Sandstone Rocks Research Articles

Elastoplastic Damage Behavior of Rocks: A Case Study of Sandstone and Salt Rock

Elastoplastic Damage Behavior of Rocks: A Case Study of Sandstone and Salt Rock

Uranium surface processes with sandstone and volcanic rocks in acidic and alkaline solutions

Understanding the behaviour of uranium waste, for disposal purposes, is crucial due to the correlation between pH values and the disposal of distinct types of waste, with low level waste typically associated with acidic pH values, and higher and intermediate level waste commonly related to alkaline pH values. We studied the adsorption of U(VI) on sandstone and volcanic rock surfaces at pH 5.5 and 11.5 in aqueous solutions with and without bicarbonate (2 mM HCO3–) using XAS and FTIR. In the sandstone system, U(VI) adsorbs as a bidentate complex to Si at pH 5.5 without bicarbonate and as uranyl carbonate species with bicarbonate. At pH 11.5 without bicarbonate, U(VI) adsorbs as monodentate complexes to Si and precipitates as uranophane. With bicarbonate at pH 11.5, U(VI) precipitated as a Na-clarkeite mineral or remained as a uranyl carbonate surface species. In the volcanic rock system, U(VI) adsorbed to Si as an outer sphere complex at pH 5.5, regardless of the presence of bicarbonate. At pH 11.5 without bicarbonate, U(VI) adsorbed as a monodentate complex to one Si atom and precipitated as a Na-clarkeite mineral. With bicarbonate at pH 11.5, U(VI) sorbed as a bidentate carbonate complex to one Si atom. These results provide insight into the behaviour of U(VI) in heterogeneous, real-world systems related to the disposal of radioactive waste.

Impact of clay mineralogy on the petrophysical properties of tight sandstones

A full petrographic and petrophysical characterization of tight sandstones has been conducted as part of ongoing study of Carbon Dioxide Enhanced Oil and Gas Recovery (CO2-EOR/EGR) and CO2sequestration. The main purpose of this study is to give novel perception into the interplay of the rock characteristics and fluid flow in tight formations, which are candidates for EOR/EGR processes (macroscopic sweep vs. microscopic displacement efficiency). To achieve this, several experimental techniques, including routine core analysis, X-ray diffraction (XRD), X-ray fluorescence (XRF), thin sections petrography, Scanning Electron Microscopy (SEM) and capillarity/pore size distributions by using Mercury Injection Capillary Pressure (MICP), Nuclear Magnetic Resonance (NMR), and Micro-Computed Tomography (Micro-CT), were conducted. Three tight sandstone rock samples (Bandera, Kentucky, and Scioto) were used in this work and particular attention was paid to the impact of clay content on rock's pore system and other petrophysical characteristics and hence fluids flow during production process.Results indicate that the presence of fibrous illite clay acting as pore bridging in Bandera and Kentucky samples have blocked the overall micro-pore system causing a significant reduction in the micro-pore throat system to 36% in Bandera sand and 50.9% in Kentucky sample. On the other hand, absence of fibrous illite and the presence of illite platelets in the Scioto sandstone led to a clear preservation of the sample's micro-pore throat attributing to a total of 59.1% of the total pore throat system.A new dimensionless number (dimensionless micro-pore throat modality) was established, defined as the ratio of micro-to macro-pore sizes. This shows that Scioto has the highest value of 1.44 implying that both macro- and micro-pore systems contribute to flow. Therefore, the mitigation of oil bypass from smaller pores should be a key criterion in selecting the proper recovery methods. Results show the effect of clay mineralogy on pore system considering a part of the physical and spatial properties the pore/grain framework of the tight sandstones.

