Rock Mechanical Properties Research Articles (Page 1)

The sonic log is a key tool for assessing the mechanical properties of rocks, identifying structural features, calibrating seismic data, and monitoring well integrity. However, sonic data are often incomplete due to time and cost constraints, tool failures, or unreliable measurements. Traditional approaches to generate synthetic sonic logs usually rely on empirical relationships or statistical methods. In this study, we applied an artificial intelligence approach in which a deep neural network was trained with real data from an oilfield in Mexico to reconstruct sonic logs based on their relationships with other geophysical well logs. Three models, each using different input logs, were trained to predict the sonic response. The models were validated on wells excluded from training, and performance was evaluated using the root mean square error (RMSE) and mean absolute percentage error (MAPE), showing satisfactory accuracy. The models achieved RMSE values between 1.4 and 1.7 [μs/ft] and MAPE values between 2.1 and 2.6% on independent test wells, confirming robust predictive performance. We also generated synthetic sonic logs for wells where no sonic data were originally acquired, demonstrating the practical value of the proposed method. This work integrates convolutional (CNN) and recurrent (GRU) layers in a single deep-learning architecture, trained under strict well-level validation. The workflow is demonstrated on wells from the Tabasco Basin, representing a field-scale deployment not previously reported in similar studies.

Abstract. Heterogeneous structures and diverse volcanic, hydrothermal, and geomorphological processes hinder characterisation of the mechanical properties of volcanic rock masses. Laboratory experiments can provide accurate rock property measurements, but are limited by sample scale and labor-intensive procedures. In this contribution, we expand on previous research linking the hyperspectral fingerprints of rocks to their physical and mechanical properties. We acquired a unique dataset characterising the visible-near (VNIR), shortwave (SWIR), midwave (MWIR), and longwave (LWIR) infrared reflectance of samples from eight basaltic to andesitic volcanoes. Several machine learning models were then trained to predict density, porosity, uniaxial compressive strength (UCS), and Young's modulus (E) from these spectral data. Significantly, nonlinear techniques such as multilayer perceptron (MLP) models were able to explain up to 80 % of the variance in density and porosity, and 65 %–70 % of the variance in UCS and E. Shapley value analysis, a tool from explainable AI, highlights the dominant contribution of VNIR-SWIR absorptions that can be attributed to hydrothermal alteration, and MWIR-LWIR features sensitive to volcanic glass content, fabric, and/or surface roughness. These results demonstrate that hyperspectral imaging can serve as a robust proxy for rock physical and mechanical properties, potentially offering an efficient, scalable method for characterising large areas of exposed volcanic rock. The integration of these data with geomechanical models could enhance hazard assessment, infrastructure development, and resource utilisation in volcanic regions.

Evolving physical and mechanical rock properties during exposure at Earth's surface

Understanding the deformation and failure behavior of rock under complex boundary and environmental conditions is critical for the design and stability assessment of geotechnical structures. In particular, the influence of water content and end friction during laboratory testing significantly affects the mechanical properties of rocks. In this study, uniaxial compression tests were conducted on dry and water-saturated limestone specimens under two end conditions: with and without a coupling agent, to investigate the coupled effects of water saturation and end friction on rock deformation and failure behavior. The results indicate that the uniaxial compressive strength (UCS) in the dry state is 84.2% higher than that in the water-saturated state, and the elastic modulus (E) shows an 84.7% increase in the dry state compared to the water-saturated state. The use of a coupling agent was found to enhance overall strain and reduce the extent of end friction effects. Radial shrinkage occurred in the early loading phase near the specimen ends and gradually weakened toward the center. Failure modes varied with test conditions: specimens without vaseline primarily exhibited X-shaped conjugate shear fractures due to strong end restraint, whereas vaseline-coated specimens showed cleavage failure characterized by more pronounced end damage. Water-saturated specimens exhibited more ductile behavior, while dry specimens showed brittle splitting. Fracture observations indicated that early crack formation and stress rebound influenced radial deformation and crack evolution.

