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This study focuses on the petrographic and geomechanical properties of the Inzari Formation rocks in Tar Khel Village, District Swabi, Khyber Pakhtunkhwa, Pakistan, on their suitability as building materials for structures such as bridges, buildings, and roads. Five fresh samples from various areas of this formation were analyzed and identified as siliciclastic mudstone through petrographic analysis. The results of physical properties (water absorption, specific gravity, and porosity) and mechanical properties (unconfined compression strength, unconfined tensile strength, Schmidt hammer test, and shear strength) indicate the Inzari Formation rocks have unconfined compressive strengths ranging from 23 to 94 MPa, specific gravity values ≥2.78, and low porosity and water absorption values (<1%), suggesting their excellent potential as building materials. Comparatively, the unconfined compressive strength values of the Inzari Formation rocks are similar to those of the NikanaiGhar limestone, which averaged 93.348 MPa, further confirming their suitability for construction. Additionally, the low porosity values of the Inzari Formation rocks align with the porosity range of 0.31% to 0.41% reported in the NikanaiGhar limestone study. Based on these findings, the Inzari Formation rocks are appropriate for use as fine aggregate in concrete, asphalt, and other construction materials. [ABSTRACT FROM AUTHOR]

This paper presents an extensive comparative analysis of the experimental results of chemical stabilisation of clayey soil in laboratory conditions by comparing the effects of adding conventional stabilisers (lime, cement binder), stabilisers that can be considered as waste material (fly ash, rock flour), as well as alternative chloride-based materials (ferric chloride, calcium chloride, potassium chloride) on the geomechanical properties of the soil. With the aim of determining the stabiliser optimal content in the mixture with the soil, in the first part of the research, the effects of stabilisation of clayey soil of medium plasticity using the considered stabilisers with different percentage share on the change in uniaxial compressive strength (UCS) and pH value of the soil at different time intervals after the treatment were analysed. In the second part of the research, additional tests were conducted on soil samples with optimal content for each of the considered stabilisers by monitoring changes in the physical and mechanical properties of the soil. These include Atterberg's limits (liquid limit and plasticity limit), modulus of compressibility in the oedometer, California bearing ratio (CBR), and swelling potential at different time intervals after the chemical treatment to determine the durability of stabilisation effects. The results of the conducted research reveal that each of the conventional, waste, and alternative materials considered as chemical stabilisers contributes to the improvement of the geomechanical properties of the clayey soil, primarily in terms of increasing the bearing capacity and reducing the swelling of the treated soil. [ABSTRACT FROM AUTHOR]

Increased demand for decarbonization and renewable energy has led to increasing interest in engineered subsurface storage systems for large-scale carbon reduction and energy storage. In these applications, a working fluid (CO2, H2, air, etc.) is injected into a deep formation for permanent sequestration or seasonal energy storage. The heterogeneous nature of the porous formation and the fluid–rock interactions introduce complexity and uncertainty in the fate of the injected component and host formations in these applications. Interactions between the working gas, native brine, and formation mineralogy must be adequately assessed to evaluate the efficiency, risk, and viability of a particular storage site and operational regime. This study reviews the current state of knowledge about coupled geochemical–geomechanical impacts in geologic carbon sequestration (GCS), underground hydrogen storage (UHS), and compressed air energy storage (CAES) systems involving the injection of CO2, H2, and air. Specific review topics include (1) existing injection induced geochemical reactions in these systems; (2) the impact of these reactions on the porosity and permeability of host formation; (3) the impact of these reactions on the mechanical properties of host formation; and (4) the investigation of geochemical-geomechanical process in pilot scale GCS. This study helps to facilitate an understanding of the potential geochemical–geomechanical risks involved in different subsurface energy storage systems and highlights future research needs. [ABSTRACT FROM AUTHOR]

The method of acid hydraulic fracturing has been actively used in recent years, for the deposits of the Vereysky horizon of the Moscowian strata in the south-east of Tatarstan. Design development and the use of hydraulic fracturing requires full-fledged studies of the geomechanical characteristics of rocks, including the prediction of the propagation of emerging fractures. It is considered the main geomechanical characteristics for reservoir rocks and dense rocks involved in the structure of the sections, on the example of the study of polyfacial reservoirs of the Vereysky horizon of the Ivinskoye oil field. It was revealed that the carbonate reservoir rocks of the middle and upper parts of the Vereysky horizon (C2 vr3 and C2 vr5) have the least strength properties and a greater susceptibility to fracturing. More durable were sandstones of the upper part of the horizon, marls and mudstones of the middle and upper parts of the horizon, as well as mudstone and dense packstone, typical for the lower part of the Vereysky horizon. The presented data can be valid for most of the sections of the Vereysky horizon of the southeast of Tatarstan and are used for the choice of optimal solutions when applying the hydraulic fracturing technology.

Understanding the effects of mineral composition on geomechanical characteristics is critical in order to design and optimize the hydraulic fracturing necessary for shale gas reservoir production. Fundamental information is still missing in effects of mineral content and the experimental methodologies used. This paper provided an indepth assessment of the various experimental methodologies and their applications in the relationship between the mineralogical and geomechanical features of the shale formation. The results revealed that more brittle minerals increase their strength, but chemical reaction that creats pores decrease their strength. High content of carbonate or quartz increases a rock's brittleness, while a high content of clay increases a rock's plasticity and decreases its brittleness. As phyllosilicate content increases, the uniaxial compressive strength decreases, and this could be because phyllosilicate minerals have a weakening effect on the mineral bond. Young's modulus often climb as clay minerals decline and as silica with carbonate concentration rises, however Poisson's ratio increases in relation to an increase in clay minerals, which also increases the ductility of the reservoir shale rock. However, compared to minerals and matrix, does not significantly impact the strength of shale rock. Besides, the benefits and drawbacks of using uniaxial and triaxial compression, ultrasonic testing, and nano-indentation techniques in unconventional reservoirs were described. The findings suggest that, because of the possibility for experimental testing repeatability for increased accuracy, ultrasonic testing is the most appropriate experimental approach in the scenes of assessing static and dynamic geomechanical properties of reservoir shale rock. We suggested that numerically-based simulation of experimental techniques used for shale geomechanical evaluations and numerical modeling of heterogeneous shale rock samples will be necessary in light of the limitations faced in the applications of experimental techniques for shale geomechanical evaluation. [ABSTRACT FROM AUTHOR]

Static Poisson's ratio (νs) is crucial for determining geomechanical properties in petroleum applications, namely sand production. Some models have been used to predict νs; however, the published models were limited to specific data ranges with an average absolute percentage relative error (AAPRE) of more than 10%. The published gated recurrent unit (GRU) models do not consider trend analysis to show physical behaviors. In this study, we aim to develop a GRU model using trend analysis and three inputs for predicting νs based on a broad range of data, νs (value of 0.1627–0.4492), bulk formation density (RHOB) (0.315–2.994 g/mL), compressional time (DTc) (44.43–186.9 μs/ft), and shear time (DTs) (72.9–341.2 μs/ft). The GRU model was evaluated using different approaches, including statistical error analyses. The GRU model showed the proper trends, and the model data ranges were wider than previous ones. The GRU model has the largest correlation coefficient (R) of 0.967 and the lowest AAPRE, average percent relative error (APRE), root mean square error (RMSE), and standard deviation (SD) of 3.228%, −1.054%, 4.389, and 0.013, respectively, compared to other models. The GRU model has a high accuracy for the different datasets: training, validation, testing, and the whole datasets with R and AAPRE values were 0.981 and 2.601%, 0.966 and 3.274%, 0.967 and 3.228%, and 0.977 and 2.861%, respectively. The group error analyses of all inputs show that the GRU model has less than 5% AAPRE for all input ranges, which is superior to other models that have different AAPRE values of more than 10% at various ranges of inputs.

