Rock Strength Properties Research Articles

Optimizing Deep Geothermal Drilling for Energy Sustainability in the Appalachian Basin

This study investigates the geological and geomechanical characteristics of the MIP 1S geothermal well in the Appalachian Basin to optimize drilling and address the wellbore stability issues encountered. Data from well logs, sidewall core analysis, and injection tests were used to derive elastic and rock strength properties, as well as stress and pore pressure profiles. A robust 1D-geomechanical model was developed and validated, correlating strongly with wellbore instability observations. This revealed significant wellbore breakout, widening the diameter from 12 ¼ inches to over 16 inches. Advanced technologies like Cerebro Force™ In-Bit Sensing were used to monitor drilling performance with high accuracy. This technology tracks critical metrics such as bit acceleration, vibration in the x, y, and z directions, Gyro RPM, stick-slip indicators, and bending on the bit. Cerebro Force™ readings identified hole drag caused by poor hole conditions, including friction between the drill string and wellbore walls and the presence of cuttings or debris. This led to higher torque and weight on bit (WOB) readings at the surface compared to downhole measurements, affecting drilling efficiency and wellbore stability. Optimal drilling parameters for future deep geothermal wells were determined based on these findings.

Leeb Hardness Approach in the Determination of Strength after Accelerated Weathering Tests

ABSTRACT This study aimed to investigate the usability of the Leeb hardness test in determining changes in strength as a result of atmospheric weathering in works of cultural heritage built with low-strength pyroclastic rocks. To this end, the effects of weathering processes on strength properties were investigated in two building stones commonly used in Niğde province located in the Cappadocia (Turkey) region, which contains the most important works of cultural heritage created using low-strength pyroclastic rocks. The index, strength, mineralogical, and petrographic properties of rocks were first investigated. Then, freeze–thaw (F-T) and salt crystallization (SC) tests, the weathering processes of which consisted of six periods, were performed on samples prepared in cubic form. After the F-T and SC processes, the macro change in the samples and changes in weight loss, uniaxial compressive strength (UCS), and Leeb hardness (HL) values were determined. Highly correlated linear relationships were obtained between the SC and F-T cycles of the samples and the UCS and HL values. The HL test was applied to samples for which the UCS test could not be applied due to the loss of sample integrity after the advancing cycles of the accelerated weathering tests. Linear relationships with high correlation were determined between the UCS and HL values obtained from the samples after the accelerated weathering test. This study revealed that the HL approach could be used as an alternative in modeling the strength parameters of the weathering processes of the structures of cultural heritage built using low-strength rocks.

Estimation of unfrozen water content of saturated sandstones using nuclear magnetic resonance, mercury intrusion porosimetry, and ultrasonic tests

The unfrozen water content (UWC) is a crucial parameter that affects the strength and thermal properties of rocks in relation to engineering construction and geological disasters in cold regions. In this study, three different methods were employed to test and estimate the UWC of saturated sandstones, including nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), and ultrasonic methods. The NMR method enabled the direct measurement of the UWC of sandstones using the free induction decay (FID). The MIP method was used to analyze the pore structures of sandstones, with the UWC subsequently calculated based on pore ice crystallization. Therefore, the MIP test constituted an indirect measurement method. Furthermore, a correlation was established between the P-wave velocity and the UWC of these sandstones based on the mixture theory, which could be employed to estimate the UWC as an empirical method. All methods demonstrated that the UWC initially exhibited a rapid decrease from 0 °C to −5 °C and then generally became constant beyond −20 °C. However, these test methods had different characteristics. The NMR method was used to directly and accurately calculate the UWC in the laboratory. However, the cost and complexity of NMR equipment have precluded its use in the field. The UWC can be effectively estimated by the MIP test, but the estimation accuracy is influenced by the ice crystallization process and the pore size distribution. The P-wave velocity has been demonstrated to be a straightforward and practical empirical parameter and was utilized to estimate the UWC based on the mixture theory. This method may be more suitable in the field. All methods confirmed the existence of a hysteresis phenomenon in the freezing-thawing process. The average hysteresis coefficient was approximately 0.538, thus validating the Gibbs–Thomson equation. This study not only presents alternative methodologies for estimating the UWC of saturated sandstones but also contribute to our understanding of the freezing-thawing process of pore water.

