Fluid Injection Research Articles

A New Development of Cross-Correlation-Based Flow Estimation Validated and Optimized by CFD Simulation

The accurate measurement of mass flow rates is important in nuclear power plants. Flow meters have been invented and widely applied in several industries; however, the operating environment in advanced nuclear power plants is especially harsh due to high temperatures, high radiation, and potentially corrosive conditions. Traditional flow meters are largely limited to deployment at the outlet of pumps, on pipes, or in limited geometries. Cross-correlation function (CCF) flow estimation, on the other hand, can estimate the flow velocity indirectly without any specific instruments for flow measurement and in any geometry of the flow region. CCF flow estimation relies on redundant instruments, typically temperature sensors, in series in the direction of flow. One challenge for CCF flow estimation is that the accuracy of the flow measurement is mainly determined by inherent, common local process variation across the sensors, which may be small compared to the uncorrelated measurement noise. To differentiate the process variations from the uncorrelated noise, this research implements periodic fluid injection at a different temperature than the bulk fluid before the temperature sensors to amplify process variation. The feasibility and accuracy of this method are investigated through flow loop experiments and Computational Fluid Dynamics (CFD) simulations. This paper focuses on a CFD simulation model to verify the previous experimental results and optimize CCF flow estimation with different configurations. The optimization study is carried out to perform a grid search on the optimal location of the sensor pair under different flow rates. The CFD results show that the optimal sensor spacing depends on the flow rate being measured and provides guidance for sensor location implementation under various anticipated flow rates.

A regularized-interface method as a unified formulation for simulations of high-pressure multiphase flows

The injection of multi-species fluids into high-pressure and high-temperature environments beyond the species' critical points is commonly found in engineering applications. At these conditions, for immiscible species, both subcritical interfacial dynamics and supercritical mixing can coexist due to variations in temperature around the mixture critical point. The modeling of these complex transcritical phenomena for large-scale configurations is so far not possible. To address this issue, we propose the Regularized-Interface Method (RIM) as a unified formulation that can describe both sub- and supercritical processes as well as the transition between them. The proposed method is derived via filtering of the nanoscale interface-resolving formulation based on van der Waals' linear gradient theory. Thus, this approach allows for the consistent modeling of interfacial dynamics that vanishes at supercritical conditions, while significantly reducing the temporal and spatial resolution constraints of the original nanoscale formulation. The resulting RIM formulation is examined in interface-capturing simulations of sub-, trans-, and supercritical fuel injection processes, involving droplets and jets. These results highlight the importance of resolving spatio-temporal transitions from subcritical interfacial dynamics to supercritical mixing in high-pressure multiphase simulations, in contrast to commonly employed diffused-interface methods, where interfacial dynamics are often neglected.

The Formation and Pressure-Bearing Characteristics of Plugging Layers in Hydraulic Fracture: A Visualization Experimental Study

