Fracture Opening Research Articles

Method for predicting the injection pressure for horizontal wells in fractured tight sandstone reservoirs

Hydraulic fracturing and horizontal well drilling are the key technologies for increasing the production of continental tight sandstone reservoirs. Taking the typical fractured tight sandstone in the Yuan-287 block of the Ordos Basin as an example, a reservoir geologic model is established based on the stratigraphic correlation of 206 wells. The model and 3D paleostress field are combined to predict fracture parameters such as fracture density and strike. Using reservoir breakdown pressure (RBP) monitoring data and other data such as reservoir physical and mechanical parameters, tectonic fracture characteristics, and in situ stress parameters, a quantitative evaluation model of the RBP, which predicts the 3D distribution of RBP, is established via stepwise regression, and the factors controlling the RBP are analyzed. The rock P-wave velocity, horizontal minimum principal stress, and fracture density are found to be three key parameters that control the breakdown pressure of this tight sandstone reservoir. By comparing the fracture opening pressure of subsurface tectonic fractures with the RBP, a new method for predicting the optimal water injection pressure of this reservoir is developed. This work provides a valuable evaluation model for accelerating the efficient development of continental tight sandstone reservoirs.

Evaluation of Lost Circulation Material Sealing for Geothermal Drilling

Lost circulation is a pervasive problem in geothermal wells that can create prohibitive costs during drilling. The main issue with treatment is that the mechanism of plug formation is poorly understood. Here we applied two experimental approaches to characterize the clogging effectiveness of different materials. Fracture flow tests with different geometries were conducted with various individual materials and mixtures at relevant conditions. A high-temperature flow loop system was also developed to inject single- and mixed-material plugs into a gravel pack with a non-uniform geometry to compare with the fracture tests. The fracture tests revealed that single materials tended to form no plug or an unstable plug, while mixtures of materials were uniformly better at sealing fractures. Gravel pack tests at high temperatures show most of the materials are intact but degraded. The fibrous materials can create partial or unstable plugs in the gravel pack, but mixed-material plugs are far more effective at clogging. Both test types suggest that (1) mixed materials are more effective at blocking fluid flow and (2) fibrous materials seal fracture openings better, while granular materials seal inside fractures or pore throats better. Further research is needed to study the long-term stability of different plug configurations.

Threshold pressure gradient in fractured reservoirs: Experimental simulation and mathematical modeling

Aiming to solve the problems of unclear fluid flow laws and controlling factors in fractured reservoirs, as well as the lack of a mathematical model of threshold pressure gradient (TPG) considering fracture structural parameters, research on the structural characterization of fractured reservoirs, physical simulation of fluid flow, and TPG prediction models has been carried out. Physical simulations demonstrate that fluid flow in fractured reservoirs under stress is nonlinear and exhibits TPG. The TPG displays a significant positive exponential relationship with confining pressure and water saturation. As the confining pressure or water saturation increases, the effective opening of fractures decreases. The TPG will increase dramatically when the fracture opening decreases to the critical thickness for the rapid increase in TPG. On the basis of the fluid flow law study, the TPG fractal prediction model is further developed based on fractal dimension of fracture length distribution (Df), fractal dimension of tortuosity (DT), water saturation (Sw), maximum fracture width (wmax), limit shear stress (η0), and sample characteristic length (L0). The results predicted by the model show good agreement with physical simulations (with average relative error of 7.56%). Experimental simulation and mathematical modeling of TPG in fractured reservoirs can reveal the fluid flow mechanism and improve the accurate evaluation of production capacity during different development processes.

Differences in Intraoperative Fluoroscopic Radiation Exposure During Ankle Fracture Open Reduction and Internal Fixation Between Orthopaedic Surgery and Podiatry.

