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Supercritical multicomponent thermal fluid injection is a new technology with great potential for offshore heavy oil thermal recovery. In the process of thermal fluid generation, the reaction conditions including temperature, pressure, and the organic mass concentration in the reaction material will significantly affect its composition and injection rate and will further affect the thermal recovery and development quality of heavy oil. However, there is a lack of relevant research on the variation rules and control methods of the composition and injection rate of supercritical multicomponent thermal fluids, resulting in a lack of technical mechanisms for effective optimization. To fill this gap, a reaction molecular dynamics simulation method was used to simulate thermal fluid generation under different temperatures, pressures, and organic mass concentrations. The changes in thermal fluid composition and yield with reaction conditions were studied, and a control model of thermal fluid composition and yield was established. The proportional relationship between the thermal fluid generation scale of an offshore heavy oil platform and the simulated thermal fluid generation scale is analyzed, and a collaborative optimization method of thermal fluid composition and injection rate in field applications is proposed. The results show the following: (1) The higher the mass concentration of organic matter, the higher the content of supercritical carbon dioxide and supercritical nitrogen in thermal fluids, and the lower the content of supercritical water. (2) The higher the temperature and pressure, the higher the thermal fluid yield, and the higher the organic mass concentration, the lower the thermal fluid yield. (3) The component fitting model conforms to the power function relationship, and the coefficient of determination R2 is greater than 0.9; the yield fitting model conforms to the modified inverse linear logarithmic function relationship, the determination coefficient R2 is greater than 0.8, and the fitting degree is high. (4) The ratio between the actual injection rate of thermal fluids in the mine field and the molecular simulated thermal fluid yield is the ratio of organic matter mass in the platform thermal fluid generator and organic matter mass in the simulated box. (5) Based on the composition and yield control model, combined with the simulation of the ratio relationship between yield and injection rate in the field, a collaborative optimization method of thermal fluid composition and injection rate was established. The research results can provide an effective technical method for predicting, controlling, and optimizing the composition and injection rate of supercritical multicomponent thermal fluids. [ABSTRACT FROM AUTHOR]

Small hydro technology is playing a crucial role in advancing sustainable, clean energy policies as part of the global hydro development strategy. Its contribution to social and economic development is becoming more prominent, particularly in ensuring electricity access for rural communities and supporting industrial expansion. The main causes of bulb turbine failures under high operating conditions are frequently attributed to variations in pressure in the draft tubes, which are aggravated when a spinning vortex rope is formed under load operation. Different fluid injection techniques, namely compressed air and water jet injection, address these issues and reduce the negative results of cavitation. The investigation covers the flow visualization on the suction side of a single hydrofoil utilizing a cavitation tunnel and a bulb turbine. This study assesses the effectiveness of compressed air injection in reducing vibration generated by cavitation in bulb turbines. Positive results of the experimental studies suggest a decrease in noise and vibration by air injection that prevents oscillations of the vortex rope. This research also considers how the hydrofoil design of bulb runner blades influences flow characteristics. Hence, it provides knowledge on cavitation structures in diverse cavitation numbers. Different studies that compare the original and modified hydrofoil designs reveal remarkable improvements that may be due to changes in the key parameters of the hydrofoil, such as later cavitation initiation and reduced intensity. To obtain the optimal output of a bulb turbine by considering air injection for vibration reduction and hydrofoil design changes to limit the negative effect of cavitation, the Reynolds number and cavitation number are to be defined. This multidisciplinary approach possesses enormous potential to increase the reliability and efficiency of bulb turbines in challenging operating conditions. [ABSTRACT FROM AUTHOR]

In this paper, we performed microseismicity detection and location using the deep learning method and obtained a high-precision earthquake catalog in the Changning gas field, which is one of the largest shale gas production demonstration areas in China. We found that the spatial and temporal characteristics of seismicity in the region are indicative of its correlation with industrial operations. The distribution of earthquakes at depth reflected variations in reservoir depth and provided valuable constraints on it. The horizontal layered distribution of earthquakes at depth is due to the formation of fracture surfaces from interconnected fractures near the reservoir during hydraulic fracturing (HF) operations, which clearly demonstrates how HF operations impact seismicity. We suggested that the horizontally layered distribution was driven by two fundamental mechanisms: reactivation of pre-existing faults during HF and injection of high-pressure fluids into the reservoir, leading to fracture creation. Several ML ≥4 earthquakes, which did not occur on well-defined seismogenic faults, may have been triggered by pore elastic coupling resulting from regional stress accumulation and fluid injection. Significantly, the ML 4.9 seismic sequence occurring at the basement indicates that fracking has reactivated and promoted pre-existing faults, highlighting the need for further investigation into potential seismic hazards in the region. [ABSTRACT FROM AUTHOR]

With the continuous development of deep oil and gas resources, the number of high‐temperature and high‐pressure wells is increasing, and the complexity of fracturing operations is becoming more pronounced. The safe conduct of fracturing operations is crucial for improving production efficiency. To investigate the strength and safety of fracturing strings in high‐temperature and high‐pressure wells, a transient calculation model of temperature‐pressure coupling was established for fracturing strings in high‐temperature and high‐pressure wells. The safety factor method and triaxial stress analysis were employed to evaluate the safety of fracturing strings in high‐temperature and high‐pressure wells. The method was used to assess the fracturing strings in high‐temperature and high‐pressure wells, and the effects of fracturing fluid injection rate and string size on the stress of the strings were analyzed. The results indicate that the axial force and equivalent stress at the wellhead of the fracturing string are the highest; as the fracturing time and injection rate of the fracturing fluid increase, the axial stress and equivalent stress at the wellhead of the fracturing string also increase. Small‐sized pipes are conducive to improving the safety factor of fracturing pipe string operations. The research findings can provide theoretical guidance for designing fracturing strings for high‐temperature and high‐pressure wells. [ABSTRACT FROM AUTHOR]

Subsurface non-isothermal fluid injection is a ubiquitous scenario in energy and water resource applications, which can lead to geochemical disequilibrium and thermally driven solubility changes and reactions. Depending on the nature of the solubility of a mineral, the thermal change can lead to either mineral dissolution or precipitation (due to undersaturation or supersaturation conditions). Here, by considering this thermo-hydro-chemical (THC) scenario and by calculating the temperature-dependent solubility using a non-isothermal solution (the so-called Lauwerier solution), thermally driven reactive transport solutions are derived for a confined aquifer. The coupled solutions, hereafter termed the "reactive Lauwerier problem", are developed for axisymmetric and Cartesian symmetries and additionally provide the porosity evolution in the aquifer. The solutions are then used to study two common cases: (I) hot CO2-rich water injection into a carbonate aquifer and (II) hot silica-rich water injection into a sandstone aquifer, leading to mineral dissolution and precipitation, respectively. We discuss the timescales of such fluid–rock interactions and the changes in hydraulic system properties. The solutions and findings contribute to the understanding and management of subsurface energy and water resources, such as aquifer thermal energy storage, aquifer storage and recovery and reinjection of used geothermal water. The solutions are also useful for developing and benchmarking complex coupled numerical codes. [ABSTRACT FROM AUTHOR]

During injection treatments, bottomhole pressure measurements may significantly mismatch modeling results. We devise a computationally effective technique for interpretation of fluid injection in a wellbore interval with multiple geological layers based on the bottomhole pressure measurements. The permeability, porosity and compressibility in each layer are initially setup, while the skin factor and partitioning of injected fluids among the zones during the injection are found as a solution of the problem. The problem takes into account Darcy flow and chemical interactions between the injected acids, diverter fluids and reservoir rock typical in modern matrix acidizing treatments. Using the synchronously recorded injection rate and bottomhole pressure, we evaluate skin factor changes in each layer and actual fluid placement into the reservoir during different pumping jobs: matrix acidizing, water control, sand control, scale squeezes and water flooding. The model is validated by comparison with a simulator used in industry. It gives opportunity to estimate efficiency of a matrix treatment job, role of every injection stage, and control fluid delivery to each layer in real time. The presented interpretation technique significantly improves accuracy of matrix treatments analysis by coupling the hydrodynamic model with records of pressure and injection rate during the treatment. [ABSTRACT FROM AUTHOR]

