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We present an approach, based on cross-coupling of quadrupole and monopole borehole acoustic modes caused by anisotropy, to investigate the in situ stress state, a critical parameter for effective CO2 sequestration and for determining subsurface injection bounds in general. We focus on in situ stress states where the vertical direction is a principal stress direction, and we aim at determining the minimum and maximum horizontal stresses. Because of non-linear elastic effects, three unequal principal stresses in an otherwise isotropic rock may create three orthogonal planes of symmetry, which characterize an orthorhombic elastic medium. Near a wellbore, where the stress field is perturbed, a stress sensitive material causes material axes and moduli to form a spatial distribution to which sonic logging is sensitive. We present a method for differentiating between stress induced and intrinsic anisotropy. Using finite element modelling, we demonstrate that in either case the quadrupole fundamental mode includes an axis-symmetric (monopole) component. We demonstrate that the acoustic amplitude at the borehole centre divided by the maximum acoustic amplitude at the wellbore periphery (dominated by the acoustic profile |$\cos(2\theta)$|⁠) is an indicator of elastic anisotropy. We denote this ratio |$I_A$| and argue that |$I_A\gt 0$| when the elastic anisotropy is of entirely intrinsic origin (meaning the elastic moduli are in -sensitive to stress), and further that |$I_A$| increases for decreasing frequency for such cases. We demonstrate that |$I_A$| attains negative values for increasing frequency in stress-sensitive formations where a cross-over (from negative to positive values) is attributed to the perturbed velocity/moduli/stress fields near the wellbore. In synthetic data, we show that the ratio |$I_A$|⁠ , in combination with the phase velocity dispersion, uniquely determines the state of stress in stress-sensitive formations. In stress in-sensitive formations, we argue that |$I_A$| at lower frequencies, that is at frequencies slightly above the cut-off frequency, is very sensitive to elastic anisotropy. We argue that in quadrupole eigenmodes, evidence of intrinsic anisotropy is present at low frequencies whereas stress induced anisotropy is better gauged at moderate to high frequencies. Finally, we discuss the practical implications of these findings. [ABSTRACT FROM AUTHOR]

Dynamic material constants obtained by wave-based methods are different from their static counterparts. Constraining rock's elastic constants' dynamic-to-static ratios (Rij) are important for understanding the geomechanical properties of earth's materials, particularly in the context of hydraulic fracturing that requires the knowledge of shale's static elastic constants. Conducting experiments with dynamic and elastic constants' anisotropy, on top of their pressure dependency, properly accounted for is challenging. Here, we measure suites of dynamic and static elastic constants, with anisotropy fully accounted for, on the shale samples extracted from the Duvernay unconventional reservoir; a comprehensive set of geochemical/petrophysical measurements are obtained too. We observe that the dynamic-to-static ratios are generally not sensitive to the increasing pressures at σ  > 50 MPa; we do not find a correlation with the samples' mineral contents either. However, we find that Rij strongly correlates to the dynamic elastic constants except for the R 11. The correlation between Rij , particularly Ri3, and the dynamic elastic constants can be explained by the sedimentary rocks' compactness and the horizontal void spaces parallel to the rock's laminated bedding planes. [ABSTRACT FROM AUTHOR]

Natural fractures are effective storage spaces and the main seepage channels of tight reservoirs, and the spacing and role of structural fractures of different scales in tight reservoirs are also different. However, the opening or height of underground natural fractures is often difficult to determine directly using seismic data or imaging logging, which restricts the characterization, modeling, and analysis of the formation mechanisms of reservoir fractures. This paper uses the morphology of water absorption profiles and conventional logging data to calculate the ratio of the isotope intensity of a single well to natural gamma values from logging and characterize the types of water absorption profiles. The size (opening and height) of the fractures is closely related to the height of the water absorption profile and the fluctuation in the water absorption intensity. The calculated rock mechanics parameters along a single well, combined with the internal friction angle of the rock and the fracture strike, are used to determine the magnitude and direction of the paleostress of the Y290-Y414 Block in the southeastern Ordos Basin during the Himalayan period. By establishing a single-well geomechanical model to simulate the three-dimensional distribution of paleostress and paleostrain during the formation of fractures, a database model for constructing the scale of fractures is established. Through correlation analysis, a model for predicting the strength and thickness of the water absorption profile is established. Finally, the three-dimensional distribution pattern of the scale of structural fractures is predicted, and the reliability of the prediction results is verified using dynamic development data. The research results have certain reference significance for explaining the mechanism of fracture formation, characterizing the scale of underground fractures, and modeling reservoir fractures. Highlights: A model for predicting the height and opening of structural fractures is established. The scale of fractures is closely related to the mechanical structure of the rock layers. The presence of large-scale fractures is the main cause of water channeling and flooding. [ABSTRACT FROM AUTHOR]

Copyright of Iraqi Journal of Chemical & Petroleum Engineering is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Our research is centered on the Gandhar oil field, which was discovered in 1983, where daily oil production has declined significantly over the years. The primary objective was to evaluate the feasibility of carbon dioxide (CO2) storage through its injection into the siliciclastic reservoirs of Ankleshwar Formation. We aimed to obtain high-resolution acoustic impedance data to estimate porosity employing model-based poststack seismic inversion. We conducted an analysis of the density and effective porosity in the target zone through geostatistical techniques and probabilistic neural networks. Simultaneously, the work also involved geomechanical analysis through the computation of pore pressure and fracture gradient using well-log data, geological information, and drilling events in the Gandhar field. Our investigation unveiled spatial variations in effective porosity within the Hazad Member of the Ankleshwar Formation, with an effective porosity exceeding 25% observed in several areas, which indicates the presence of well-connected pore spaces conducive to efficient CO2 migration. Geomechanical analysis showed that the vertical stress (Sv) ranged from 55 MPa to 57 MPa in Telwa and from 63.7 MPa to 67.7 MPa in Hazad Member. The pore pressure profile displayed variations along the stratigraphic sequence, with the shale zone, particularly in the Kanwa Formation, attaining the maximum pressure gradient (approximately 36 MPa). However, consistently low pore pressure values (30–34 MPa) considerably below the fracture gradient curves were observed in Hazad Member due to depletion. The results from our analysis provide valuable insights into shaping future field development strategies and exploration of the feasibility of CO2 sequestration in Gandhar Field. [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]

Abstract Geotechnical engineering projects are often at risk from threats related to mineral dissolution and loss of particles that constitute the matrix of the geomaterial. Moreover, the impact of climate change can exacerbate these risks by accelerating the physical processes. To address such challenges, it is a pre-requisite to understand and quantify the effect of mineral dissolution on geomechanical behaviour. A general theoretical approach to mechanical consequences of geomaterials experiencing mineral dissolution was first proposed. Following, a series of oedometer tests were conducted using mixtures of salt and sand with various salt contents to observe and characterise the effect of dissolution on the mechanical behaviour of granular materials. The dissolution of salt crystals was performed in three different stress states to observe the stress-dependent response of the material. The effect of dissolution was dependent both on the amount of dissolved salt particles and the applied stress state. The laboratory experiments and the discussion followed shares insights into the effect of grain dissolution on the mechanical behaviour of granular materials and proved the potential of the framework presented in this paper. Finally, the paper ends by discussing the engineering implications bearing in mind the climate change we are facing today.