Surgical ankle fractures pose a unique situation because both podiatrists and orthopaedic surgeons manage these injuries. Intraoperative fluoroscopy is routinely used; however, excessive radiation can be harmful to both the patient and the surgical team. The primary goal of this study was to determine whether there is a difference in the amount of intraoperative radiation exposure during ankle fracture open reduction and internal fixation (ORIF) when performed by orthopaedic surgeons versus podiatrists. This is a retrospective review of patients who underwent ankle fracture ORIF at an urban level I trauma center between January 1st, 2018, and April 1st, 2023. The electronic health record was queried using International Classification of Diseases nine and 10 codes associated with ankle fractures. Patients aged older than 18 years with an ankle fracture managed surgically were included. Subjects were then stratified by procedure. The mean total radiation dose (mRad) and mean total fluoroscopic time (seconds) were then compared between those performed by orthopaedic surgeons and podiatrists. Of the 333 included procedures, 186 were done by orthopaedic surgeons and 147 were done by podiatrists. Using multiple linear regression analysis to control for age, sex, race, ethnicity, and body mass index, patients undergoing isolated malleolus ORIF with syndesmosis repair performed by orthopaedic surgery were found to have a significantly lower mean fluoroscopic time compared with those performed by podiatry (68.4 s versus 104.8 s; P = 0.028). In addition, trimalleolar ORIF with syndesmotic repair performed by orthopaedic surgery had a significantly lower mean total radiation dose compared with those performed by podiatry (244.6 mRad v 565.6 mRad; P = 0.009). Patients and surgical teams are exposed to markedly less radiation in isolated malleolar and trimalleolar fracture ORIF with syndesmosis repair when performed by an orthopaedic surgeon as compared with those performed by a podiatrist.

Right Distal Tibial Oblique Fracture Open Reduction and Internal Fixation (ORIF) with Medial Neutralization Non-locking Plate

Right Distal Tibial Oblique Fracture Open Reduction and Internal Fixation (ORIF) with Medial Neutralization Non-locking Plate

Dynamic Simulation Research on Microprofile Control Mechanism of Foam in Fractured Media Based on Level Set Method.

Fractured reservoirs are an important source of oil and gas energy. After depletion of production, the production capacity of this reservoir decreases rapidly. Effective profile control is needed to improve the sweep efficiency and reservoir heterogeneity. Foam can solve such problems, but its profile control mechanism is not fully understood. Based on this, this paper uses the level set method to study the microscale control mechanism of foam in fractured media. The results show that artificial fractures and high-permeability microfractures are tighter than natural fractures, the Jamin effect of foam is stronger, and the secondary foaming ability is better. Therefore, the plugging ability of foam to natural fractures is far less than that of foam to artificial fractures and high-permeability microfractures. The larger the fracture opening, the larger the foam volume and the smaller the flow rate. As the opening ratio increases gradually, the generated foam flows more to the natural fractures with a large opening, and the effect of foam blocking large fractures becomes worse. The diversion rate curves of different opening ratios show that the foam has a good profile control effect when the opening ratios are 4:1 and 2:1, and even the diversion rate overturns, while the profile control diversion effect is poor when the opening ratio is 10:1, so it cannot play an effective role in profile control. The foam shows the profile control process of preferentially plugging the high-permeability area and allowing more subsequent fluids to enter the low-permeability area. The research reveals the profile control mechanism of foam on fractured reservoirs from the micro level, which is the supplement and verification of relevant macro research and provides a theoretical basis for the efficient development of fractured reservoirs.