Multistage fracturing of horizontal wells is a critical technology for unconventional oil and gas reservoir stimulation. Ball-throwing temporary plugging fracturing is a new method for realizing uniform fracturing along horizontal wells and plays an important role in increasing oil and gas production. However, the transportation and sealing law of temporary plugging balls (TPBs) in the perforation section of horizontal wells is still unclear. Using COMSOL computational fluid dynamics and a particle tracking module, we simulate the transportation process of TPBs in a horizontal wellbore and analyse the effects of the ball density, ball diameter, ball number, fracturing fluid injection rate, and viscosity on the plugging efficiency of TPB transportation. This study reveals that when the density of TPBs is close to that of the fracturing fluid and a moderate diameter of the TPB is used, the plugging efficiency can be substantially enhanced. The plugging efficiency is greater when the TPB number is close to twice the number of perforations and is lower when the number of TPBs is three times the number of perforations. Adjusting the fracturing fluid injection rate from low to high can control the position of the TPBs, improving plugging efficiency. As the viscosity of the fracturing fluid increases, the plugging efficiency of the perforations decreases near the borehole heel and increases near the borehole toe. In contrast, the plugging efficiency of the central perforation is almost unaffected by the fracturing fluid viscosity. This study can serve as a valuable reference for establishing the parameters for temporary plugging and fracturing. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing is widely recognized as a key technology for enhancing coalbed methane production. The fracturing fluid has physicochemical reactions with the coal fractures, along with their duration, critically affecting fracture permeability, thereby determining the effectiveness of the technology. However, the study has not received enough attention. In this study, coal fracture seepage tests were carried out using in situ continuous injection of fracturing fluid. The seepage evolution of viscoelastic surfactant fracturing fluid (VESFF) was investigated at different times (0, 1, 2, 3, 4, and 5 days), and de-ionized water (DW) and potassium chloride solution (KCL) were used for comparison. The results showed that the flow rate increased compared to initial flow rate after VESFF treatment for two to four days, while the flow rate could not be recovered after DW and KCL treatment. The optimal treatment duration for VESFF was two days: marked by a sevenfold increase in the flow rate, an 84% increase in initial hydraulic aperture, and minimal momentum loss. After two more days of VESFF treatment, the pressure gradient and effective confining pressure became greater than 6 MPa/m and 3.5 MPa, respectively, and showed a significant excessive discharge characteristics (β < 0), which resulted from the generation and dilation of microcracks, increasing the number of flow channels due to coupled fluid–mechanical behavior. The degree of flow nonlinearity decreased with increasing VESFF treatment duration and increased with increasing effective confining pressure. These results have profound implications for optimal treatment duration and mechanism of VESFF strengthening coal fracture seepage. [ABSTRACT FROM AUTHOR]

The mixing performance of non-Newtonian fluids is critical in various industrial processes, directly impacting efficiency and product quality. This study investigates the mixing behavior of Xanthan Gum solutions, a widely used non-Newtonian fluid, compared to water using different injection techniques. Comprehensive flow visualization, wall shear stress measurements, pressure drop assessments, and mixing index evaluations were conducted within a cylindrical channel equipped with vortex generators. Results reveal that wall shear stress in Xanthan Gum solutions is significantly higher than in water and increases with rising Reynolds numbers. Additionally, Xanthan Gum solutions exhibit higher pressure drops and lower mixing index values due to their high viscosity and shear-thinning properties, which hinder mass transfer and diffusion. The central injection technique demonstrated superior mixing performance compared to lateral injection for both fluids. Notably, the mixing index for Xanthan Gum solutions stabilizes at Reynolds numbers of 500 and above, indicating that generated vortices do not alter the fluid's consistency. These findings align with the Herschel–Bulkley rheological model, characterizing the non-Newtonian behavior of Xanthan Gum solutions. [ABSTRACT FROM AUTHOR]

The process of extracting shale gas, particularly the study of the utilization law of shale reservoirs modified by hydraulic fracturing technology, is crucial for understanding the effective development of shale gas. This understanding can significantly influence the estimated ultimate recovery of reserves. Our study focused on Longmaxi Formation shale in the Changning–Weiyuan block. To investigate the hydraulic fracturing expansion mechanism and utilization law, we employed shale reservoir physical and mechanical characterization, indoor triaxial hydraulic fracturing experiments, and numerical simulations. The findings are as follows. The rupture pressure of hydraulic fractures increases with the peripheral pressure, and high stress is conducive to the formation of internal microfractures. Additionally, a high rate of water injection enhances fracture extensions along the direction of fluid injection. Under varying injection pressures, the length of crack extensions and number of bond damages in shale are positively correlated with the injection pressure. Conversely, under different differential ground stresses, the length of crack extensions and number of bond damages are negatively correlated with the injection pressure. The six main factors affecting the effective utilization of shale gas are as follows: the stimulated reservoir volume, number of hydraulic fracture clusters, fracture length, fracture height, number of fracture stages, and cluster spacing, accounting for 27.13%, 14.74%, 10.31%, 9.58%, 9.53%, and 9.29%, respectively, with a cumulative contribution rate of 80.58%. This study clarifies the hydraulic fracturing mechanisms of shale reservoirs and the laws governing shale gas production, providing technical support for the development of shale gas reservoirs. [ABSTRACT FROM AUTHOR]

Introduction: Knee osteoarthritis (OA) is a highly prevalent and debilitating condition with significant emotional and economic impacts. Current treatment options may only provide temporary pain relief and are not regenerative, thus the progression of knee OA is not deterred and total knee arthroplasty is inevitable. Injection therapies with orthobiologics possess regenerative potential and are an emerging treatment option. We present a prospective study aimed at examining patients with knee OA who had received an autologous platelet concentrate fluid (APCF) injection produced through a fluid volume reducer. Methods: This was an observational review of the results following an APCF injection in a cohort of patients at a single site. Patients were included in the study if they were diagnosed with K/L grade 2–3 knee OA and treated with an APCF knee injection. Patients were excluded if they had obtained an orthobiologic injection in the three months prior to study enrollment or if baseline data were unavailable. Knee score and function score were used to assess patients at the baseline and post-injection follow-ups. Results: Improvements for knee score were statistically significant for the follow-ups at three months, six months, one year, and three years. Function score improved, with statistically significant changes for the three month and three year follow-ups. Conclusions: Our study demonstrates that there is some utility in using APCF injection for knee OA, with improvements that may be sustained up to three years in some patients. [ABSTRACT FROM AUTHOR]

We employ the IllustrisTNG simulation data to investigate the turbulent and thermal motions of the cosmic baryonic fluid. With continuous wavelet transform techniques, we define the pressure spectra, or density-weighted velocity power spectra, as well as the spectral ratios, for both turbulent and thermal motions. We find that the magnitude of the turbulent pressure spectrum grows slightly from |$z=4$| to 2 and increases significantly from |$z=2$| to 1 at large scales, suggesting progressive turbulence injection into the cosmic fluid, whereas from |$z=1$| to 0, the spectrum remains nearly constant, indicating that turbulence may be balanced by energy transfer and dissipation. The magnitude of the turbulent pressure spectra also increases with environmental density, with the highest density regions showing a turbulent pressure up to six times that of thermal pressure. We also explore the dynamical effects of turbulence and thermal motions, discovering that while thermal pressure provides support against structure collapse, turbulent pressure almost counteracts this support, challenging the common belief that turbulent pressure supports gas against overcooling. [ABSTRACT FROM AUTHOR]

Deep closed-loop geothermal systems are a potential technology to provide heating and power generation. Although these systems are not new, they have recently regained interest because the design avoids reservoir stimulation (and potential fluid injection induced seismicity) and thermal short-circuiting of the working fluid. However, the poromechanical response to long-term heat depletion of closed-loop wells at large depths is largely unexplored. This paper investigates the response of rock around closed-loop geothermal system over 30-years of heat depletion through numerical simulation. The numerical solution is based on the theory of thermo-poroelastoplasticity and is solved through the Fenicsx finite element computing platform. The formulation takes effective poroelastoplastic properties of the bulk rock mass to indirectly account for strength and permeability of a rock mass with pre-existing fractures. Results for a normal faulting scenario show that the reservoir response to heat depletion causes vertical and horizontal stress redistribution far around the wellbores. Moreover, the rock mass may respond with partially undrained behavior in deep locations with a sparse fracture network. Shear failure may occur within a fraction -up to 30%- of the geothermal reservoir volume (limited by the thermal diffusion length) mostly driven by increase of effective stress anisotropy between vertical and horizontal stresses. The potential of induced microseismicity in deep closed-loop geothermal systems depends on the shear reactivated reservoir volume and effective rock stiffness. Energy dissipation depends case by case and can extend over the entire operation period, likely a consequence of the elastic perfectly-plastic model. Heat-drainage induced microseismicity is most likely expected to occur for closed-loop wells in geothermal reservoirs under normal faulting regime where small changes of horizontal effective stress may reactivate pre-existing fractures. Furthermore, heat depletion may increase stress intensities around the wellbore and facilitate tensile fracturing. Highlights: Heat depletion around wells changes effective stresses Effective rock stiffness has a first-order impact on mechanical response to cooling Shear reactivated reservoir volume due to heat depletion can be up to 30% in our simulation case Likelihood of thermally induced tensile fracturing of the wellbore increases with operation time [ABSTRACT FROM AUTHOR]