To enhance the development efficiency of ultra-deep fault-controlled carbonate reservoirs, large-scale rock mechanical experiments were conducted to reveal the deformation and connectivity mechanisms of high-angle to near-vertical fault surfaces. Based on the mechanical and flow coupling principles of high-pressure water injection production, geomechanical modeling was employed to clarify the current in-situ stress field and fault activity distribution patterns in fault-controlled carbonate reservoirs. Significant differences were found in fault activities in different directions and in the connectivity of fracture and cavity bodies in different parts. The development effects of different wellbore trajectories were then analyzed, and an integrated geological and engineering working method was proposed to scientifically guide the design of wellbore trajectories and the optimization of water injection schemes. The results show: ① Large-scale fractured bodies and high-angle fracture systems in strike-slip fault deformation are key factors affecting reservoir quality. High-pressure water injection can activate existing fractures on one hand, and on the other hand, it can extend and expand based on existing fractures, even generating new fractures, promoting the interconnection of fault-controlled fracture and cavity bodies in both vertical and horizontal directions; ② During the high-pressure water injection process, coupling changes between mechanics and flow occur inside the fault body, improving the seepage environment, and increasing oil and gas recovery rate through cyclic lifting; ③ According to the shape and the occurrence of the fault body, and the dynamic shear deformation connectivity of the fault surface, the best well point and well trajectory for directional wells can be selected, and the water injection scheme can be optimized; ④ In the fault-controlled oil reservoir test area of Tarim Basin, the recovery rate was increased by 5% through high-pressure water injection. This method provides a good theoretical basis and technical support for the efficient development of ultra-deep fault-controlled reservoirs.

Underground hydrogen storage (UHS) in salt caverns is a sustainable energy solution to reduce global warming. Salt rocks provide an exceptional insulator to store natural hydrogen, as they have low porosity and permeability. Nevertheless, the salt creeping nature and hydrogen-induced impact on the operational infrastructure threaten the integrity of the injection/production wells. Furthermore, the scarcity of global UHS initiatives indicates that investigations on well integrity remain insufficient. This study strives to profoundly detect the research gap and imperative considerations for well integrity preservation in UHS projects. The research integrates the salt critical characteristics, the geomechanical and geochemical risks, and the necessary measurements to maintain well integrity. The casing mechanical failure was found as the most challenging threat. Furthermore, the corrosive and erosive effects of hydrogen atoms on cement and casing may critically put the well integrity at risk. The research also indicated that the simultaneous impact of temperature on the salt creep behavior and hydrogen-induced corrosion is an unexplored area that has scope for further research. This inclusive research is an up-to-date source for analysis of the previous advancements, current shortcomings, and future requirements to preserve well integrity in UHS initiatives implemented within salt caverns. [ABSTRACT FROM AUTHOR]

An integrated Equation of State (EOS) and strength/pore‐crush/damage model framework is provided for modeling near to source (near‐field) ground‐shock response, where large deformations and pressures necessitate coupling EOS with pressure‐dependent plastic yield and damage. Nonlinear pressure‐dependence of strength up to high‐pressures is combined with a Modified Cam‐Clay‐like cap‐plasticity model in a way to allow degradation of strength from pore‐crush damage, what we call the "Yp‐Cap" model. Nonlinear hardening under compaction allows modeling the crush‐out of pores in combination with a fully saturated EOS, that is, for modeling partially saturated ground‐shock response, where air‐filled voids crush. Attention is given to algorithmic clarity and efficiency of the provided model, and the model is employed in example numerical simulations, including finite element simulations of underground explosions to exemplify its robustness and utility. [ABSTRACT FROM AUTHOR]

Introduction: The research is aimed to identify the vulnerable areas of quarry slopes through the creation of a stress-strain state model for the rock mass at the Vostochny quarry, East Saryoba field of the Zhi-landy Group of cupriferous sandstones, as well as their subsequent strengthening. Methods: The research is based on the development of a database containing information on mining-geological, geophysical, geodetic and aerospace surveys. The authors of the research use modern geodetic, aerospace and geophysical technologies for scientifically based predicting of technogenic disasters and the rock mass stress-strain state modeling to ensure safe and optimal mining of fields in difficult mining-geological conditions. Results: The results obtained show that the strengthening of weakened quarry slopes based on the rock mass stress-strain state modeling contributes to the scientific-practical profitability of field mining and provides safe mining in difficult mining-geological conditions. Discussion: Novelty is in the scientific substantiation of the method for strengthening quarry slopes, which is based on the rock mass stress-strain state modeling. The research is of great practical importance, as the rock mass stressstrain state modeling increases the reliability of predicting the rock mass state during its mining. Strengthening of quarry slopes using the proposed method reduces risks and increases safety and economic efficiency of mining the solid mineral deposits in difficult mining-geological conditions. [ABSTRACT FROM AUTHOR]

Unconsolidated, undrained triaxial deformation tests were performed on sandy facies Opalinus Clay at 50 MPa confining pressure to characterize the effect of water and microfabric orientation on the deformation behavior, mechanical properties, and P-wave velocity evolution. Dry and wet (≈ 8 and > 95% initial water saturation, respectively) samples with 12.6 ± 0.4 vol% porosity were deformed parallel and perpendicular to the bedding direction at a constant strain rate of 5 × 10–6 s−1. Dry samples revealed semi-brittle behavior and exhibited strain localization at failure, while deformation was more ductile at saturated conditions, promoting stable, slow faulting. Peak strength, Young's modulus, and number of cumulative acoustic emissions decreased significantly for wet samples compared to dry samples; the opposite was observed for Poisson's ratio. P-wave velocity anisotropy was significantly altered by differential stress, primarily due to the interplay between pore and fracture closure and stress-induced microcrack formation. For samples that were deformed perpendicular to bedding, we observed a reduction and reversal of P-wave velocity anisotropy with increasing differential stress, whereas anisotropy of parallel samples increased. The results suggest that water saturation reduces the pressure at the brittle-ductile transition and that the elastic properties and anisotropy of sandy facies Opalinus Clay can be significantly altered in an anisotropic stress field, e.g., adjacent to fault zones or tunnel excavations. Changes in elastic anisotropy are primarily controlled by the orientation between the pre-existing microfabric and the maximum principal stress direction, stress magnitude, and the degree of water saturation. Highlights: The presence of water reduces compressive strength, stiffness and P-wave velocity anisotropy of sandy facies Opalinus Clay, accompanied by increasing strain delocalization, promoting stable, slow faulting during triaxial deformation Triaxial deformation alters the elastic wave velocity anisotropy and symmetry of sandy facies Opalinus Clay, depending on water content and on the orientation of bedding relative to loading direction Changes in elastic anisotropy are mainly controlled by the closure of pores and microcracks and the formation of stress-induced fractures [ABSTRACT FROM AUTHOR]

