Experimental Investigation on Microstructure Evolution and Creep Behaviour of Red Sandstone at Elevated Temperature

The physical and mechanical properties of rocks are called those that determine their behavior under the influence of external forces (loads) and manifest themselves in resistance to destruction and deformation. The property of rocks to resist destruction and the formation of large residual deformations under the influence of the load or, more precisely, to perceive, without breaking down within certain limits and conditions, certain loads are called strength, and their property to change under load the shape of folding and volume is deformation. These properties express and evaluate the strength and deformation indicators. The article compares the physical and mechanical properties and structure of the effusive volcanoes of Zimin and Kamen, which are located on the Kamchatka Peninsula. The physical and mechanical properties of the effusive rocks of these volcanoes are rather well studied, which allows to make their detailed characterization, as well as to compare the rocks with each other, highlighting the similarities and differences. By analyzing the data obtained, it is possible to use this information in similar studies, identifying the results or explaining them if there are differences. The conducted studies allow to more accurately explain the influence of structural features on changes in the physical and mechanical properties of the rocks of the Kamen and Zimin volcanoes.

This study is concerned with structural and mineralogic transformations and changes in the physical and mechanical properties of volcanogenic sedimentary rocks in the North Paramushir hydrothermal magmatic system as a result of the interaction with thermal waters of various compositions and origins. We identified the following hydrothermal metasomatic facies that developed in tuffites and tuffs: opalites (monoopalite, opal–clay, and opal–alunite), as well as low- and moderate-temperature propylites. We show the position of each new facies in the structure of the hydrothermal magmatic system. We obtained correlative relationships of the physical and mechanical properties of the rock to the intensity and character of secondary alteration. It is pointed out that all of these rocks obey a common trend in the interrelationships between their properties, which may provide evidence of a common origin and progressive direction of hydrothermal processes in the interior of the North Paramushir system.

In this study, density, porosity, void ratio, and ultrasonic P- and S-wave first arrival times were measured on limestone, sandstone, and siltstone samples obtained by using mechanical soundings in the city of Zonguldak. Turkey. Fracture and fissure indexes of rocks were calculated from ultrasonic P- (Vp) and S-wave (Vs) velocities. Multi-parameter relationships occurred between ultrasonic velocities with seismic fracture and fissure indexes and physical and mechanical properties of the rocks. Root mean squared error (RMSE = 0.5–0.8%) values correlated between measured densities and densities calculated from Vp and Vs. The correlation coefficients of experimental relations between densities, void ratio, and porosity with seismic velocities that were obtained ranged from 78, 86, 67, and 84%, respectively. Consequently, natural, water-saturated and grain densities, porosity, and void ratio values were determined from new multi-parameter relationships obtained from the combined use of Vp and Vs. In addition, the results of this study suggest that the rock quality may wrongly be determined using the only Vp, whereas it can be obtained more accurately by using Vp and Vs together. The reason for this is that the P wave spreads in solid, liquid, and gas media, while the S-wave spreads only in solid media. Therefore, S-waves will not be altered by fracture filling (gas or liquid), while P-waves are affected by fracture filling. In the present study, the use of Vp and Vs together in relationships was more useful in determining the strength and hydraulic properties of rock mass that the use of either Vp or Vs alone. Also, Rock Quality Designation (RQD) and Rock Mass Rating (RMR) values can be correctly calculated from the combined use of Vp and Vs. As a result, interpretation of crack fill and classification of the rocks can be quickly performed using seismic velocities.

Physical aging in polystyrene was studied by annealing samples isothermally (at 22°, 57°, and 93°C) for various lengths of time and measuring the changes in the enthalpy and the flexural creep property. The enthalpy decrease reached a constant value after about 10 hours of aging at 93°C, indicating an apparent attainment of equilibrium, whereas the creep behavior continued to change with prolonged aging even after 10 hours. At room temperature it took about a year of aging to induce a measurable change in enthalpy, while the creep behavior showed changes clearly only after hours of aging. These and other items of evidence indicate that the effect of aging on the creep behavior cannot be interpreted solely in terms of the free volume concept. Thus the hope of being able to predict the mechanical properties of aged polymers from the measurement of specific volume or enthalpy alone is not likely to be realized.

Modelling and analysis of creep data for plastics at elevated temperatures

The mechanical properties of rocks play a critical role in many geotechnical and geological applications. A good understanding of the mechanical properties of rocks and the factors influencing them enables accurate prediction of the behaviour of rocks in various applications. The aim of this study was to investigate the correlation between the failure pattern and the mechanical properties of granite using the Schmidt hammer rebound test, p-wave velocity measurement, and thin section analysis. The average result of the Schmidt rebound test showed the lowest and highest values of 45.3 MPa and 77.3 MPa, respectively. The results of the p-wave measurement for the lowest and highest values are 3.380 m/sec2 and 6.776 m/sec2 respectively and the thin section confirmed the presence of mineralogical compositions such as quartz, biotite, muscovite, mica, and feldspar of the granitic rock. The results of this study have shown the importance of considering multiple techniques when investigating the mechanical properties of rock and performing a combination of tests that ultimately provide a complete understanding of the mechanical behaviour of rock. This study highlights the need for further research to deepen the understanding of the relationship between rock failure patterns and mechanical properties and to improve the accuracy and precision of rock property measurements.