Hydraulic fracturing has gained escalating significance in recovering unconventional reservoirs. However, the failure mechanism and its evolution with progressive fluid injection are not fully understood for granitic materials. To investigate, triaxial hydraulic fracturing on Harcourt granite and acoustic emission (AE) monitoring was performed by the self-developed multi-physical rock testing platform (MRTP). Source mechanism analysis suggests that tensile cracks account for the majority (62%) of all cracks throughout the hydraulic fracturing process. Tensile cracks with large energy are induced mainly around the borehole bottom, but their average energy is smaller than shear cracks. The entire hydraulic fracturing process is divided into three stages by injection measurements. In Stage 1, AE events are recorded with low energy emissions but high signal-to-noise ratios, revealing the initiation of hydraulic fractures before peak injection pressure. Tensile cracks are more dominant (78%) than other stages. In Stage 2, the number and magnitude of AE events increase exponentially along the trace formed in Stage 1. In Stage 3, hydraulic fractures have the largest magnitude among all stages. Shear cracks are nearly the same proportion as Stage 2, but more shear cracks with large magnitudes are observed following the trace formed by tensile cracks. A dense population of shear cracks can be found at the borehole bottom, and their distribution follows the average slip plunge of individual shear cracks induced by the injection fluid. Highlights: Mapping the spatial and temporal distribution of different source mechanisms induced by tri-axial hydraulic fracturing on Harcourt granite. Tensile cracks possess a much greater proportion than shear cracks among all hydraulic fractures. The proportion of tensile cracks during the initiation of hydraulic fractures is much larger than that in other periods. Majority of high-energy shear cracks are induced after the occurrence of massive tensile cracks. The trace of shear cracks follows the average slip plunge of individual shear cracks. [ABSTRACT FROM AUTHOR]

Paleoseismological research for a slowly deforming intraplate fault can provide essential information for understanding not only the spatiotemporal characteristics of past earthquakes but also seismic behavior in the case of long recurrence intervals. To reveal the paleoseismological properties and faulting processes of the intraplate fault, the Geumwang Fault Zone in the central Korean Peninsula, we conducted comprehensive paleoseismological investigations along the fault zone, incorporating geomorphological mapping with airborne light detection and ranging (LiDAR), electrical resistivity tomography (ERT), borehole drilling, trench excavation, optically stimulated luminescence (OSL) dating, and microstructural analysis. Along NE-SW-striking lineaments of the Geumwang Fault Zone, surface deformation is weakly recognized by LiDAR imagery in a damage zone along the northern section of the fault zone (Suha site). Results of ERT and borehole logging at the Suha site suggest a localized zone of low resistivity and unconformity level separation in sedimentary layers, respectively. A trench section excavated along the ERT traverse and borehole sites exposes a fault contact between granite and unconsolidated Quaternary strata comprising boulders (47 ± 3 ka), clayey sand (24 ± 2 ka), pebbly cobbles, coarse sand, and artificial layers from bottom to top. The < 5-cm-wide slip zone is oriented N09°E/85°NW and cuts the granite to the west and the boulder layer to the east. This slip zone that covered by the clayey sand stratum records an apparent vertical offset of ∼1.5 m and has sub-horizontal striations indicating dextral movement. Microstructures at the contact between the granite and the boulder layer support the occurrence of seismic slip propagation along the contact and include injected sedimentary materials, clay-clast aggregates, and fresh, open fractures in quartz and feldspar grains in the boulder layer. The slip zone consists of a < 4.5-cm-wide zone of cataclasite and a < 5-mm-wide principal slip zone (PSZ). Microstructures in the slip zone and sediments near the slip zone include seismic-slip indicators of pressurized gouge materials and fluid injection within PSZ, and deformed sediments. These reveal that the slip zone underwent repeated seismic slip events during uplift to the surface. Our paleoseismological analyses with microstructures show that the boulder layer was cut by strike-slip faulting with a minor vertical component between 47–24 ka, following which the overlying sediments were deposited along the exposed fault scarp as incision fill. The results show that microstructural observations can provide key information on the deformation of unconsolidated sediments and on the nature and timing of seismic faulting. [ABSTRACT FROM AUTHOR]

We present an earthquake simulator, Quake-DFN, which allows simulating sequences of earthquakes in a 3D discrete fault network governed by rate and state friction. The simulator is quasi-dynamic, with inertial effects being approximated by radiation damping and a lumped mass. The lumped mass term allows for accounting for inertial overshoot and, in addition, makes the computation more effective. Quake-DFN is compared against three publicly available simulation results: (1) the rupture of a planar fault with uniform prestress (SEAS BP5-QD), (2) the propagation of a rupture across a stepover separating two parallel planar faults (RSQSim and FaultMod), and (3) a branch fault system with a secondary fault splaying from a main fault (FaultMod). Examples of injection-induced earthquake simulations are shown for three different fault geometries: (1) a planar fault with a wide range of initial stresses, (2) a branching fault system with varying fault angles and principal stress orientations, and (3) a fault network similar to the one that was activated during the 2011 Prague, Oklahoma, earthquake sequence. The simulations produce realistic earthquake sequences. The time and magnitude of the induced earthquakes observed in these simulations depend on the difference between the initial friction and the residual friction μi -- μf, the value of which quantifies the potential for runaway ruptures (ruptures that can extend beyond the zone of stress perturbation due to the injection). The discrete fault simulations show that our simulator correctly accounts for the effect of fault geometry and regional stress tensor orientation and shape. These examples show that Quake-DFN can be used to simulate earthquake sequences and, most importantly, magnitudes, possibly induced or triggered by a fluid injection near a known fault system. [ABSTRACT FROM AUTHOR]

Airfoil leading-edge fluid-blowing control is computationally studied to improve aerodynamic efficiency. The fluid injection momentum coefficient Cμ (the ratio of injection to incoming square velocities times the slot's width to airfoil's half chord length) varies from 0.5% to 5.4%. Both static and dynamic conditions are investigated for a NACA0018 airfoil at low speed and Reynolds number of 250 k based on the airfoil's chord length. The airfoil is dynamically pitched at a reduced frequency (the pitching tangential speed to the freestream speed ratio), varying between 0.0078 and 0.2. Reynolds-averaged Navier–Stokes (RANS) and unsteady RANS (URANS) is used in the simulations as based on the Transition SST and Spalart–Allmaras models, generally achieving good agreement with experimental results in lift and drag coefficients and in the pressure coefficient distributions along the airfoil. It is found that oscillating the airfoil can delay stall, as expected, in dynamic stall (DS). Leading-edge blowing control can also significantly delay stall both in static and dynamic conditions as long as sufficient momentum is applied to the control. On the other hand, for a small Cμ such as 0.5%, the leading-edge control worsens the performance and hastens the appearance of stall in both static and dynamic conditions. The airfoil's oscillation reduces the differences between pitch-up and pitch-down aerodynamic performances. Detailed analysis of vorticity, pressure, velocity, and streamline contours is given to provide plausible explanations and insight to the flow. [ABSTRACT FROM AUTHOR]

Carbon capture and storage (CCS) is a method of reducing carbon dioxide (CO2) emissions, which could be crucial in addressing global warming. Accurately estimating the pH of CO2-saturated water/brine binary systems is an important physical–chemical property of reservoir fluids at CO2 injection sites. Although there has been substantial research on the pH of CO2-saturated brines, it mainly focuses on brine systems containing monovalent cations. Research on the pH of brine systems containing bivalent cations is lacking. The aim of this paper is to develop a chemical equilibrium model based on pressure–volume–temperature (PVT) data around the mechanism of CO2 dissolution–acidification and the CO2 chemical equilibrium process in brine aquifers, which can be used to predict the pH value of the CO2-saturated brine system (0–4 mol kg−1) under high-temperature (273–473 K) and high-pressure (up to 100 MPa) conditions. The model employs phase equilibrium equations to describe the CO2-water/brine dissolution–acidification process, with corrections to the CO2 activity coefficient part of the Spycher and Pruess model. The results showed that the predicted pH values were in good agreement with the experimental data. The pH of the CO2-saturated CaCl2(aq) and MgCl2(aq) systems was predicted using both a chemical equilibrium model and the PHREEQC geochemical simulator based on the Pitzer model. The differences in the predicted values of the two models were analyzed. Based on the process of CO2 dissolution acidification, a reliable empirical equation was established to calculate the pH of CO2-saturated water/brine system, and it was applied to the storage of CO2 brine layer. [ABSTRACT FROM AUTHOR]

