Matrix Permeability Research Articles

Unlocking the potentials of gel conformance for water shutoff in fractured reservoirs: Favorable attributes of the double network gel for enhancing oil recovery

The double-network prepared with an in-situ monomer gel and a fast-crosslinked Cr(III) gel is introduced to develop a thixotropic and high-strength gel (THSG), which is found to have many advantages over the traditional gels. The THSG gel demonstrates remarkable thermal stability, and no syneresis is observed after 12 months with high salinity brine (95,500 mg/L). Moreover, the SEM and XRD results indicate that the gel is intercalated into the lamellar structures of Na-MMT, where the gel can form a uniform and compact structure. In addition, the THSG gel has an excellent swelling behavior, even in the high salinity brine. In the slim tube experiments, the THSG gel exhibits high rupture pressure and improves blocking capacity after being ruptured. The core flooding results show that a layer of gel filter cake is formed on the face of the fracture, which may be promoted by a high matrix permeability, a small aperture fracture, and a high injection rate. After the gel treatment, the fracture can be completely blocked by the THSG gel. It is found that a high incremental oil recovery (65.3%) can be achieved when the fracture was completely blocked, compared to 40.2% if the gel is ruptured. Although the swelling of ruptured gel can improve oil recovery, part of the injected brine may be channeled through the gel-filled fractures, resulting in a decrease in the sweep efficiency. Therefore, the improved blocking ability by gel swelling (e.g., in fresh water) may be less efficient to contribute to an enhancement of oil recovery. It is also found that the pressure gradient and residual resistance factor to water (Frrw) are higher if the matrix is less permeable, indicating that the fractured reservoir with lower matrix permeability may require a higher gel strength for treatment. The findings of this study may provide novel insights on designing robust double network gels for water shutoff in fractured reservoirs.

Influence Factors on EGS Geothermal Reservoir Extraction Performance

The heat extraction performance of the enhanced geothermal system is simulated by using COMSOL software. The effects of six factors, such as the thermal conductivity of heat reservoir, matrix permeability, fracture width, injection temperature, injection flow rate, and the number of wells, on the heat extraction performance of EGS heat reservoir for 40 years are analyzed. The results show that the matrix permeability and injection flow are the main factors affecting the heat production performance of the EGS geothermal reservoir, while the thermal conductivity, fracture width, and injection temperature have little effect on the heat production performance of the EGS geothermal reservoir. Although increasing the number of production wells can improve the uneven distribution of the flow field to improve the system heat performance, taking into account the existing drilling technology and cost, the cost is higher, and the two-well system is still the basic form of absorbing rock heat.

Three-Dimensional Free Convective Heat Transmission Flow of Copper–Water Nanofluid in a Glass Bead Permeable Matrix within a Right Trapezoidal Cavity in Consideration of Thermal Non-Equilibrium Conditions

Three-Dimensional Free Convective Heat Transmission Flow of Copper–Water Nanofluid in a Glass Bead Permeable Matrix within a Right Trapezoidal Cavity in Consideration of Thermal Non-Equilibrium Conditions

A Simple Analytical Model for Oil Production from Partially Fractured Reservoirs to Estimate Size of Finite Fracture Networks