This study investigates the influence of rock physical and mechanical properties on the integrity of the cement sheath barrier in oil and gas wells, with a focus on the rock-cement paste interface under geomechanical loading. Key rock characteristics, including structure, porosity, permeability, compressive strength, and tensile strength, were evaluated to determine their impact on adhesion strength and failure modes. Diametral compression tests were performed on disk-shaped specimens with a 2:1 diameter-to-thickness ratio, composed of semi-disks of rock and cement paste. The experimental program included Botucatu sandstone and Roman travertine, combined with both standard API and stabilized cement paste formulations. Variables such as cement curing time, sandstone stratification, and curing temperature were examined, while micro-CT, thin-section microscopy, and scanning electron microscopy (SEM) provided qualitative analysis of the interfaces. Results revealed contrasting behaviors between the two rock types: porosity did not influence adhesion strength in Roman travertine, whereas in Botucatu sandstone, high porosity and microroughness significantly enhanced interface bonding, often exceeding the cement paste strength. Curing time played a critical role at early ages, particularly at three days, but its influence diminished between seven and twenty-eight days. Curing temperature showed no effect on low-porosity sandstone interfaces, though higher temperatures (70 °C) improved the intrinsic strength of the cement paste. This work provides novel insights into the role of rock crystalline structure and porosity in CSB performance, contributing to a more comprehensive understanding of rock-cement interactions essential for ensuring long-term well integrity.

The long-term geological sequestration of carbon dioxide (CO2) in underground formations (deep saline aquifers) is the most economically viable option to decrease the emissions of greenhouse gas in the atmosphere which are the main contributing factors for global warming. The injection of CO2 in carbonate aquifers dissolves some of the calcite rock due to the formation of carbonic acid as a result of the interaction between CO2 and brine. This rock dissolution may affect the rock integrity and in turn will affect the rock mechanical properties. The effect of CO2 on the rock mechanical properties is a key parameter to be studied to assess the aquifer performance in the process of geological sequestration and to get safe and effective long-term storage. The main objective of this study is to address the impact of geological sequestration of CO2 on the mechanical properties of carbonate aquifer and cap rocks. In addition, the effect of the storage time on these properties are investigated. Moreover, the effect of CO2 sequestration on rocks with different mechanical properties are studied, and the good candidate carbonate rocks for geologic sequestration are identified. In this study the CO2 was injected and soaked with the brine with the core at high pressure and high temperature (2000 psi and 100°C) to simulate the actual downhole conditions The carbonate cores were analyzed for mechanical properties using indirect tensile strength, unconfined compression, and acoustics testing machines. Results show that CO2 sequestration affected the mechanical properties of the carbonate rocks as well as the cap rocks. Long time soaking of CO2 in brine allowed for the formation of enough carbonic acid to react with the cores and this greatly impacted the rock mechanical and acoustic properties. The significant impact of CO2 storage was noted on Khuff limestone and the good candidate among the carbonate rocks studied here for geological sequestration of CO2 is found to be Indiana limestone.

Thermal transformations of binary mixtures of hydrocarbons and fluorocarbons under high pressures demonstrate significantly lower initiation temperature thresholds for all major transformation stages, including carbonization, graphitization, and diamond formation, than the transformations of pure hydrocarbon and fluorocarbon components. In addition, along with the formation of micrometer-size diamond fraction, typical for transformation products of pure hydrocarbons, massive formation of nanosize diamond fraction has been observed in the products of conversion of mixtures. In order to gain understanding of the nature of simultaneous formation of micro- and nanosize fractions of diamond in the binary mixtures of hydrocarbon and fluorocarbon compounds, a comparative studies of the attributes of thermal transformations of pure hydrocarbon, fluorocarbons and their homogeneous and heterogeneous mixtures has been carried out under pressure of 8 GPa and temperatures up to 1500 °C. Naphthalene (C10H8) and octaflu...

Rock type characterization is an essential issue in mining and other geosciences. At every stage of mining operations, the rock type is the critical parameter in determining the procedures to be carried out and the equipment to be used. The description of rock types often requires detailed investigations by geologists in the field and laboratory. The experience of the geologists conducting these investigations is also very influential in rock type description. In many cases, this process is time-consuming. With these investigations come extra costs, and, in some cases, relative or inaccurate descriptions can also affect operating costs. This paper shows that it is possible to predict rock type from some physical and mechanical properties of rocks without incurring these costs. The paper’s main objective is to present the applicability of data mining algorithms in rock type determination. The physical and mechanical properties of the rocks were evaluated with different data mining algorithms, and the rock types were predicted 95.6% correctly with the model generated with the Support Vector Machine algorithm. Therefore, it is possible to predict rock types by data mining in extensive databases. This method provides both reliable and cost-effective results.