Strength, Deformation and Fracture Properties of Hard Rocks Embedded with Tunnel-Shaped Openings Suffering from Dynamic Loads

In rock engineering, the dynamic loads caused by mechanical action and rock blasting have an extremely significant influence on the stableness of surrounding rock masses. To examine the impact of dynamic load on the mechanical properties and fracturing characteristics of hard rocks as well as the failure responses of underground openings, a number of prismatic samples with holes of different numbers and configurations were prepared for dynamic tests employing an SHPB loading device. The experimental results demonstrate that the order of dynamic compressive strength of each group of samples under the impact nitrogen pressure of 0.45 MPa is: G3 > G2 > G5 > G4 > G7 > G6, and the dynamic deformation process of the samples is parted into three phases: linear elastic deformation, plastic deformation and post-peak deformation. A total of three categories of cracks, i.e., spalling cracks, shear cracks and tensile cracks, occur in the specimens. The failure mode of the samples having one or two holes arranged in a vertical direction is controlled by shear cracks, whilst that of the rest groups of pre-holed specimens belongs to tensile-shear failure. The existence of the fabricated holes in the samples significantly weakens the mechanical properties and affects the fracture evolution characteristics, which rely on the quantity and layout of the cavities in the specimens. The interesting results are also discussed and explained, and could supply some insight in the mechanisms of tunnel surrounding rock failure and rock dynamic hazards such as rock burst.

Обобщённая математическая модель основных задач теории упругости для анизотропных тел

Introduction. The assessment of the strength of underground structures is a complex task that requires a comprehensive approach. In many cases empirical methods based on experience are not sufficient. For effective application of analytical methods, it is necessary to use mathematical modelling. This allows to simplify the problem considerably, to consider different variants, to identify cases to obtain a solution in a closed form. Materials and methods. The model is based on a system of singular integral equations with a shift and complex conjugate terms. The solution of the system is the complex elastic potential. Systems of singular equations with a Carleman shift are considered on the space of random functions converging in the mean square to expand the possibility of practical use of the work results. Results. The results of the study are: a mathematical model formulation, the development of an algorithm for reducing a system of singular equations to a system of known Fredholm integral equations of the second kind, a method for determining the solvability conditions and the number of solutions. Discussion. As a result of the study: (1) a general algorithm for finding a solution to a mathematical model is obtained; (2) the methodology for determining the number of solutions and the type of solvability conditions is given; (3) The solution algorithm is extended for the stochastic case; (4) The possibility of wider application of the mathematical apparatus of functions of complex variable for research of strength properties of rocks is proved. Conclusion. The proposed comprehensive approach to assessing the strength characteristics of underground structures, combining a set of analytical methods in conjunction with mathematical modelling, expands the variability of calculation and allows to simplify the problem significantly and obtain a solution in closed form. Resume. The paper develops a mathematical model of the stress state of an elastic body, which allows solving the basic problems of elasticity theory for a variety of media. Suggestions for practical applications and directions for future research. The results of the study make it possible to improve the efficiency of analytical methods in the study of the strength of underground structures. The obtained results are applicable for predicting the strength and safety of underground structures.

Experimental investigation on the influence of NaCl concentration on triaxial mechanical behaviors of a low-clay shale

During a hydraulic fracturing operation, a large quantity of salinity fracturing fluids will be retained in the shale reservoir, which may cause the problem of wellbore instability. Previous studies mainly focused on the change mechanism of clay-rich shale after brine immersion. However, the influence of NaCl concentration on mechanical behaviors of a low-clay shale is still unclear. Therefore, in this investigation, conventional triaxial compression tests were carried out on low-clay shale specimens saturated with NaCl solutions at different concentrations (0%, 5%, 15%, 25%) under different confining pressures (0 MPa, 15 MPa, 30 MPa, 45 MPa), and their mechanical properties were analyzed systematically. Optical microscopy, polarized light microscopy and scanning electron microscopy were used to understand the microscopic changes in shale samples after saturation in NaCl solutions. The brittleness indices of saturated shale specimens were evaluated based on rock strength properties and the energy evolution law. According to the experimental results, compared with the water-saturated specimens, the peak strength, elastic modulus, cohesion and internal friction angle of specimens saturated with 5%NaCl solution all showed a downward trend. However, for the specimens saturated with the NaCl solution at concentrations of 15% and 25%, higher NaCl concentration showed a greater rebound effect on the mechanical parameters compared with the 5%NaCl saturation. The microscopic observation showed that the brine could invade the interior of shale specimens from micropores, microcracks and bedding fractures, which were mainly parallel to the bedding direction. And the bedding fractures and some of micropores seemed to be filled by deposited NaCl crystals and mineral particles. The brittleness index of the brine-saturated shale specimen decreased at the low-concentration (5%) and increased at the high-concentration (15% and 25%). This investigation could provide a theoretical basis and mechanical parameters for analyzing the stability of shale wellbore affected by the salinity fracturing fluids.