Frost quakes in wetlands in northern Finland during extreme winter weather conditions and related hazard to urban infrastructure

Abstract. The paper reports the first results of an experiment in northern Finland during winter 2022–2023 that aimed at studying seismic events caused by seasonal freezing in the so-called critical zone (CZ) of the Earth. These events have attracted public attention recently, as multiple reports about them from local inhabitants in Arctic and sub-Arctic areas appeared on social networks. To make an instrumental study of such events, to reveal the relationship between their occurrence and winter weather conditions, and to evaluate the possible hazard, we installed two high-resolution seismic arrays with co-located soil temperature stations at two sites in Finland, one of them being in the city of Oulu in the sub-Arctic area (65.04° N, 25.61° E) and the other one above the polar circle in the municipality of Sodankylä (67.36° N, 26.63° E). The equipment recorded continuous seismic and soil temperature data during November 2022–April 2023. Based on reports from the inhabitants of Talvikangas (Oulu) about the ground shaking and unusual noises on 6 January 2023 and their observations of new fractures on the roads there, we selected the time interval for the identification of frost quakes that originated during that day from continuous seismic records in Talvikangas and in Sodankylä. During the selected time interval, the extremely rapid air temperature drops of about −1.4 °C h−1 in Talvikangas and −0.88 °C h−1 in Sodankylä were observed. We identified and located two types of seismic events – namely, frost quakes with frequencies of about 10–20 Hz, with waveforms like those of tectonic events, and irregularly shaped frost tremors with frequencies of about 120–180 Hz. The sources of frost quakes in Talvikangas are mainly located on irrigated wetland, while in Sodankylä, about 50 % of registered frost quakes were caused by ice fracturing on the Kitinen River. However, several relatively strong events, with their origin in the wetlands, were also recorded. A significant number of sources of frost tremors are confined to wetland areas cut by irrigation channels and to roads cleaned from snow during winter both in Talvikangas and in Sodankylä. We calculated ground accelerations and ground velocities for the strongest events from both groups and compared them to equivalent properties of other seismic signals, like distant local earthquakes in the area, mining production blasts, and cargo train vibration. Our study shows that high-frequency frost tremors corresponding to surface fracture opening in the uppermost frozen surface layer of a thickness of up to 5 cm can directly damage infrastructure objects like roads and basements of buildings. Surface waves, produced by frost quakes and propagating inside the shallow soil layer, have large enough ground accelerations at epicentral distances of hundreds of metres. Therefore, frost quakes should be considered a phenomenon that can potentially damage infrastructures, and they have to be taken into account in seismic hazard assessments. Our research is the first instrumental study of seismic events originating from wetland areas. These events occur as a result of the interaction between the uppermost layer of the solid Earth's CZ and atmosphere processes that deserves further study.

Stable Clinical and Radiological Outcomes at Medium and over 5 Year Follow Up of Calcaneus Fracture Open Reduction Internal Fixation Using a Sinus Tarsi Approach

The sinus tarsi approach is increasingly growing in popularity for open reduction internal fixation of calcaneus fractures. Multiple studies have demonstrated favorable short-term results compared to the traditional extensile L incision, however long-term data over 5 years is currently limited to a single retrospective case series. Following local ethical approval, all patients who had completed a minimum 5 years from time of operation were contacted with a Standardized Telephone Questionnaire completed. This followed a previous retrospective chart review, with follow up telephone or clinic consultation performed by Davey et al. of this cohort at mean 35 months. Thirty-four fractures (31 patients) completed minimum 5 year follow up from the eligible group of 54 fractures (49 patients). Regarding functional outcomes, a significant improvement in mean Maryland Foot Score was observed between short- (mean 35.8 months) and medium-term (mean 81.9 months) of 77.6 (SD 15.0) to 86 (SD 7.9) (p = .0082). There was no significant difference in postoperative and long term radiographic Bohler's angle (p = .9683). Eleven feet (32%) proceeded to require reoperation, with removal of metal performed in 10 (29%), fusion in 2 (6%), and skin grafting following wound breakdown for 1 (3%). Four feet (12.9%) experienced post operative wound complications, including 3 (9.68%) cases of infection and 2 (6.45%) of delayed wound healing. This study demonstrated stable clinical and radiographic outcomes over 5 years following Calcaneus Fracture Open Reduction Internal Fixation using a sinus tarsi approach, supporting its continued usage when treating intraarticular calcaneus fractures for which operative intervention is indicated.