Scale Effects on Shear Strength of Rough Rock Joints Caused by Normal Stress Conditions

Scale effects on the mechanical behavior of rock joints have been extensively studied in rocks and rock-like materials. However, limited attention has been paid to understanding scale effects on the shear strength of rock joints in relation to normal stress σn applied to rock samples under direct shear tests. In this research, a two-dimensional particle flow code (PFC2D) is adopted to build a synthetic sandstone rock model with a standard joint roughness coefficient (JRC) profile. The manufactured rock model, which is adjusted by the experiment data and tested by the empirical Barton’s shear strength criterion, is then used to research scale effects on the shear strength of rock joints caused by normal stresses. It is found that the failure type can be affected by JRC and σn. Therefore, a scale effect index (SEI) that is equal to JRC plus two times σn (MPa) is proposed to identify the types of shear failure. Overall, shearing off asperities is the main failure mechanism for rock samples with SEI > 14, which leads to negative scale effects. It is also found that the degree of scale effects on the shear strength of rock joints is more obvious at low normal stress conditions, where σn < 2 MPa.

Petrography of Sandston Units in Gercus Formation, Shaqlawa and Dokan areas Northern Iraq

The present study deals with the petrographic investigations revealed that the sandstone of Gercus Formation the studied samples of sandstone units composed primarily of rock fragments (sedimentary, igneous and metamorphic), quartz grains (monocrystalline and polycrystalline), and feldspars (orthoclase, microcline and plagioclase). These components are cemented by carbonate and iron oxides. The studied sandstones are classified as litharenites, Sandstone rocks of Gercus Formation are chemically and mechanically unstable due to the high percentage of rock fragments ,such a grain assemblage infers that the source of the rock fragments is nearby. The petrographic analyses indicate that the studied sandstones are immature mineralogically because of high content of unstable components, such as lithic fragments and feldspars. the tectonic provenance for Gercus formation can be described as lithic recycled.

Pore Structure and Fractal Characteristics of Coal-Measure Sedimentary Rocks Using Nuclear Magnetic Resonance (NMR) and Mercury Intrusion Porosimetry (MIP)

Analyzing and mastering the fractal features of coal-measure sedimentary rocks is crucial for accurately describing the pore structure of coalbed methane resources. In this work, mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) are performed on coal-measure sedimentary rocks (i.e., shale, mudstone, and sandstone) to analyze their pore structure. Pore size distributions (PSDs) and the multifractal dimensions of the investigated samples are discussed. Moreover, multivariable linear regression models of multifractal dimensions are established through a comprehensive analysis of multifractal characteristics. The results show that sandstone (SS-1) and clay rocks are dominated by nanopores of 0.01 to 1 μm, while sandstone (SS-2) is mostly mesopores and macropores in the range of 1 to 10 μm. The fractal characteristics of the investigated rock samples show a prominent multifractal characteristic, in which DA reflects the surface structure of micropores, while DS represents the pore structure of macropores. Multifractal dimension is affected by many factors, in which the DA is greatly influenced by the pore surface features and mineral components and the DS by average pore diameters. Moreover, multivariate linear regression models of adsorption pore and seepage pore are established, which have a better correlation effect on the multifractal dimension.

Improvement in CO2 geo-sequestration in saline aquifers by viscosification: From molecular scale to core scale

Carbon dioxide (CO2) storage in the subsurface is a viable approach to mitigate climate change by reducing anthropogenic greenhouse gas emissions. The unfavorable mobility ratio in brine displacement by CO2 would lead to poor sweep efficiency. In this investigation, the efficiency of an engineered CO2 oligomer viscosifier with about twenty repeat units of 1-decene is evaluated in mobility control and sweep efficiency improvement in drainage. We have performed brine displacement experiments in sandstone rock with supercritical CO2. The viscosifier at 1.5 wt% concentration increases the viscosity of supercritical CO2 by 4.8 folds at pressure of 3500 psi and temperature of 194 ˚F. We observe significant delay of CO2 breakthrough time by 2.6 ± 0.1 folds in a large number of experiments by viscosified CO2. The molecule does not have appreciable adsorption on the rock surface. The pressure drop from displacement of neat CO2 by viscosified CO2 at 1 PV injection provides the evidence of low adsorption. Molecular simulations are conducted to investigate adsorption. Low adsorption is a key measure of the effectiveness of the molecule. The results from molecular simulations agree with the experiments. In addition to viscosification, the novelty of the molecule is that there is a significant decrease in the residual brine saturation. Consequently, the residual trapping is also increased. The combination of decrease in residual brine saturation, and mobility control are expected to significantly improve the storage capacity through increase in residual trapping and sweep efficiency in CO2 storage in saline aquifers. As a result, CO2 storage may become more efficient.