DESTRUCTION OF ROCKS BY EXPLOSION DURING OIL TRANSPORTATION

When oil and gas wells are ready for operation, when drilling is carried out at the bottom of the well to establish contact with the formation, it is considered that the degree of crushing of the rocks is proportional to the speed of application of the load. As a result of the stresses created by them, the degree of fragmentation is higher. In the article, it is proposed to take into account the quality of crushing of the necessary rock by using some empirical coefficients in the calculation formulas. The dynamics of the rock dispersion process is studied on the basis of the hydrodynamic hypothesis. Here, the solution of the system of differential equations is given based on the fundamental laws of conservation of mass, energy and momentum. Based on the strength properties of mountain rocks, broken lines are found in the continuum of the whole environment, which determines the final effect of rock crushing. However, the accepted assumptions about the incompressibility of the rock and the transfer of the explosive impulse to the immediate environment significantly reduce the practical value of the results. It should be noted that in the immediate area directly adjacent to the load, the mountain rock is under uneven volume compression. In this case, the largest tangential stresses occur mainly in planes oriented at an angle of 450 to the radial direction. Thanks to this, a system of spiral sliding lines breaks the rock into small blocks. Outside this zone, a system of radial cracks is formed as a result of the expansion of the massif. When the pressure in the gas cavity decreases and the mass moves back in the direction of the load, tangential cracks appear. The combination of the volume compression zone and the reach zone constitutes the controlled crushing area. When the compression wave reaches the bare surface, it becomes a stress wave. As this wave travels from the surface to the load, it forms a system of jump cracks. The high explosive effect of explosive gases with sufficient explosion energy causes the release of such shattered rock. Obviously, this concept is very important for the development of the theory of explosive disintegration of mountain rocks. Because there is no unequivocal relationship between the nature of the dissolution of the rock and the acoustic hardness. One of the first to clearly describe the mechanism of shock wave formation and its transformation into a more explosive and seismic wave when detonation reaches the boundary of the charge cavity. In rocks, shock waves are formed during the entire time of expansion of the gas cavity. It explains in detail the mechanism of cracking phenomena by considering the cracks as a source of multiple reflections of the stress wave. Keywords: rock strength, constant material, scale effect, rocks, destruction probability, fractured, robustness theory, microcrack, mineral, experience constant, density of defects, displacement, compression.

Material and mechanical properties of young basalt in drill cores from the oceanic island of Surtsey, Iceland

Characterization of 2017 drill core samples from Surtsey, an oceanic island produced by 1963−1967 eruptions in the offshore extension of Iceland’s east rift zone, reveals highly heterogeneous microstructural, physical, and mechanical properties in subaerial, submarine, and subseafloor basaltic deposits. The connected porosity varies from 42% in weakly consolidated lapilli tuff in a submarine inflow zone to 21% in strongly lithified lapilli tuff in upper subseafloor deposits near the explosively excavated conduit. Permeability, however, varies over six orders of magnitude, from 10−18 m2 to 10−13 m2. Uniaxial compressive strength, P-wave velocity, and thermal conductivity are also highly variable: 10−70 MPa, 1.48−3.74 km·s−1, and 0.472−0.862 W·m−1·K−1, respectively. Synchrotron X-ray microdiffraction analyses integrated with major-element geochemistry and quantitative X-ray powder diffraction analyses describe the initial alteration of fresh glass, incipient consolidation of a fine-ash matrix, and partial closure of pores with mineral cements. Permeability, micromechanical, and thermal property modeling highlight how porosity and pore size in eruptive fabrics—modified through diverse cementing microstructures—influence the physical properties of the pyroclastic deposits. Borehole temperatures, 25−141 °C (measured from 1980 to 2018), do not directly correlate with rock strength properties; rather, the abundance and consolidation of a binding fine-ash matrix appears to be a primary factor. Analytical results integrated with archival data from 1979 drill core samples provide reference parameters for geophysical and heat transfer studies, the physical characteristics of pyroclastic deposits that lithify on a decadal scale, and the stability and survival of oceanic islands over time.