Summary Most oil reservoirs are partially fractured, characterized by finite fracture networks (FFNs) in a sea of isolated fractures. It is necessary to determine size and shape of each FFN explicitly for reservoir simulation. FFN size is correlated with fracture connectivity, which is a function of fracture density, length, and angular scatter. Oil production from FFNs exhibits a long-term dual-porosity behavior. The initial fast rate (Phase I) represents depletion of matrix within FFN, and the subsequent gradual decline phase represents radial flow from the matrix outside the FFN perimeter. Thus, FFN size can be calculated from the cumulative oil production from Phase I, taking into account the pore volume, oil compressibility, and pressure decline. It is not always possible to identify the dual-porosity behavior by visual inspection. A mathematical model is needed to estimate FFN size. For this purpose, a set of three fundamental equations are derived for production rate, cumulative production, and pressure as a function of time. The model is a modified and simplified version of material balance equations with easy analytical solution. It is designed for fractured reservoirs with layer-bound fractures. Production is single-phase black oil under depletion drive. The analytical model was tested on four vertical wells. The unknown parameters such as FFN size, size of well drainage area, and fracture aperture are adjusted until an optimum fit to actual production data is obtained. FFN elliptical shape is estimated from average fracture strike and strike standard deviation. The results are validated by FFN size, fracture length, and aperture measurements from borehole images. The results are approximate but sufficient for preliminary mapping of FFNs with location and size and other critical attributes including fracture drainage area, matrix block size, fracture aperture, and permeability in partially fractured reservoirs.

Pollinator distribution in patches of suitable habitat depends more on patch isolation than on floral abundance

Intrinsic complexity of real-world systems makes particularly difficult to decipher which factors influence the dispersal of pollinators in the landscape matrix and their distribution amongst patches of suitable habitat. Saltmarshes are an ideal and naturally simplified landscape to study the ability of different groups of pollinators to disperse across a landscape matrix, as they consist of a matrix of flooded areas surrounding patches of suitable habitat with different degrees of isolation from the mainland and different levels of floral abundance. We hypothesise that pollinator distribution to flowering plants depends more on patch isolation than on floral abundance, with pollinator richness and visitation rates to flowering plants decreasing with increasing distance from the mainland. To this end, we established 60 permanent plots at varying distances from the mainland and monitored pollinator visitation to entomophilous plants. We also quantified the reproductive success of entomophilous species in the surveyed plots by calculating fruit set. We found that the pollinator community of saltmarshes consisted only of flying pollinators with good dispersal abilities, while we recorded no flightless pollinator species. Both pollinator richness and visitation rate decreased with increasing distance of patches of suitable habitat from the mainland, affecting reproductive success of a non-autogamous entomophilous species. Interestingly, floral abundance did not affect pollinator richness and visitation rate to flowering plants, nor did it affect reproductive success of target plant species. In saltmarshes, the pollinator distribution depends more on patch distance from the mainland than on floral abundance. Our results suggest that the presence of patches of suitable habitat in a landscape matrix does not necessarily ensure the maintenance of pollinators. Rather, our results suggest that suitable habitat isolation is the critical factor in pollinator dispersal and distribution that should be considered to improve landscape matrix permeability to pollinators.

Global sensitivity analysis of CO2 storage in fractured aquifers via computer experiments

• Accelerated CO 2 storage sensitivity analysis via Computer Experiments as surrogate modes. • Rigorous dynamic models use to model non-reactive CO 2 storage mechanisms, inspired by the Teapot Dome in Wyoming dataset. • Demonstration that a network of connected fractures in an eolian sandstone shifts the importance of CO 2 storage controlling parameters. In this work, we use the “Design and Analysis of Computer Experiments” (DACE) technique to analyze the sensitivity of CO 2 storage in fractured aquifers. The aquifer static or geogical model was inspired by the Tensleep formation at Teapot Dome, a potential CO 2 storage target in Wyoming. The CO 2 storage performance in aquifers is comprehensively simulated in our dynamic model by considering all the trapping mechanisms, except for mineralization, i.e. structural, dissolution and residual, as well as local capillary trapping. Operational strategies are investigated to achieve an effective trade-off between higher CO 2 trapping efficiency and delayed CO 2 breakthrough at producers. The effect of natural fractures is explored by running single-porosity, dual-permeability and dual-porosity models. Results show that different models produce significantly different trapping efficiencies, which indicates that natural fractures and their type impact the CO 2 storage practice appreciably. To carry out the global sensitivity analysis, two 100-point computer experiments were designed using the modified space-filling method considering a bottom aquifer, matrix permeability and porosity, fracture permeability and spacing, and water Total Dissolved Solids (TDS). Results show that an active bottom aquifer reduces trapping efficiency noticeably. In addition, dissolution trapping becomes the dominant trapping mechanism. The variability of CO 2 trapping efficiency is explained primarily by fracture permeability, then depth, and finally matrix permeability. In contrast, in the absence of aquifer drive, the variability is almost completely explained by matrix permeability. Furthermore, our results provide guidance to the collection of information as to reduce the most dominant uncertainties.