Evaluating underground gas storage (UGS) sealing capacity is essential for its safe construction and operational efficiency. This involves evaluating both the static sealing capacity of traps during hydrocarbon accumulation and the dynamic sealing capacity of UGS under intensive gas injection and withdrawal, and alternating loads. This study detailed the methodology developed by Sinopec. The approach merges disciplines like geology, geomechanics, and hydrodynamics, employing both dynamic-static and qualitative-quantitative analyses. Sinopec's evaluation methods, grounded in the in situ stress analysis, include mechanistic studies, laboratory tests, geological surveys, stress analysis, and fluid-solid interactions. Through tests on the static and dynamic sealing capacity of UGS, alongside investigations into sealing mechanisms and the geological and geomechanical properties of cap rocks and faults, A geomechanics - rock damage - seepage mechanics dynamic coupling analysis method has been developed to predict in situ stress variations relative to pore pressure changes during UGS operations and evaluate fault sealing capacity and cap rock integrity, thereby setting the maximum operational pressures. Utilizing this evaluation technique, Sinopec has defined performance metrics and criteria for evaluating the sealing capacity of depleted gas reservoirs, enabling preliminary sealing capacity evaluations at UGS sites. These evaluations have significantly informed the design of UGS construction schemes and the evaluation of fault sealing capacity and cap rock integrity during UGS operations. [ABSTRACT FROM AUTHOR]

Copyright of Petroleum Geology & Experiment is the property of Petroleum Geology & Experiment Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Petrophysical and Geomechanical properties of rocks are important parameters in the design of engineering works and classification of rocks for engineering purposes. Recent studies indicate that geophysical methods, especially seismic and electrical, are able to estimate mechanical parameters and recognize spatial variations. In this research, to develop a predictive model for the uniaxial compressive strength (UCS), special electrodes were installed on the saturated core samples and simultaneously, the uniaxial compressive strength test and electric current flowing through the samples was done and variation of electrical resistivity during loading was measured in the laboratory. The results indicated that the structure and texture of rock had an important effect on the resistivity behavior during a mechanical loading. In this study, thirty core samples from the Fault breccias and Bimrocks (Block-in-matrix-rocks), were collected from different locations of Sabzkouh tunnel route in Chahar Mahal and Bakhtiari Provence. Regression analysis showed that there were generally strong correlations between the UCS and Resistivity in the samples having volumetric block proportion (VBP) of 25–75%. Multiple regression equations were derived for the prediction of UCS based on the resistivity and VBP values. The coefficient of determination (R2) and the root mean square error (RMSE) and the geometric mean error ratio (GMER) indices were calculated as 89.13%, 8.683 and 0.911, respectively, to characterize the prediction performance of the MLR model. The statistical test showed that the MLR model was valid and acceptable for predicting UCS. [ABSTRACT FROM AUTHOR]

Faults in general, and in clay materials in particular, have complex structures that can be linked to both a polyphased tectonic history and to the anisotropic nature of the intact rock. Drilling through faults in shaly materials allows measuring properties such as the structure, mineralogical composition, stress orientation and physical properties. We combine different petrophysical measurements on core samples retrieved from a borehole drilled perpendicularly to a fault zone affecting Toarcian shales from the Tournemire underground research laboratory (France). The borehole is cross-cutting the entire fault thickness which is of the order of 10 m. We perform several types of measurements: density, porosity, saturation directly in the field and P -wave velocities together with P -waves anisotropy on core samples taken at regular intervals. Special protocols were developed to preserve as much as possible the saturation state of the samples. From our measurements, we were able to track the increase of damage, characterized by a smooth decrease in elastic moduli from the intact zone to the fault core. We then calculated Thomsen's parameters to quantify the elastic anisotropy evolution across the fault. Our results show strong variations of the elastic anisotropy with the distance to the fault core as well as the occurrence of anisotropy reversal. [ABSTRACT FROM AUTHOR]

Fracture modeling in the section of the Suvlu-Kaya Mountain, southwestern Crimea, has been performed. A three-dimensional geological model of the section has been constructed, geomechanical modeling has been performed, and stress fields have been calculated in the three-dimensional geological structure. The modeling results have been compared with the real measurements of fracturing in the field. [ABSTRACT FROM AUTHOR]

Fluid flow through fractured media is typically governed by the distribution of fracture apertures, which are in turn governed by stress. Consequently, understanding subsurface stress is critical for understanding and predicting subsurface fluid flow. Although laboratory‐scale studies have established a sensitive relationship between effective stress and bulk electrical conductivity in crystalline rock, that relationship has not been extensively leveraged to monitor stress evolution at the field scale using electrical or electromagnetic geophysical monitoring approaches. In this paper we demonstrate the use time‐lapse 3‐dimensional (4D) electrical resistivity tomography to image perturbations in the stress field generated by pressurized borehole packers deployed during shear‐stimulation attempts in a 1.25 km deep metamorphic crystalline rock formation. Plain Language Summary: Time‐lapse electrical geophysical sensing is used to image 3D changes in rock stress generated by an isolated and pressurized interval of a borehole in a deep, dense, fractured rock formation. Key Points: Remotely monitoring stress is challenging but important for relating geomechanical behavior to flow pathways during energy productionBulk electrical conductivity is sensitive to stress in crystalline rockTime‐lapse electrical resistivity tomography can be used to remotely monitor 3D changes in effective stress [ABSTRACT FROM AUTHOR]