This study presents a comprehensive reservoir geomechanical characterization of the Middle Jurassic Lower Safa sandstones from the Shushan Basin, Egypt. Petrographical thin sections, SEM, XRD, routine core analysis, wireline logs, downhole measurements and drilling data were integrated to characterize the studied reservoirs. The reservoir is composed of mesoporous quartz arenites with dominantly primary intergranular porosity, and exhibits an isotropic pore system with 7–14% effective porosity and ≤1 mD permeability. Cementation (silica and clay) and mechanical compaction were identified as the primary diagenetic factors reducing the reservoir quality. The reservoir exhibits a low shale volume, high hydrocarbon saturation and a hydrostatic pore pressure gradient. The relative gradients of in situ stresses indicate a normal to strike-slip faulting stress regime. Based on the ‘C-quality’ breakouts from multi-arm caliper log analysis, the maximum horizontal stress azimuth is interpreted as N140°E. Utilizing the stress-based model, the risks of wellbore instability, depletion-induced reservoir instability and sand production were assessed. The assessment indicated the possibility of production-induced shear failure at a depleted pore pressure magnitude of 1000 psi, which can be considered the abandonment pressure. The hydraulic fracturing simulation confirmed the presence of a stress barrier that would restrict the vertical propagation of fractures into the overburden/underburden during stimulation. The horizontal wells drilled along a NE–SW azimuth offer higher sand-free critical drawdown and therefore this is considered the preferred lateral azimuth to minimize sand production risk. The sensitivity of collapse pressure, fracture initiation pressure and sand-free critical drawdown pressure was assessed for various wellbore trajectories, rock-mechanical property and depletion magnitudes.

This study characterized the mechanical behaviours of massive fractured (MLS), fossiliferous (FLS), and siliceous (SLS) limestone lithofacies under natural, dry, and saturated conditions. Uniaxial compressive strength (UCS), point load index (PLI), and indirect tensile strength (ITS) tests, along with petrographic, mineralogical, and geochemical analyses, were used to evaluate the impacts of the lithofacies composition and environmental conditions on rock strength. The results indicate that lithofacies composition, including mineralogy and texture, has a considerable effect on rock strength and durability. Under dry conditions, UCS values increased by up to ~ 200% in MLS and SLS relative to natural conditions, while saturation reduced UCS by 30–60% depending on lithofacies. Similar trends were observed in ITS, which decreased by up to 55% under saturation. The high silica content of SLS produced the most durable lithofacies, whereas the high porosity of FLS made it the most vulnerable to weakening from water exposure. MLS exhibited intermediate properties, as it loses strength considerably when existing fractures become saturated. Statistical analysis indicates that the CaO, SiO2, and MgO contents strongly influenced the rock mechanical properties. The study reveals relationships between lithofacies geochemistry, microstructural attributes (fractures, porosity, fossil interfaces), and mechanical responses under different moisture states. These insights allow for predictions about carbonate rock mechanical performance, making them crucial for geological research, engineering projects, industrial applications, and infrastructure design.

Abstract The chemical and mechanical interactions between fluids and rocks, impairing the permeability and porosity of the reservoir, can lead to operational and economic challenges. These interactions can have a negative impact on the mechanical virtues of the rock, ultimately altering the petrophysical characteristics of the rock. The interactions cause alterations in the geometry of the pore space and the strength of the rock. Therefore, it is crucial to assess these variables before designing any oil recovery and gas storage project. The rock properties, particularly strength, permeability, and porosity, are changed during various stages such as drilling, production, and the injection of water or chemicals. In this regard, this research presents an examination review of the impact of fluid-rock interactions on the mechanical attributes of the formation rock, specifically focusing on the occurrence of formation damage. Generally, it is crucial to possess a strong comprehension of the interactions between fluids and rocks, as well as their effects on mechanical attributes and formation damage. This manuscript compiles recent studies to study the effect of interactions on rock petrophysical properties as well as mechanical properties, and in this regard, provides new perspectives on fluid-rock interactions in reservoirs. This understanding is vital in order to minimize both economic losses and technical complexities. Also, this manuscript can help researchers gain a complete perspective on the effect of fluids on rock mechanical properties in storage operations.