Multiscale modeling of gas-induced fracturing in anisotropic clayey rocks

In the context of repositories for nuclear waste, understanding the behavior of gas migration through clayey rocks with inherent anisotropy is crucial for assessing the safety of geological disposal facilities. The primary mechanism for gas breakthrough is the opening of micro-fractures due to high gas pressure. This occurs at gas pressures lower than the combined strength of the rock and its minimum principal stress under external loading conditions. To investigate the mechanism of microscale mode-I ruptures, it is essential to incorporate a multiscale approach that includes subcritical microcracks in the modeling framework. In this contribution, we derive the model from microstructures that contain periodically distributed microcracks within a porous material. The damage evolution law is coupled with the macroscopic poroelastic system by employing the asymptotic homogenization method and considering the inherent hydro-mechanical (HM) anisotropy at the microscale. The resulting permeability change induced by fracture opening is implicitly integrated into the gas flow equation. Verification examples are presented to validate the developed model step by step. An analysis of local macroscopic response is undertaken to underscore the influence of factors such as strain rate, initial damage, and applied stress, on the gas migration process. Numerical examples of direct tension tests are used to demonstrate the model's efficacy in describing localized failure characteristics. Finally, the simulation results for preferential gas flow reveal the robustness of the two-scale model in explicitly depicting gas-induced fracturing in anisotropic clayey rocks. The model successfully captures the common behaviors observed in laboratory experiments, such as a sudden drop in gas injection pressure, rapid build-up of downstream gas pressure, and steady-state gas flow following gas breakthrough.

Fracture ellipticity as a measure of chemical reaction-controlled fracture growth

Fracture ellipticity as a measure of chemical reaction-controlled fracture growth

Tectonic fractures induced by strike-slip faulting in intracratonic ultradeep carbonate rocks: Insights from the finite element method and self-adaptive constraints computational model for boundary conditions

Numerical simulations of the paleostress field during a period of tectonic fracture formation and rock failure criteria are used to quantitatively predict the development and occurrence of tectonic fractures induced by the formation of the SB18 fault zone in the Middle Ordovician Yijianfang Formation of the Shunnan area, Tarim Basin, China. The results of acoustic emission experiments, mechanical property measurements, and tectonic fracture occurrence observations obtained from core descriptions and fullbore formation microimager logs are combined with the Andersonian model of faulting and the finite element method, which is widely used for the numerical simulation of stress fields, to investigate the paleotectonic and in situ stress fields via numerical simulation. The quantitative prediction of the opening pressure and opening sequence of tectonic fractures is based on the occurrence of tectonic fracture, numerical simulation of in situ stresses, and coordinate system conversion. The results show that the width of the fracture zone induced by strike-slip faulting is ∼310 m. The degree of fracture development is significantly increased when the Young’s modulus, paleostress difference, and paleostress difference coefficient of the rock are elevated. The current horizontal principal stress is positively correlated with the distance from the fault, and the elevated areal density of the secondary faults causes a clockwise deflection of the horizontal stress direction. SSE-striking shear fractures with orientations ranging from 140° to 150° and two sets of tensional fractures with orientations ranging from −40° to −35° and 55° to 60° are preferentially opened in the water injection development stage of the reservoir. As the horizontal stress difference, horizontal stress difference coefficient, and angle between the maximum horizontal principal stress and a fracture decrease, the fracture opening pressure decreases. At the structural highs (burial depths <6225 m) and lows (burial depths >6225 m), the fracture burial depth is positively and negatively correlated with the opening pressure, respectively. Quantitative prediction of tectonic fracture developmental characteristics, opening pressure, and the opening sequence and investigation of the main factors that control their development can help to identify and support opportunities for hydrocarbon exploration and development of fractured carbonate reservoirs.