Summary Temporary plugging and diversion fracturing (TPDF) is an important means for improving the artificial fracture complexity in shale gas reservoirs. At present, most scholars’ studies on TPDF mainly focus on the formation conditions of the plugging layer in a horizontal fracture and the fracture propagation behavior after the plugging layer is formed. However, there is a lack of thorough study on the formation and pressure-bearing characteristics of the plugging layer in vertical fracture. For this paper, we conducted a plugging experiment using temporary plugging particles in a hydraulic fracture by use of a visualization hydraulic fracture experimental device to analyze the formation and pressure-bearing characteristics of plugging layers. The research results show that (1) when the ratio of temporary plugging particle diameter to fracture width (d/w) becomes larger, the fluid viscosity and injection rate have less influence on the formation of the plugging layer, and the concentration of temporary plugging particles required to form the plugging layer decreases. When d/w is equal to 0.45, the plugging layer has difficulty forming if the fluid viscosity is greater than 3 mPa·s or the mass concentration of temporary plugging particles is less than 20 kg/m3. If d/w is equal to 0.60, the plugging layer has difficulty forming when the concentration is less than 10 kg/m3. When d/w is equal to 0.75, a plugging layer forms when the concentration is 2.5 kg/m3, and the formation is not affected by the fluid viscosity and injection rate. (2) A smaller d/w, higher carrier fluid viscosity and injection rate, or lower temporary plugging particle concentration all lead to more pronounced fluctuation of the fracture flow channels at the location where the plugging layer is formed. (3) If the plugging layer can form, it is denser and has stronger plugging ability when the temporary plugging particle diameter is smaller and fluid viscosity and injection rate are larger. (4) Due to different lengths and d/w, the plugging layer can be divided into three types according to its morphological change characteristics after pressure-bearing: failure-unstable, locally-damaged, and stable-unchanged plugging layer. To improve the probability of forming the plugging layer with higher stability, the fluid with a viscosity of 3 mPa·s, in which is a temporary plugging particle with a d/w of 0.75, is recommended to plug the hydraulic fractures under an injection rate of 0.65 m3/min.

An Empirically Constrained Forecasting Strategy for Induced Earthquake Magnitudes Using Extreme Value Theory

Abstract Induced seismicity magnitude models seek to forecast upcoming magnitudes of induced earthquakes during the operation of subsurface industries such as hydraulic fracturing, geothermal stimulation, wastewater disposal (WWD), and carbon capture and storage. Accurate forecasting models could guide operational decision making in real time; for example, operations could be reduced or paused if forecast models indicate that magnitudes may exceed acceptable levels. Robust and transparent testing of forecasting models is required if they are to be adopted by operators and regulators of such industries. We develop and test a suite of models based on extreme value estimators to forecast the magnitudes of upcoming induced seismic events based on observed seismicity. We apply these models to multiple induced seismicity cases from WWD in Oklahoma and in western Texas, as well as other cases of seismicity caused by subsurface fluid injection in North America, Europe, and China. In total, our testing dataset consists of >80 individual sequences of induced seismicity. We find that all the models produce strong correlation between observed and modeled magnitudes, indicating that the forecasting provides useful information about upcoming magnitudes. However, some models are found to systematically overpredict the observed magnitudes, whereas others tend to underpredict. As such, the combined suite of models can be used to define upper and lower estimators for the expected magnitudes of upcoming events, as well as empirically constrained statistical expectations for how these magnitudes will be distributed between the upper and lower values. We conclude by demonstrating how our empirically constrained distribution can be used to produce probabilistic forecasts of upcoming induced earthquake magnitudes, applying this approach to two recent cases of induced seismicity.

Transpiration-induced convective heat transfer in ternary hybrid nanofluid flow due to dual stretching on wedge: Reverse flow analysis

Boundary layer separation is a common challenge in fluid dynamics, where flow separates from a surface due to adverse pressure gradients. Transpiration, the injection or suction of fluid through a surface, is a technique used to mitigate this issue. This study investigates transpiration’s effects on boundary layer separation over a stretching wedge conveying ternary hybrid nanoparticles, which is crucial for optimizing various engineering systems. The study establishes a mathematical model incorporating transpiration, dual stretching, viscous dissipation, and nanoparticle volume fractions. The model is reduced to ordinary differential equations using similarity transformations and then solved numerically with MATLAB’s bvp4c package. Here, the convective heat transfer increases with suction and decreases with blowing due to changes in boundary layer thickness. This insight provides valuable information for engineers seeking to control temperature gradients in their systems. Moreover, the study highlights transpiration’s efficacy in mitigating boundary layer separation induced by adverse pressure gradients. Furthermore, flow enhancement with blowing depends on specific conditions, such as the value of the blowing parameter, highlighting its nuanced influence.