This study focuses on the petrographic and geomechanical properties of the Inzari Formation rocks in Tar Khel Village, District Swabi, Khyber Pakhtunkhwa, Pakistan, on their suitability as building materials for structures such as bridges, buildings, and roads. Five fresh samples from various areas of this formation were analyzed and identified as siliciclastic mudstone through petrographic analysis. The results of physical properties (water absorption, specific gravity, and porosity) and mechanical properties (unconfined compression strength, unconfined tensile strength, Schmidt hammer test, and shear strength) indicate the Inzari Formation rocks have unconfined compressive strengths ranging from 23 to 94 MPa, specific gravity values ≥2.78, and low porosity and water absorption values (

Wellbore failure criteria are essential issues during drilling deep wells. When drilling activities begin, the major stresses will change, and a new set of forces will be created in the rocks that surround the borehole. These stresses will be caused by the drilling operations themselves. This study concern with estimating stress state and magnitude around the wellbore by constructing a one-dimensional mechanical earth model (1D-MEM) that will help to predict failure criteria during deep wells drilling. A set of well logs data measurement has been used to compute failure criteria parameters for nine formations along the studied well. Repeated formation pressure and laboratory core testing are used to validate the calculated results of 1-D MEM. The prediction of failure criteria along the nine studied formations shows that for Ahmadi, Nahr Umr, Shuaiba, and Zubair formations, the wellbore failure criteria appear unsafe compared to other formations. The results of stress analyses indicate that the breakout factors wasn't affected by wellbore azimuth because of low-stress contrast along the these formations. Furthermore, shear failure can be prevented by drilling the well with an inclination of less than 350. As well as, to prevent breakdown the well should be drilled with an inclination between 25o to 65o in the direction of minimum horizontal stress. These important results could be used to pridict accurate wellbore trajectory when planning to drill nearby wells in the future. [ABSTRACT FROM AUTHOR]

The strength of rock under uniaxial compression, commonly known as Uniaxial Compressive Strength (UCS), plays a crucial role in various Geomechanical applications such as designing foundations, mining projects, slopes in rocks, tunnel construction, and rock characterization. However, sampling and preparation can become challenging in some rocks, making it difficult to determine the UCS of the rocks directly. Therefore, indirect approaches are widely used for estimating UCS. This study presents a multivariate Regression Model implemented in Matlab to calculate the UCS of Limestone rocks. To validate the proposed model's effectiveness, a comprehensive dataset of 22 limestone rock samples is collected from the old city center of Annaba, Algeria. The dataset included measurements of Ultrasonic Pulse Velocity (UPV), Schmidt rebound number (SRN), and actual UCS values from laboratory tests. Three regression metrics, including Coefficient of Regression (R²), Root Mean Square Error (RMSE), and Mean Absolute Error (MAE), were used to evaluate and compare the performance of the models. The results indicate a high predictive capability of the developed model, with an R² value of 0.848, an RMSE of 3.562 MPa, and an MAE of 2.962 MPa. To place these findings in the frame of the international state of the art, our model was compared with other established models from previous studies. Our model demonstrates significant practical applicability by effectively predicting UCS with a minimal number of parameters, showcasing a lower RMSE compared to many existing models. [ABSTRACT FROM AUTHOR]

An experimental method is proposed to assess blasting requirements based on in-situ cratering behavior. The method relies on single hole blast (SHB) tests to derive burden-dependent relationships. A non-linear crater model of the form Y = C b s is calibrated from SHB test results to describe the cratering behavior. Parameters C and s represent characteristic blastability index parameters that depend on geomechanical and operational conditions. A series of experimental SHB tests were conducted at three hard rock mines. The craters were mapped to capture the breakout profile and calibrate the model. Results showed that coefficient C presents an inverse linear correlation with burden B , while exponent s is approximately constant for a considerable range of burden values. Experimental results are used to define burden dependent relationship for bench blast designs and blasthole placement in underground development rounds. A complementary analysis addresses the prevalence of multiple cratering mechanisms according to geology and burden dimension. [ABSTRACT FROM AUTHOR]

Understanding the effects of mineral composition on geomechanical characteristics is critical in order to design and optimize the hydraulic fracturing necessary for shale gas reservoir production. Fundamental information is still missing in effects of mineral content and the experimental methodologies used. This paper provided an in-depth assessment of the various experimental methodologies and their applications in the relationship between the mineralogical and geomechanical features of the shale formation. The results revealed that more brittle minerals increase their strength, but chemical reaction that creats pores decrease their strength. High content of carbonate or quartz increases a rock's brittleness, while a high content of clay increases a rock's plasticity and decreases its brittleness. As phyllosilicate content increases, the uniaxial compressive strength decreases, and this could be because phyllosilicate minerals have a weakening effect on the mineral bond. Young's modulus often climb as clay minerals decline and as silica with carbonate concentration rises, however Poisson's ratio increases in relation to an increase in clay minerals, which also increases the ductility of the reservoir shale rock. However, compared to minerals and matrix, does not significantly impact the strength of shale rock. Besides, the benefits and drawbacks of using uniaxial and triaxial compression, ultrasonic testing, and nano-indentation techniques in unconventional reservoirs were described. The findings suggest that, because of the possibility for experimental testing repeatability for increased accuracy, ultrasonic testing is the most appropriate experimental approach in the scenes of assessing static and dynamic geomechanical properties of reservoir shale rock. We suggested that numerically-based simulation of experimental techniques used for shale geomechanical evaluations and numerical modeling of heterogeneous shale rock samples will be necessary in light of the limitations faced in the applications of experimental techniques for shale geomechanical evaluation.

This paper presents an extensive comparative analysis of the experimental results of chemical stabilisation of clayey soil in laboratory conditions by comparing the effects of adding conventional stabilisers (lime, cement binder), stabilisers that can be considered as waste material (fly ash, rock flour), as well as alternative chloride-based materials (ferric chloride, calcium chloride, potassium chloride) on the geomechanical properties of the soil. With the aim of determining the stabiliser optimal content in the mixture with the soil, in the first part of the research, the effects of stabilisation of clayey soil of medium plasticity using the considered stabilisers with different percentage share on the change in uniaxial compressive strength (UCS) and pH value of the soil at different time intervals after the treatment were analysed. In the second part of the research, additional tests were conducted on soil samples with optimal content for each of the considered stabilisers by monitoring changes in the physical and mechanical properties of the soil. These include Atterberg’s limits (liquid limit and plasticity limit), modulus of compressibility in the oedometer, California bearing ratio (CBR), and swelling potential at different time intervals after the chemical treatment to determine the durability of stabilisation effects. The results of the conducted research reveal that each of the conventional, waste, and alternative materials considered as chemical stabilisers contributes to the improvement of the geomechanical properties of the clayey soil, primarily in terms of increasing the bearing capacity and reducing the swelling of the treated soil.