An Efficient Laboratory Method to Measure Stress-Dependent Tight Rock Permeability With the Steady-State Flow Method

The matrix permeability of tight formations is important for many geological and engineering applications, such as CO2 geological sequestration, disposal of nuclear waste, and production of unconventional hydrocarbon and coalbed methane. In the case of hydrocarbon production, the reservoir permeability decreases with decreasing pore pressure or increasing effective stress. Laboratory characterization of the relationship between matrix permeability and effective stress (and pore pressure) is generally time consuming since the current methods are based on the so-called point-by-point approach that measures one permeability data point only with one test run, and the relationship is generally represented with multiple data points. In this paper, we present a method to determine matrix permeability, its relationship with effective stress, and the Biot coefficient of a tight rock sample with three steady-state flow test runs using large pressure gradients. Unlike the traditional steady-state flow method based on linear flow theories, analytical results based on a nonlinear flow theory are used for determining the related relationship and parameters. The gas properties and permeability along the core sample vary with gas pressure and effective stress, while the traditional method treats them as constants for a given test run. To get the same set of parameters, our method only requires three test runs, and each test run of our method takes a much shorter time than the traditional method because our method is based on nonlinear flow theory and thus allows for the use of large pressure gradients. Comparisons of the permeability measurements with those obtained using traditional methods and numerical simulations demonstrate that our new method can get satisfactory results.

Effect and mechanism analysis of resonance on physical parameters of unconventional reservoirs

Inducing shale reservoir resonance is an environmentally friendly and efficient unconventional oil/gas production technology. It is necessary to study the effect of resonance on shale physical parameters. This paper clarifies the resonance mechanism of improving shale reservoirs and constructs the natural frequency parameter equation under a single excitation direction using vibration system theory and rock mechanics. The resonance experiment is carried out after the physical parameters of the shale and coal samples are verified by material characterization technology. Meanwhile, CT scanning technology and matrix permeability tests are used to measure the samples’ pore development and permeability changes. Eventually, the coalbed methane field in Qinshui Basin, Shanxi province, was selected as the experimental object for the reservoir resonance test. We analyzed the production data of the test wellhead. The results indicate that the mechanism of resonance improvement of shale physical parameters promotes the redevelopment of primary cracks in the rock mass; the porosity and permeability of rock mass are increased by 2–12 times and 2–8 times, respectively, after the once resonance test. The CBM (coalbed methane) wells whose productivity is in a state of decay have been significantly enhanced after resonance stimulation, and the relative daily gas production is increased by 101.61%.

Three-Dimensional Physical Simulation of Horizontal Well Pumping Production and Water Injection Disturbance Assisted CO2 Huff and Puff in Shale Oil Reservoir

In view of the problems of low matrix permeability and low oil recovery in shale reservoirs, CO2 huff and puff technology is considered as an effective method to develop shale oil reservoirs. However, the production behaviors of actual shale reservoirs cannot be reproduced and the EOR potentials cannot be evaluated directly by scaled models in the laboratory. Conventional CO2 huff and puff has problems such as early gas breakthrough and gas channeling leading to inefficient development. In this article, with the help of a three-dimensional experimental simulation apparatus, a new method of CO2 huff and puff with a horizontal well assisted by pumping production and water injection disturbance is developed. The dynamic characteristic, pressure field distribution of soaking and the enhanced oil recovery effect are comprehensively evaluated. The results show that the soaking stage of CO2 huff and puff can be divided into three stages: differential pressure driving, diffusion driving and dissolution driving. According to the pressure field distribution, after water injection disturbance, the fluctuation boundary and distribution of pressure becomes more stable and uniform and the sweep rate is greatly improved. Water injection disturbance realizes the combination of CO2 injection energy enhancement and water injection energy enhancement and the CO2 injection utilization rate is improved. It has the dual effect of stratum energy increase and economic benefit. The new huff and puff method can increase the oil recovery rate by 7.18% and increase the oil–gas replacement rate to 1.2728, which confirms the potential of horizontal well pumping production and water injection disturbance-assisted CO2 huff and puff technology to improve oil recovery.