ИССЛЕДОВАНИЕ ФИЗИКО-МЕХАНИЧЕСКИХ СВОЙСТВ ГОРНОГО МАССИВА ПРИ ОСВОЕНИИ НЕДР

The article presents the results of studying the strength properties of rocks of the Zhilandinsky groups of deposits. The methods of mathematical statistics and correlation analysis made it possible to generalize the data of the physical and mechanical properties of rocks and to obtain graph-analytical dependences between the strength properties of rocks and the depth of their occurrence in the subsurface. The possibility of predicting the strength properties of rocks is scientifically substantiated.

ИЗУЧЕНИЕ ФИЗИКО-МЕХАНИЧЕСКИХ СВОЙСТВ ПОРОД МЕСТОРОЖДЕНИЯ БАССЕЙНА ПАРАТАУ

The article presents the results of studies of the structural features of the massif and the strength properties of rocks of the Karatau phosphorite deposits. The general pattern of variability of the strength properties of rocks in the massif was considered by the method of mathematical statistics and correlation analysis, as well as data on rock properties for deposits in the Karatau basin, where a stable relationship between average density, strength, adhesion, resistance and depth of their occurrence was established. The stress-strain state of the massif was determined by the unloading method and the correlation dependence of horizontal stresses on the depth of occurrence, as well as an assessment of the degree of strength, elasticity, plasticity of rocks and their ability to fracture or deformation under various loads. The regularities and parameters of the process of displacement of rock massifs similar in geological and tectonic structure for predicting the properties of rocks in the deposits of the basin are revealed. The results of the research can be useful in solving a number of technical problems in quarries and underground mines in assessing the stability of ledges and sides of quarries, in predicting angular displacement parameters, in calculating targets and ceiling spans.

Investigation of the stress state of an elastic hollow ball during filtration of liquid through its wall

When determining the stress state of an elastic hollow ball when filtering liquid through its wall, it is necessary to solve the stress problem for the case of liquid filtration to the center of the ball with a decrease in pressure in its cavity. This case represents for us an element of the general problem of the stressed state of the annular filter behind the casing during well operation. First, the problem of liquid filtration is solved -pressure changes in the body under study are determined during liquid filtration. Then the equilibrium equation with respect to radial deformation is solved. A change in the sign of the filtration potential leads to a change in the tangential stresses on the well wall to a value equal to a tripled depression of reservoir pressure (with radial stresses equal to zero). This explains the negative effect of well shutdowns, and even more so the change in the direction of the filtration flow in the downhole part of the formation on the stability of the walls of wells, the operation of which is complicated by sand formation. The maximum difference of the main normal stresses is observed on the well wall, therefore, in order to prevent formation destruction near the bottom, a necessary condition is that the strength properties of rocks correspond to the stresses acting in this zone. When operating wells prone to plugging, it is necessary to limit the depression of reservoir pressure to the maximum permissible value when the material of the filter zone is in an elastic state throughout the volume.

Prediction Unconfined Compressive Strength for Different Lithology Using Various Wireline Type and Core Data for Southern Iraqi Field

Unconfined Compressive Strength is considered the most important parameter of rock strength properties affecting the rock failure criteria. Various research have developed rock strength for specific lithology to estimate high-accuracy value without a core. Previous analyses did not account for the formation's numerous lithologies and interbedded layers. The main aim of the present study is to select the suitable correlation to predict the UCS for hole depth of formation without separating the lithology. Furthermore, the second aim is to detect an adequate input parameter among set wireline to determine the UCS by using data of three wells along ten formations (Tanuma, Khasib, Mishrif, Rumaila, Ahmady, Maudud, Nahr Umr, Shuaiba and Zubair). After calibration with core test, the results revealed that Young’s Modulus correlations are the best to predict UCS with RMSE (53.23 psi). Furthermore, the result showed that using the static Young Modulus as an input parameter in predicting UCS gives a closer result to the laboratory test than using a sonic log. This study found that many previous equations were developed for only one type of rock and tended to generalize poorly to the broader database. This study also provided more accurate rock strength estimation, leading to better prognosis in operational strategies and hydraulic fracturing location planning in oil well development when geomechanical analysis needs to be addressed where no core is available. Finally, the expected continuous rock mechanical profile indicates the formation's strength and stability around the wellbore.