Optimization Simulation of Different Injection and Production Parameters of Enhanced Geothermal Systems

Enhanced Geothermal System (EGS), as a key technology for the extraction and utilization of geothermal energy in deep strata and high temperature rock mass, has a broad application prospect in the field of energy. In order to understand the sustainable utilization capacity of the enhanced geothermal system, explore the influence law of different factors on the heat production capacity of geothermal Wells, and design a reasonable geothermal energy development and utilization program. The influence of different injection and production parameters on thermal recovery performance was studied by numerical simulation, and the main influencing factors were analyzed by orthogonal experiment. The results show that water injection rate has the greatest effect on the injection-production parameters, followed by well spacing and water injection temperature, and fracture opening and fracture number have the least effect. The optimal parameter combination is water injection rate of 10kg/s, well spacing 500m, water injection temperature 40℃, crack opening 0.09mm and crack number 60.

CO2 fracturing of volcanic rocks under geothermal conditions: Characteristics and process

An enhanced geothermal system using carbon dioxide (CO2) for both reservoir creation and thermal energy extraction has attracted attention; however, studies on the CO2 fracturing of volcanic rocks under geothermal conditions are lacking. This study aimed to elucidate CO2 fracturing characteristics and processes in geothermal volcanic rocks via integrated lab-scale fracturing experiments and numerical simulations of basalt and andesite at 250°C and a confining pressure of 30 MPa. Moreover, it proposed and demonstrated an efficient CO2-based fracturing method based on the obtained insights. Fracturing experiments on basalt and andesite with relatively low initial porosity or permeability implied that CO2 fracturing can be initiated at a lower pressure and produce a more complex fracture pattern than water fracturing because of the ease of fluid permeation (e.g., fluid pressure propagation) in rocks owing to the lower viscosity of CO2. The experiments also revealed that the ease of CO2 permeation can produce thinner fractures than those produced by water fracturing, which may severely inhibit the fracturing of andesite rocks with high initial porosity/permeability. Fracturing simulations of rocks with different initial porosity/permeability provided results consistent with the experimental observations. Moreover, the simulations clarified that fluid pressure propagation during CO2 permeation within an unfractured part of the rock and between induced fractures and the surrounding rock matrix could reduce the fracture initiation pressure by effective stress reduction, increase the complexity of the fracture pattern by large stimulated zone development, and inhibit fracture opening and propagation by decreasing the pressure difference between the fractures and matrix. Based on these findings, we proposed a combined CO2-water fracturing system that addresses the drawbacks while maintaining the advantages of CO2 fracturing.

Thermal Fracture Simulation in Depleted Gas Field Carbon Capture and Storage: Implications for Injectivity and Flow Assurance

Summary CO2 injection into depleted gas fields causes long-term cooling of the reservoir. Therefore, even if injection pressure stays below the fracture initiation pressure, the cooled volume still creates an extensive stress disturbance that can induce the propagation of large fractures over time. The enhanced injectivity after the onset of this thermal fracturing might jeopardize injection operations due to the risk of hydrate plugging in the injection well caused by the combination of low pressure and low temperature, and large fractures may also increase the risk of loss of containment. Modeling the fracture evolution provides an estimate of the magnitude and timing of these effects. In this study, commercial compositional reservoir simulation software capable of modeling the physical phenomena associated with CO2 injection into depleted natural gas reservoirs has been used. These encompass CO2 mixing with natural gas, water vaporization, thermal effects, and geomechanics. The finite-element geomechanics module used “two-way” coupling, which computes pressure and temperature in the flow simulation module, transmits this information to the geomechanics module to update stress and strain parameters, and uses these parameters to adjust porosity and permeability, thereby enhancing the accuracy and reliability of the overall simulation results. The thermal fracture opening is simulated as increased permeability in the fracture domain by using a fracturing criterion based on the effective stress. The fracture simulations were developed in close relation with flow assurance modeling to determine the operational windows that avoid hydrate formation while maintaining the required injection target. Unlike matrix injection, thermal fracturing shows a substantial reduction in injection bottomhole pressure (BHP), reaching 26 000 kPa (260 bar) in a specific scenario. These findings underscore the crucial consideration of cooling effects and thermal fracturing in carbon capture and storage (CCS) operations, particularly in flow assurance studies where well injectivity significantly influences overall outcomes. Due to the intense cooling-induced stress reduction, thermal fractures may propagate uncontrollably, potentially reaching faults within the reservoir. Temperature distributions along boundary faults may differ markedly from matrix flow conditions, highlighting the need to incorporate these effects into geomechanical studies to mitigate risks associated with fault stability during cooling processes.