The impact of hydrothermal alteration on the physiochemical characteristics of reservoir rocks: the case of the Los Humeros geothermal field (Mexico)

Hydrothermal alteration is a common process in active geothermal systems and can significantly change the physiochemical properties of rocks. To improve reservoir assessment and modeling of high-temperature geothermal resources linked to active volcanic settings, a detailed understanding of the reservoir is needed. The Los Humeros Volcanic Complex, hosting the third largest exploited geothermal field in Mexico, represents a natural laboratory to investigate the impact of hydrothermal processes on the rock properties through andesitic reservoir cores and outcropping analogs. Complementary petrographic and chemical analyses were used to characterize the intensities and facies of hydrothermal alteration. The alteration varies from argillic and propylitic facies characterized by no significant changes of the REE budget indicating an inert behavior to silicic facies and skarn instead showing highly variable REE contents. Unaltered outcrop samples predominantly feature low matrix permeabilities (< 10–17 m2) as well as low to intermediate matrix porosities (< 5–15%), thermal conductivities (0.89–1.49 W m−1 K−1), thermal diffusivities (~ 0.83 10–6 m2 s−1), and sonic wave velocities (VP: ~ 2800–4100 m s−1, VS: ~ 1600–2400 m s−1). Average magnetic susceptibility and specific heat capacity range between 2.4–7.0 10–3 SI and 752–772 J kg−1 K−1, respectively. In contrast, the hydrothermally altered reservoir samples show enhanced porosities (~ 7–23%), permeabilities (10–17–10–14 m2), and thermal properties (> 1.67 W m−1 K−1; > 0.91 10–6 m2 s−1), but a significant loss of magnetic susceptibility (10–3–10–6 SI). In particular, this latter characteristic appears to be a suitable indicator during geophysical survey for the identification of hydrothermalized domains and possible pathways for fluids. The lack of clear trends between alteration facies, alteration intensity, and chemical indices in the studied samples is interpreted as the response to multiple and/or repeated hydrothermal events. Finally, the proposed integrated field-based approach shows the capability to unravel the complexity of geothermal reservoir rocks in active volcanic settings.

Effect of vitrification on mechanical properties of porcine articular cartilage.

Articular cartilage (AC) injuries do not heal primarily and large lesions progress to degenerative osteoarthritis. Osteochondral allograft transplantation is an effective surgical treatment but is limited by the lack of donor tissue availability. Fresh allografts can be stored hypothermically up to 28–45 days after which the tissue is no longer viable for transplantation. Vitrification is a method of cryopreservation with the potential to extend the storage time of AC. A specific protocol has been demonstrated to preserve high chondrocyte viability; however, its effect on various mechanical properties of the extracellular matrix (ECM) remains unknown and is the focus of this initial study. Porcine AC was subject to a defined vitrification protocol, using fresh and frozen samples as positive and negative controls, respectively; n = 20 for all three groups. Unconfined compression testing was used to assess mechanical properties of the tissue under rapid load, stress relaxation, and equilibrium conditions. The stress relaxation time constants (modeled with a 2-term Prony series) and were significantly lower for frozen (p = 0.014, p < 0.001) and vitrified (p = 0.009, p = 0.003) tissue compared to fresh, with no differences between frozen and vitrified samples (p = 0.848 and 0.105 for and , respectively). These values indicate that frozen and vitrified samples relaxed more rapidly than fresh, which may suggest altered matrix composition and permeability post-treatment. These results represent the initial study in our experimental path to evaluate differences in mechanical properties of vitrified tissues.