Drill-string stability and stress localization: Influence of complex delay effects and dry friction

With the aim of enhancing the understanding of the complex dynamics of deep drilling, an integrated model with complex time delays and Stribeck friction is presented for studies on the axial-torsional dynamics of a drill string. Various aspects of the drill string are considered, including spatial distribution, structural and external damping, dry friction-induced damping, boundary conditions, and complex bit-rock interactions. The drill-string structure is spatially discretized by using the finite element method. With the resulting discretized complex delay system, stability analysis is conducted following the semi-discretization procedure. Through parametric studies, the effects of drilling parameters, dry friction, boundary conditions, and rock-strength properties on the drilling stability are obtained. Subsequently, an optimally tuned boundary condition with compliance is deployed at the top drive to expand the stable region and mitigate self-excited vibrations in the operational parameter space of drilling. To find the distribution of stress along the drill string, numerical simulations are conducted. The dynamical stress caused by self-excited vibrations is illustrated in the spatial–temporal plane. Strain and stress analysis reveal wave propagation along the drill string, including traveling and standing waves. The dynamic effective stress along the drill string is studied, and the von Mises effective stress is determined by combining the axial stress and torsional stress. On the basis of this information, the locations of the vulnerable points along the drill string are found in terms of structural strength. Finally, the tuned boundary condition at the top is deployed in the numerical simulations to show vibration control effectiveness. The results point to two possible vibration-cancellation approaches that can benefit from a tuned top boundary. The findings of this work can serve as a basis for identifying the locations of vulnerable points and alleviating the levels of axial-torsional vibrations in drilling applications.

OPTIMIZATION OF TECHNOLOGICAL SOLUTIONS FOR THE CONSTRUCTION OF WELLS FOR LOW-PRESSURE GAS PRODUCTION

Link for citation: Shalyapin D.V., Shalyapina A.D. Optimization of technological solutions for the construction of wells for low-pressure gas production. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 9, рр. 163-171. In Rus. The relevance of the research is caused by the necessity to apply the geomechanical modeling to substantiate the possibility for exploitation of low-pressure layers of the Cenomanian complex of the West Siberian oil and gas province with drilling liquids with density of 0,6 g/cm3 and to increase the profitability of drilling by constructing small-diameter wells. The main aims: collection of information necessary for geomechanical modeling; construction of a mathematical model of the mechanical properties of rocks composing the drilling interval for the production string; correlation analysis of calculated values and values obtained during core tests; correction of the model of mechanical properties based on experimental data; determination of boundary conditions for destabilization of the walls of wells under the influence of multidirectional effective stresses; establishing a safe interval of drilling mud density for exploitation low-pressure reservoirs; justification of the possibility of using washing liquids with density of 0,5–0,8 g/cm3; calculation of the strength characteristics of the well support, taking into account the reduction of its metal consumption; conducting economic justification of the feasibility of using small-diameter wells for field development at a late stage. Objects: lightweight drilling fluids, depression drilling technology, small-diameter wells. Methods: geomechanical modeling of the strength properties of rocks composing the geological section of wells for the production of low-pressure gas of the Cenomanian deposit; calculation of casing strings for strength at various stages of operation. Results. The authors have constructed the mathematical model of the elastic-strength properties of rocks of the drilling interval for the production string and determined the stress values at which the walls begin to fall out. They substantiated the possibility of drilling low-pressure wells using drilling fluids with density of 0,6 g/cm3, taking into account the prevention of fallings and collapses of the walls of wells and proved the possibility of reducing the metal consumption of the design of low-pressure wells to increase economic efficiency of drilling.

Heating-path dependency of fracture behavior of sandstone subjected to thermal treatment

The thermal effect has a negative impact on the strength and fracture properties of rocks, and much related research has been carried out around heat treatment methods such as temperature levels, heating rates and cyclic thermal shocks. In fact, the temperature history to which rocks are subjected is often complex, and the effects of this accumulation of thermal damage on the rock cannot be ignored. In this work, we have carried out three-point bending tests on sandstone subjected to thermal treatments under conventional and complex heating paths based on digital image correlation (DIC) method. The results show that the P-wave velocity, peak load and fracture toughness all tend to decrease with increasing temperature under conventional heating paths, and that 600 °C is the sandstone threshold temperature for strong and weak transformation. Under complex heating paths, a constant temperature of 200 °C for two hours and further heating to the target temperature does not weaken the mechanical properties of the sandstone, whereas a constant temperature of 400 °C for two hours and further heating results in a significant reduction. The variation trend of crack opening displacement (COD) with axial load shows that the cracks transition from slow opening in the early loading stage to rapid propagation near the peak load and develop into decelerated extension in the later stage. Finally, the crack propagation process was refined by determining the jump points of the maximum principal strain at different positions on the crack propagation path. At room temperature, the sandstone cracks at approximately 0.8Pm and propagates at a higher rate, exhibiting clear brittle characteristics. Both the crack initiation load and propagation rate show a significant decrease with increasing temperature after 200 °C, with ductile characteristics gradually becoming apparent.