Mapping of Groundwater Potential Zones in the Kuzhithuraiyar Sub Basin of Kodayar River, Kanniyakumari District, Tamilnadu: Using Analytic Hierarchy Process (AHP) and GIS


 
 
 Groundwater plays a very important role for all living beings. It is decisive to have a scientific understanding of groundwater management since, with careful use and replenishment, groundwater may help solve issues. The distribution of groundwater tables, slope, land-form, drainage pattern, lithology, topography, geological structure, fracturing density, opening and connectivity of fractures, secondary porosity, and landuse landcover all affect the occurrence and efficiency of groundwater in an aquifer system. An essential tool for assessing, tracking and protecting groundwater resources is the integration of geospatial techniques such as Remote Sensing and Geographic Information System for the identification of groundwater potential zones. This study aims to find the groundwater potential zones using Analytical Hierarchy Process (AHP) and managing the resources by creating different thematic layers such as rainfall, geology, geomorphology, drainage density, soil, slope, lineament and landuse landcover (LULC) of the Kuzhithuraiyar sub basin of the Kodayar river in Tamilnadu using the application of geospatial technologies. The thematic maps for all the thematic layers have been prepared using tools such as Interpolation, contour lines, Classification in ArcGIS 10.8. Theme weight and class rank were assigned to different thematic layers in weighed overlay analysis. The results were validated through field work and groundwater potential map was created. The groundwater potential zonation mapping was done by the overlay analysis in ArcGIS 10.8 software. The obtained map was classified into four categories namely very high groundwater potential zone, high groundwater potential zone, medium groundwater potential zone and low groundwater potential zone. The North Eastern part of the basin is considered as low groundwater potential zone while the Southern portion has high groundwater potentiality. The low groundwater potential zone covers an area of 10.58 sq.km and high groundwater potential zone covers an area of about 388.37sq.km.This study will be helpful for useful groundwater management for different tenacities.
 
 

Prediction of fractures by using the stress field in medium to deep shale gas reservoirs: A case study of Late Ordovician–early Silurian shale gas reservoirs in the Nanchuan region, South China

Containing representative shale gas reservoirs, the Wufeng–Longmaxi Formations in the Nanchuan region in South China have been modified by three compressional tectonic movements (in the Late Jurassic to Early Cretaceous, Late Cretaceous, and Cenozoic to present). These movements formed deeply buried reservoirs with complex in situ stresses and rapid directional changes, influencing the state of shale gas reservoirs fractures. Numerical modeling applied to model the stress field in the three periods showed that the maximum compressive horizontal principal stress (σHmax), strain rate, and fault slip rate regimes transformed from a thrust and strike-slip regime to a thrust and strike-slip regime to a thrust regime. The σHmax direction changed from NW–SE and WNW–ESE to WNW–ESE and nearly E–W and then to multiple directions. The magnitude of strain rate changed from -16 ∼ -15 to -17.7 ∼ -15.6 to -18.8 ∼ -15.8. The fault slip rate changed from 0 to 0.029 mm/a to 0–0.0026 mm/a to 0–0.0012 mm/a. These data strongly agree with data from drilled wells and outcrops and show that the present-day stress field is the superposed effect of multistage movements. Semiquantitative research was conducted on shale gas fracture openness and fracture development. Fracture openness is favorable when the angle between the σHmax direction and nearby faults is ≤45° and the distance from the fault is >2 km, and fracture development is favorable when the magnitude of the strain rate is <-17.6 and the fault slip rate is <0.00036 mm/a. Accordingly, we predicted fractured shale gas reservoirs.

