–Tibet Plateau; (2) the rushing reverse fault played a crucial role in heat control and conduction from the hot field; and (3) high-temperature heat storage existed, including four layers of geothermal resources. This study proposed a triple-polymorphism model of hot-dry rock in the area; that is, the high-conductivity layer in the Middle–Late Cenozoic crust was the principal heat source; the Middle–Late Triassic granite was the essential heat-storing body, as well as a parent rock to the hot-dry rock; and the Cenozoic sedimentary rock was the effective caprock. This model is critical to understanding geothermal causes, predicting geothermal resources, and planning, on the Qinghai–Tibet Plateau.

Three-Dimensional Geological Modeling and Resource Estimation of Hot Dry Rock in the Gonghe Basin, Qinghai Province

The Gonghe Basin, situated on the northeastern margin of the Qinghai–Tibet Plateau, is a strike-slip pull-apart basin that has garnered considerable attention for its abundant high-temperature geothermal resources. However, as it is located far from the Himalayan geothermal belt, research on the geothermal resources in the Gonghe Basin has mainly focused on the heat source mechanism, with less attention given to the distribution and resource potential of hot dry rock. In this project, a comprehensive approach combining geological surveys, geophysical exploration, geochemical investigations, and deep drilling was employed to analyze the stratigraphic structure and lithological composition of the Gonghe Basin, establish a basin-scale three-dimensional geological model, and identify the lithological composition and geological structures within the basin. The model revealed that the target reservoirs of hot dry rock in the Gonghe Basin exhibit a half-graben undulation pattern, with burial depths decreasing from west to east and reaching a maximum depth of around 7000 m. Furthermore, the distribution of the temperature field in the area was determined, and the influence of temperature on rock density and specific heat was investigated to infer the thermal properties of the deep reservoirs. The Qiabuqia region, situated in the central-eastern part of the basin, was identified as a highly favorable target area for hot dry rock exploration and development. The volume method was used to evaluate the potential of hot dry rock resources in the Gonghe Basin, which was estimated to be approximately 4.90 × 1022 J, equivalent to 1.67 × 1012 t of standard coal, at depths of up to 10 km.

Multifactor analysis of heat extraction performance of coaxial heat exchanger applied to hot dry rock resources exploration: A case study in matouying uplift, Tangshan, China

To obtain an excellent heat exchange effect, it is necessary to optimize the technical processes of single-well coaxial heat exchange. Based on numerical simulation and field investigation, this study shows that a high inlet temperature can significantly improve the outlet temperature while a low inlet temperature can obtain a high heat extraction power. The outlet temperature and heat extraction power show a positive correlation binomial relation with the inlet flow rate, the thermal conductivity of cement, the thermal conductivity of reservoir and the borehole diameter, which exhibit linear negative and positive correlation relationships with the thermal conductivity of inner tube and geothermal gradient. The inlet flow rate, geothermal gradient and thermal conductivity of the inner tube are the most significant factors, followed by the thermal conductivity of reservoir and the borehole diameter, while the inlet temperature and thermal conductivity of cement are the insignificant factors. It is recommended to select the reservoirs with high geothermal gradient, good thermal conductivity and wide stable distribution, develop fixing well cement with high thermal conductivity and inner pipe materials with excellent insulation performance, reduce the inlet temperature, increase the inlet flow rate of working fluid and expand the well diameter while considering costs.

Model for economic evaluation of closed-loop geothermal systems based on net present value

Closed-loop geothermal systems (CGSs) represent an effective means of extracting low-grade thermal energy from hot dry rock (HDR). Thus far, there has been much debate on whether they can be profitable because no economic evaluation model has been available. This study highlights the profitability of geothermal projects by developing a techno-economic coupling model for economic evaluation of CGSs based on net present value (NPV) for the first time. The proposed model was applied and analyzed in the case of the Gonghe Basin, Qinghai, China. The results indicate the following conclusions. (1) The technical model was extremely accurate, and the results were consistent with experimental results and the results of calculations using other classical models (the relative errors were all less than 9.8 %). (2) In terms of the heat extraction effect, the heat extraction power of U-shaped closed-loop geothermal systems (UCGSs) is ∼ 1.3 times that of coaxial closed-loop geothermal systems (CCGSs). The heat extraction power for direct heating is ∼ 1.1 times that for electricity generation. (3) Increasing the rate of the one-off government subsidy to 30 %, increasing the heat price by 30 %, and reducing the drilling cost by 30 % can make a CGS profitable within a production time of 50 years. This study will serve as a theoretical foundation for policymakers and engineers to develop HDR resources using CGSs.

Risk assessment of earthquakes induced during HDR development: A case study in the Gonghe Basin, Qinghai Province, China

Earthquakes induced during hot dry rock (HDR) geothermal development have attracted extensive attention and constrained the further exploitation of HDR resources. Seismic risk evaluation of HDR projects is essential. The first HDR demonstration project in China is located in the Gonghe Basin in Qinghai. The EGS (enhanced geothermal systems) site is located near Gonghe County and is very seismically sensitive. The seismic risk induced by hydraulic fracturing and long-term cycling during the HDR development process was evaluated using a multi-field coupling method based on analysis of the geothermal geological conditions, ground stress, and natural fracture characteristics. During hydraulic fracturing, the predicted magnitude of earthquake events is generally below 2.0, with a range of 0.7–1.3. During a 30-year development period, the predicted maximum earthquake magnitude is less than 1.28. The HDR development will not have an impact on the local geological safety. Considering the uncertainty of the geology, a further discussion of measures to reduce the risk of earthquakes is presented. An entire induced seismic risk evaluation process method is developed, which can provide a reference for related research.