Reservoir characterisation of unconventional rock units in the middle jurassic Sargelu Formation, atrush field, zagros folded belt

The heterogeneous lithological components of the Middle Jurassic Sargelu Formation in the Atrush field of the high folded zone were examined using rock samples, conventional wireline logs, mud logs and well test results throughout two wells. The Sargelu Formation is 45 m thick and has been divided into three units based on lithological characteristics and shale volume. The upper unit of the Sargelu Formation is composed of argillaceous limestone with intercalation of dolostone and anhydrite beds. The middle unit of the Sargelu Formation is composed of organic rich laminated shales, which contain residual bitumen, whilst the lower unit of the formation is dominated by argillaceous limestones. Lithological variation, mineralogy and organic matter contents are shown to be essential factors in controlling the reservoir matrix porosity and permeability. The maximum matrix porosity and permeability were observed within the dolomite plug samples (13.40%, 10.40 mD) and the lowest values were recorded in the anhydrite samples, both found in the upper unit of the Sargelu Formation. The fracture permeability is three orders of magnitude higher than the matrix permeability and the hydrocarbon production is predominately derived from the fractured intervals throughout the Sargelu Formation. The interconnected fracture pathways are influenced by the lithological variation and mineralogical components of the formation along with the tectonic position of the field. It was found that as the confining pressure increased the fracture permeability reduced. The different lithologies were also found to be sensitive to increases in the confining pressure. The clastic shale rich rocks are most sensitive to increases in confining pressure, whilst the more carbonate rich rocks showed the lowest variation as a function of confining pressure.

Numerical upscaling of nonlinear flow in low-permeability sandstone matrix system

The matrix system's apparent permeability model based on nano- and micro-scale mechanism modeling is limited in its role in low-permeability reservoir numerical simulation due to the lack of suitable up-scaling methods. This paper developed a numerical simulation method to evaluate the microporous structure's apparent permeability contribution to total permeability of the heterogeneous representative elementary volume (REV)-scale matrix under macroscopic pressure gradients. First, a local apparent liquid permeability (LALP) model considering the heterogeneous microporous structure and multiple water-transport mechanisms was established to describe the nonlinear seepage behavior of fluid in microscopic computational domain. Then, a multiresolution-image-based REV-scale domain reconstruction method was proposed, in which the microporous structural characteristics were quantified by fractal heterogeneous-porous-media model, and the REV-scale matrix was subsequently stochastic reconstructed based on the porosity distribution characteristics of microporous structures. Finally, the microscopic LALP model and macroscopic continuum model were fully coupled to numerical simulate the nonlinear seepage progress in REV-scale matrix domain. The comparisons between simulation results and experimental results demonstrated that the developed numerical simulation method can effectively predict the nonlinear flow velocity curve of REV-scale sandstone matrix. The influences of internal factors (microporous structural characteristics and seepage fluid properties) and external factors (temperature and pressure) on absolute permeability and apparent permeability of REV-scale matrix were investigated. The results demonstrated that (1) microporous structural characteristics determines the approximate level of intrinsic reservoir permeability, especially the average maximum pore size of discrete domain; (2) with microporous structure's permeability distribution heterogeneity increasing, the macroscopic intrinsic permeability decreases and the differences between apparent permeability and intrinsic permeability increase.

Correlation of alpha-1 antitrypsin levels and exosome associated neutrophil elastase endothelial injury in subjects with SARS-CoV2 infection.