Increased demand for decarbonization and renewable energy has led to increasing interest in engineered subsurface storage systems for large-scale carbon reduction and energy storage. In these applications, a working fluid (CO2, H2, air, etc.) is injected into a deep formation for permanent sequestration or seasonal energy storage. The heterogeneous nature of the porous formation and the fluid–rock interactions introduce complexity and uncertainty in the fate of the injected component and host formations in these applications. Interactions between the working gas, native brine, and formation mineralogy must be adequately assessed to evaluate the efficiency, risk, and viability of a particular storage site and operational regime. This study reviews the current state of knowledge about coupled geochemical–geomechanical impacts in geologic carbon sequestration (GCS), underground hydrogen storage (UHS), and compressed air energy storage (CAES) systems involving the injection of CO2, H2, and air. Specific review topics include (1) existing injection induced geochemical reactions in these systems; (2) the impact of these reactions on the porosity and permeability of host formation; (3) the impact of these reactions on the mechanical properties of host formation; and (4) the investigation of geochemical-geomechanical process in pilot scale GCS. This study helps to facilitate an understanding of the potential geochemical–geomechanical risks involved in different subsurface energy storage systems and highlights future research needs.

In Burkina Faso, the most commonly used road construction material is lateritic soil. However, in its raw state, this soil does not meet the required recommendations. To overcome this problem, previous studies have often focused on improving these soils by adding cement. However, these studies have rarely included a multi-criteria characterisation of the main geomechanical parameters of treated soils. It was also noted that the identification parameters of lateritic soils could have an influence on their improvement with cement. The aim of this study is to highlight the influence of the physical and mineralogical properties of lateritic soils on the effectiveness of improving their geomechanical properties by adding a low content of cement (<3% wt.). The soils were taken from two sites: Saaba (LAS) and Kamboinsé (LAK). The effects of cement addition on the plasticity index, CBR index, Young's modulus, unconfined compressive strength, tensile strength and shear strength were studied. In their raw state, LAS and LAK have different physical properties and cannot be used as sub-bases. The addition of cement improves the overall physical and mechanical properties of both soils, but to different degrees. Indeed, after adding 3% cement to the raw soils, the CBR index of LAS increases by 1275% compared with 257% for LAK; the unconfined compressive strength of LAS is twice as high as that of LAK, and the Young's modulus increases by around 460% for LAS compared with 360% for LAK. After improvement, these two soils met all the CEBTP specifications except for tensile strength. The effect of cement was more significant on LAS due to its better physical properties and higher clay mineral content, which would improve pozzolanic reactivity during cement hydration. Knowing the mineralogy of lateritic soils when treating them with cement would allow us to reduce the quantity of cement, thereby mitigating its negative impact on the environment. [ABSTRACT FROM AUTHOR]

An eco-friendly way to improve the engineering properties of lower-strength soils becomes attractive. This study investigates the feasibility of two industrial by-products, i.e., coal gangue (CG) and calcium carbide residue (CCR), as a sustainable CG–CCR geopolymer binder for soil stabilization. The geomechanical properties, compressibility, and microstructure of marine clay stabilized using CG–CCR geopolymer with different content by mass from 0 to 30% are measured by conducting consolidated undrained (CU) triaxial compression tests, oedometer tests, X-ray diffraction, mercury intrusion porosimetry, and field-emission scanning electron microscopy. A new empirical model is proposed to predict the failure strength of stabilized soils. Results indicate that the CG–CCR geopolymer can enhance the geomechanical properties of marine clay. Increasing the geopolymer content to 15% transforms the behavior of stabilized soils from a strain-hardening response (ductile failure) into a strain-softening response (brittle failure). The failure strength increases with the geopolymer content, confining pressure, and curing time. Increasing the geopolymer content to 30% improves the cohesion and internal friction angle to 479.8 kPa and 21.1°, respectively, being approximately 96.1 and 4.9 times those of unstabilized soil. The geopolymer content of 30% is found as the optimum to achieve the lowest compressibility. Microstructural analyses show that the reaction products of CG–CCR geopolymer binder could fill the intergranular pores and densify the soil by reducing the void space between soil particles, explaining the strength improvement of marine clay. This study provides a potential strategy for enhancing the geomechanical properties of marine clay by utilizing industrial geological waste. [ABSTRACT FROM AUTHOR]

Sedimentary phosphate extraction in open-pit operations generates large volumes of waste rock (WR), which are mainly overburdens and interburdens. Traditionally, the WR is mixed and stored on the surface in waste rock piles (WRPs). This paper presents a case study of the Benguerir mine site in Morocco. It investigates the potential valorization of each WR lithology based on the geological and geomechanical properties to reduce their environmental footprint and create added value to "waste." The WR samples (soils and rocks) were collected from drill cores and mining trenches in the Benguerir mine. The geological characterization results using petrographic descriptions indicate the presence of nine phosphate layers and, in addition to the overburdens, eight interburdens. Four types of WR are identified: carbonate, siliceous, marly clay, and phosphate. The geomechanical characterization of soil-like samples showed an average plasticity index (PI) of 50% according to the methylene blue value (MBV) of 7.1, classifying them in the A3–A4 categories as plastic and clayey marl soils. The hard rock samples have excellent mechanical properties in terms of their uniaxial compressive strength (UCS), Los Angeles abrasion value (LA), and micro-Deval value (MD). The average compressive strength is 104 MPa for the flint, 35 MPa for the phosphate flint, 32 MPa for the silexite, 26 MPa for the limestone, 11 MPa for the indurated phosphate, and 8 MPa for the marly limestone. Based on the obtained results, these WRs can be considered as an excellent alternative secondary raw material for use in civil engineering applications, ceramics, and cement industries. [ABSTRACT FROM AUTHOR]

In this study, the changes in various geomechanical properties were studied for sandstones cropped out at the Mescitli region of the Gümüşhane city under different saturation and anisotropy conditions. For this purpose, 225 specimens were prepared considering the lamination planes of those were chosen to have orientation of 0, 30, 45, 60 and 90° relative to loading direction. Index properties of the sandstones such as dry unit weight (γdry), saturated unit weight (γsat), water absorption by weight (Aw) and water absorption by volume (Av) were assigned. In accordance with the objective of study P wave velocity, uniaxial compressive strength and indirect tensile strength values were determined based on different saturation and anisotropy conditions. It was noted as a result of the observations carried out that specimens parallel to lamination have higher wave velocities in general when compared with specimens that are perpendicular to lamination planes. While uniaxial compressive strength values for sandstones are high for specimens which are parallel and perpendicular to lamination, the lowest strength value was observed in specimens with an anisotropy angle of 30°. In addition, it was also observed that the strength values decrease at a significant level with increasing saturation conditions. Strength anisotropy ratio (RUCS) for sandstones varies between 1.28–1.49 based on different saturation conditions. Similarly, while indirect tensile strength values were higher in specimens that were parallel and perpendicular to lamination, they were lower for other anisotropy orientations. Indirect tensile strength values also decreased with increasing degree of saturation. [ABSTRACT FROM AUTHOR]