Young’s Modulus is an important mechanical property of rocks in hydraulic fracturing design, as it determines their stiffness and indicates the extent to which they will deform elastically under uniaxial compressive stress. Young’s Modulus for reservoir ro ck can be determined via laboratory testing or using well log geophysical data. However, the laboratory testing depends on the availability of core samples, while data analysis based on well log data requires appropriate conversion formulas, which demand significant time, cost, and complexity. The approach presented in this study is based on the fact that real time drilling data, such as weight on bit (WOB), torque on bit (TQR), standpipe pressure (SPP), rotary speed (RPM), rate of penetration (ROP), and drilling fluid flow rate (FLOWIN), are re adily available in the early stages of the drilling process without incurring additional costs. Two machine learning algorithms were used to correlate drilling data with the dynamic Young’s Modulus : Random Forest and Decision Tree. Two different datasets were used in this study, the first dataset was utilized to develop and train the model, while the other dataset was used to validate the developed models. The first of the two methods employed demon strated a remarkable match between the given values and the predicted values. The correlation coefficients ranged from 0.71 to 0.95, with the average absolute percentage error being less than 5%. Based on the obtained results, the use of drilling data combined with artificial intelligence models for predicting Young’s Modulus proves to be a viable approach.

The damage to rock masses due to the action of freezing is one of the most important factors in the development of landscapes, the performance of civil structures, and the efficiency of mining operations. In this research paper, the effect has been studied on the physical and mechanical performance of seven different natural building rock samples. The testing program included an experimental study on both dry and saturated intact rock samples and therefore, the effect of saturation on the extent of damage on the tested samples has been discussed as well. Based on the obtained results, freezing–thawing cycles increase the porosity of rock samples and decrease the values of P-wave velocity, uniaxial compressive strength, elastic modulus, and Brazilian tensile strength. Moreover, the behavior of different rock types differs to some extent when exposed to weathering cycles under dry and saturated conditions. A multivariate linear regression analysis was used to predict the changes in the physical and mechanical properties of different rock types. It was been shown that with some cautions, the obtained correlations can be generalized for practical cases and can be used to predict the change of rock physical and mechanical properties during the lifetime of rock engineering projects. Such predictions have a high potential of applicability in quite different types of natural stone applications in cold climates. From the stability of structures created in rock materials to the durability of structures created by different natural stones.

ABSTRACTOwing to deposition, weathering, and historical loading variations, the mechanical properties of underground rock and soil masses demonstrate significant spatial variability and stratified distribution. This study investigates the influence of multi‐layer soil spatial variability on ground settlement and tunnel reliability during shield tunnel construction by developing a refined stochastic finite element model. The CPSO‐TLOOA‐Stacking hybrid intelligent algorithm optimizes the inversion of multi‐stratum mechanical parameters based on the measured surface settlement data from tunnel engineering and the Conditional Tabular GAN (CTGAN) data extension framework. Utilizing the Karhunen–Loève (K‐L) series expansion method and random field theory, a joint analysis framework of stochastic finite element and probability statistics is constructed to evaluate the impact of spatial random field parameters of different soil layers on formation deformation and failure probability. Coupled with the Hamiltonian Monte Carlo‐Subset Simulation algorithm, the reliability of tunnel deformation under conditions of cross‐correlated random fields with multiple surrounding rock parameters is effectively assessed. The results indicate that the R2 value of the expanded dataset fitted by the CPSO‐TLOOA‐Stacking hybrid intelligent algorithm is 99.46%, and the relative error between the dataset and the measured value is 0.7%. The Hamiltonian Monte Carlo‐Subset Simulation algorithm significantly enhances the calculation efficiency of tunnel deformation reliability and provides valuable guidance for shield tunnel construction and design.

There is currently a lack of studies on mechanical characteristics for nano-grouted rock under deep high temperature and disturbance conditions. This research actively explores this issue. Meanwhile, the dynamic mechanical properties of superfine cement-grouted rock are also listed for comparison. The key findings indicate that both nano-grouted and superfine cement-grouted fractured rocks exhibit an upward trend in dynamic compressive strength with increasing temperature. However, a notable contrast arises: at relatively low temperatures (room temperature and 100 °C), nano-grouted specimens demonstrate superior dynamic strength compared to those of superfine cement-grouted specimens. Conversely, at a higher temperature of 300 °C, the compressive strength of the nano-grouted specimen drops significantly, where scanning electron microscope (SEM) tests explain this phenomenon from a microscopic perspective. Additionally, both types of grouted specimens show an increasing tendency in dynamic peak strain with temperature, with nano-grouted specimens generally exhibiting higher peak strain, except at 100 °C where it is slightly lower than that of the superfine cement-grouted specimen. SEM analysis further reveals that nano-grouted regions display a characteristic “honeycomb” structure with numerous closely packed small pits, with surface compactness notably higher at 300 °C than at 100 °C, which is consistent with the conclusion that the mechanical strength at 300 °C is higher than that at 100 °C in the dynamic impact experiments for nano-grouted specimens.