BackgroundSevere acute respiratory syndrome caused by a novel coronavirus 2 (SARS-CoV-2) has infected more than 18 million people worldwide. The activation of endothelial cells is a hallmark of signs of SARS-CoV-2 infection that includes altered integrity of vessel barrier and endothelial inflammation.ObjectivesPulmonary endothelial activation is suggested to be related to the profound neutrophil elastase (NE) activity, which is necessary for sterilization of phagocytosed bacterial pathogens. However, unopposed activity of NE increases alveolocapillary permeability and extracellular matrix degradation. The uncontrolled protease activity of NE during the inflammatory phase of lung diseases might be due to the resistance of exosome associated NE to inhibition by alpha-1 antitrypsin.Method31 subjects with a diagnosis of SARS-CoV2 infection were recruited in the disease group and samples from 30 voluntaries matched for age and sex were also collected for control.ResultsWe measured the plasma levels of exosome-associated NE in SARS-CoV-2 patients which, were positively correlated with sign of endothelial damage in those patients as determined by plasma levels of LDH. Notably, we also found strong correlation with plasma levels of alpha-1 antitrypsin and exosome-associated NE in SARS-CoV-2 patients. Using macrovascular endothelial cells, we also observed that purified NE activity is inhibited by purified alpha-1 antitrypsin while, NE associated with exosomes are resistant to inhibition and show less sensitivity to alpha-1 antitrypsin inhibitory activity, in vitro.ConclusionsOur results point out the role of exosome-associated NE in exacerbation of endothelial injury in SARS-CoV-2 infection. We have demonstrated that exosome-associated NE could be served as a new potential therapeutic target of severe systemic manifestations of SARS-CoV-2 infection.

Dissolved organic matter tracers reveal contrasting characteristics in the concentrated flow zone and matrix-with-fractures zone of a sulfate-contaminated karst aquifer in South China

Dissolved organic matter (DOM) is of great importance in biogeochemical processes, such as sulfate reduction, in groundwater. H2S is generated from microbial-mediated sulfate reduction fueled by DOM and erodes carbonate. However, understanding the transformation and fate of DOM in sulfated-contaminated karst aquifers is still poor. Here, fluorescence spectroscopy was used to characterize the DOM pool in the sulfate-contaminated (from human activities) karst aquifer of the Zengpiyan Site, South China, by investigating the groundwater flow system. A comparison of fluorescence DOM (FDOM) characteristics between the concentrated flow zone (CFZ) composed of highly permeable small conduits and fracture networks and the matrix-with-fractures zone (MFZ) made of low permeable fractures and matrix rock aquifers was done. The relative groundwater residence times for all sample sites were estimated using γCa/γMg, which are consistent with those of the groundwater tracer test. The FDOM in groundwater in the CFZ was composed mainly of terrestrial-derived fulvic acid (FA)- and humic acid (HA)-like components, with relatively small contributions of microbially derived tryptophan (TPH)-like components. Compared with CFZ groundwater, the MFZ groundwater showed a longer residence time and reducing conditions, more bioavailable DOM, dominant TPH-like components with relatively small contributions of FA-like components, and fewer humus and hydrophobic structures. Hydrogeological conditions indirectly altered DOM composition by altering the biotic and abiotic activity conditions. The coexistence of relatively strong reducibility conditions and the higher proportion of bioavailable DOM in the MFZ would promote sulfate reduction to H2S gas, possibly amplifying carbonate dissolution, leading to the erosion of cultural relics. It is hoped that this study will contribute to knowledge on DOM behavior in karst aquifers and provide a scientific basis for cave site protection.

A composite model based on semi-analytical method for multiwell horizontal pad with stimulated reservoir volume