Rock properties in geomechanical models depend on electrofacies. Electrofacies classification is a crucial task for generating accurate rock property models. Insufficient information about core samples and image logs at all locations is the major drawback in electrofacies classification. This study classified electrofacies by the multi-resolution graph-based clustering (MRGC) approach using the well-log data from the Scotian shelf, Offshore Canada. The unsupervised method such as MRGC, ascendant hierarchical clustering, and self-organizing map uses the K-nearest neighbors and kernel index for defining the cluster dots which characterize the electrofacies. These classified facies are incorporated with core information to establish a relationship. This relation can develop electrofacies in the non-core zone/wells. The electrofacies were predicted using the MRGC approach to generate rock mechanical properties such as Young's modulus, Poisson's ratio, unconfirmed compressive strength, and internal friction coefficient. [ABSTRACT FROM AUTHOR]

Deep shale gas (burial depth > 3500 m) in the Longmaxi Formation of southern Sichuan Province will be the primary target for exploration and development in China for a relatively long period. However, the lack of a physical basis for the "sweet-spots" seismic and well-logging prediction is caused by uncertainty in the rock physical properties of deep shale gas in the research area. Acoustic and hardness measurements were performed on shale samples from a deep layer of the Longmaxi Formation in southern Sichuan. Microtextural characteristics of the shale samples were also analyzed by conventional optical microscopy and scanning electron microscopy. Based on these measurements, the rock physical properties of the shale samples and control factors are discussed. It is shown that the deep shale samples have similar properties to the shallow shale in mineral composition, microtexture, and pore type. However, the organic pore in deep shale samples is relatively undeveloped, while the dissolved pores are more developed. For high-quality shale samples (total organic content > 2%), crystal quartz of biological origin forms the framework of rock samples, resulting in effective dynamic and static properties, reflecting the elastic behavior of rigid quartz aggregates. For organic-lean samples (total organic content < 2%), orientated detrital clay particles take the role of load-bearing grains. Therefore, these shale samples' overall rock physical properties are mainly controlled by the elastic properties of "soft" clay. The load-bearing grain variation from organic-rich shale samples to organic-lean samples results in an overturned "V"-type change in terms of velocity versus content. Organic-rich shale samples also show an apparent low Poisson's ratio. Organic-rich shale has a slight velocity–porosity trend, while organic-lean shale shows a significant velocity–porosity trend. In addition, due to the difference in rock microtexture between organic-rich and organic-lean shale, these two kinds of reservoir rocks can be discriminated in cross plots of P-wave impedance versus Poisson's ratio and Young's modulus versus Poisson's ratio. Change in hardness also reflects the control of microtexture, and shale samples with biological-origin quartz as load-bearing grains show higher hardness and brittleness. However, the variation in quartz content has less of an impact on hardness and brittleness in shale samples with clay as the load-bearing grain. Our results provide an experimental basis for the geophysical identification and prediction of deep shale gas layers. [ABSTRACT FROM AUTHOR]

Geomechanical brittleness of tight formations calculated from Poisson's Ratio with Young's Modulus requires laboratory testing of cores and/or estimation from shear wave acoustic logs. In shale exploitation budgets are not available to provide those measurements in many wells and it is desirable to estimate a geomechanical brittleness index (BIg) from a basic, often limited, suite of available well logs. BIg helps field operators to select the most prospective sections of tight rocks that are likely to benefit most from fracture stimulation. A machine-learning (ML) approach that combines a few recorded well logs with derivative and volatility attributes calculated from that recorded data is applied to two wellbores that penetrate the Middle Devonian formations (Appalachian Basin). This technique is novel as it has not been previously applied to predict BIg. The results demonstrate that ML models involving just two or three recorded well logs plus selected attributes as input variables provide BIg predictions that are as accurate as ML models that involve three and five recorded well logs as input variables, respectively. Moreover, the ML models involving attributes are as generalizable as ML models based only on multiple recorded well logs when applying models trained with data from one well to predict BIg from well log data in another nearby well. Extreme gradient boosting and elastic net models provide the lowest BIg prediction errors when the trained models are applied to log data from another well. Feature importance analysis identifies that the recorded compression sonic log, bulk density and gamma ray, in that order, are the most influential features in the BIg prediction models applied to the two Marcellus Shale wells. However, two of calculated well-log attributes (moving averages of the well-log derivative and volatility) are particularly effective at improving the BIg predictions when used in combination with just those three recorded well logs. The technique is worth testing in other shale basins.

Predictive modeling of CO2 storage sites requires a detailed understanding of physico-chemical processes and scale-up challenges. Dramatic injectivity decline may occur due to salt precipitation pore clogging in high-salinity aquifers during subsurface CO2 injection. This study aims to elucidate the impact of CO2-induced salt crystallization in the porous medium on the geomechanical properties of reservoir sandstones. As the impact of salt precipitation cannot be isolated from the precursor interactions with CO2 and acidified brine, we present a comprehensive review and discuss CO2 chemo-mechanical interactions with sandstones. Laboratory geochemical CO2–brine–rock interactions at elevated pressures and temperatures were conducted on two sandstone sets with contrasting petrophysical qualities. Interaction paths comprised treatment with (a) CO2-acidified brine and (b) supercritical injection until brine dry-out, salt crystallization, and growth. Afterward, the core samples were tested in a triaxial apparatus at varying stresses and temperatures. The elastic moduli of intact, CO2-acidified brine treated, and salt-affected sandstones were juxtaposed to elucidate the geochemical–geomechanical-coupled impacts and identify the extent of crystallization damages. The salt-affected sandstones showed a maximum of 50% reduction in Young’s and shear moduli and twice an increase in Poisson’s ratio compared to intact condition. The deterioration was notably higher for the tighter reservoir sandstones, with higher initial stiffness and lower porosity–permeability. We propose two pore- and grain-scale mechanisms to explain how salt crystallization contributes to stress localization and mechanical damage. The results highlight the potential integrity risk imposed by salt crystallization in (hyper)saline aquifers besides injectivity, signaling mechanical failure exacerbated by pressure buildup. [ABSTRACT FROM AUTHOR]

In Burkina Faso, the most commonly used road construction material is lateritic soil. However, in its raw state, this soil does not meet the required recommendations. To overcome this problem, previous studies have often focused on improving these soils by adding cement. However, these studies have rarely included a multi-criteria characterisation of the main geomechanical parameters of treated soils. It was also noted that the identification parameters of lateritic soils could have an influence on their improvement with cement. The aim of this study is to highlight the influence of the physical and mineralogical properties of lateritic soils on the effectiveness of improving their geomechanical properties by adding a low content of cement (

This paper presents laboratory analyses of the influence of an acidic environment, salinity and temperature change are able to exert on the geomechanical properties of the opoka-rocks. This rock material, deriving from four sites in East–Central Poland, was found to be variously resistant to factors like the destructive action of water-soluble salts and the effects of an acidic environment, on account of the actuallydiverse nature of the rocks in question. Ultimately, the work offered a basis for a distinction to be drawn between the light opoka-rocks present at the Annopol and KazimierzWielki sites, and the heavy opoka-rocks from Bochotnica and Krasnobród, in terms of both textural and physical-mechanical features. The heavy opoka-rocks from Krasnobród proved least resistant to an acidic environment, which left strength reduced significantly. This kind of rock also experiences both an increase in porosity and absorbability and a decrease in weight. Furthermore, the influence of an acidic environment on aesthetic features of the examined rocks was in all cases negative, salts formed a patina on surfaces that obscured original structural and textural features. None of the tested types of rock presented resistance to the crystallization pressure such salt is able to exert.