The permeability, heat conductivity, and reaction rate will be varied with the change of natural gas hydrate saturation when thermal fluid is injected into the natural gas hydrate reservoirs. In order to characterize the variation of the physical field parameters with hydrate saturation, DDF-LBM was applied to simulate the hydrate dissociation process by thermal fluid injection under pore-scale modelling. Based on the forced conjugate heat transfer case, the relaxation frequency of the thermal lattice in the pores is corrected. Based on the P-T phase equilibrium relationship of hydrates and considering the heat absorbed by the hydrate reaction, the solid–liquid state of the hydrate lattice is judged in real time, and the dynamic simulation of the heat flow solidification multi-physics field is realized. The simulation results show that the dissociation rate of the hydrates by thermal fluid injection was higher than that by heating the hydrate surface alone and was positively correlated with the hydrate saturation. On the basis of the above results, this paper provided exponential fitting equations between different hydrate saturations and average permeability, effective thermal conductivity, and inherent reaction rate. The fitting results show that saturation has a negative correlation with relative permeability and effective thermal conductivity, and a positive correlation with the inherent reaction rate. The above results can provide a reference basis for accurately describing the heat and mass transfer of natural gas hydrate under the macroscale. [ABSTRACT FROM AUTHOR]

During the early screening phase of Carbon Capture and Storage (CCS) site evaluations limited time and data are available and hence CO2 plume evaluations using time and data intensive reservoir simulations are almost never performed. However, there is still a need for early plume evaluations to risk and rank injection sites relative to each other. Therefore, an alternative fluid migration method called invasion percolation is adopted for the CCS screening phase to predict the extent and location of CO2 plumes in the subsurface. Invasion percolation as part of basin modeling is a rapid method, which requires limited data and is ideal for the early screening phase. Invasion percolation results are compared to uncalibrated reservoir models, typical for the screening phase, revealing that plume location shape and size are very reasonable especially when compared to seismic observed plume outlines. It can be concluded that invasion percolation as part of basin modeling is a fit for purpose method, which can assess multiple opportunities rapidly during the early intake screening phase to risk and rank opportunities relative to each other and to build a CCS injection site portfolio. In addition to the plume evaluation, basin models can provide useful basin‐scale or injection site specific pressure and temperature predictions as well as CO2 density estimates for static volume calculations before detailed reservoir and stratigraphic models are available. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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Two‐phase flow displacement in rock fractures is crucial for various subsurface mass transfer processes and engineering applications. In fractures, the displacement of a less viscous fluid by a more viscous one (i.e., viscosity ratio M > 1) involves viscous forces help stabilizing the displacement front in presence of capillary pressure fluctuations. Although previous studies have reported displacement patterns in isotropic fractures, the impact of anisotropic fractures on displacement patterns has not been systematically examined. In this study, we conducted flow‐rate‐controlled drainage experiments to examine how anisotropic aperture fields affect displacement patterns. We observed the transition of displacement patterns from capillary fingering (CF) to crossover zone (CZ) to compact displacement pattern (CD) based on variations in transverse pore‐filling event (TPFE) frequency, which characterizes the competition between capillary and viscous forces. Increasing aperture correlation length in the transverse direction leads to increased TPFE frequency at a low flow rate, destabilizing displacement front. While the increasing aperture correlation length in longitudinal direction suppressed TPFE frequency, stabilizing displacement front. Therefore, the critical capillary number (CaCF‐CZ), which indicates the onset of the CF‐CZ transition, decreases as the aperture field varies from transversely to longitudinally correlated. At high flow rates, TPFEs almost disappeared, indicating that anisotropy did not affect CZ‐CD transition (CaCZ‐CD). Furthermore, we modified theoretical models of CaCF‐CZ and CaCZ‐CD by incorporating the aperture anisotropy factor, achieving a good fit with the experimental data. This study demonstrates the critical role of aperture field anisotropy in controlling two‐phase displacement patterns and provides a theoretical framework for predicting multiphase flow behavior in natural fractures. Plain Language Summary: Understanding how a viscous fluid displaces a less viscous one in rock fractures is important for various underground processes and engineering applications. Previous studies on two‐phase flow have mainly focused on isotropic fractures. Natural fractures are often anisotropic, and the impact of fracture anisotropy on two‐phase flow patterns has not been thoroughly studied. Here we conducted laboratory experiments to examine how anisotropy affects displacement process. We found that more viscous injection fluid forms thin fingers that penetrate fractures and sometimes forms a compact displacement (CD) front. The movement of injection fluid depends on anisotropy and fluid velocity. At low and intermediate flow velocities, when the aperture correlation length in the main flow direction is much shorter than that in transverse direction, fingering of injection fluid is enhanced and the front tends to be unstable. When large‐aperture patches extend in main flow direction, fingering is suppressed and the front tends to be compact. Additionally, at high flow velocities, formation of thin fingers is restrained, and impacts of anisotropy on displacement process diminishes. We have conducted theoretical analyses on the interplay between capillary and viscous forces to better understand whether two‐phase flow through anisotropic fractures will exhibit fingering or a CD pattern. Key Points: Aperture field anisotropy controls displacement pattern transitions by influencing the competition between viscous and capillary forcesTheoretical analyses of the competition between viscous and capillary forces are conducted to predict displacement pattern transitionsA phase diagram incorporating anisotropy, flow rate, and viscosity ratio has been developed to predict two‐phase displacement patterns in anisotropic fractures [ABSTRACT FROM AUTHOR]

Composites were fabricated using maleic anhydride‐grafted high‐density polyethylene as the matrix material and wheat straw as the filler. Differential scanning calorimetry and rheological properties of these composites were investigated to determine the processing parameters for supercritical fluid (SCF) microcellular injection with and without gas counter pressure (GCP) technology. The impacts of different proportions and dimensions of wheat straw, along with process parameters related to GCP, were determined on both the cellular structure and mechanical characteristics of foamed injection molded components. Experimental results revealed that an increase in the ratio of wheat straw and a reduction in its size led to enhancements in both storage modulus and complex viscosity of the composites, while also improving their cell structure when foamed with SCF. By adjusting GCP process parameters, it was possible to regulate both cell morphology and mechanical properties of foamed injection molded parts. Higher GCP or longer GCP holding time resulted in increased skin thickness and tensile strength but decreased notched Izod impact strength. Highlights: Built relations between GCP technology parameters and cell morphologies.Compared the influence of wheat straw powder and GCP parameters quantitatively.Explored the correlation between cellular morphology and mechanical properties.The regulatory mechanism of cell morphology, size ratio, and distribution.GCP effectively modulates cell morphologies and mechanical properties. [ABSTRACT FROM AUTHOR]

Doublet system has been widely used in the geothermal system heat extraction, which mainly involved the hot groundwater extraction and geothermal water reinjection into the underground thermal reservoir. Many factors can influence the thermal reservoir performance, such as the production or injection mass flow rate, injection fluid temperature, and lateral well spacing. In this study, taking the specific heat capacity varying with the formation temperature, the rock porosity, and permeability variations into consideration, a three‐dimensional thermo‐hydraulic coupled numerical model was established to assess the influence of heat capacity variation with formation temperature and other correlation parameters on the sandstone and carbonate thermal reservoir performance over a period of 40 years. Results show that the influence of specific heat capacity variation on the thermal reservoir performance was less than the rock porosity variation and less than the rock permeability variation. On the other hand, the influence of the above three parameter variations is more significant on the sandstone reservoir than the carbonate formation, in which the specific heat capacity variation hardly made any difference for the carbonate thermal reservoir, but for the sandstone reservoir, the specific heat capacity and its temperature variation can yield a 1.3 K decreasing for the average output temperature and a 0.02 × 107 W decreasing for the average energy production rate over the 40 years. Finally, in this case, the temperature and energy production rate from the production well is higher after considering the rock porosity variation no matter for the sandstone or the carbonate. But the result may be opposite after changing the initial and boundary conditions or parameter selection. The influence of rock permeability variation on the thermal reservoir performance was also studied, which can produce a decreasing 10.1 K for the average output temperature and 0.19 × 107 W for the energy production rate over the 40 years. [ABSTRACT FROM AUTHOR]