Featured Application: This study emphasizes the importance of comprehensive monitoring, calibration, and optimization of storage strategies in a saline aquifer. It also highlights the need to manage geomechanical risks and uncertainties. By understanding these risks and employing suitable monitoring techniques, the integrity and safety of GCS can be ensured, contributing to the reduction of CO2 emissions. Geological Carbon Storage (GCS) involves storing CO2 emissions in geological formations, where safe containment is challenged by structural and stratigraphic trapping and caprock integrity. This study investigates flow and geomechanical responses to CO2 injection based on a Brazilian offshore reservoir model, highlighting the critical interplay between rock properties, injection rates, pressure changes, and ground displacements. The findings indicate centimeter-scale ground uplift and question the conventional selection of the wellhead as a monitoring site, as it might not be optimal due to the reservoir's complexity and the nature of the injection process. This study addresses the importance of comprehensive sensitivity analyses on geomechanical properties and injection rates for advancing GCS by improving monitoring strategies and risk management. Furthermore, this study explores the geomechanical effects of modeling flow in the caprock, highlighting the role of pressure dissipation within the caprock. These insights are vital for advancing the design of monitoring strategies, enhancing the predictive accuracy of models, and effectively managing geomechanical risks, thus ensuring the success of GCS initiatives. [ABSTRACT FROM AUTHOR]

The effects of pore fluids on the elastic properties of sedimentary rocks can be broadly categorized into two mechanisms: variations in pore compressibility due to the physical properties of the fluids and alterations in the stiffness of the rock frame resulting from rock–fluid interactions. Particularly, as rock–fluid interactions alter the stiffness of contacts between mineral grains, changes in the fluid properties around grain contacts can induce volumetric deformation of the rock as well as in variations of the associated elastic coefficients. Even though many previous studies have explored the influence of swelling of clay minerals, the relationships between changes in elastic moduli and deformation in rocks, which hardly contain swellable minerals, remain to date enigmatic. In this paper, to evaluate quantitatively these effects, drying rates, strains and ultrasonic velocities of small cylindrical Berea sandstone samples were measured as their water saturation was decreased by evaporative drying. The measurements clearly showed drying shrinkage and drastic increases in shear and compressional moduli for all the samples under an almost fully dried condition. Previous studies considered that the alteration in surface energy of grain minerals between wet and dry states affected the contact stiffness between them. Some of them used micromechanical model, uniting the Digby grain contact model with the effective medium theory, to interpret the changes in elastic moduli observed in the non-swellable sandstones during water adsorption on the grain surface. The conventional micromechanical model assumes that a mineral grain is a pure sphere and that the number of contacts between the grains is one. However, grains in a sedimentary rock are generally not purely spherical, and the contact surface is composed of several adhesive asperities. We therefore modified the conventional model by introducing the curvature radius and the number of asperities per contact surface. The modified model well reproduced the shear moduli under wet conditions using the strain and moduli measured under dry conditions. On the other hand, the predictions of the compressional moduli using the model were partially in agreement with the experimental results. Therefore, we attempted to qualitatively interpret the relationship by combining the model with the viscoelastic effect associated with wave-induced fluid flow. The deformation and changes in the elastic moduli of rocks resulting from multiple pore fluids within them can be better understood by the present combined model. [ABSTRACT FROM AUTHOR]

The current crustal stress field is of key importance to understand geodynamic processes and to assess stability aspects during subsurface usage. To provide a 3-D continuous description of the stress state, linear elastic forward geomechanical-numerical models are used. These models solve the equilibrium of forces between gravitational volume forces and surfaces forces imposed mainly by plate tectonics. The latter are responsible for the horizontal stress anisotropy and impose the inverse problem to estimate horizontal displacement boundary conditions that provide a fit best to horizontal stress magnitude data within the model volume. However, horizontal stress magnitude data have high uncertainties and they are sparse, clustered and not necessarily representative for a larger rock volume. Even when Bayesian statistics are incorporated and additional stress information such as borehole failure observations or formation integrity test are used to further constrain the solution space, this approach may result in a low accuracy of the model results, that is the result is not correct. Here, we present an alternative approach that removes the dependence of the solution space based on stress magnitude data to avoid potential low accuracy. Initially, a solution space that contains all stress states that are physically reasonable is defined. Stress magnitude data and the additional stress information are then used in a Bayesian framework to evaluate which solutions are more likely than others. We first show and validate our approach with a generic truth model and then apply it to a case study of the Molasse foreland basin of the Alps in Southern Germany. The results show that the model's ability to predict a reliable stress state is increasing while the number of likely solutions may also increase, and that outlier of stress magnitude data can be identified. This alternative approach results in a substantial increase in computational speed as we perform most of the calculations analytically. [ABSTRACT FROM AUTHOR]

For a reservoir with high storage capacity and low ability to produce, the serious problem is the sharp reduction in the recorded well productivity within a short period. One solution to this problem is to create hydraulic fractures that increase formation permeability and keep its production at high rates for a sufficient time. The field under study is the East Baghdad oil field of three formations: Saadi, Tanuma, and Khasib. Knowing the geomechanical behavior of these reservoirs has a critical effect on the success of hydraulic fracturing operations. In this study, rock stress magnitude and direction, rock elasticity, rock strength to fracturing initiation, and all these parameters in addition to petrophysical properties will be used to identify whether the hydraulic fracturing operation could be successful or not. An integrated modeling of the studied reservoir is an essential step including 1-D geomechanical evaluation of many formations in order to choose the perfect layer to create hydraulic fracture. Then, a 3-D distribution of geomechanical properties and petrophysical properties was presented to make a perfect selection of these properties. The geomechanical evaluation of the reservoirs under study is supported by experimental evaluation of core samples including Energy Dispersive X-ray spectroscopy (EDS), Scanning Electron Microscopic (SEM) image, and thin section (TS) image. The results show that a reduction in the calculated geomechanical properties in terms of Poisson ratio young modulus and compressive strength are favorable for candidate layer selection. Among the studies of rock mechanical properties, it is also noticed that unconfined compressive strength is a crucial parameter for best layer selection. The suitable depths for fracturing jobs are given in detail in this study using brief data collected from four wells.