Multiscale Seismic Monitoring in the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG)

Abstract The Bedretto Underground Laboratory for Geoenergies and Geosciences (BULGG) is located in south-central Switzerland in the middle of a 5.2-km-long tunnel, which connects the Bedretto valley to the Furka railway tunnel. BULGG is a multidisciplinary laboratory that facilitates experiments and research across various fields. From a seismological perspective, a dense seismic network is deployed that allows real-time monitoring of both natural and induced seismicity occurring in the tunnel and the surroundings. In addition, a multilevel monitoring approach during experiments leads to the generation of real-time high-resolution earthquake catalogs issuing event-based alerts and is the input for a simple traffic light system (magnitude and/or ground-motion based), which provides essential information for the advanced traffic-light system (probabilistic approach). We have set up two separate real-time monitoring systems that monitor the background seismicity, as well as injection experiments, with both systems built on the SeisComP framework. The background monitoring, serving as the backbone network, includes broadband sensors at the surface and along the tunnel, as well as strong-motion sensors and high-frequency geophones along the tunnel and in boreholes. The sampling rate is divergent and depends on sensor type and proximity to faults (200–2000 Hz). Acoustic emission sensors and high-frequency accelerometers sampled at 200 kHz constitute the experimental setup that locates in multiple experimental volumes, which include fluid injections, extractions, and tunneling activities. All sensors transmit real-time data to a common server (SeedLink), which serves multiple clients for processing, real-time visualization, archiving via SeisComP, and risk control via dedicated software. A standardized workflow is applied to both background and experimental monitoring, encompassing automatic picking, automatic phase association and location, and magnitude estimation. Advanced methods are implemented in real time that include double-difference relocation and earthquake detection based on waveform cross correlation. BULGG provides a unique environment to implement novel methods in observational and network seismology across scales.

Investigation of Oil Well Blowouts Triggered by Wastewater Injection in the Permian Basin, USA

AbstractAged hydrocarbon wells, if proper care is not ensured, can crack, get corroded, and leak subsurface fluids. Permian Basin in Texas, home to thousands of such wells, has seen numerous blowouts and wastewater leaks. Our study employs surface deformation derived from satellite observations, and injection well records to investigate these events. The results reveal an over‐pressurized wastewater aquifer producing a surface uplift of 20 cm/yr, likely due to wastewater being injected tens of kilometers away. Focusing on a January 2022 blowout resulting in 3 cm subsidence in 2 weeks, our geophysical model suggests aquifer over‐pressurization as the cause. With an excess pressure of over 3 MPa in the aquifer, several more such blowouts are possible in the near future. This research highlights the urgent need to better understand the impact of subsurface fluid injection and calls for prompt action to mitigate the environmental effects of oil and gas production.

Experimental and numerical analysis of injection-induced permeability changes in pre-existing fractures

This paper presents a combined laboratory and numerical investigation on the injection-induced permeability changes in pre-existing fractures. The analyses conducted were primarily based on the results of an innovative laboratory experiment designed to replicate the key mechanisms that occur during hydraulic stimulation of naturally fractured rocks and/or faulted zones. The experiment involved pressure-controlled fluid injection into a laboratory-scale pre-existing fracture within a granite block, which was subjected to true triaxial stress conditions. Rough and smooth fractures are investigated, and the results are discussed. Based on the experimental results, two contributing mechanisms were considered to describe the pressure-driven permeability changes in pre-existing fractures: (1) elastic opening/closure leading to a reversible permeability change, and (2) fracture sliding in shear mode, causing dilation and hence an irreversible permeability increase. With these assumptions, an aperture-dependent permeability function was adopted to couple the hydraulic flow with the mechanical deformations along the fracture. Subsequently, a 3D coupled hydro-mechanical model was developed to replicate fluid-injection tests conducted at various conditions, including different stress conditions and fracture surface roughness. The employed modeling framework effectively captured the experimental observations. Our results indicate that the maximum permeability increases twofold.