Analytical Model of Hydraulic Fracturing for Low Permeability Hot Dry Rock Reservoirs and DEM Simulation Base on Fluid-Solid Coupling

The formation of a rich underground-seam network is the key problem in the development of low-permeability hot dry rock (HDR) resources. Considering the lack of macroscopic continuum theory to study hydraulic fracturing having preset fracture-interface element, the particle-flow method of micro-mechanical discrete-element theory is introduced to simulate the mechanical behavior of hydraulic fracturing for HDR low permeability reservoirs. The reservoir is simulated as a round particle; the fracturing fluid movement is described by the seepage field equation, and rock movement is described by the displacement field equation. Finally, the particle-flow numerical model of hydraulic fracturing for HDR low permeability reservoirs is established under the condition of fluid-solid coupling: the model contains two parts (rock and fracture). Based on the parallel-bond model, a definition of micro-fractures of hydraulic fracturing is given. The relation between the fracturing effect and influence parameters is discussed. The results show that the fracture-initiation pressure is proportional to the magnitude of minimum horizontal stress, particle normal-contact stiffness, and particle normal- and tangential-connection strengths; the pressure is also independent of maximal horizontal stress and tangential contact stiffness. At the same time, the formation temperature of dry hot rock will reduce the strength of the rock, so particle-flow numerical models of hydraulic fracturing in different temperatures are discussed. Results show that fracture length and width show a trend of increase before decrease with the increase of injection pressure, an inverse relationship with minimums horizontal principal stress, and a positive relationship with HDR reservoir permeability.

Evaluation of the Fault Activation Risk Induced by Hot Dry Rock Reservoir Development Based on Thermal-Hydraulic-Mechanical Coupling.

Due to the nature of hot dry rock resources and the particularity of the development methods, the fault activation induced by injection and production of hot dry rocks involves a complex multifield coupling mechanism. Traditional methods cannot effectively evaluate the fault activation behavior in hot dry rock injection and production. Aiming at the above-mentioned problems, a thermal-hydraulic-mechanical coupling mathematical model of injection and production of hot dry rocks is established and solved by a finite element method. At the same time, the fault slip potential (FSP) is introduced to quantitatively evaluate the risk of fault activation induced by injection and production of hot dry rocks under different injection and production conditions and geological conditions. The results show that under the same geological conditions, the greater the well spacing of injection and production wells, the greater the risk of fault activation induced by injection and production and the greater the injection flow, the greater the risk of fault activation. Under the same geological conditions, the lower the reservoir permeability, the greater the fault activation risk and the higher the initial reservoir temperature, the greater the fault activation risk. Different fault occurrences result in different risks of fault activation. These results provide a certain theoretical reference for the safe and efficient development of hot dry rock reservoirs.

Seismic Diffraction Attribute Fusion for Geological Discontinuities in Hot Dry Rock Resources

For the safe development and utilization of hot dry rock resources, it is essential to understand the distribution characteristics of underground faults. However, the commonly used reflection attribute analysis method has an insufficient resolution, and the diffraction attribute analysis method is affected by multiple solutions. Moreover, both are highly dependent on the interpreters’ experience and take a long time. Therefore, based on the classical U-Net model, a diffraction attribute fusion model (DAF-U-Net) with 27-layer convolution is proposed. The DAF-U-Net network takes four-channel diffracted attributes as an input and underground fracture distribution as an output. The new network adds a spatial attention and channel attention mechanism to improve the positioning and extraction ability of the U-Net model for the attribute characteristics of diffractions. After optimizing the diffraction attributes of hot dry rock slices in the Gonghe basin, Qinghai, the slices are input into the network to train the model. According to the prediction and identification results of the network model, the DAF-U-Net network has a high reliability in predicting fracture distributions. It has a specific reference role in the subsequent exploitation of hot dry rock.

Study on the Hydraulic Fracturing Failure Behaviour of Granite and Its Comparison with Gas Fracturing

Efficient technology is needed to realise reservoir stimulation for deep geothermal energy exploitation. However, the main control parameters of traditional hydraulic fracturing technology are not clear, as well as their coupling effects; besides, the damage mechanism of novel gas fracturing technology is still not determined, which restricts the mining of hot dry rock resources. Therefore, through a series of true triaxial hydraulic fracturing tests, this paper explores the coupling effect of horizontal stress difference and injection rate on hydraulic fracturing; then, the cohesive element is used to establish hydraulic fracturing and gas fracturing models under the same test conditions. Differences in fracture width and fracture network morphology between the two technologies were compared, and the rock-breaking effects in in-situ reservoirs were analysed. The results show that the breakdown pressure of granite increases gradually with the increase of injection rate, at the small horizontal stress difference; but this trend is opposite at the large horizontal stress difference. Under a higher horizontal stress difference, the increment of the maximum fracture width of gas fracturing becomes larger than that of hydraulic fracturing after increasing the injection rate. When the fracturing cluster spacing is reduced, the fracture width and length of gas fracturing gradually become larger than those of hydraulic fracturing; when the injection rate is increased, the hydraulic fracturing network becomes more complex than gas fracturing. This study can provide useful information for applying hydraulic fracturing and gas fracturing in deep geothermal reservoirs.