Assessing the Strength and Deformation Properties of Serpentinite Rocks in Dry and Saturated Conditions

It is clear that the engineering properties of various rocks in dry and wet conditions are different. In general, the properties decrease with the presence of water. The present research investigates the effect of rock saturation on the strength and deformation properties of serpentinites collected from central Greece. A comprehensive laboratory test program was planned to evaluate unit weight, effective porosity, uniaxial compressive strength, elasticity modulus, and Brazilian tensile strength in saturated states. All the results of the above-mentioned saturated properties were compared with the respective properties measured in dry conditions taken from previous studies. Simple regression analyses were used to correlate the physical and mechanical properties of the two referred states. The obtained results revealed that the values of the considered physical and mechanical properties of the studied serpentinite rocks are deceased with the presence of water. There are good relations between different rock properties in dry and saturated states. Generally, the relations are better in dry state. All correlations between the same rock properties in dry and saturated states are as direct linear relations, whereas relationships between the mechanical and physical properties are mainly exponential. Some of them are logarithmic or power equations.

Petrographic and Geotechnical Features of Dir Volcanics as Dimension Stone, Upper Dir, North Pakistan

The utilization of dimension stone in construction has been prevalent since ancient times; however, its application in modern construction has gained significant attention over the last few decades. This research aimed to assess the physical and strength properties of volcanic rocks from the Kohistan Island Arc for their potential use as dimension stone. Five types of andesites (MMA, PMA-1, PMA-2, CMA, and FMA) and two types of agglomerates (AG-1 and AG-2) were identified based on their composition, color, and texture. The samples were characterized in terms of their petrography (compositional and textural), physical properties (specific gravity, water absorption, and porosity), and strength properties (unconfined compressive strength and unconfined tensile strength). Two non-destructive tests (ultrasonic pulse velocity test and Schmidt hammer) were conducted, and the degree of polishing was evaluated. Correlation analyses were carried out to establish possible relationships among these parameters. The presence of chlorite, epidote, sericite, and recrystallized quartz indicated signs of low-grade metamorphism in andesites. The study revealed that feldspar, amphibole, and quartz imparted good physical and strength properties to samples MMA, CMA, FMA, AG1, and AG2. On the other hand, PMA-1 and PMA-2 exhibited reduced physical and strength properties due to the abundance of alteration products like chlorite, sericite, and epidote. The unconfined compressive strength exhibited a strong correlation with ultrasonic pulse velocity, skeletal density, porosity, and water absorption. Weathering grade considerably affected the values of ultrasonic pulse velocity and Schmidt hammer. Consequently, samples PMA-1 and PMA-2 are not recommended for load-bearing masonry units and outdoor applications due to their high water absorption and low strength values. On the other hand, samples FMA and MMA exhibited excellent properties like high strength and good polishing, indicating their potential use as decorative and facing stones, external pavement, ashlar, rubbles, and load-bearing masonry units.

Experimental study of the influence of the degree of saturation on physical and mechanical properties of carbonate rocks in the Jurassic Tuwaiq Mountain Formation (Saudi Arabia)