Abstract Shear wave transit time is a crucial parameter in petroleum engineering and geomechanical modeling with significant implications for reservoir performance and rock behavior prediction. Without accurate shear wave velocity information, geomechanical models are unable to fully characterize reservoir rock behavior, impacting operations such as hydraulic fracturing, production planning, and well stimulation. While traditional direct measurement methods are accurate but resource-intensive, indirect methods utilizing seismic and petrophysical data, as well as artificial intelligence algorithms, offer viable alternatives for shear wave velocity estimation. Machine learning algorithms have been proposed to predict shear wave velocity. However, until now, a comprehensive comparison has not been made on the common methods of machine learning that had an acceptable performance in previous researches. This research focuses on the prediction of shear wave transit time using prevalent machine learning techniques, along with a comparative analysis of these methods. To predict this parameter, various input features have been employed: compressional wave transit time, density, porosity, depth, Caliper log, and Gamma-ray log. Among the employed methods, the random forest approach demonstrated the most favorable performance, yielding R-squared and RMSE values of 0.9495 and 9.4567, respectively. Furthermore, the artificial neural network, LSBoost, Bayesian, multivariate regression, and support vector machine techniques achieved R-squared values of 0.878, 0.8583, 0.8471, 0.847 and 0.7975, RMSE values of 22.4068, 27.8158, 28.0138, 28.0240 and 37.5822, respectively. Estimation analysis confirmed the statistical reliability of the Random Forest model. The formulated strategies offer a promising framework applicable to shear wave velocity estimation in carbonate reservoirs.

An understanding of fault reactivation induced by water injection is of great significance for geothermal energy development and utilization. We conducted a series of water injection shear tests on low-permeability granite samples that each contained a single saw-cut fault under locally undrained conditions. Slip characteristics were analyzed by varying the fluid pressurization rate, confining pressure, and stress state of the fault to understand fault reactivation. The experimental results demonstrated that at a high pressurization rate, a higher local fluid pressure was needed to reactivate the fault than had been estimated theoretically, and the required fluid pressure increased with an increase in pressurization rate. The fluid pressurization rate and confining pressure both controlled the slip mode of the fault. The slip mode changed from dynamic slip to quasi-static slip at a high pressurization rate, and the peak slip rate of dynamic slip increased with an increasing pressurization rate. The fault showed significant stick-slip characteristics under a high confining pressure, as fault locking and reactivation phenomena occurred repeatedly. Faults with different initial stress states had little influence on the slip mode after the onset of slip. [ABSTRACT FROM AUTHOR]

Shear wave velocity (Vs) has significant applications in geoengineering investigations. With the ongoing rise in carbon capture and storage (CCS) initiatives, the role of Vs in monitoring the CO2 sequestration sites is escalating. Although many studies have been conducted to assess CCS-induced risks, no inclusive research has been conducted integrating those investigations. This study strives to collate and integrate the applications of Vs in geoscience with an emphasis on CCS risk assessment. Based on this research, major CCS-induced risks were detected: induced seismicity, caprock failure, groundwater contamination, fault reactivation, and reservoir deformation. These risks were inclusively described, and the mathematical formulations incorporating the Vs parameter in risk analysis were elaborated. It was concluded that Vs applications can be further extended in monitoring CO2 plume migration, optimizing CO2 injection pressures, preventing shallow water contamination, and predicting CCS-induced seismic events. All these applications require fully coupled hydromechanical analysis based on poroelasticity theory. Hence, various factors including pore pressure, in situ stresses, faults distribution, and poroelastic parameters must be carefully determined before the CO2 injection phase. The mathematical formulations presented in the present study are quite applicable for granting the safety and long-term success of subsurface carbon sequestration. [ABSTRACT FROM AUTHOR]

In fractured and stress‐sensitive reservoirs and aquifers, hydromechanical coupling is important, in connection with their heat and solute transport properties, and because the fluid production or extraction leads to land subsidence and potentially to induced seismicity. Classical dual‐porosity poroelasticity (DPP) models cannot upscale pressure diffusion and deformation in fractured porous media, which are characterized by anomalous behaviors that manifest in strong tailing in the temporal evolution of flow rate and subsidence. We study these behaviors using detailed numerical simulations of fluid production in naturally fractured formations characterized by multi‐Gaussian distributions of the matrix permeability. We find that the tailing behaviors depend on the permeability contrast between fracture and matrix, on the permeability distribution in the matrix, and on the correlation length. We use a non–equilibrium, multi‐porosity model to quantify the coupled behaviors of anomalous pressure diffusion, fluid flow and deformation. The model is parameterized by medium and fluid properties, which set the characteristic pressure diffusion time scales. It allows to identify the emerging scaling regimes and scaling behaviors of flow rate and subsidence. We propose a model implementation that captures the full anomalous evolution of flow rates and displacements observed in the detailed numerical simulations in terms of the permeability distribution and matrix length scales. The presented results shed new light on the controls of medium heterogeneity and geometry on pressure diffusion, fluid production and subsidence in highly heterogeneous fractured media. Key Points: Fluid production and subsidence are studied for three‐dimensional fractured poroelastic mediaStrong tailing in the temporal evolution of the fluid production rate and displacement is observedA multi‐porosity model explains scaling regimes and behaviors, and quantifies the full evolution of coupled flow and deformation [ABSTRACT FROM AUTHOR]

We perform a simulation study of hydrogen injection in a depleted gas reservoir, to assess the geomechanical impact of hydrogen storage, relative to other commonly injected gases (methane, CO 2). A key finding is that the differences in hydrogen density, compressibility, viscosity and thermal properties, compared to the other gases, result in significantly less thermal perturbation at reservoir level. The risks of fault reactivation and wellbore fractures due to thermally-induced stress changes are significantly lower when storing hydrogen compared to results observed in CO 2 scenarios. This implies that hydrogen injection and production has a much smaller geomechanical footprint, with benefits for operational safety. We also find that use of nitrogen cushion gas ensures efficient deliverability and phase separation in the reservoir. However, in this study, a large fraction of cushion gas was back-produced in each cycle, demonstrating the need for further studies of the surface processing requirements and economic implications. [Display omitted] • Geomechanical modelling assesses the risks associated with hydrogen storage. • Diffusivity, dissolution and methanogenesis have negligible effect on models. • Thermal perturbations associated with storage alter fracture pressures. • Significant mixing of hydrogen with cushion gas is observed. • Hydrogen storage presents less geomechanical risk than CO 2 or methane storage. [ABSTRACT FROM AUTHOR]

The Xianshuihe fault zone in the eastern Qinghai-Tibetan Plateau is an important active tectonic boundary. Understanding its stress state is important for characterizing the dynamic evolution of the Qinghai-Tibet Plateau and the mechanism of the frequent occurrence of large earthquakes. Using 30 years of in-situ stress data from the Xianshuihe active fault zone, we statistically analyzed the spatial distribution characteristics of the stress in the region. The study area is generally characterized by a strike-slip stress field. Nevertheless, the stress state is vulnerable to topography and shows high spatial variation near the Earth's surface at a depth of 0-400 m. The local stress near the fault zone varies from the far-field stress. The orientations of the maximum horizontal principal stress possess an elliptical shape around the fault zone, while its magnitudes become hump-like as the distance increases from the fault. The large difference in properties between the fault zone and its adjacent rocks contributes to the differentiation of the direction of the local stress field near the fault. The results allow us to formulate a preliminary hypothesis that a rigid lateral extrusion model may control the nonuniformity of the local stress field in the Xianshuihe fault zone and preferentially interpret the tectonic uplift of the southeastern margin of the Qinghai-Tibet Plateau. Further, the stress accumulation in the shallow crustal regions of the Xianshuihe fault zone is relatively high, indicating that some segments of the fault zone are critically unstable. Kangding area (the Zheduotang segment and the Yalahe segment) and Luhuo segment hold relatively high potential for large earthquakes. The results of this study are of great significance for revealing the mechanism of fault-stress field interactions and for understanding the dynamic evolution mechanism of the uplift of the Qinghai-Tibet Plateau. [ABSTRACT FROM AUTHOR]