Due to complexities in geologic structure, heterogeneity, and insufficient borehole information, shale formation faces challenges in accurately estimating the elastic properties of rock which triggers severe technical challenges in safe drilling and completion. These geomechanical properties could be computed from acoustic logs, however, accurate estimation is critical due to log deficit and a higher recovery expense of inadequate datasets. To fill the gap, this study focuses on predicting the sonic properties of rock using deep neural network (Bi-directional long short-time memory, Bi-LSTM) and random forest (RF) algorithms to estimate and evaluate the geomechanical properties of the potential unconventional formation, Permian Basin, situated in West Texas. A total of three wells were examined using both single-well and cross-well prediction algorithms. Log-derived single-well prediction models include a 75:25 ratio for training and testing the data whereas the cross-well includes two wells for training and the remaining well was used for testing. The selected well input logs include compressional wave slowness, resistivity, gamma-ray, porosity, and bulk density to predict shear wave slowness. The results using RF and Bi-LSTM show a promising prediction of geomechanical properties for Permian Basin wells. RF algorithm performed superior for both single and grouped well prediction. The single-well prediction method using the RF algorithm provided the highest accuracy of 99.90% whereas Bi-LSTM gave 93.60%. The best accuracy for a grouped well prediction was achieved employing Bi-LSTM and RF models, i.e., 96.01% and 93.80%. The average prediction including RF and Bi-LSTM algorithms demonstrated that accuracy for single well and cross well prediction is 96% and 94% respectively with an error below 7%. These outcomes show the astonishing capability of artificial intelligence (AI) models trained to create a realistic prediction to unlock unconventional potential when datasets are inadequate. Given adequate training data, operators could leverage these efficient tools by utilizing them to examine fracture interpretations with reduced cost and time when datasets are incomplete and thus increase the hydrocarbon recovery potential. [ABSTRACT FROM AUTHOR]

The index mechanical properties, strength, and stiffness parameters of rock materials (i.e., uniaxial compressive strength, c, ϕ, E, and G) are critical factors in the proper geotechnical design of rock structures. Direct procedures such as field surveys, sampling, and testing are used to estimate these properties, and are time-consuming and costly. Indirect methods have gained popularity in recent years due to their time-saving and highly accurate results, which are comparable to those obtained through direct approaches. This study presents a procedure for establishing a deep learning-based predictive model (DNN) for obtaining the geomechanical characteristics of marlstone samples that have been recovered from the South Pars region of southwest Iran. The model was implemented on a dataset resulting from the execution of numerous geotechnical tests and the evaluation of the geotechnical parameters of a total of 120 samples. The applied model was verified by using benchmark learning classifiers (e.g., Support Vector Machine, Logistic Regression, Gaussian Naïve Bayes, Multilayer Perceptron, Bernoulli Naïve Bayes, and Decision Tree), Loss Function, MAE, MSE, RMSE, and R-square. According to the results, the proposed DNN-based model led to the highest accuracy (0.95), precision (0.97), and the lowest error rate (MAE = 0.13, MSE = 0.11, and RMSE = 0.17). Moreover, in terms of R2, the model was able to accurately predict the geotechnical indices (0.933 for UCS, 0.925 for E, 0.941 for G, 0.954 for c, and 0.921 for φ). [ABSTRACT FROM AUTHOR]

The article describes the possibility of using the granulometric analysis of rock cuttings formed in controlled core scratching tests to estimate the angle of internal friction.The study object is the Kovykta gas-condensate field (GCF) that occupies a wide area in the southeastern part of the Irkutsk amphitheater of the Siberian platform. This uniquely complex geological structure holds significant reserves of hydrocarbons. Its sedimentary cover is composed of the Vendian – lower Paleozoic and partly Riphean formations. Their total thickness exceeds 6000 m, as estimated from the new seismic survey data [Vakhromeev et al., 2019].The sedimentary cover of the Kovykta GCF has been studied by surface and borehole geophysical techniques, remote sensing and geostructural methods, in combination with the tectonophysical approach [Seminsky et al., 2018] based on drilling data, including standard and special core sampling data.

The drilling fluid invasion into hydrate-bearing sediments will change the geomechanical properties of the reservoir and may lead to uncontrolled geological disasters in the worst case. Native sediments are replaced with artificial samples in this study to investigate the effect of drilling fluid invasion on the strength behaviors of hydrate-bearing sediments. The triaxial test is used primarily to assess the strength behaviors of hydrate-bearing sediments at varying temperatures, pressures, and hydrate saturation levels. The process of water-based drilling fluid penetrating into hydrate-bearing sediments is then experimentally imitated under various experimental conditions, with reservoir temperature of 4°C and pore pressure of 10 MPa. The possible repercussions of drilling fluid invasion and hydrate phase transition are identified by testing the mechanical properties of sediments under various invasion times and temperatures. The findings reveal that when hydrate saturation rises from 5% to 35%, the gas hydrate sediments shift from strain hardening to strain softening, with the critical hydrate saturation value of transition is between 15% and 25%. Peak strength increases with increasing hydrate saturation and pressure, and decreases with increasing temperature, whether drilling fluid invasion is present or not. The peak strength, Young’s modulus, shear modulus, and secant modulus of hydrate sediments all decreased significantly after drilling fluid invasion, although the Poisson’s ratio rose. These mechanical parameters are related to temperature and pressure under the action of drilling fluid. Finally, engineering and research recommendations for reducing the risk of drilling fluid invasion and hydrate dissociation are made based on experimental findings and theoretical analysis. This study innovatively examine the geomechanical mechanical properties of drilling fluid invading hydrate reservoir, which is critical for avoiding production concerns.

In the present investigation, composite coal seam III–IV of the Ramagundam coalfield of the Godavari Basin has been studied through scanning electron microscopy (SEM), optical microscopy, Fourier transform infrared spectroscopy (FTIR), proximate and ultimate analyses, porosimetry and permeametry. Vitrinite reflectance ( R ¯ r from 0.38 to 0.49%) and proximate parameters put sub-bituminous rank to this coal. Vitrinite (48.3% mmf basis) and inertinite (37.2% mmf basis) are abundant while liptinite (14.5% mmf basis) occurs in subordinated amount. Cleats and the fractures are more in the vitrain band but they are partially filled with mineral matter. Dead-end types of pores are common. Open and unmineralized cell pores and cavities in the fusain band offer adsorption sites and micro-permeability, but at places, they are broken, homogenized and mineral filled, which eventually reduce the permeability. Porosity (1.88–2.75%) and permeability (0.017–0.029 millidarcy, mD) substantiate the availability of adsorption sites but poor methane migration in coal seam. The compressive strength value (24.28–29.55 megapascal, MPa) gradually increases from the top towards the bottom of the coal seam and leads to compaction, and lesser permeability and porosity in the coal seam. The elastic modulus value suggests less cleat development (face and butt cleat). The studied coals are thermally less mature and yet to approach the oil window. Most of the samples show a volatile matter content more than 37.8%, a value below which thermogenic methane generation begins. Nevertheless, FTIR supports a moderate hydrocarbon-generating potential. Besides, the biogenic gases are likely to occur in variable quantity. [ABSTRACT FROM AUTHOR]