Efficacy of Ultrasound-Guided Injection of Platelet-Rich Plasma in Treatment of Sports-Related Meniscal Injuries

Abstract Purpose Meniscal injuries are a common occurrence in sports-related activities, often leading to pain, reduced joint function, and impaired athletic performance. This study aimed to evaluate the role of ultrasound-guided intra-articular platelet-rich plasma (PRP)-rich fluid injection which was obtained through serial centrifugation in the treatment of meniscal injuries resulting from sports activities. Materials and Methods A prospective study was conducted involving 54 cases with grade I, II, and III meniscal injuries, aged 18 and 43 years. PRP-rich fluid was prepared by subjecting autologous blood samples to a two-step centrifugation process. Patients were assessed pretreatment and at regular intervals posttreatment. Results Patients reported reduced pain and improved joint functionality following treatment. Average age of the patients was 34.4 years, and average follow-up period was 275.1 days. It is noteworthy that no cases of bilateral meniscal injuries were identified; indicating that the focus was primarily on single knee injuries. Predominance of grade II injuries suggests that the PRP intervention might be particularly effective in addressing more severe meniscal tears. Conclusion The results of our study provide compelling evidence for the positive impact of PRP augmentation in meniscus repair. Our findings indicate that PRP therapy has the potential to bring about substantial benefits for individuals with meniscus tears of the knee, particularly in terms of pain relief and enhanced functional capabilities.

An investigation on the pyrolysis of low-maturity organic shale by different high temperature fluids heating

This study evaluates the potential of oil and gas generation from thermal pyrolysis of low-maturity organic rich shales by high temperature fluids injection. This method aims to convert the solid organic matter into hydrocarbons, thereby enhancing the quality of shale oil. The effectiveness of this technique hinges on its ability to convert retained heavy compounds and kerogen into light, moveable hydrocarbons, while also improving the oil recovery factor. Our experimental findings reveal that the decrease of total organic carbon content predominantly occurs between 400–550 °C or even higher. Different heating fluid media were tested for their pyrolysis effectiveness, among the heating media tested, CO2 and steam mixture proved the most productive. A comparison of CO2, steam and CO2-steam pyrolysis experiments were carried out. It is observed that the oil yield is the lowest in a pure CO2 atmosphere, while oil yield from the mixture of CO2-steam pyrolysis is the highest. In addition, the pore structure and mechanical properties of shales during pyrolysis process are examined.This investigation provides a theoretical basis for the large-scale upgrading of organic-rich shale formations, highlighting the critical influencing factors of thermal pyrolysis in optimizing shale oil recovery and quality.

Effect of fluid patch clustering on the P-wave velocity-saturation relation: a critical saturation model

Quantitative analysis of the relationship between seismic wave velocities and fluid saturation in porous media is of great significance for any fluid injection and extraction operation in subsurface rock formations. However, seismic velocities are not only dependent on the amount of saturation, but also on the distribution of fluid patches and their size. The patch size variation during changes in saturation is oftentimes ignored in modeling studies, even though it is natural to assume that with increasing saturation, fluid patches will form larger and, at some critical saturation, percolating clusters. To capture the evolution of patch size with saturation implied in the velocity-saturation relations, we are inspired by percolation theory. By incorporating the connectivity of water-filled patches in the continuous random medium model, we develop a critical saturation model. We apply this critical saturation model to examine recently reported experimental measurements, specifically analyzing the patch size changes. For measurements of drainage or imbibition processes in four sandstone samples, we indeed find a clear indication of growing patch size with water saturation. The predictions of the critical saturation model are in reasonable agreement with observations. Our approach improves the accuracy of the interpretation of the velocity-saturation relations in partially saturated rocks and forms a basis for exploring its underlying mechanisms.