Seismic resonance and surface displacement measurements can be implemented in tandem to improve landslide characterization and progressive failure monitoring. Crack aperture data are frequently used in rock slope stability monitoring and often exhibit recognizable trends prior to failure, such as accelerated crack opening. Alternatively, ambient resonance data offer multiple parameters including modal frequencies, damping, and polarization that can be monitored alongside crack aperture and may respond differently to environmental forcings and complex failure evolution. We analyzed data from continuous ambient vibration monitoring and concomitant crack aperture measurements at the Courthouse Mesa instability, a large toppling sandstone slab in Utah, USA. Three years of data revealed crack aperture increases of 2-4 mm/year with no clearly detectable irreversible changes in modal parameters, including frequency. Annually, frequency and displacement varied by 29% and 19% of the mean, respectively, with average and maximum daily frequency fluctuations of 6.5% and 16%, respectively. These reversible cyclic changes were primarily temperature-driven, but annually, frequency was in-phase with temperature whereas crack aperture lagged temperature changes by ~37 days. Polarization and damping also varied seasonally but were less strongly correlated with temperature. Conceptual 3D finite element modeling demonstrated consistent frequency decreases associated with crack propagation but variable changes in crack aperture measured at a single point; i.e., crack propagation did not always result in increased crack opening but always generated a resonance frequency decrease. Taken together, our data suggest a possible thermal wedging-ratcheting mechanism at the Courthouse Mesa instability, where annual thermoelastic crack closure is impeded by debris infill but the absence of downward crack propagation during the monitoring period is evidenced by no permanent resonance frequency changes. Our study demonstrates that combined seismic resonance and crack aperture data provide an improved description of rock slope instability behavior, supporting refined characterization and monitoring of changes accompanying progressive failure. [ABSTRACT FROM AUTHOR]

This study carried out a research on the distribution characteristics of the geostress field of ultra-deep strike-slip faults, aiming to improve the exploration efficiency and development benefits of ultra-deep fault-controlled reservoirs. This study combines multiple geological information, drilling information, seismic data, and seismic attribute analysis. Taking the FI12 fault zone in the Fengman Oilfield as an example, it carried out numerical simulation of the geostress field, clarified the distribution pattern of geostress, analyzed the effectiveness of fracture mechanics, and proposed a reservoir quality evaluation method and production increase strategy based on geostress analysis. The study includes the following three aspects: 1) research on the heterogeneity of fault-controlled fractured carbonate reservoirs: Due to the existence of faults, fractures, and pores, carbonate reservoirs exhibit strong heterogeneity. These discontinuous structures lead to local stress field decreases to varying degrees. By analyzing the changes in geostress, it is possible to infer the development of faults, fractures, and pores. This provides important basis for predicting and evaluating reservoirs. 2) research on the distribution pattern of geostress: The geostress of fractured bodies exhibits a "shell-type" distribution pattern. Inside the fractured body, the geostress values are lower, indicating that this part is a favorable reservoir body. On the outside of the fractured body, the geostress exhibits high-value concentration, and this part has relatively poor permeability and can be regarded as an unfavorable drilling target. 3) research on the relationship between fault-fracture mechanical activity and reservoir quality and production capacity: Geostress and its influence on fault-fracture mechanical activity are directly related to the quality and production capacity of fault-controlled fractured carbonate reservoirs. When deploying well locations and optimizing well trajectories, geostress factors should be fully considered, and reservoir reformation efficiency should be taken into account to promote single well production increases and reservoir economic devel. [ABSTRACT FROM AUTHOR]

Oil and gas extraction is difficult without understanding the subsurface formation up to the desired depth. Wellbore instability, such as lost circulation and pipe sticking, is an issue when drilling a well for a high-temperature, high-pressure reservoir. To maintain the stability of the borehole, optimum drilling mud should be simulated by preventing formation fracture or formation break-out. The main goal of this work is to propose a model with a 3D extended Mohr–Coulomb criterion that helps to achieve maximum wellbore stability using drilling fluid weight as a controlling parameter. This criterion includes the effect of the intermediate principal stress as a linear relation of principal stresses. this study also validated the extended Mohr–Coulomb criterion for in situ failure. To implement a new criterion on the wellbore for stability, a numerical mechanical earth model (NMEM) is developed as an empirical correlation of the wire-line well-log data. The mud weight is calculated using mechanical parameters derived from NMEM and lithology. The pore pressure, fracture pressure, and stress profile were also predicted by this NMEM, which gives insights into the subsurface formation's faulting regime. To achieve maximum wellbore stability, optimum mud weight is recommended based on the stress profile and faulting regime. One onshore and one offshore well is taken as a case study from the online dataset via the Dutch Oil and Gas Portal (NLOG) to simulate the NMEM. Mud weight using Mohr–Coulomb and Mogi–Coulomb criteria was also used to compare mud weight predicted by the proposed new 3D linear failure criterion. The treading line for the mud weight by the new 3D linear criterion is more accurate as a new criterion considering the effect of σ 2 . The new criterion has been proved to be more specific, easy to compute, and a unique solution for estimating parameters using NMEM. This NMEM, which includes a new linear 3D criterion, can also solve sand production issues, hydrofracturing, and CO2 sequestration. Highlights: A study about safe mud weight prediction using the new Extended Mohr–Coulomb criterion to prevent break-out and drilling-induced fracture with all six combinations of stress regimes. A numerical mechanical earth model is developed to stimulate appropriated reservoir conditions from actual well-log data. The prediction of mud weight to maintain wellbore stability is further compared with the Mohr–Coulomb and Mogi–Coulomb criteria results. A new 3D criterion with a numerical earth model has the potential to solve sand production issues and is also helpful for modeling hydrofracturing and CO2 sequestration. [ABSTRACT FROM AUTHOR]