Understanding the impact of saturation levels on the mechanical and physical properties of limestone and marly limestone deposits is very critical for geotechnical and mechanical studies in the energy and construction industries. This research aims to link the strength characteristics of carbonate rock (limestone and marly limestone) with physical and mechanical properties at saturation levels of 0, 0.25, 50%, 75% and 100%. To complete this work, 100 samples were collected and analysed employing an orderly research facility testing. According to experimental findings, the strength and durability of the limestone and marly limestone declined with rising saturation levels, while the P‐wave velocity Vp showed an upward trend from 0% to 100%. The uniaxial compressive strength (UCS) of the limestones employed in this research significantly decreased (up to 36%) between the dry and saturated stages for limestone samples. While marly limestone, there is a drop (up to 32%) in UCS. The findings of a straightforward regression study show that it is possible to predict the strength properties of rocks directly from various saturation levels. Additionally, a number of various estimate connections were created utilizing independent variables like Vp and saturation level. The experimental outcomes showed that Vp showed an upward tendency with an increasing degree of saturation. The deformability and strength parameters of the samples declined with increasing saturation degrees. The elastic modulus and strength both decrease as clay and water amounts increase. The quality index (QI) number for limestone is 45, which indicates that it has extremely good quality and can be used as a building material at 0% saturation. At 25%, 50%, 75% and 100% saturation, it is evaluated at 43, 40, 33 and 31, respectively. The marly limestone samples have high quality at 0% (QI = 36), but poor quality at 25%, 50%, 75% and 100% saturation (QI = 33, 30, 27 and 23). This research provides a better understanding of the relationship between saturation levels and the mechanical, physical and depositional characteristics of marly limestone and limestone, which might be helpful in industrial studies. Advance examination of distinctive sorts of carbonate rocks can be more supportive of broadening our understanding of this idea.

Влияние статической нагрузки от горнотранспортного оборудования на устойчивость уступов, расположенных в скальных породах

Most of the enterprises applying open-pit mining method at deposits face challenges of pit wall steepening when approaching the pit wall to the final position or reducing productivity. The main task when increasing the angle of pit slope is to determine its stability. One of the ways to steepen the open-pit wall is to increase the slope angle of benches composing the open-pit wall. The bench stability is primarily determined by its physical properties and structural uncertainty. The higher the strength properties of rocks, the steeper the slope angle formed in these rocks can be. The "Rules of stability..." provide for the possible accounting the loads from mining equipment when assessing the stability, but this possibility is provided for the calculation of bench stability of open-pits and cuts, formed by semi-hard and dispersed rocks, dumps formed from clay or semi-hard rocks and (or) from a mixture of clay and hard rocks. At the same time, it is of interest to assess the impact of static loading from the located mining transport equipment in a stationary state on the stability of the benches located in hard rocks. It is shown that the load from the track dozer scraping the berms has an impact of no more than 6-7% for a distance of about 15 m from the top crest of a 30-meter long bench with a slope angle of 80° to the edge of the track, which is generally insignificant for maintaining bench stability. The minimum value of the safety factor of the bench with the load from the BELAZ-75306 mining dump truck is at a distance of 8 to 10 m from the top crest to the edge of the wheel. That is, at this distance the mining dump truck has the maximum impact. At 30 m distance from the bench’s top crest, mining dump truck has no impact on the bench stability. The maximum impact of the dump truck on the stability is 22 to 25%.

Evaluation of formation susceptibility and sand production potential in an offshore field, Niger Delta Basin, Nigeria

Wellbore instability and sand production are all common challenges in the Niger Delta oil province, resulting in high drilling and production cost as well as damage to oil facilities. The vulnerability of lithologic formations to wellbore instability and resultant sand production is investigated in the four delineated reservoirs of the “Areo” field, western part of Niger Delta Basin. The foundation for establishing the geomechanical properties in this study was a 1-dimensional mechanical earth model, using gamma ray (GR), density (RHOB), compressional slowness (DTC), and shear slowness (DTS) logs. Within the Areo oil field, two wells (well 001 and well 002) were correlated. The evaluated formations are still primarily composed of compacted shale and unconsolidated sandstone, with reservoir sand units exhibiting lower elastic and rock strength properties than shale units. High compressibility and porosity make sand more brittle, while low compressibility and porosity make shale stiffer due to high moduli. The maximum force that can be applied to a shale unit without causing it to fail is 17.23 MPa, which is the maximum average rock strength of the shale. It means that shale requires more vertical stress or pressure than sand does in order to deform it (15.06 MPa). The three sand prediction approaches used in the analysis of sand production predictions have cut-off values that are higher than the average values of the formations. The Schlumberger sand production index method (S/I) indicates that the reservoir has potential for sand influx in the two wells, with the average of the four reservoirs studied in wells 001 and 002 being 1.55 × 1012 psi and 1.14 × 1012 psi respectively. However, when a formation's sand production index is less than 1.24 × 1012 psi, as it is in this study, the formation is likely to produce sand. These findings support the notion that the defined sandstone units are highly unconsolidated and have a high potential for producing sands; therefore, sand control techniques must be factored into process optimization and cost reduction plans.