A non‐ionic green surfactant extracted from the Anabasis setifera plant for improving bulk properties of CO2‐foam in the process of enhanced oil recovery from carbonate reservoirs

AbstractFoam, as a gas‐in‐liquid colloid, has a higher appearance viscosity than the one of both gas and liquid that form it. Adjusting the mobility ratio of the injected fluid–oil system and increasing gas diffusion in the foam injection process increase oil production. With these properties, foam as an injection fluid in fractured reservoirs has a major effect on oil production from the matrixes and prevents premature production of injection fluid. Surfactants are common foaming agents in injection water. Saponins are known as plant‐derived surfactants for forming stable foam. This feature, along with its cheap price and availability, can make them candidates for enhanced oil recovery (EOR) by the foam injection method. However, the utilization of CO2 as the gaseous phase in foam introduces additional machanisms of CO2 injection to the oil recovery operations. In this assessment, a non‐ionic green surfactant derived from the Anabasis setifera plant was used as a foaming agent, while CO2 served as the gas phase. A series of surface tension tests in CO2 environment were performed to determine the optimal concentration of the surfactant. Foaming tests were performed by a designed foam generator. The produced CO2‐foam was then injected into a fractured carbonate plug with six matrixes (with one horizontal and two vertical fractures). Based on the results, the water–CO2 surface tension was reduced to 20.549 mN/m. The optimum salinity based on the foam stability was 10,000 ppm. The half‐life of the foam was determined to be 40 min. Also, the foam characterization showed that the foamability of the surfactant was favourable for increasing oil production so that by secondary flooding, an oil recovery of more than 66% was achieved from the fractured carbonate plug.

A breakdown pressure model for supercritical CO2 fracturing considering fluid infiltration effect using the point stress criterion

Precisely predicting the breakdown pressure of rock fractured by supercritical CO2 (SC-CO2) is one of the major challenges for optimize in-situ fracturing schemes. However, the influence of the infiltration effect caused by the unique properties of SC-CO2 on the fracture mechanism remains unclear, which may lead to inaccurate prediction of breakdown pressure. In this work, a pressurization rate model considering the physical properties changes of SC-CO2 is proposed to describe the relationship between the pressurization rate and the injection pressure of the fracturing fluid in a wellbore. Ultimately, combined with the pressurization rate model and the point stress criterion, a breakdown pressure model is established by considering the changes in the in-situ stress of wellbore surrounding rock, the fluid injection pressure inside the wellbore, and the pore pressure distribution. The results show that for permeable reservoirs, the breakdown pressure increases as the viscosity and injection rate of fracturing fluid increase, but it decreases with increasing rock permeability. The low viscosity and pressurization rate of SC-CO2 effectively increase the stress generated by the infiltration effect, which is negatively correlated with the breakdown pressure. In addition, the unique pressurization rate of SC-CO2 is the key factor for the abnormal breakdown pressure at different injection rates.

Reactivated Seismogenic Faults and Earthquake Source Mechanisms in the Snyder Area of Texas

Abstract Stretching across New Mexico and Texas of the United States, the greater Permian basin is composed of two subunits—the Delaware and the Midland basins. Induced seismicity in the greater Permian basin has significantly increased since 2008, which has revealed previously unmapped seismogenic structures in several geographic regions. Among them, the Snyder area of northwest Texas has a long history of oil and gas activities, resulting in a higher rate of induced seismicity. In this study, we investigated these previously unknown seismogenic structures using three main approaches: (1) relocated and delineated seismicity, (2) performed waveform moment tensor inversion to determine earthquake source mechanisms, as well as (3) conducted stress inversion to assess the stress state. The results show that the overall depth range of seismicity is 0–5.5 km and concentrated in a range of 2–3 km below mean sea level, in the top portion of the crystalline basement. As we have determined 297 source mechanisms, their collective pattern presents a mix of strike-slip and normal faulting, suggesting an extensional strain field at the edge of the Midland basin. We have identified nine significant seismogenic episodes by distinctive increases of seismic moment release in 2017–March 2024. The results also demonstrate a temporal variation of b-value spanning across the seismogenic episodes, associated with the progression of fault reactivation initiated by fluid injection.