A theory for modelling the evolution of elastic moduli of grain packs under increasing pressure is combined with a method that accounts for the presence of fine-grained particles to develop a new conceptual framework for computing the seismic velocities of compacting sediments. The resulting formulation is then used to construct a seismic velocity model for California's Central Valley. Specifically, a set of 44 sonic logs from the San Joaquin Valley are combined with soil textural data to derive the 3-D velocity variations in the province. An iterative quasi-Newton minimization algorithm that allows for bounded variables provided estimates of the nine free parameters in the model. The estimates low- and high-pressure exponents that resulted from the fit to the sonic log velocities are close to 1/2 and 1/3, respectively, values that are observed in laboratory experiments. Our results imply that the grain surfaces are sufficiently rough that there is little or no slip between grains. Thus, the deformation may be modelled using a strain energy function or free energy potential. The estimated Central Valley velocity model contains a 27 per cent increase in velocity from the surface to a depth of 700 m. Lateral variations of around 4 per cent occur within the layers of the model, a consequence of the textural heterogeneity within the subsurface. [ABSTRACT FROM AUTHOR]

We conducted an extensive study on the elastic properties of Opalinus Clay and the overlying and underlying rock formations, which range in the overall clay mineral content from nearly 0 to 60 wt.%. Our laboratory experiments focused on seismic and ultrasonic frequencies to determine the extent to which seismic dispersion affects elastic parameters and seismic wave velocities. The results comprise the static stiffness from undrained triaxial cycles (axial–confining stress: 8–10 MPa), the dynamic stiffness at seismic frequencies (0.5–143 Hz), intrinsic attenuation (0.5–20 Hz), compressional velocity measurements (0.5–2 Hz) and ultrasonic velocity measurements (250 and 500 kHz). We compared these laboratory results to in situ sonic logging measurements to assess the role of frequency in measured elastic parameters. The results suggest a notable correlation between clay mineral content and dispersion. Specifically, high clay mineral content leads to increased dispersion, even within the seismic frequency band. The overall dispersion of P -wave velocity in the frequency range from 1 Hz to 500 kHz is up to 16%. This frequency dependency is crucial when establishing a relationship between sonic well log data and static stiffness for geomechanical modelling. The results are discussed with respect to possible dispersion mechanisms, including the role of bound water in clay. [ABSTRACT FROM AUTHOR]

The seismic cycle of repeated earthquake failure requires that faults regain frictional strength during the interseismic phase, when the fault is locked or undergoing quasi-static creep. Fault healing plays a central role in determining earthquake stress drop, recurrence interval, elastic radiation frequency and other source parameters. In particular, the longer a fault remains quasi-stationary, the stronger it becomes and the larger the potential stress drop can be for the next event. Here, we address the role of shear strain and strain localization on fault healing and healing rate. We performed slide-hold-slide friction experiments on quartz gouge in the double-direct shear configuration for shear strain up to 25 and hold times from 10 to 1000 s. The results show that both healing and healing rate increase nonlinearly with increasing shear strain. Frictional healing scales with volumetric strain within the laboratory fault zone. Using the volumetric strain upon reshear as a proxy for strain localization, we demonstrate that the capacity of a fault to heal is directly proportional to shear bandwidth and degree of strain localization. The more the deformation is localized, the higher are the healing and healing rate, and thus, the fault strength. Our data provide a framework for understanding variations in fault strength over the seismic cycle and the role of brecciation and strain localization on spatiotemporal variations in fault strength. [ABSTRACT FROM AUTHOR]

Numerical modeling of complex underground engineering projects such as caverns, tunnels, and bulk mining zones is an essential part of the design phase. Large-scale models require significant reductions in complexity from the real-world scenario, which often leads to low confidence in the model output. In this work, a mine-scale numerical model is developed to simulate a room and pillar extraction mining operation. The model inputs are calibrated through the comparison of the model response to pillar extraction in an analogous mine geometry with measured strain values collected using a novel distributed optical fiber strain sensing technique after pillar extraction. Calibration efforts resulted in the identification of the extent of rock mass damage that resulted from the pillar extraction operation. Numerical model inputs were calibrated for geologic strength index (GSI), rock mass damage, discontinuity properties, and applied horizontal stress conditions. A range of calibrated model input parameters are provided, which show good correlation with measured field strain values and are shown to have an accuracy from 78.2 to 89.1% within a 50% tolerance interval of field data. The model calibration presented in this work represents the first step in a calibration process, from which the model will be used for the forward analysis of various mining scenarios, the results of which will inform future calibration and analysis. [ABSTRACT FROM AUTHOR]

Shear wave transit time is a crucial parameter in petroleum engineering and geomechanical modeling with significant implications for reservoir performance and rock behavior prediction. Without accurate shear wave velocity information, geomechanical models are unable to fully characterize reservoir rock behavior, impacting operations such as hydraulic fracturing, production planning, and well stimulation. While traditional direct measurement methods are accurate but resource-intensive, indirect methods utilizing seismic and petrophysical data, as well as artificial intelligence algorithms, offer viable alternatives for shear wave velocity estimation. Machine learning algorithms have been proposed to predict shear wave velocity. However, until now, a comprehensive comparison has not been made on the common methods of machine learning that had an acceptable performance in previous researches. This research focuses on the prediction of shear wave transit time using prevalent machine learning techniques, along with a comparative analysis of these methods. To predict this parameter, various input features have been employed: compressional wave transit time, density, porosity, depth, Caliper log, and Gamma-ray log. Among the employed methods, the random forest approach demonstrated the most favorable performance, yielding R-squared and RMSE values of 0.9495 and 9.4567, respectively. Furthermore, the artificial neural network, LSBoost, Bayesian, multivariate regression, and support vector machine techniques achieved R-squared values of 0.878, 0.8583, 0.8471, 0.847 and 0.7975, RMSE values of 22.4068, 27.8158, 28.0138, 28.0240 and 37.5822, respectively. Estimation analysis confirmed the statistical reliability of the Random Forest model. The formulated strategies offer a promising framework applicable to shear wave velocity estimation in carbonate reservoirs. [ABSTRACT FROM AUTHOR]