In areas of induced seismicity, earthquakes can be triggered by stress changes due to fluid injection and static deformation from fault slip. Here we present a method to distinguish between injection‐driven and earthquake‐driven triggering of induced seismicity by combining a calibrated, fully coupled, poroelastic stress model of wastewater injection with interpretation of a machine learning algorithm trained on both earthquake catalog and modeled stress features. We investigate seismicity from Paradox Valley, Colorado as an ideal test case: a single, high‐pressure injector that has induced thousands of earthquakes since 1991. Using feature importance analysis, we find that injection‐driven earthquakes are approximately 22± $\pm $5% of the total catalog but act as background events that can trigger subsequent aftershocks. Injection‐driven events also have distinct spatiotemporal clustering properties with a larger b‐value, closer proximity to the well, and earlier occurrence in the injection history. Generalization of our technique can help characterize triggering processes in other regions where induced seismicity occurs. Plain Language Summary: The Paradox Valley Unit, Colorado in the central United States has had a remarkable increase in seismicity coincident with over 8 million cubic meters of brine fluid injection since 1991, inducing thousands of earthquakes within an aquifer 4.5 km below the surface. We use a physics‐based model of the Earth combined with statistical and machine learning techniques to help discern which earthquakes are triggered by other earthquakes and which earthquakes are directly triggered by the stress changes from the well as well as their comparative characteristics. Discerning which earthquakes are directly caused from pressure changes due to the fluid injected by the well can inform our understanding of earthquake physics and provide useful information to operators of energy production sites. Key Points: Physics‐based models with interpretable machine learning can identify likely triggering mechanism of earthquakes within an induced sequenceWith this technique, we show that only 22土5% of earthquakes in Paradox Valley are primarily injection‐drivenInjection‐driven events have a larger b‐value, are closer to the well, and occur earlier in the injection history [ABSTRACT FROM AUTHOR]

Soft robots typically involve manual assembly of core hardware components like actuators, sensors, and controllers. This increases fabrication time and reduces consistency, especially in small-scale soft robots. We present a scalable monolithic fabrication method for millimeter-scale soft-rigid hybrid robots, simplifying the integration of core hardware components. Actuation is provided by soft-foldable polytetrafluoroethylene film-based actuators powered by ionic fluid injection. The desired motion is encoded by integrating a mechanical controller, comprised of rigid-flexible materials. The robot's motion can be self-sensed using an ionic resistive sensor by detecting electrical resistance changes across its body. Our approach is demonstrated by fabricating three distinct soft-rigid hybrid robotic modules, each with unique degrees of freedom: translational, bending, and roto-translational motions. These modules connect to form a soft-rigid hybrid continuum robot with real-time shape-sensing capabilities. We showcase the robot's capabilities by performing object pick-and-place, needle steering and tissue puncturing, and optical fiber steering tasks. This work introduces a fabrication method for mechanically controllable, self-sensing soft-rigid hybrid robots. Translational, bending, and roto-translational modules are designed and assembled as a continuum robot with real-time shape-sensing. [ABSTRACT FROM AUTHOR]

Summary: A new mixed nonlocal finite element framework is developed for nonlinear thermo‐poro‐elasto‐plastic simulation of porous media with multiphase pore fluid flow and thermal coupling. The solid‐fluid interaction is accounted for using the mixture theory of Biot based on the volume fractions concept. Different sources of nolinearities arising from the multiphase fluid flow effects, advective‐diffusive heat transfer, inelastic deformation, fluid flux injection induced mechanical tractions, solid skeleton deformation permeability dependence, and temperature dependent viscosity are included in developing a robust numerical solver for the targeted coupled multiphysics problem. To address the effect of microstructure in inelastic localized deformation behaviour with dilational softening, a nonlocal plasticity model is proposed based on a characteristic length scale which rectifies the non‐physical pathological mesh dependence problem encountered in conventional plasticity. The accuracy and strength of the developed model is shown with comparing the obtained numerical results of a benchmark bilateral compression test with existing published data in the literature. To show the versatility and robustness of the developed computational framework in modelling the geomechanics of real‐case engineering practices, large scale thermo‐hydro‐mechanical (THM) subsurface stimulation processes with applications in enhanced oil recovery (EOR) are effectively simulated and the targeted enhanced recovery and performances are demonstrated. The current formulation does not include phase transformation modelling capability, and therefore, the developed models may not be applicable for simulation of the engineering processes that involve phase change behaviour (e.g., steam injection). [ABSTRACT FROM AUTHOR]

Background: Regional anaesthesia education, especially for ocular procedures, necessitates reliable surgical training models. While cadaveric models offer anatomical fidelity, conventional embalming methods may compromise tissue integrity. We aimed to assess the effectiveness of Thiel cadavers for training in sub-Tenon's blocks by evaluating ocular tissues and measuring insertion forces. Methods: Experimental design, using twenty eyes from ten Thiel cadaver heads. These cadavers were specifically prepared to test the administration of sub-Tenon's blocks. The research was conducted in a controlled laboratory setting appropriate for handling cadaveric materials and conducting precise measurements. Each cadaver eye underwent an initial ultrasound examination, and its axial length was noted. An intravitreal injection of heptastarch solution followed, to re-establish the eye's sphericity. After this volume injection, the axial length and intraocular pressure were measured again. Mock sub-Tenon's blocks were administered in 2 separate quadrants of the eye, with insertion forces measured using a pressure gauge. These were compared to a data set of insertion forces measured in a series of isolated pig's eyes on which STBs had been performed. Main outcome measurements were macroscopic assessment of the ocular tissue layers and the insertion forces required for the sub-Tenon's blocks. In a second set of 10 Thiel cadaver heads, 5 ml of sodium chloride were injected as sub-Tenon's blocks and the emergence of a periocular "T-sign" ascertained and measured by ultrasound. Results: Four of twenty eyes (20%) retained near-natural sphericity, with the remaining requiring volume injection to approximate physiological shape and pressure. The conjunctiva and Tenon's layer were intact, and correct cannula placement was achieved in all cases. In 16 of 20 eyes where T-signs could be measured, the median thickness of the T-sign amounted to 2.72 mm (range 1.34 mm–5.28 mm). The average maximum cannula insertion force was 2.92 Newtons. Insertion forces in intact Thiel cadaver heads were consistently higher than in isolated pig's eyes (3.6 N vs 2.0 N). Conclusion: These findings suggest that Thiel cadavers are a promising model for training in sub-Tenon'sblocks, despite the challenge of often desiccated and involuted eyes. Key points: • Thiel cadaver eyes were evaluated as training model for sub-Tenon's blocks for the first time • The cadaver eyes were often involuted and required fluid injection to reproduce physiological bulbar tonus • The ocular tissues and anatomical layers were well preserved • T-signs as a hallmark of successful sub-Tenon's block can be ascertained in Thiel cadaver eyes • Dynamic insertion forces were measured during cannula placement and can be used as reference for future studies comparing haptics of different models by an objective measure-insertion force. [ABSTRACT FROM AUTHOR]

The development of low-permeability and tight oil reservoirs is challenged by insufficient natural energy and rapid production decline. Fracturing-flooding is a technique that relies on high-pressure and large-volume fluid injection to replenish reservoir energy, making it a significant method for rapidly boosting formation energy. To evaluate the energy replenishment effect of fracturing-flooding technology in low-permeability and tight reservoirs, this study proposes a semi-analytical method for quick calculation. This approach employs dimensionless simplification, Pedrosa's substitution, Laplace transformation, and Stehfest inversion methods to derive pressure solutions for both the stimulation region and the external matrix region, each with varying flow capacities. The average formation pressure (AFP) of the reservoir is determined using the area-weighted average method, and numerical verification is performed using a commercial simulator. A case study from the Binnan area, along with a sensitivity analysis, demonstrates that after 30 days of fracturing-flooding, the AFP of the reservoir increases to 46.97 MPa, the corresponding reservoir pressure coefficient rises from 1.2 to 1.68, and reservoir energy increases by 40%. The factors influencing energy replenishment are ranked as follows: reservoir thickness, injection rate, stress sensitivity coefficient, matrix permeability, stimulation region radius, and mobility ratio. This study provides theoretical guidance for optimizing fracturing-flooding development schemes in low-permeability and tight oil reservoirs and offers valuable reference for the industry. [ABSTRACT FROM AUTHOR]