The multiwell horizontal pad is an effective method to enhance oil recovery for unconventional reservoirs. Microseismic evidence indicates that the stimulated reservoir volume (SRV) may have originated in the overlap region created by multi-well fracturing. However, the majority of SRV modeling studies have concentrated on a single well, ignoring the interference from offsetting wells. In this study, a novel model for modeling the SRV and multiwell horizontal pad in unconventional reservoirs is developed using an effective semi-analytical method. The proposed semi-analytical model is capable of simulating the behaviors of a multiwell horizontal pad with an irregularly shaped SRV and an impermeable boundary. The transient pressure behaviors of the multiwell horizontal pad with SRV are significantly different than that of a single isolated well, as demonstrated by the results. The linear flow between wells, the pseudoradial flow (PRF) of the multiwell pad in SRV, the transitional flow, and the final pseudoradial flow (PRF) of the multiwell pad all correspond to an extremely unusual transient pressure response. Due to the high flow capability of SRV, pressure diffusion occurs at a faster rate, resulting in the appearance of these flow regions in advance. Sensitivity analysis confirms that as the scale of SRV increases, the duration of the flow influenced by the SRV increases. The SRV and compensating wells result in a negligible PRF, while the pressure behaviors exhibit a gradual rise. This phenomenon may serve as a demonstration of the extremely rare occurrence of radial flow or PRF in unconventional reservoirs. The horizontal line value for the PRF in SRV is proportional to the total production of the well pad. The horizontal line value for the final PRF is also related to the unstimulated region's mobility ratio, the well pad's production rate and 0.5. The case in Junggar Basin shows that the natural fracture permeability in the SRV is 2.5 mD, the matrix permeability is 0.044 mD, the rectangular SRV side lengths are 1600 m and 880 m, the mobility ratio and dispersion ratio are 15, and the wellbore storage coefficient is 0.5 m3/MPa.

Analysis of factors influencing recovery of low permeability and strong heterogeneous gas reservoirs and establishment of prediction model

Jialingjiang Formation is a typical low permeability carbonate reservoir in Sichuan Basin, which is characterized by strong heterogeneity, low matrix permeability and high-water saturation. Based on seven influencing factors, such as permeability, reservoir thickness and reservoir porosity, this paper evaluates and predicts the oil recovery of Jialingjiang Formation gas reservoir by using two neural network models of multilayer perceptor and radial basis function and nonlinear surface fitting method. The results show that: 1) In the neural network prediction model, the correlation coefficient between the prediction result curve of multilayer perceptron and the original recovery curve reaches 0.88, which is higher than the radial basis function (0.81), indicating that the use of multilayer perceptron can better predict the recovery of gas reservoirs. 2) In the nonlinear curved surface fitting prediction model, the two influencing factors with the greatest linear correlation with the recovery factor, reservoir thickness and gas recovery rate, are selected to fit the prediction model, and the prediction model is obtained. According to the prediction model, the recovery factor is positively correlated with the reservoir thickness and gas recovery rate on the whole. The model can be used to estimate gas recovery from two factors: reservoir thickness and gas recovery rate.

Thermo-hydro-mechanical optimization of the enhanced geothermal system for commercial utilization

Enhanced geothermal system (EGS) has been commercialized worldwide, yet the complex thermal-hydraulic-mechanical coupling processes were not well illuminated. With the reservoir regarded as the fractured porous media of rock matrix and discrete fractures, this work establishes a three-dimensional EGS model based on the thermal non-equilibrium theory to study the heat extraction in the EGS. After model validations, the evolution of three fields (i.e., temperature field, seepage field, and stress field) and the effects of several crucial operating parameters (e.g., injection flow rate, depth, and length) on heat extraction performance are discussed. The results show that the change of pressure and temperature in the reservoir alters the fracture displacement and the flow preferential paths and rock matrix permeability. For the given EGS reservoir, the total heat extraction rate reaches 60% at 50 years and approaches 86% at 100 years. Increasing the elastic modulus of the rock matrix promotes the overall recovery and then decreases the average temperature of the rock matrix. Decreasing injection flow rate, increasing length, increasing depth, and decreasing the elastic modulus of rock matrix give rise to (i) increasing the period for maintaining stable average outlet temperature; (ii) elevating the average outlet temperature after specific years. Running for 100 years, the final injection pressure of the EGS is 130 MPa, 48 MPa, and 45 MPa for the three fracture widths, 26%, 14%, and 10% lower than the initial injection pressure. Changing the fracture width from 0.005 m to 0.05 m is beneficial for the EGS operation on economic efficiency. Based on the commercial standards, the optimal operating conditions are proposed for the EGS.