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 220649, “Automated Sand-Influx-Mitigation Workflow Using Geomechanical Analysis and Minimum Tubinghead-Pressure Estimation,” by Prince Kumar, Upasana Gogoi, and Bhartendu Bhatt, SPE, SLB, et al. The paper has not been peer reviewed. _ The authors describe an automated workflow that helps mitigate sanding caused by excessive drawdown by determining the minimum tubinghead pressure (THP). The automated workflow is designed to autocalibrate, analyze, and recommend actionable measures to control THP to prevent sand ingression. This enables oil and gas operators to control sand production, resulting in production enhancement and fewer workover jobs. Field Background Field A is an onshore gas field producing for over 15 years. With bottomwater drive, no depletion of reservoir pressure was evident. The main reservoir sand, of Oligocene to Miocene age, is weak in nature and prone to sanding. In the absence of a geomechanical study, determining the critical drawdown pressure (CDDP) for the reservoir poses a challenge for sand-free production. The wells were dying out frequently because of choking of perforations from produced sand settling in the well. As a result, frequent workovers were required for continuous flow from the wells. Based on the data availability and feasibility of the solution with respect to utility and functionality of the potential solution, six naturally flowing gas wells from the field were shortlisted for the study. Study Objectives With the aim of developing a digital oilfield solution to calculate minimum THP to be maintained for sand-free production, a workflow was established. The workflow has four major components: 1D geomechanical analysis, sand-ingression analysis, well modeling and autocalibration, and automated THP estimation. Fig. 1 shows the steps followed to develop the sand-influx-mitigation workflow. The output of the overall workflow is CDDP from the geomechanics workflow and minimum THP limit from the well-model-based workflow; the geomechanics part is an offline study and the well-model part features an automated workflow for sensitivity execution. Methodology Geomechanical Analysis. 1D Mechanical Earth Model (MEM) Construction for Wells. The 1D MEM is a set of rock-mechanical parameters, pore pressures, and stresses as a function of depth that can be used to understand and quantify the behavior of subsurface formations when they are subjected to deformation and change in pressure, temperature, and stress. Once an MEM is constructed, it can be used to conduct wellbore-stability and sand-production analyses for drilling and completion. Wellbore-Stability Analysis. Wellbore-stability analysis can be performed to check sanctity and calibrate the 1D MEM. Using the computed rock properties and horizontal stresses, history matching is performed with actual drilling events and observations, such as breakouts or drilling-induced tensile fractures observed in image logs and breakouts interpreted from caliper logs. When the predicted failures and events match with the actual observations during drilling, one can conclude that the 1D MEM is calibrated and represents the subsurface rock-mechanical properties.

The mechanical behavior of landslide rock masses and slip zone soils plays a crucial role in the initiation and evolution of landslides, particularly under prolonged rainfall conditions, where the saturation process leads to strength degradation and changes in failure mechanisms. This study focuses on the Shibanping landslide in Yunyang County, Chongqing, and systematically investigates the mechanical properties and energy evolution of the rock and soil mass in the slip zone under different saturation durations. Conventional triaxial compression tests were conducted on sandstone and argillaceous sandstone to examine their strength, elastic modulus, and failure modes under natural and saturated conditions. In situ direct shear tests were performed on slip zone soils to evaluate the degradation trend of shear strength parameters with changing water content. The results indicate that the peak strength and elastic modulus of the rock mass increase with confining pressure, while water saturation significantly weakens the rock strength, with argillaceous sandstone exhibiting greater water sensitivity and structural degradation. After saturation, the cohesion and internal friction angle of the slip zone soil decreased by 29.7% and 25.0%, respectively, leading to a pronounced reduction in shear resistance. Furthermore, energy evolution curves during the rock mass loading process reveals that energy release occurs earlier and more violently under saturated conditions, indicating a more abrupt failure process. This study can enhance the understanding of the stability evolution mechanism of rainfall-induced landslides, and provides theoretical and parameter support for disaster early warning and engineering mitigation.