An enhanced geothermal system (EGS) is a crucial method for extracting geothermal resources. Enhancing the efficiency and recovery capacity of EGS hinges on the essential use of temporary plugging and diversion fracturing technology. Consequently, studying the migration patterns of temporary plugging agents within hot dry rock (HDR) fractures is crucial. However, existing research on the movement of temporary plugging agents in HDR fractures often neglects the influence of ambient temperature changes. These variations significantly impact the degradation and migration of particles. This study uses computational fluid dynamics and the discrete element method to analyze how changes in the ambient temperature field affect the temperature within fractures and the movement of temporary plugging agents. The study introduces three dimensionless numbers: dimensionless temperature change T, dimensionless time t, and dimensionless position X, to evaluate the migration behavior of temporary plugging agents. It also explores the effects of temporary plugging fracturing fluid injection rate, viscosity, and branch fracture structure on the migration of temporary plugging agents. Results indicate that when t = 2 and X = 1, the temperature change T without considering HDR temperature field changes is 13.55%; with temperature field changes, T is 7.44%, resulting in a simulation difference of 82.12%; Within the simulation parameter range, as the injection rate of temporary plugging fracturing fluid increases, the dimensionless temperature change T decreases; as the viscosity of temporary plugging fracturing fluid increases, the dimensionless temperature change T initially decreases and then stabilizes; the branch fracture structure has a great influence after the branch. [ABSTRACT FROM AUTHOR]

Fluid injection into subsurface reservoirs may cause existing faults/fractures to slip seismically. To study the effect of temperature on injection-induced fault slip, at a constant confining pressure of 10 MPa, we performed a series of injection-induced shear slip experiments on critically stressed sandstone samples containing saw-cut fractures (laboratory-simulated faults) under varying fluid pressurization rates (0.1 and 0.5 MPa/min, respectively) and temperatures (25, 80, and 140 °C, respectively). At 25 °C, slow fault slip events with a peak slip velocity of about 0.13 μm/s were observed on a tested sample in response to a low fluid pressurization rate of 0.1 MPa/min. In contrast, fluid injection with a high pressurization rate of 0.5 MPa/min caused fault slip events with a peak slip rate up to about 0.38 μm/s. In response to a given fluid pressurization rate, several episodes of slip events with a higher slip velocity were induced at an elevated temperature of 140 °C, indicating an appreciable weakening effect at elevated temperatures. We also experimentally constrained the rate-and-state frictional (RSF) parameters at varying effective normal stresses and temperatures by performing velocity-stepping tests. The obtained RSF parameters demonstrate that for a relatively high normal stress, increasing temperature tends to destabilize fault slip. Post-mortem microstructural observations reveal that elevated temperatures promote the generation of abundant fine-grained gouge particles associated with injection-induced shear slip. Our experiments highlight that injection-induced fault slip is affected by temperature-related wear production over the fault surface. [ABSTRACT FROM AUTHOR]

Introduction Intraosseous (IO) infusion, the pressurized injection of fluids into bone through a catheter, is a life-preserving resuscitative technique for treating trauma patients with severe hemorrhage. However, little is known regarding the application times, placement accuracy, and end-user ratings of battery-powered and manual IO access devices. This study was specifically designed to fill these knowledge gaps on six FDA-approved IO access devices. Materials and Methods Three experienced U.S. Navy Emergency Medicine residents each placed commercially available 15-gauge IO catheters in cadaveric swine (Sus scrofa) proximal humeri and sternums in a randomized prospective experimental design. Devices included the battery-powered EZ-IO Rapid Infuser and the manual Jamshidi IO, PerSys NIO, SAM Manual IO, Tactical Advanced Lifesaving IO Needle (TALON), and PYNG First Access for Shock and Trauma 1 (30 trials per device, 10 per user, 210 total trials). Application times, placement accuracy in medullary (zone 1) and trabecular (zone 2) bone while avoiding cortical (zone 3) bone, and eight subjective user ratings were analyzed using ANOVA and nonparametric statistics at P  < .05. Results The EZ-IO demonstrated the fastest application times, high rates in avoiding zone 3, and the highest user ratings (P  < .0001). The TALON conferred intermediate placement times, highest rates of avoiding zone 3, and second-highest user ratings. The SAM Manual IO and Jamshidi performed poorly, with mixed results for the PerSys NIO and PYNG First Access for Shock and Trauma 1. Conclusions The battery-powered EZ-IO performed best and remains the IO access device of choice. The present findings suggest that the TALON should be considered as a manual backup to the EZ-IO. [ABSTRACT FROM AUTHOR]

It is suggested that in addition to seismicity deep fluid injection may cause surface uplift and subsidence in oil and gas‐producing regions. This study uses the Raton Basin as an example to investigate the hydromechanical processes of surface uplift and subsidence during wastewater injection. The Raton Basin, in southern central Colorado and northern central New Mexico, has experienced wastewater injection related to coalbed methane and gas production starting in 1994. In this study, we estimate the extent and magnitude of total vertical deformation in the Raton Basin from 1994 to 2020 and incremental deformation between the years 2017 to 2020. Results indicate a modeled uplift as much as 15 cm occurring between 1994 and 2020. Between 2017 and 2020, up to 3 cm of uplift occurred, largely near the northwestern injection wells. Most modeled uplift between 1994 and 2020 occurred near the southern wells, where the greatest cumulative volume of wastewater was injected. However, modeled subsidence occurred around the southern and eastern wells between 2017 and 2020, after the rate of injection decreased. Modeling indicates that while the magnitude of modeled uplift corresponds to cumulative injection volume and maximum rate in the long‐term, short‐term incremental deformation (uplift or subsidence) is controlled by changes in the rate of injection. The number of yearly earthquake events follows periods of rapid modeled uplifting throughout the Basin, suggesting that measurable surface deformation may be caused by the same injection‐induced pore pressure perturbations that initiate seismicity. [ABSTRACT FROM AUTHOR]

Stimulating long and persistent fractures from multiple perforations in horizontal wells plays a vital role in enhancing the recovery of hydrocarbons from unconventional reservoirs. However, interaction among fractures may lead to dramatic nonuniformity, but the mechanism that drives the competition still eludes explanation. We proposed an improved two‐dimensional discrete element model to simulate fluid competition and stress interaction among perforations in the same fracturing stage. The fluid partitioning is implemented by dynamically dividing the injected fluid into different perforations to maintain pressure consistency and fluid conservation. The model is validated by comparing the induced stress, fracture aperture, and the evolution of the fracture height and the injection pressure with theoretical models. The influences of the perforation friction, fluid viscosity and injection rate are examined systematically. Simulation results reveal that fluid competition tends to stimulate one dominant fracture with other perforations suppressed. The effect of increasing the perforation friction for promoting the fluid partitioning is not remarkable while using more viscous fracturing fluid helps to initiate more fractures at the perforations. With a higher injection rate all fractures can propagate to the borders but the asymmetrical fracture pattern cannot be avoided. Four typical fracture patterns are distinguished by changing operational parameters. [ABSTRACT FROM AUTHOR]

Altered minerals introduced by water-rock reactions during geothermal energy recovery may play a role in the frictional properties of fault gouges, perhaps inducing earthquakes. Based on the geological conditions of potential geothermal reservoirs in northeastern Shenzhen, this paper considers the critical pore pressure (about 50 MPa) and critical effective normal stress (about 20 MPa), which may lead to reactivation of the Henggang-Luohu fault zone due to fluid injection into a potential geothermal reservoir at a buried depth of about 2.5 km with the temperature of 150 °C. Under such hydrothermal conditions (50 MPa fluid pressure and 150 °C), thermodynamic calculations suggest that the reaction of Yanshanian granular granite and water, at equilibrium, can produce silica, kaolinite, and chlorite at a mass ratio of 16:7:2. Here we report 19 direct shear experiments performed on simulated fault gouges consisting of the binary mixture of silica + granite, kaolinite + granite, and chlorite + granite, and the multivariate mixture of silica + kaolinite + chlorite + granite, to investigate the effects of altered minerals on frictional properties of simulated granite fault gouges. Velocity stepping experiments were conducted on the wet samples with 10% water content at an initial normal stress of 20 MPa under drained conditions at room temperature. On this basis and together with acoustic emission observation and microstructural analysis, we discussed the likely mechanism responsible for the observed behavior. The results show that, for the presence of a single altered mineral, silica has little effect on the friction coefficient, though it contributes to velocity weakening and even stick-slip events. Whereas, clay minerals can significantly decrease the friction coefficient, though they have a contribution to velocity strengthening. For the presence of a mixture of silica + kaolinite + chlorite, clay minerals play a dominant role in controlling frictional properties of the simulated fault gouges: altered minerals can also significantly decrease the friction coefficient and contribute to velocity strengthening. Development of R1 shear planes was observed using microstructural analysis for the simulated granite fault gouges consisting of 0% or 33% of the altered minerals, while the R1 shear plane cannot be observed anymore in the sample consisting of 67% of the altered minerals. The number of acoustic emission events decreases significantly when the content of the altered minerals is 33%~67%. This may indicate a transition in the deformation mechanism from brittle to semi-plastic. Our study suggests that if geothermal energy recovery is carried out in northeastern Shenzhen, the fluid injection pressure should be controlled to avoid the slip of the fault. [ABSTRACT FROM AUTHOR]