Seismic data provide evidence about hydrocarbon deposition, geological and geophysical subsurface information, including geomechanical aspects. Deriving and understanding geomechanical properties is crucial for reservoir management as it can avoid drilling and production-related problems that cause environmental impacts associated with land subsidence and uplift. The Poison's ratio (PR), Young Modulus (YM), and elastic moduli for a reservoir block were estimated using 3D seismic pre-stack data and well data. 3D Mechanical Earth Models (MEM) were also developed using the well logs, seismic horizons, and drilling data. Seismic data-derived geomechanical properties were compared with the mechanical earth models for the first time for this field. Well-tie analysis was used for inversion of 3D seismic data to extract detailed waveform and amplitude information. The brittleness index of the subsurface layers was estimated, which is a critical rock property that provides information about rock hardness and fragility phenomenon. The brittleness index has a diverse range from 5-35%, with significant contrast at shallow zones. PR and YM models generated from 3D MEM and seismic data have average values of 0.2 -0.6 and 5 - 28 GPa with significant contrast from shales and carbonates. The study recommends that the drilling through these problematic zones should be avoided to avoid wellbore problems that cause challenges in maintaining wellbore integrity and reservoir management in the North-Heera field, Mumbai Offshore Basin.

The effect of poroelastic properties of the shale matrix on gas storage and transport mechanisms has gained significant attention, especially during history-matching and hydrocarbon production forecasting in unconventional reservoirs. The common oil and gas industry practice in unconventional reservoir simulation is the extension of conventional reservoir simulation that ignores the dynamic behavior of matrix porosity and permeability as a function of reservoir effective net stress. This approach ignores the significant impact of the poroelastic characteristics of the shale matrix on hydrocarbon production. The poroelastic characteristics of the shale matrix highly relate to the shale matrix geomechanical properties, such as the Young’s Modulus, Poisson’s ratio, bulk modulus, sorption behavior, total organic content (TOC), mineralogy and presence of natural fractures in the multi-scale shale structure. In this study, in order to quantify the effect of the poroelasticity of the shale matrix on gas production, a multi-continuum approach was employed in which the shale matrix was divided into organic materials, inorganic materials and natural fractures. The governing equations for gas transport and storage in shale were developed from the basic fundamentals of mass and momentum conservation equations. In this case, gas transport in organics was assumed to be diffusive, while gas transport in inorganics was governed by convection. Finally, a fracture system was added to the multi-scale shale gas matrix, and the poroelastic effect of the shale matrix on transport and storage was investigated. A modified Palmer and Mansoori model (1998) was used to include the pore compression, matrix swelling/shrinkage and desorption-induced deformation of shale organic matter on the overall pore compressibility of the shale matrix. For the inorganic part of the matrix, relations between rock mechanical properties and the pore compressibility were obtained. A dual Langmuir–Henry isotherm was also used to describe the sorption behavior of shale organic materials. The coupled governing equations of gas storage and transport in the shale matrix were then solved using the implicit finite difference approach using MATLAB. For this purpose, rock and fluid properties were obtained using actual well logging and core analysis of the Marcellus gas well. The results showed the importance of the poroelastic effect on the pressure response and rate of gas recovery from the shale matrix. The effect was found to be mainly due to desorption-induced matrix deformation at an early stage. Coupling the shale matrix gas production including the poroelastic effect in history-matching the gas production from unconventional reservoirs will significantly improve engineering completion design optimization of the unconventional reservoirs by providing more accurate and robust production forecasts for each hydraulic fracture stage.

One of the criteria in the operational efficiency of drilling is the rate of penetration of the drill bit. Numerous factors affect the rate of penetration. Identification of the effective factors on rate of penetration may lead to a more accurate assessment of drilling time, and as a result, the controlling of operational costs. The concurrent effect of the entire influential factors as well as the differing significance of each of them on the rate of penetration makes the study and optimization of drilling operations much more complicated and difficult. Using the rock engineering systems (RES), the impact of effective operational and geomechanical factors on the rate of penetration has been assessed in this article and a model has been proposed for the prediction of the rate of penetration. Data from one of the wells within the Azadegan oilfield have been used in order to study the impact of effective factors on the rate of penetration. To this end, the effective factors on rate of penetration are initially identified and then an index called “the rate of penetration index (ROPi)” is proposed through the application of the rock engineering systems approach. This index has been calculated at four different depths along the aforementioned well. The results suggested the compliance of penetration rate predictions with field observations. Moreover, porosity and uniaxial compressive strength are the most effective factors on the rate of penetration whereas the weight of drilling fluid has the smallest impact. Finally, a classification for the penetration rate index is presented.

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Optimum perforation location selection is an important study to improve well production and hence in the reservoir development process, especially for unconventional high-pressure formations such as the formations under study. Reservoir geomechanics is one of the key factors to find optimal perforation location. This study aims to detect optimum perforation location by investigating the changes in geomechanical properties and wellbore stress for high-pressure formations and studying the difference in different stress type behaviors between normal and abnormal formations. The calculations are achieved by building one-dimensional mechanical earth model using the data of four deep abnormal wells located in Southern Iraqi oil fields. The magnitude of different stress types and geomechanical properties was estimated from well-log data using the Techlog software. The directions of the horizontal stresses are determined in the current wells utilizing image-log formation micro-imager (FMI) and caliper logs. The results in terms of rock mechanical properties showed a reduction in Poisson's ratio, Young modulus, and bulk modulus near the high-pressure zones as compared to normal pressure zones because of the presence of anhydrite, salt cycles, and shales. Low maximum and minimum horizontal stress values are also observed in high-pressure zones as compared to normal pressure zones indicating the effects of geomechanical properties on horizontal stress estimation. Around the wellbore of the studied wells, formation breakouts are the most expected situation according to the results of the wellbore stress state (effective vertical stress (σzz) > effective tangential stress (σθθ) > effective radial stress (σrr)). [ABSTRACT FROM AUTHOR]

Ground fissures, especially if they open due to a sudden collapse of the surface, is a serious risk for populated areas. Their common occurrence in unconsolidated sediments of the Main Ethiopian Rift was found to be mostly a result of piping. The fissures start by piping in linear sub‐horizontal underground voids, which often propagate upwards resulting in ceiling collapse and formation of deep and long ground fissures with vertical walls. In the southern and central Main Ethiopian Rift the fissures pose a serious risk to infrastructure and settlements. The ground fissures are often linear (up to several kilometres long and often tens of metres deep) and accompanied by sinkholes (along the length). A detailed field mapping of the geological (rock composition, orientation and character of lithological boundaries, primary fabrics and brittle structures) and geomorphological features (especially a length, width and depth of fissures, sinkholes and gullies) followed by in situ seismic anisotropy measurements and a laboratory determination of the geomechanical properties of volcanoclastic deposits was carried out to investigate the ground fissures' origin. The conditions and factors leading to the formation of the ground fissures have been linked to: (a) the presence of regional normal faults and the associated extensional joints and (b) the alternation of lithological units with contrasting hydraulic permeability. The latter corresponds to a sequence of less permeable hard rocks (e.g., rhyolitic ignimbrites) overlain by heterogeneous, soft and permeable, unconsolidated volcaniclastic deposits with a low amount of clay (less than 10%). The ground fissures' occurrence has shown affiliation to areas which have a significantly high seismic anisotropy (more than 20% at the study sites), which can be used as a proxy to map out high risk areas prone to piping and ground fissure formation. [ABSTRACT FROM AUTHOR]