Purpose. Analysis of the impact of mining-geological and mining-technical factors on the stability of excavation site products. Methods. Analysis of studies of the state of the geotechnical system “massif-mining-protection structure” analytically, in laboratory and production conditions. Results. The analysis of the factors affecting the stability of the excavation workings showed that the mining factors associated with the parameters of the workings (width of the workings, shape of the cross-section of the workings, the scheme of erection of support anchors, type of permanent support of the workings) come to the fore: the speed of the face movement and the parameters of the workings protection. The effect of a high speed of face advancement on the mechanism of bearing pressure on the edge part of the massif can be compared to the rolling of a massive sea wave, wide at the foot but with a lower crest height. At a high speed of its movement, there is no pronounced area or “peak” of additional loads. Among the mining and geological factors, the tectonic structure of the deposit, the depth of development and, as a result, the stress state of the rock mass are of great importance. The physical and mechanical properties of rocks are of subordinate importance, with the influence of layering, fracturing and water cut being particularly noticeable. The relationship between the convergence of side rocks in the working faces and the speed of the face advancement is periodic. The minimum displacement values are observed when the number of coal mining cycles per day is a multiple of three. It can be assumed that this pattern is due to the influence of tidal fluctuations and coincides with even harmonics. Scientific novelty. Based on the analysis, it was found that when addressing the issue of increasing the stability of excavation workings, it is necessary, first of all, to pay attention to mining factors (width of the workings, shape of the cross-section of the workings, scheme of erection of support anchors,) the speed of advancement of the cleaning face, parameters of the protective elements of the workings at the face-strip junction, and link them to mining and geological conditions, especially the tectonic structure of the deposit and the depth of its development. Practical implication. When determining the parameters of the geomechanical system “massif-mining-protection structure”, it is necessary to take into account the parameters of the production, the speed of the cleaning pit, the protection parameters of the production with the cohesive tectonic structure of the deposit, the depth of development and the physical and mechanical properties of the rocks.

A full-stage creep model for rocks based on the variable-order fractional calculus

The knowledge of rock mechanical properties of the Zubair Formation is required to assure the success of future exploration and development of this reserves. Hence, high consistency and quality of these parameters could expressively increase the economic revenues derivable from the reservoir. The main objective of the current work is to generate a high-resolution continuous profile of the rock mechanical properties using microresistivity image log across the thin-bed intervals along with rock mechanical properties laboratory tests. Retrieved core samples from the Zubair sandstone formation were run through extensive laboratory testing. The rock strength parameters were determined using consolidated drained (CD) multistage triaxial tests, while static elastic parameters were measured using consolidated drained (CD) triaxial tests. A petrophysical log enhancement technique was applied to achieve enhanced resolution neutron porosity log (with a vertical resolution of 0.2 in.). The critical components of this process were achieved high-resolution neutron porosity log from microresistivity image log. This log was directly utilized to calculate high-resolution rock mechanical property logs through porosity empirical correlations. The resulting downscaled rock mechanical logs exhibited a reasonable degree of positive agreement between the estimated rock mechanical property logs (i.e., unconfined compressive strength (UCS), internal friction angle (φ), Young's modulus (E), Poisson's ratio (v), bulk modulus (K), and shear modulus (G)) and those acquired from the lab measurements, with 1.42%, 2.21%, 2.44%, 1.86%, 2.33%, and 1.92% absolute relative average difference (ARAD), respectively.

The article deals with the distribution of disturbances in the coal-bearing deposits of Donbas and establishment of the relationship between the indices of physical and mechanical properties of coal and rock, gas saturation and tectonic dislocation. To solve the problems, statistical methods were used (correlation and regression analysis). The schemes of deformations of Donbas have been built, both in individual indices and in indices of complex dislocation, which reflect the regional patterns of distribution of the deformations of various types throughout the Donetsk basin. Close statistical relationship has been established between indices of tectonic dislocation, gas saturation, physical and mechanical properties of coal and rocks, which allows the use of the indices of tectonic dislocation to predict gas content at the regional level.

This study evaluates the physical and mechanical properties of gypsum rocks from quarries in northwest Kirkuk, Iraq, to assess their durability under local environmental conditions. Six stations were selected for sample collection, with seven samples analyzed for porosity, specific gravity, water absorption, moisture content, point load strength, and durability through wet-dry cycles. Results revealed low porosity (1.15–2.70%), minimal moisture content (0.48–1.01%), and moderate water absorption (0.74–1.77%), indicating high cohesion and limited susceptibility to water infiltration. Durability tests classified the rocks as