Fracture/fault instability induced by fluid injection in deep geothermal reservoirs could not only vary the reservoir permeability but also trigger hazardous seismicity. To address this, we conducted triaxial shear experiments on granite fractures with different architected roughnesses reactivated under fluid injection, to investigate the controls on permeability evolution linked to reactivation. Our results indicate that the fracture roughness and injection strategies are two main factors affecting permeability evolution. For fractures with different roughnesses, a rougher fracture leads to a lower peak reactivated permeability (kmax), and varying the fluid injection strategy (including the confining pressure and injection rate) has a less impact on kmax, indicating that the evolution of permeability during fluid pressurization is likely to be determined by the fracture roughness along the shear direction. Both the fracture roughness and injection strategies affect the average rates of permeability change and this parameter also reflects the long-term reservoir recovery. Our results have important implications for understanding the permeability evolution and the injection-induced fracture/fault slips in granite reservoirs during the deep geothermal energy extraction.

This study is important for the fields of pharmaceutical nano-drug suspension, biomedical engineering, pressure surges and food processing systems. The slip condition is necessary for polishing internal cavities and artificial heart valves in a variety of manufactured objects, micro- or nano-channels, and applications. Low Reynolds number (Re → 0) and long wavelength (δ ≪ 1) considerations are used in the formulation of the mathematical model at low non-Newtonian parameter values, nonlinear boundary conditions and the governing nonlinear equation are analytically solved using the perturbation method. The graphs of frictional force, pressure rise, velocity, pressure gradient, and streamline graphs are done using Wolfram MATHEMATICA software. In this paper, we compared the results of the total slip condition with those of the first-order slip condition and the absence of any slip effects. It has been noticed that increasing the suction and injection parameters leads to a decrease the pressure rate with complete slip effects, partial slip effects and no slip effects. We show that an increase in the third grade fluid parameter Γ increases the magnitude of axial velocity. From a physical perspective, it shows the shear thinning characteristic, which causes a decrease in viscosity and an increase in fluid velocity. Frictional force behaves differently when compared to pressure rate. In other words, the pressure gradient acts as an obstacle to the peristalsis-driven flow. The objective of the study is to find the impact of the peristaltic flow phenomena and the impact of peristaltic on third-grade non-Newtonian fluid where the suction and injection are prevailing which is similar to the thing in biomechanical devices, like blood vessels, etc. there is a change of oxygen and carbon dioxide from the tissue layer to the fluid within the blood vessel. [ABSTRACT FROM AUTHOR]

Horizontal well fracturing in the roof of coal seams has been demonstrated to be an effective technique for extracting coalbed methane. However, the mechanism of hydraulic fracturing fracture expansion from roof to coal seam and penetrating the interlayer in multiple stage fracturing is not comprehensive. Mechanical properties of the reservoir, fracturing parameters, and fracturing mode are the mainly factors that influence extraction efficiencies. To explain the relationship between fracturing behaviors and coal, the interlayer and roof along with the fracture propagation and penetration in multiple stages of fracturing; the interaction mechanism of fracture propagation; and penetration with elastic modulus, injection velocity, and fluid viscosity are simulated in single and staged fracturing. Additionally, the effect of the fracturing mode on fracture propagation is considered. The results show that the coal seam strength dominantly influences longitudinal fracture propagation while marginally affecting circumferential stress. Significant modulus differences between coal-rock interlayers and coal seams hinder fracture propagation. In the case of a low injection rate and fluid viscosity, increasing the injection rate and fluid viscosity can help enlarge the fracture area and facilitate penetration. Multistage fracturing and its high injection rates are conducive to maximizing the efficiency of fracturing operations. These results contribute to understanding and optimizing hydraulic fracturing in coal seams for efficient coalbed methane extraction. [ABSTRACT FROM AUTHOR]

The rapid expansion of reservoir fractures and the enlargement of the area affected by working fluids can be accomplished solely through fracturing operations of oilfield working fluids in geological reservoirs. Supercritical CO2 is regarded as an ideal medium for shale reservoir fracturing owing to the inherent advantages of environmental friendliness, excellent capacity, and high stability. However, CO2 gas channeling and complex propagation of fractures in shale reservoirs hindered the commercialization of Supercritical CO2 fracturing technology. Herein, a simulation method for Supercritical CO2 fracturing based on cohesive force units is proposed to investigate the crack propagation behavior of CO2 fracturing technology under different construction parameters. Furthermore, the shale fracture propagation mechanism of Supercritical CO2 fracturing fluid is elucidated. The results indicated that the propagation ability of reservoir fractures and Mises stress are influenced by the fracturing fluid viscosity, fracturing azimuth angle, and reservoir conditions (temperature and pressure). An azimuth angle of 30° can achieve a maximum Mises stress of 3.213 × 107 Pa and a crack width of 1.669 × 10−2 m. However, an apparent viscosity of 14 × 10−6 Pa·s results in a crack width of only 2.227 × 10−2 m and a maximum Mises stress of 4.459 × 107 Pa. Additionally, a weaker fracture propagation ability and reduced Mises stress are exhibited at the fracturing fluid injection rate. As a straightforward model to synergistically investigate the fracture propagation behavior of shale reservoirs, this work provides new insights and strategies for the efficient extraction of shale reservoirs. [ABSTRACT FROM AUTHOR]

Conventional fracturing design generally only considers the propagation of a single fracture in homogeneous storage, but the heterogeneity characteristics of the reservoir and the development of complex natural fractures will affect the fracturing effect. In order to study the horizontal well fracture propagation law under the synergistic effect of complex natural fracture reservoir heterogeneity, the globally embedded cohesive element finite model is established, and the heterogeneous reservoirs are built by Python programming. The influencing factors of multi-fracture propagation with heterogeneous reservoirs are analyzed, including the in situ stress difference, the injection rate of fracturing fluid, the perforation spacing, and the perforating clusters number. The results show that the heterogeneity and the natural fracture of the reservoir will affect the in situ stress distribution and propagation direction. When the in situ stress difference is low, the reservoir heterogeneity and natural fractures have a great influence on the fracture morphology. With the increase in injection rate, the fracture length and fracture width increase. With the in situ stress difference increase, the fracture deflection angle decreases. With the increase in fracturing fluid injection rate, the fracture length increases. The number of hydraulic fractures communicating with natural fractures increases with the natural fracture number and the number of perforation clusters under the synergistic effect of complex natural fracture and reservoir heterogeneity. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing, especially pulse hydraulic fracturing, is an important method for extracting oil and gas from low-permeability reservoirs, improving recovery rates significantly. Pulse hydraulic fracturing, which involves varying injection rates to create pressure waves, outperforms traditional constant-flow fracturing methods significantly. However, during pulse hydraulic fracturing operations, the flow properties of the fluid in the column change from moment to moment. Furthermore, current research on pulse hydraulic fracturing primarily focuses on vertical wells, while horizontal wells have become a common operational strategy. Therefore, a transient flow model of fluid within a horizontal well, considering variable-flow injection and unsteady friction conditions, is established in this paper. The model is solved using both the characteristic line method and the finite difference method. The hydrodynamic properties of the fracturing fluid were analyzed, and the propagation mechanisms of pressure waves within horizontal wells under various fluid injection schemes and well depths are analyzed to provide a reference for selecting appropriate fluid injection schemes in engineering practice. The study highlights the impact of fluid viscosity and injection flow amplitude on bottomhole pressure fluctuations, advancing the efficient development of low-permeability oilfields. [ABSTRACT FROM AUTHOR]