We test three different methods for selecting the fault plane from the two nodal planes in an individual focal mechanism, which are implemented in a linear stress inversion technique, to constrain the geometry of subsurface seismogenic faults. The three fault-selection methods use the misfit angle between the slip orientation and maximum shear stress direction on the nodal planes, fault instability and slip tendency, respectively, to select the fault planes. These three fault-selection methods are applied to various types (synthetic, simulated and real) of focal mechanism data sets where the fault planes are already known. In particular, synthetic focal mechanism data sets are generated with the assumption of different levels of pore pressure variation (up to 60 per cent of the minimum principal stress) that may be involved in activating faults with diverse orientations. The instability method performs the best among the three fault-selection methods, with 60–100 per cent of the faults correctly selected in each of the tested data sets. The slip-tendency method is slightly less accurate than the instability method, especially when the earthquakes occur in a highly variable pore pressure environment, and the misfit-angle method is relatively ineffective in selecting the faults, especially in noisy data sets. The test results show that the instability method is the most effective in correctly selecting the faults when the instability of the selected fault plane is significantly higher than that of the auxiliary plane, whereby the instability ratio of the selected (fault) plane to the auxiliary plane is above ∼1.4; this constraint can improve our ability to identify subsurface seismic faults. We apply this stress inversion technique, which implements the instability method, to the 2016–2017 induced earthquakes in Pohang, South Korea. We invert 53 well-constrained, well-located focal mechanism solutions to derive the stress condition, with the nodal planes possessing a higher instability selected as faults. The earthquakes, which occurred in spatially distinct areas of the region, have been associated with water injection into two boreholes (PX-1 and PX-2). Approximately 70 per cent of the identified faults for the PX-2-related earthquakes are well aligned in terms of both their locations and orientations, thereby indicating that these earthquakes occurred along a single, large-scale fault. The fault planes with instability ratios above ∼1.3 are all correctly selected for the PX-2 fault. Although there are more variations in the identified fault orientations of the PX-1-related earthquakes, some of the fault planes with high instability ratios (>1.4) are generally subparallel to one another. Both the locations and orientations of these high-instability-ratio planes are well aligned, suggesting the presence of a large-scale fault that is subparallel to the PX-2 fault. This study demonstrates the potential of effectively identifying and imaging subsurface seismic faults using only information on fault mechanics (i.e. stress and focal mechanisms). [ABSTRACT FROM AUTHOR]

Currently, there are no reliable universal dependencies of the Poisson’s ratio on the geomechanical and geophysical characteristics of productive objects. This study aims to investigate the influence of geophysical parameters on the Poisson’s ratio for oilfield productive objects using machine learning methods. The analysis is based on data from several oil and gas fields, presenting results of dependencies between the Poisson’s ratio and parameters such as natural radioactivity of rocks and P-wave velocity. The elastic parameters were identified through triaxial tests of rock samples under reservoir conditions conducted on the PIK-UIDK/PL triaxial system at Perm National Research Polytechnic University. A brief overview of existing standards for conducting triaxial tests is also provided. The importance of standardizing methods for determining the Poisson’s ratio and other elastic parameters of rocks is emphasized to ensure comparability of research results from different fields and their applicability in various geological conditions. The proposed data analysis method relies on linear regression and machine learning methods to establish stable relationships between the Poisson’s ratio and geophysical parameters obtained from various well logging studies. These dependencies allow for more accurate estimation of the Poisson’s ratio for different types of rocks and fields, representing a significant step in developing methods for assessing elastic properties of rocks in oil fields. The obtained results can be used for more precise modeling and forecasting of oil field development processes, contributing to increased efficiency in hydrocarbon extraction and optimization of production processes in the oil industry.

Introduction: The research is aimed to identify the vulnerable areas of quarry slopes through the creation of a stress-strain state model for the rock mass at the Vostochny quarry, East Saryoba field of the Zhi-landy Group of cupriferous sandstones, as well as their subsequent strengthening.Methods: The research is based on the development of a database containing information on mining-geological, geophysical, geodetic and aerospace surveys. The authors of the research use modern geodetic, aerospace and geophysical technologies for scientifically based predicting of technogenic disasters and the rock mass stress-strain state modeling to ensure safe and optimal mining of fields in difficult mining-geological conditions.Results: The results obtained show that the strengthening of weakened quarry slopes based on the rock mass stress-strain state modeling contributes to the scientific-practical profitability of field mining and provides safe mining in difficult mining-geological conditions.Discussion: Novelty is in the scientific substantiation of the method for strengthening quarry slopes, which is based on the rock mass stress-strain state modeling. The research is of great practical importance, as the rock mass stress-strain state modeling increases the reliability of predicting the rock mass state during its mining. Strengthening of quarry slopes using the proposed method reduces risks and increases safety and economic efficiency of mining the solid mineral deposits in difficult mining-geological conditions.

Abstract Fluid flow through fractured media is typically governed by the distribution of fracture apertures, which are in turn governed by stress. Consequently, understanding subsurface stress is critical for understanding and predicting subsurface fluid flow. Although laboratory‐scale studies have established a sensitive relationship between effective stress and bulk electrical conductivity in crystalline rock, that relationship has not been extensively leveraged to monitor stress evolution at the field scale using electrical or electromagnetic geophysical monitoring approaches. In this paper we demonstrate the use time‐lapse 3‐dimensional (4D) electrical resistivity tomography to image perturbations in the stress field generated by pressurized borehole packers deployed during shear‐stimulation attempts in a 1.25 km deep metamorphic crystalline rock formation.

Safety assessment of geological nuclear waste repositories is essential for the permanent disposal of spent nuclear fuels and high-level radioactive waste. The long-term integrity of the host rock as well as the engineered barrier system (e.g., bentonite buffer) surrounding nuclear waste canisters is of particular importance as decay heat from nuclear waste canisters, which will last over thousands of years, significantly disturbs the thermo-hydromechanical (THM) state of the repository. In this study, THM coupled simulations were carried out to investigate the effect of time-dependent deformation (i.e., creep) of shale on the long-term integrity of a generic subsurface nuclear waste repository. The Norton-Bailey creep model, which is also known as the Lemaitre-Menzel-Schreiner model, was employed to simulate the power-law type creep that is observed in shales. The TOUGH-FLAC simulator was employed for the THM coupled modeling of the repository. The objective of this study is to assess the effect of creep in different shales (i.e., high creep shale vs. low creep shale) on long-term stress and permeability changes in the repository. Results show potential advantages of constructing repositories in the high creep shale, as deviatoric stress levels in the formation decreased to zero in 100 years since the emplacement of nuclear waste canisters and the permeability also decreased to the undamaged, intrinsic levels in 10,000 years. Also, mean effective stress levels in the bentonite buffer increased by 100% in the high creep shale case relative to the low creep shale case at 10,000 years due to creep-induced contraction of the nuclear waste disposal tunnel. However, in earlier periods (e.g., 1000 years), the stress levels in the bentonite buffer were twice smaller in the high creep shale case than in the low creep shale case, which shows a tradeoff between the intermediate- (∼1000 years) and long-term (>10,000 years) compaction levels in the bentonite buffer depending on the creep characteristics of the host shale.