In shale reservoirs, fracturing fluid can be easily absorbed into the pore space due to the strong capillary force of shale. These invading fluids can impact the rock mechanical properties and creep behavior characteristics of shale under water-rock interaction. This paper discussed the influence of water-rock interaction on the mechanical parameters and creep behavior of shale rocks based on shale hydration swelling experiments, acoustic-triaxial compression tests, and shale creep experiments. The experiments show that: There are two stages of shale hydration swelling: rapid swelling stage and stable swelling stage. Temperature mainly impacts the hydration swelling rate, while the type of liquid mainly impacts the hydration swelling amplitude. Water-rock interaction can damage the shale mechanical properties and cause the decrease of the Young's modulus, Poisson's ratio, and compressive strength. The degradation rate of Young's modulus and compressive strength significantly decreases after 10 days of water rock interaction. Water rock interaction can also alter the creep characteristics of shale, increasing the amplitude and rate of shale creep. The lower the liquid mineralization, the stronger the shale creep. The higher the temperature, the stronger the creep of shale.

Anisotropy has a significant impact on the elastic and mechanical properties of rocks. Misidentifying a rock formation as isotropic can lead to significant errors in predicting stress distribution and mechanical deformation in the subsurface. Sandstone-shale laminated rocks are intrinsically anisotropic and are of great interest in subsurface engineering applications, as they constitute important assets in global oil and gas reserves. Under specific conditions (layer thickness, property contrast), these rocks can be effectively represented by an equivalent homogeneous transversely isotropic (TI) medium. The elastic moduli of the TI medium are calculated as the product of the properties of each layer and their respective thicknesses. We examine the latter concept through laboratory testing and angle-dependent ultrasonic reflection-coefficient measurements. Experimental data acquired from synthetic 3D-printed layered samples with varying layer thicknesses (smaller or greater than the receiver size) are compared with semi-analytical and numerical simulations. This comparative analysis yields valuable insights into the resolution of the method and helps to determine the conditions under which spatially heterogeneous samples can be accurately represented by effective-medium models of elastic rock behavior. Laboratory measurements acquired in a controlled environment confirm that samples characterized by weak anisotropy and layer thickness smaller than the receiver diameter can be accurately represented by an equivalent vertical TI medium. However, the receiver size-to-layer thickness condition is only valid under the assumption that the receiver aperture spans several wavelengths and that the measurements are subject to spatial averaging. Noteworthy differences arise when measurements are taken parallel and perpendicular to the sample bedding plane. Measurements acquired perpendicular to the layering reflect the properties of the effective medium. Reflection coefficients acquired parallel to the layers can effectively capture the elastic properties of the layer with differences below 5% compared with the homogeneous material.

Study on the effect of supercritical carbon dioxide on rock mechanical properties of carbonate reservoirs

The article presents the results of a comprehensive analysis of the floor pillars and room fenders stability for the Mayskoye deposit based on geomechanical studies. The key parameters of the room-and-pillar mining system with backfilling of the excavated space are examined, including the impact of the dip angle of the ore body, the depth of mining operations, as well as the mechanical properties of the host rock and backfill material on the optimum dimensions of the pillars. Numerical modeling was performed using advanced software suites, which allowed estimating the stress-and-strain state of the rock mass under various mining scenarios. Special attention is paid to technological solutions aimed at improving pillar stability and mining efficiency, including the choice of a rational mining sequence, optimization of the room geometry and backfill parameters. It is shown that the deposit dip angle and mining depth have a significant impact on the load distribution in pillars, which should be taken into account when designing the mining systems. Practical recommendations are provided to reduce the risk of the roof collapse and improve the safety of mining operations. The research results can be used in the design and operation of similar fields with the room-and-pillar mining and backfill systems. The paper discusses parameters of the room-and-pillar mining system with backfilling of the mined space as well as the impact of the dip angle of the ore body and the depth of the mining operations on the dimensions of the pillars. Technological solutions are presented to ensure the stability and efficiency of mining operations