In order to analyse the effect of the injection point size of the CBM (Coalbed Methane) well level monitor on the amplitude and frequency of pressure pulsations in the wellhead manifold, numerical simulations and experiments were carried out to investigate the effect of different injection point sizes on the amplitude and frequency of pressure pulsations downstream of the sudden expansion structure. Using compressed air as the fluid and the size of the injection point as the variable, the amplitude and frequency of pressure pulsations at different locations downstream of the sudden expansion structure were tested. The results show that the pressure pulsation amplitude is affected by the size of the injection point, and the larger the injection point is, the larger the pressure pulsation amplitude is; the size of the injection point has less influence on the pressure pulsation frequency downstream of the protruding and expanding structure, and the pressure pulsation frequency at 0.5 m and 1 m downstream of the protruding and expanding structure is in the vicinity of 76 Hz. Therefore, the echo signal processing should be filtered around this frequency to obtain accurate liquid level echo signals, so as to improve the accuracy of liquid level monitoring and realise the efficient development of coalbed methane wells. [ABSTRACT FROM AUTHOR]

The spatiotemporal evolution of earthquakes induced by fluid injections into the subsurface can be erratic owing to the complexity of the physical process. To effectively mitigate the associated hazard and to draft appropriate regulatory strategies, a detailed understanding of how induced seismicity may evolve is needed. In this work, we build on the well-established continuous-time random walk (CTRW) theory to develop a purely stochastic framework that can delineate the essential characteristics of this process. We use data from the 2003 and 2012 hydraulic stimulations in the Cooper Basin geothermal field that induced thousands of microearthquakes to test and demonstrate the applicability of the model. Induced seismicity in the Cooper Basin shows all the characteristics of subdiffusion, as indicated by the fractional order power-law growth of the mean square displacement with time and broad waiting-time distributions with algebraic tails. We further use an appropriate master equation and the time-fractional diffusion equation to map the spatiotemporal evolution of seismicity. The results show good agreement between the model and the data regarding the peak earthquake concentration close to the two injection wells and the stretched exponential relaxation of seismicity with distance, suggesting that the CTRW model can be efficiently incorporated into induced seismicity forecasting. [ABSTRACT FROM AUTHOR]

Hydraulic stimulation is a critical process for increasing the permeability of fractured geothermal reservoirs. This technique relies on coupled hydromechanical processes induced through pressurized fluid injection into the rock formation. The injection of fluids causes poromechanical stress changes that can lead to fracture slip and shear dilation, as well as tensile fracture opening and propagation, so-called mixed-mechanism stimulation. The effective permeability of the rock is particularly enhanced when new fractures connect with pre-existing fractures. While hydraulic stimulation can significantly improve the productivity of fractured geothermal reservoirs, the process is also related to induced seismicity. Hence, understanding the coupled physics is central, for both reservoir engineering and seismic risk mitigation. This article presents a modelling approach for simulating the deformation, propagation and coalescence of fractures in porous media under the influence of anisotropic stress and fluid injection. It uses a coupled hydromechanical model for poroelastic, fractured media. Fractures are governed by contact mechanics and a fracture propagation model. For numerical solutions, we employ a two-level approach, combining a finite volume method for poroelasticity with a finite element method for fracture propagation. The study investigates the impact of injection rate, matrix permeability and stress anisotropy on stimulation outcomes. This article is part of the theme issue 'Induced seismicity in coupled subsurface systems'. [ABSTRACT FROM AUTHOR]

Enhanced geothermal systems (EGSs) developed by hydraulic stimulation are promising for exploiting petrothermal heat by improving fluid pathways in low-permeable geothermal reservoir rocks. However, fluid injection into the subsurface can potentially cause large seismic events by reactivating pre-existing faults, which is a significant barrier to EGSs. The management of injection-induced seismicity is, therefore, essential for the success of EGSs. During the hydraulic stimulation of an EGS, fluid can be injected into a fault zone or into the rock matrix containing pre-existing faults adjacent to the injection well. The differences in hydromechanical responses between fluid injection into and adjacent to a fault have not been investigated in detail. Here, we performed triaxial fluid injection experiments involving injecting fluid directly and indirectly into a fault in granite rock samples to analyse the distinct hydromechanical responses and estimate the injection-induced seismicity in both cases. Our results suggest that in addition to directly injecting fluid into a critically stressed fault, injecting into nearly intact granite adjacent to the fault could also cause injection-induced seismic hazards owing to the high fluid pressure required to create new fractures in the granite matrix. It is, therefore, important to carefully identify pre-existing faults within tight reservoirs to avoid injecting fluid adjacent to them. Additionally, once prior unknown faults are delineated during hydraulic stimulation, appropriate shut-in strategies should be implemented immediately to mitigate seismic risks. This article is part of the theme issue 'Induced seismicity in coupled subsurface systems'. [ABSTRACT FROM AUTHOR]

This article discusses the phenomenon of induced seismicity, which refers to the human-caused generation of tremors and seismic events that alter the state of subsurface stresses. The occurrence of induced seismicity during subsurface technologies, such as shale gas development and renewable energy extraction, can lead to project delays and concerns about safety and environmental impact. The article highlights the need to understand the mechanisms of induced seismicity and develop strategies to minimize its effects. It presents a collection of research papers that explore fluid-induced seismicity in various energy production and storage technologies, offering insights into the interplay between fluid injection, fault behavior, and subsurface structures. The findings contribute to evidence-based policymaking and regulatory processes, supporting the development of sustainable subsurface operations for renewable energy and decarbonization technologies. [Extracted from the article]

We examine the temporal evolution of sequences of induced seismicity caused by long-term fluid injection using a compilation of over 20 case studies where moderate magnitude (M > 3.0) induced events have been recorded. We compare rates of seismicity with injection rates via the seismogenic index and seismic efficiency parameters, computing both cumulative and time-windowed values. We find that cumulative values tend to accelerate steeply as each seismicity sequence initiates—most cases reach a value that is within 0.5 units of their maximum value within 1–3 years. Time-windowed values tend to increase to maximum values within 25%–35% of the overall sequence, before decreasing as levels of seismicity stabilize. We interpret these observations with respect to the pore pressure changes that will be generated in highly porous, high permeability reservoirs. In such situations, the rate of pore pressure change is highest during the early phases of injection and decreases with time. If induced seismicity scales with the rate of deformation, which in turn is controlled by the rate of pore pressure change, then it is to be expected that induced seismicity is highest during the early phases of injection, and then decreases with time. This article is part of the theme issue 'Induced seismicity in coupled subsurface systems'. [ABSTRACT FROM AUTHOR]

Intraplate earthquakes induced by anthropogenic fluid injection present unexpected seismic risk to previously quiescent or low seismicity-rate regions. Despite many studies of induced seismicity, there are relatively few with detailed openly accessible constraints on the interaction between seismic sources and subsurface structures. In this study of the Raton Basin, we refine source observations from a dense nodal array and constrain basin structure using teleseismic receiver functions. The cross-correlation-based relocated hypocentres and a new set of focal mechanisms light up active fault segments and show clear spatiotemporal patterns. The geometric complexity of reactivated fault clusters appears greatest near higher rate injection wells. Simpler normal fault structure is found farther from injection wells and near abrupt structural transitions suggested by receiver functions. While less induced seismicity in the crystalline basement is expected when injection is >1 km from the top of the basement (like Raton), our receiver function analysis identified a basin thickness ~3 km beneath the nodal array and lateral variations in sedimentary structures. Our results explain potential fluid connectivity between the injection depths focused at ~1–1.5 km below the surface and basement fault activity that begins at ~3 km and reaches peak activity at ~4–8 km depths. This article is part of the theme issue 'Induced seismicity in coupled subsurface systems'. [ABSTRACT FROM AUTHOR]

Induced seismicity poses a challenge to the development of Enhanced Geothermal Systems (EGS). Improving monitoring and forecasting techniques is essential to mitigate induced seismicity and thereby fostering a positive perception of EGS projects among local authorities and population. Induced seismicity is the result of complex and coupled thermo-hydro-mechanical-chemical mechanisms. Injection flux and pressure are crucial controlling parameters for both hydraulic stimulation and circulation protocols. We develop a methodology combining a hydro-mechanical model with a seismicity rate model to estimate the magnitude and frequency of mainshocks and aftershocks induced by fluid injection. We apply the methodology to the case of the Basel EGS (2006, Switzerland) to compare the effects of progressive, cyclic and constant injections on the mechanical response of discrete faults. Results from the coupled hydro-mechanical models show that the pore pressure diffusion and consequent enhancement of fault permeability are limited to the vicinity of the injection well during cyclic injection. Additionally, constant injection induces seismicity from the start of the injection but enhances the permeability of most of the faults within a shorter duration, inducing less post-injection seismicity. The methodology can be adapted to any numerical model and allows new projects to be developed by anticipating the safest injection protocol. This article is part of the theme issue 'Induced seismicity in coupled subsurface systems'. [ABSTRACT FROM AUTHOR]