Numerical investigation on the influence of CO2-induced mineral dissolution on hydrogeological and mechanical properties of sandstone using coupled lattice Boltzmann and finite element model

The impact of CO2-induced mineral reactions, specifically the CO2-water-rock interactions, has been widely recognized for its potential to compromise the hydrogeological and mechanical properties of porous media, thereby deteriorating their integrity and mechanical characteristics. This raises concerns regarding the safety of numerous projects such as CO2 geological storage. However, the mechanism underlying the influence of CO2-induced mineral reactions on these parameters is still not fully understood, thereby introducing uncertainty into the reliability of predicted outcomes. Direct pore-scale simulation plays a crucial role in deepening the understanding of CO2 -water-rock interaction and its associated impacts. The present study proposes a novel simulation model that integrates the lattice Boltzmann and finite element methods to simulate the dissolution of calcite in a 3D sandstone sample invaded by saturated CO2 solution, aiming to investigate the resulting evolution of hydrogeological parameters (i.e., porosity and permeability) and mechanical properties (i.e., bulk and shear moduli). The injection rates of reactive fluid (i.e., CO2 solution) were varied in the model to simulate different operational conditions of CO2 geological storage project. The simulation results demonstrate that the decrease in injection velocity inhibits the dissolution of calcite in the middle and downstream regions, concentrating it near the inlet. These distinct modes of calcite dissolution result in differentiated permeability and mechanical properties within rocks possessing identical porosity levels. In general, the increase in fluid injection velocity leads to a more pronounced enhancement in permeability and a greater attenuation in bulk and shear moduli under the same porosity. Thus, it is confirmed that the utilization of porosity is inadequate in accurately characterizing the evolution of rock permeability and mechanical properties resulting from mineral reactions. We ascertain that the application of fractal parameters, i.e., succolarity and fractal dimension, can more precisely depict the progression of permeability and bulk/shear modulus, respectively.

Permeability evolution of fluid-injection-reactivated granite fractures of contrasting roughnesses

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.

Modelling of mixed-mechanism stimulation for the enhancement of geothermal reservoirs.

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'.

Forecasting fluid-injection induced seismicity to choose the best injection strategy for safety and efficiency.

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'.

Numerical simulation study on propagation mechanism of fractures in tight oil vertical wells with multi-stage temporary plugging at the fracture mouth

The multi-stage temporary plugging and diverting fracturing technique stands as a pivotal method for enhancing production in tight oil reservoirs. At present, fracture propagation models in temporary plugging and diverting fracturing primarily focus on single-stage temporary plugging, disregarding intricate mechanisms influenced by multi-stage temporary plugging and inter-fracture interference on the redirection and propagation of artificial fractures. To address this gap, this study employs the extended finite element method and establishes a mechanical model for the propagation of multi-stage temporary plugging fractures in tight oil reservoirs based on the maximum circumferential stress criterion. Relevant numerical simulations are conducted, considering key factors such as horizontal stress differences, fracturing fluid viscosity, injection rate, and initial fracture angle, all of which influence the morphology of diversion fracture propagation. The study rigorously analyzes and compares characteristics such as the radius of diversion fractures, diversion angle, and fracture width profile corresponding to different numbers of temporary plugging stages. Numerical simulations reveal that the primary controlling factor influencing the extension of fractures is the horizontal stress difference. A smaller horizontal stress difference makes fracture diversion easier, resulting in larger redirection radii. The impact of fracturing fluid viscosity on the diversion radius and diversion angle of fractures can be deemed negligible. Larger injection rates during construction facilitate easier diversion, leading to larger diversion radii. Furthermore, when the initial fracture angle exceeds 90°, the diversion radius of fractures is significantly larger compared to cases where the initial fracture angle is less than 90°, indicating a more facile diversion of fractures.

Injection-induced basement seismicity beneath the Raton Basin: constraints from refined fault architectures and basin structure.

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'.