During the long-term operation of salt cavern gas storage, multiple injections and extractions of gas will cause periodic temperature changes in the storage, resulting in thermal fatigue damage to the surrounding rock of the salt cavern and seriously affecting the stability of the storage. This article takes the salt rock samples after thermal fatigue treatment as the research object, adopts a uniaxial compression test, and combines DIC and Acoustic Emission (AE) technology to study the influence of different temperatures and cycle times on the mechanical properties of salt rock. The results indicate that as the number of cycles and upper limit temperature increase, thermal stress induces continuous propagation of microcracks, leading to continuous accumulation of structural damage, enhanced radial deformation, and intensified local displacement concentration, causing salt rock to enter the failure stage earlier. The initial stress for expansion and the volume expansion at the time of failure both show a decreasing trend. After 40 cycles, the compressive strength and elastic modulus decreased by 23.8% and 27.4%, respectively, and the crack failure mode gradually shifted from tension-dominated to tension-shear composite. At the same time, salt rock exhibits typical “elastic-plastic creep” behavior under uniaxial compression, but the uneven expansion and thermal fatigue effects caused by periodic temperature changes suppress plastic slip, resulting in an overall decrease in peak strain energy. The proportion of elastic strain energy increases from 21% to 38%, and the deformation process shows a trend of enhanced elastic dominant characteristics. The changes in the physical and mechanical properties of salt rock under periodic temperature effects revealed by this study can provide an important theoretical basis for the long-term safe operation of underground salt cavern storage facilities.

Rock mechanical properties undergo significant deterioration in high-temperature environments, resulting in reduced rock mass strength and stability. To reveal the strength degradation patterns and deformation characteristics of fractured surrounding rock in deep high-temperature tunnels, this study conducted stress path loading and unloading tests on rock specimens subjected to various high temperatures. These tests were based on the stress evolution characteristics of the fractured zone in high-temperature tunnels, using an MTS815 rock mechanics servo testing machine. Results show that high temperatures induce varying degrees of damage to rock specimens, with damage severity increasing as temperature rises. A temperature of 300°C is identified as the critical damage-sensitive zone for high-temperature rock specimens. As temperature increases, the strength, cohesion, and internal friction angle of initially damaged high-temperature rock specimens all exhibit decreasing trends of varying magnitudes. Peak strength degradation is most significant, with a maximum reduction of 67.38% and a minimum of 18.49%. Additionally, cohesion undergoes a sudden change at 300°C, decreasing by 44.31%, while the internal friction angle shows a less substantial reduction. Throughout the experiment, both circumferential strain and volumetric strain increase noticeably. Volumetric strain changes from negative to positive values, which signifies substantial dilation. Rock specimens that have undergone high-temperature damage exhibit clear characteristics of strain softening and residual strength following the attainment of peak strength. The ultimate macroscopic failure is primarily characterized by mechanisms associated with combined shear failure.

To investigate the evolution mechanism of rock mechanical properties under high-stress conditions, marble samples from deep underground were selected for a series of triaxial compression tests, microscopic fracture surface scanning, and discrete element numerical simulations. The results indicate that significant changes in the mechanical properties of marble occur when the confining pressure exceeds 30MPa. Under low confining pressure conditions, the stress-strain curve of the rock exhibits relatively weak post-peak deformation capacity. As the confining pressure increases, the peak strength of the rock increases significantly, while the elastic modulus remains relatively stable. The rock exhibits low cohesion and high internal friction angle. Under high confining pressure conditions, the stress-strain curve demonstrates more ideal plastic deformation characteristics. As the confining pressure increases, the increase in peak strength becomes less pronounced, while the elastic modulus rises. The rock exhibits high cohesion and low internal friction angle. Analysis of the fracture surface morphology shows that under high confining pressure, the failure mechanism of the rock gradually shifts from primarily grain boundary cracking to predominantly transgranular fracture. The microscopic differences in the internal fracture mechanism of the rock are the key factors driving the evolution of its mechanical properties.