Low Geriatric Nutritional Risk Index Predicts Early Complications following Distal Radius Fracture Open Reduction Internal Fixation

Abstract Background While previous studies have investigated the association between the Geriatric Nutritional Risk Index (GNRI) and functional outcomes following distal radius fracture (DRF), no large-scale studies have investigated the associations between GNRI and postoperative outcomes following DRFs. Objectives The purpose of this study is to investigate the association between GNRI, a simple multifaceted measure of malnutrition risk, and 30-day postoperative complications following DRF open reduction internal fixation (ORIF). Materials and Methods The American College of Surgeons National Surgical Quality Improvement Program database was queried for patients who underwent DRF ORIF from 2015 to 2021. Patients were organized into three groups based on preoperative GNRI: normal/reference (GNRI &gt; 98), moderate malnutrition (92 ≤ GNRI ≤ 98), and severe malnutrition (GNRI &lt; 92). Logistic regression analysis was conducted to investigate the relationship between preoperative GNRI and postoperative complications. Results Severe malnutrition was independently associated with a greater likelihood of any complication (odds ratio [OR]: 3.22, 95% confidence interval [CI]: 2.48–4.17; p &lt; 0.001), sepsis (OR: 15.41, 95% CI: 1.66–143.32; p = 0.016), cardiac arrest or myocardial infarction (OR: 20.58, 95% CI: 1.62–261.26; p = 0.020), pulmonary embolism (OR: 9.40, 95% CI: 1.76–50.11; p = 0.009), surgical site infection (OR: 7.73, 95% CI: 1.99–30.02; p = 0.003), nonhome discharge (OR: 2.55, 95% CI: 1.87–3.49; p &lt; 0.001), readmission (OR: 2.47, 95% CI: 1.47–4.14; p &lt; 0.001), and length of stay &gt; 2 days (OR: 3.51, 95% CI: 2.67–4.62; p &lt; 0.001). Conclusions Malnutrition is an independent significant predictor of early complications following DRF ORIF. Level of Evidence Level III; retrospective cohort comparison; prognosis study.

Influence of fracture parameters on hydraulic shear seepage characteristics of granite

To reveal the influence mechanism of different fracture parameters on the permeability characteristics of hot dry rock after hydraulic shear. The self-made high temperature true triaxial hydraulic shear test device and rock roughness profile tester were used. The granite in Daqing area of Songliao Basin is taken as the research object. The prefabricated fractured granite is subjected to high-temperature treatment. The geological characteristics of different geothermal reservoirs are simulated by changing the three-dimensional stress. The roughness coefficient of the fracture surface is used to characterize the variation characteristics of fracture before and after hydraulic shear. The influence of different fracture angles and roughness on the permeability of granite after hydraulic shear was tested. Combined with numerical simulation, the relationship between fracture parameters and geothermal mining performance is analyzed. The results show that the maximum water injection pressure of hydraulic shear decreases with the increase of fracture angle by quadratic polynomial law and increases with the increase of fracture roughness by quadratic polynomial law. The variation of fracture surface roughness coefficient fluctuates within 0–2 with the increase of volume stress before and after hydraulic shearing. The variation of fracture surface roughness coefficient increases linearly with the increase of water injection flow rate and increases with the increase of water injection time, and there is a fluctuation range of 0.38–0.44. After hydraulic shear, the permeability of granite increases first and then decreases with the increase of fracture angle. When the fracture angle is 15°, the permeability has the maximum value. The permeability increases with the increase of fracture surface roughness. The numerical simulation results show that the high fracture opening (15 mm), high fracture number, and high fracture penetration performance significantly improve the geothermal mining efficiency.