Causes of a premature thermal breakthrough of a hydrothermal project in Germany

Sustainable heat extraction is of utmost importance for the economic life of geothermal production systems. Especially in hydrothermal sedimentary basins, a temperature decrease at the production well prompts a financial loss. A premature thermal breakthrough occurred in one of the geothermal projects in the Greater Munich Area, a well-known region for deep, low enthalpy geothermal development in the Upper Jurassic carbonate reservoir (syn. Malm) beneath the North Alpine Foreland Basin. Accordingly, questions are raised regarding the geologic controls on the reservoir´s permeability, the occurring type of heat and mass transport mechanism, and the fitting reservoir model type. 3D seismic data interpretation delineates seismic scale structures potentially influencing the reservoir permeability. Geophysical borehole data characterize sub-seismic scale elements (fractures, karst, and lithofacies), where we correlate them with the inflow zones and the interpreted seismic scale structures. The integration of both scales delineates the reservoir heterogeneity controlled by a lateral change in the carbonate lithofacies overprinted by faults and fractures. A NNW-SSE oriented seismic scale structure matches the orientation of hydraulically active sub-seismic scale fractures, where they are aligned with the maximum horizontal stress orientation. This structure induces additional anisotropic permeability, providing a preferential hydraulic pathway between the wells of the project. This study recommends considering fractured reservoir models to simulate the mass and heat flow in the highly heterogeneous Malm carbonates instead of composite reservoir models of equivalent hydraulic properties. Finally, we present a hydrogeological model describing the reservoir's structural and matrix permeability distribution to act as a basic concept for future thermal-hydraulic numerical modeling. The applied methods in this study are applicable in similar geothermal systems with adequate seismic and geophysical borehole data for future geothermal reservoir characterization, modeling, and management.

Experimental and Numerical Investigation of the Flow Behaviour of Fractured Granite under Extreme Temperature and Pressure Conditions

As a result of negligible connected porosity—and thus, minimal matrix permeability—the fluid-transport characteristics of crystalline rocks are strongly influenced by the fractures at all scales. Understanding the flow behaviour of fractured rock under extreme stress and temperature conditions is essential for safe and effective deep geo-engineering applications, such as deep geothermal recovery, geological nuclear waste disposal, oil and gas extraction, geological storage and deep mining operations. Therefore, this study aims to investigate the flow characteristics of mechanically fractured Australian Strathbogie granite under a wide range of stress (confining pressures 1–80 MPa) and temperature conditions (20 °C to 350 °C). The study utilised a sophisticated high-temperature, high-pressure tri-axial setup capable of simulating extreme geological conditions, followed by a numerical simulation. According to the experimental results, a linear increment in the steady-state flow rate was observed, with increased injection pressure for the experimental conditions considered. Therefore, linear laminar Darcy flow was considered, and the fracture permeability was calculated using the cubic law. It was found that stress and temperature strongly depend on the flow of fluid through fractures. The steady-state flow rate decreased exponentially with the increase in normal stress, showcasing fracture shrinkage with an increment in effective stress. With regard to permeability through the fractures, increasing temperature was found to cause an initial reduction in fracture permeability due to an increased interlock effect (induced by thermal overclosure), followed by increments because of the thermally induced damage. Furthermore, the increasing temperature caused significant non-linear increments in the fluid flow rates due to the associated viscosity and density reduction in water. Considering the laboratory-scale flow-through exercises, a fully coupled numerical model that can predict hydro–thermo–mechanical variations in the reservoir rocks was developed using the COMSOL Multiphysics simulator. The developed model was calibrated, utilising the temperature- and pressure-dependent properties of granite rocks and fluid (water); was validated against the experimental results; and was used to predict the permeability, pressure development and strain of rock samples under extreme conditions, which were difficult to achieve in the laboratory.