Amid the ever-increasing urgency to develop oil fields with complex mining and geological conditions and low-efficiency reservoirs, in the process of structurally complex reservoir exploitation a number of problems arise, which are associated with the impact of layer fractures on filtration processes, significant heterogeneity of the structure, variability of stress-strain states of the rock mass, etc. Hence an important task in production engineering of such fields is a comprehensive accounting of their complex geology. In order to solve such problems, the authors suggest a methodological approach, which provides for a more reliable forecast of changes in reservoir pressure when constructing a geological and hydrodynamic model of a multi-layer field. Another relevant issue in the forecasting of performance parameters is accounting of rock compressibility and its impact on absolute permeability, which is the main factor defining the law of fluid filtration in the productive layer. The paper contains analysis of complex geology of a multi-layer formation at the Alpha field, results of compression test for 178 standard core samples, obtained dependencies between compressibility factor and porosity of each layer. By means of multiple regression, dependencies between permeability and a range of parameters (porosity, density, calcite and dolomite content, compressibility) were obtained, which allowed to take into account the impact of secondary processes on the formation of absolute permeability. At the final stage, efficiency of the proposed methodological approach for construction of a geological and hydrodynamic model of an oil field was assessed. An enhancement in the quality of well-by-well adaptation of main performance parameters, as well as an improvement in predictive ability of the adjusted model, was identified.

Abstract The Pyramids complex in Giza consists of three main pyramids in addition to the famous Sphinx and small queen’s pyramids. Recently, the pyramids of Cheops (Khufu), Chephren (Khafre) and Mykerinos (Menkaure) on the Giza plateau have been threatened by a rising groundwater table resulting from water leakage from the suburbs irrigation canals, and mass urbanization surrounding the Giza pyramids. The pyramids at Giza suffer from a lot of Geo-environmental and structural problems. The main objectives of this study are (1) to assess the current status of the preservation of this unique and high valuable archaeological site, (2) to analyze the various actions that cause the destruction of the pyramid complex, in particular the weathering activities and strong seismic event, and (3) to determine the geochemical and engineering properties for construction materials using different types of tools and advanced analytical and diagnostic techniques. Structural stability analysis requires good assessment of present conditions of major materials used such as stones and structural mortar. The paper shows a thorough analysis of the current condition of the Great Pyramids at Giza. The work includes a discussion and analysis of the natural character and source of the pyramids building stones, geological context, damage survey, petrographic investigation, and physical and mechanical characterization of the stones and structural mortars, by means of laboratory and in situ testing. The results are displayed, described and analyzed in the paper in the context of potential threats to the monuments. The experimental study indicates the dependence of mechanical geological properties on the physical properties and the mineral composition of the studied building materials. The physical and petrographic characteristic of the stones are related. The modeling of properties indicates a reliable relationship between the various visible pores and uniaxial compression force parameters that can be applied to predict and characterize limestone elsewhere.

Drilling operation is among the most complex engineering activities as it is affected by a wide variety of factors. Many researchers have considered the effects of geomechanical parameters (GPs) of the reservoir rock on the drilling parameters (DPs), so that one can contribute to enhancing the drilling efficiency by building on the knowledge about the interaction between the GPs and the DPs. In this paper, artificial intelligence (AI) methods were used to investigate the association between wide range of the DPs and the GPs and provided new approach to improve drilling operations in carbonate reservoirs. Indeed, as aspect of the types of parameters and also machine learning methods, the study is novel method and seeks coverage in the lake of considering GPs in terms of drilling and its effectiveness. Dataset was collected from two oil wells located in the southwest of Iran. Firstly, 1-D geomechanical models were built to represent two reservoir formations, namely Asmari and Sarvak. Acknowledging the differences in resolution between the mud-logging and petrophysical data, the data was preprocessed (up-scaled) to have it prepared for further analysis. Subsequently, two methods were applied on the preprocessed data: (1) K2 algorithm as an instance of the so-called Bayesian network, showing both direct and indirect associations between the considered variables, and (2) multilayer perceptron (MLP) as an artificial neural network. The results of the K2 algorithm confirmed the direct impact of the unconfined compressive strength (UCS), a GP, and on the rate of penetration (ROP), a DP. It was further found that the internal friction angle and vertical effective stress (GPs) tend to affect the weight on bit (WOB) and torque (DPs). Focusing on the Asmari and Sarvak Formations, the results of the MLP implied that, as far as the effects of GPs were concerned, the rotational speed (RPM) was most greatly affected by the internal friction angle followed by the UCS. Comparative charts were prepared to compare the corresponding GPs and DPs against different geomechanical units (GMUs). Given the non-controllable nature of the DPs, the results showed that the choice of such adjustable DPs as WOB and resultant torque could affect the ROP as indicators of the drilling operation quality. Finally, the results were used to propose optimal values of the adjustable DPs for different classes of rock properties. [ABSTRACT FROM AUTHOR]

Due to complexities in geologic structure, heterogeneity, and insufficient borehole information, shale formation faces challenges in accurately estimating the elastic properties of rock which triggers severe technical challenges in safe drilling and completion. These geomechanical properties could be computed from acoustic logs, however, accurate estimation is critical due to log deficit and a higher recovery expense of inadequate datasets. To fill the gap, this study focuses on predicting the sonic properties of rock using deep neural network (Bi-directional long short-time memory, Bi-LSTM) and random forest (RF) algorithms to estimate and evaluate the geomechanical properties of the potential unconventional formation, Permian Basin, situated in West Texas. A total of three wells were examined using both single-well and cross-well prediction algorithms. Log-derived single-well prediction models include a 75:25 ratio for training and testing the data whereas the cross-well includes two wells for training and the remaining well was used for testing. The selected well input logs include compressional wave slowness, resistivity, gamma-ray, porosity, and bulk density to predict shear wave slowness. The results using RF and Bi-LSTM show a promising prediction of geomechanical properties for Permian Basin wells. RF algorithm performed superior for both single and grouped well prediction. The single-well prediction method using the RF algorithm provided the highest accuracy of 99.90% whereas Bi-LSTM gave 93.60%. The best accuracy for a grouped well prediction was achieved employing Bi-LSTM and RF models, i.e., 96.01% and 93.80%. The average prediction including RF and Bi-LSTM algorithms demonstrated that accuracy for single well and cross well prediction is 96% and 94% respectively with an error below 7%. These outcomes show the astonishing capability of artificial intelligence (AI) models trained to create a realistic prediction to unlock unconventional potential when datasets are inadequate. Given adequate training data, operators could leverage these efficient tools by utilizing them to examine fracture interpretations with reduced cost and time when datasets are incomplete and thus increase the hydrocarbon recovery potential.