Geometric characteristics of diverting fractures for multi-stage dynamic temporary plugging and diverting fracturing in fractured reservoir

Temporary plugging and diverting fracturing (TPDF) technology constitutes a pivotal stimulation methodology in the advancement of unconventional resources, given its efficacy in establishing communication with natural fractures (NFs). Presently, the comprehension of TPDF is primarily confined to laboratory-scale experiments, with a notable dearth of accurate knowledge regarding the diverting law and geometric characteristics of diverting fractures at the field scale. This study introduces a hydro-mechanical-damage model for hydraulic fracture (HF) propagation, developed through the derivation and refinement of the phase field method. The model integrates the dynamic flow distribution process among multi-perforation clusters under stress interference, alongside the construction of a dynamic transportation and plugging model for the temporary plugging agent in TPDF. Subsequently, a coupled model encompassing multi-cluster and multi-stage dynamic TPDF is established using the finite element method. Utilizing this model, an exploration of the diverting fracture's opening and propagation mechanisms, as well as the impact of stimulation and reservoir factors on geometric characteristics, is conducted at the field scale. The results show that the TPDF model has high accuracy, and for the first time, it realistically simulates the gradual increase and decrease in fracturing pressure in the field after temporary plugging. The diverting fracture propagation is affected by the stress interference from the initial HF (ini HF), NF, and horizontal stress difference. The energy required to open NFs to form a diverting fracture is higher than that to cross NFs after temporary plugging, and there is a strong positive correlation between the energy rise and the approach angle and the horizontal stress difference. The use of multi-scale plugging agents can promote a more uniform distribution of diverting fractures. When the NF angle is near 60°, the diverting fracture has a larger fracture control volume. The NF distribution and the interaction between NF and HF are of great significance to the opening position of diverting fractures in TPDF. According to the propagation pattern of diverting fractures, they can be divided into five categories. The temporary plugging agent can alleviate the directional propagation of HFs caused by NF induction. The alleviating effect is not only controlled by the interaction mode between HF and NF but also related to the NF density. The propagation distance of the diverting fracture formed by the inferior fracture will be about 50% farther compared with the superior fracture. The diverting fractures are mainly interfered by the stress of the HFs in the same perforation cluster at the early stage and mainly interfered by the HFs of different perforation clusters at the middle and late stages.

Hydrogeological controls on microbial activity and habitability in the Precambrian continental crust.

Earth's deep continental subsurface is a prime setting to study the limits of life's relationship with environmental conditions and habitability. In Precambrian crystalline rocks worldwide, deep ancient groundwaters in fracture networks are typically oligotrophic, highly saline, and locally inhabited by low-biomass communities in which chemolithotrophic microorganisms may dominate. Periodic opening of new fractures can lead to penetration of surface water and/or migration of fracture fluids, both of which may trigger changes in subsurface microbial composition and activity. These hydrogeological processes and their impacts on subsurface communities may play a significant role in global cycles of key elements in the crust. However, to date, considerable uncertainty remains on how subsurface microbial communities may respond to these changes in hydrogeochemical conditions. To address this uncertainty, the biogeochemistry of Thompson mine (Manitoba, Canada) was investigated. Compositional and isotopic analyses of fracture waters collected here at ~1 km below land surface revealed different extents of mixing between subsurface brine and (paleo)meteoric waters. To investigate the effects this mixing may have had on microbial communities, the Most Probable Number technique was applied to test community response for a total of 13 different metabolisms. The results showed that all fracture waters were dominated by viable heterotrophic microorganisms which can utilize organic materials associated with aerobic/facultative anaerobic processes, sulfate reduction, or fermentation. Where mixing between subsurface brines and (paleo)meteoric waters occurs, the communities demonstrate higher cell densities and increased viable functional potentials, compared to the most saline sample. This study therefore highlights the connection between hydrogeologic heterogeneity and the heterogeneity of subsurface ecosystems in the crystalline rocks, and suggests that hydrogeology can have a considerable impact on the scope and scale of subsurface microbial communities on Earth and potentially beyond.