The index mechanical properties, strength, and stiffness parameters of rock materials (i.e., uniaxial compressive strength, c, ϕ, E, and G) are critical factors in the proper geotechnical design of rock structures. Direct procedures such as field surveys, sampling, and testing are used to estimate these properties, and are time-consuming and costly. Indirect methods have gained popularity in recent years due to their time-saving and highly accurate results, which are comparable to those obtained through direct approaches. This study presents a procedure for establishing a deep learning-based predictive model (DNN) for obtaining the geomechanical characteristics of marlstone samples that have been recovered from the South Pars region of southwest Iran. The model was implemented on a dataset resulting from the execution of numerous geotechnical tests and the evaluation of the geotechnical parameters of a total of 120 samples. The applied model was verified by using benchmark learning classifiers (e.g., Support Vector Machine, Logistic Regression, Gaussian Naïve Bayes, Multilayer Perceptron, Bernoulli Naïve Bayes, and Decision Tree), Loss Function, MAE, MSE, RMSE, and R-square. According to the results, the proposed DNN-based model led to the highest accuracy (0.95), precision (0.97), and the lowest error rate (MAE = 0.13, MSE = 0.11, and RMSE = 0.17). Moreover, in terms of R2, the model was able to accurately predict the geotechnical indices (0.933 for UCS, 0.925 for E, 0.941 for G, 0.954 for c, and 0.921 for φ).

Material properties is one of the most significant variables in terms of efficiency. The sediment layer in a coal pit mine has a possibility of sticking to the equipment bucket and reducing its productivity, especially in the disposal area. Consequently, stickiness has a close definition of adhesivity level; thus it may be associated with geomechanical properties. Various soil classification in the disposal area was investigated to identify the relationship between adhesivity and geomechanical properties such as water content, density, cohesion, and internal friction angles. Multivariate regression analysis and statistical test (F-test and t-test) were used to investigate geomechanical properties related to adhesivity on each disposal area. Primary data was taken from a standard and modified laboratory testing. The results showed that disposal materials were high-plasticity materials with different grain-sizes. The dominant grain size on disposal 1, 2, and 3 were clay, sand, and clay, respectively. Based on regression analysis, the adhesivity on each disposal was increased along with the water content until its optimum value. Using a statistical test with a significance level of 95% (P-value 0.04), water content, cohesion and internal friction angle affected the adhesivity level on disposal 1 by 99% (adjusted R² 0.99). Adhesivity level in disposal 2 was only affected with density by 63% (adjusted R² 0.63). Meanwhile, in disposal 3, the significance level of 33% (P-value 0.50) was used to define that water content, cohesion, and internal friction angle as parameters affecting adhesivity level by 33% (adjusted R² 0.33). [ABSTRACT FROM AUTHOR]

The lower Silurian Qusaiba Shale is one of the major source rocks for Paleozoic oil/gas reservoirs in Saudi Arabia and recently considered a potential unconventional shale gas resource. The study aims to evaluate the reservoir heterogeneity and production potential of Qusaiba Shale through the integration of geological, geomechanical and fractures characteristics. Three lithofacies were identified in Qusaiba shale. Mineralogical composition resulted in variable amounts of quartz ranging from 39 to 40, 45–55 and 60–78% for Lithofacies-I, II and III, respectively. Inter-granular porosity of these lithofacies is very low; however, fractures along laminations, at angle with laminations, and few micro-faults enhance porosity up to 5–6, 2–3, and < 1% in Lithofacies-I, II and III, respectively. The Lithofacies-I hosts the lowest fracture density (1.2 fractures/foot), likely due to the relatively lower quartz content (39%) as compared to other lithofacies. The fracture densities in Lithofacies-II and III are 2.1 and 3.2 fractures/foot, respectively. Lithofacies-I exhibits low stiffness in terms of low Young's modulus (average 26 GPa) and high Poisson's ratio (average 0.34). Mineralogy- and elastic parameters-based brittleness indices exhibited ductile behavior of this lithofacies. The brittleness index exhibited brittle behavior for silica-rich Lithofacies-III and has highest intensity of natural fractures. Hence, it is concluded that mineralogy and geological characteristics are the main controlling factors on shale brittleness, mechanical properties and fractures characteristics. The integration of geology, mineralogy and geomechanics plays the key role to better evaluate the prospectivity of shale reservoirs. [ABSTRACT FROM AUTHOR]

Abstract Sand production is a major problem that the oil and gas industry has been facing for years. It can lead to loss of production, equipment damage or complete well abandonment. Prediction of sand has been historically challenging due to the periodic nature of sand production, insufficient laboratory tests and lack of field tests validation. Analyses have been performed to identify weak zones for planned wells, and common technique is the application of shear modulus and mechanical properties log (MPL) criteria developed by Tixier et al. (J Pet Technol 27:283–293, 1975). However, the set criteria have been found to be generally inadequate to detect transition zone or predict weak formation in some fields. In this study, using the knowledge of rock behavior, geomechanical properties and well log data, we have established new simple criteria for identifying fragile sections within a transition zone. In situ logging data from a field X, located in Sabah, Malaysia, and Field Y, located in Shimokita, Japan, were used in this study. Using the threshold for shear modulus and MPL, the criteria for the geomechanical properties are set to differentiate formation strengths at different depths. The threshold for Poisson’s ratio is 0.34, Young’s modulus at 1.6 × 106 psi and the unconfined compressive strength at 2400 psi. The MPL and geomechanical models were generated to predict sanding incident. The results were subsequently validated with artificial neural network using MATLAB. Also, critical wellbore pressure is calculated and acts as a guide to operate outside the sand failure envelope. Thus, the prediction of the weak formation using geomechanical properties has been further established in this study.

Evaluating the physical and mechanical properties of materials such as rock or concrete is among the most significant issues in engineering studies. Measurement of the properties of the rocks either in the laboratory or in the field needs the standards and specific methods. Also, most of these tests need time and a large number of rock samples. Therefore, finding a method that can be accurately, quickly, and reliably predict the properties of rocks will provide a great advance in the quality of studies before or during the projects. The purpose of this paper is to find a method for predicting and determining the geomechanical properties of hard rocks during the drilling operation. For this purpose, after the preparation of the rock samples, acoustic and vibration signals propagated during the drilling process were recorded and processed. After analysing the acoustic and vibration signals, statistical analysis for investigation of the relationship between the properties of the rocks and the acoustic parameters was performed. Sound Pressure Level (SPL), First Dominant Frequency (FDF), and Vibration Level (VL) were selected as predictor variables for measuring and predicting Uniaxial Compressive Strength (UCS), Brazilian Tensile strength (BTS) and Schmidt rebound number (SRN) by multivariable regression. Results of statistical analysis show that there is an acceptable correlation coefficient between rock properties and properties of acoustic and vibration signals of the rock drilling operation. Hence, this method can be used as a relatively inexpensive, non-destructive, reliable and real-time method in large-scale mining or civil operation for predicting the rock properties. [ABSTRACT FROM AUTHOR]