A robust Gaussian process regression-based model for the determination of static Young’s modulus for sandstone rocks

A robust Gaussian process regression-based model for the determination of static Young’s modulus for sandstone rocks

Dynamic stability analysis of metro tunnel in layered weathered sandstone

In this study a coupled-eulerian–lagrangian (CEL) approach has been applied to assess the internal blast loading conditions, for the tunnel built in three layers of sandstone rock. The three weathered stages of sandstone have been considered in this study i.e., slightly, medium and also highly weathered sandstone in three different layers. The sandstone rock weathering increases as we move towards the ground surface from deep subsurface. The elastoplastic finite element model with varied overburden depth with dimensions of 60 m (L × B × H) each to incorporate different parametric cases. An explosive is assumed at the center of the tunnel, with the capacity of hundred kg of trinitrotoluene (TNT), the explosive is assumed to be hanging in the air inside the tunnel opening with equal distance from all sides. The TNT sphere and air that is inside the rock tunnel has been modelled through CEL technique to simulate actual in-situ condition. Through Mohr-Coulomb, Concrete Damage Plasticity, and Johnson-Cook constructive material model the elastoplastic behaviour of different materials like rock, steel bars and concrete has been simulated respectively. The cage of steel bars has been embedded through interaction constraint in concrete liner to produce reinforced concrete liner. In the initial stages of simulation with 5 m of overburden depth the tunnel has been placed in the upper layer of sandstone. For further analysis, the position of the tunnel has been changed for overburden depth of fifteen, twenty-five and thirty-five meter. In accordance with the result of the simulation, for rock in terms of acceleration, velocity, and dis-placement, the depth of the overburden and the displacement of the crown are inversely related. No damage in terms of compression is seen in this simulation, but in all instances, a small damage owing to tensile failure has been noted.

The effect of rock permeability and pore structure on foam in carbonate rocks

Foam is considered a successful method for providing conformance control during enhanced oil recovery. It helps reduce gravity segregation, viscous fingering, and minimizes injected fluid loss into high permeability zones. Foam rheology has been studied and well understood in sandstones but its behavior in carbonate rocks is not well defined. This study aims to quantify the impact of pore properties represented by permeability, pore throat size (dT), pore body size (dB) and aspect ratio (R) on foam rheology in carbonate rocks. The results are contrasted with foam rheology in natural sandstone rocks. The studied carbonates possess complex pore structures, with bimodal distributions of pore throat and pore body sizes. Pore properties were shown to affect the magnitude of foam viscosity (μa)-foam quality relationship, but the observed trend is unchanged in different rocks. μa was found to linearly correlate with (dT2) and permeability. It was shown to increase exponentially with dB with a marked increase at dB > 30 μm. All the carbonates had aspect ratios R ≫ 2.5 indicating plentiful foam germination sites. As a result, the aspect ratio does not correlate strongly with μa. Pore structure properties were shown to have a strong impact on the μa-shear rate (γ̇a) relationship, by directly impacting the magnitude of both μa and γ̇a, and also by influencing the foam texture. Finally, pore properties were shown to impact factors governing foam transient behavior. Rocks with smaller (dT) are shown to have weaker foam generation and propagation, as well as a larger specific surface area leading to larger dynamic adsorption. Overall, the results of this work indicate that the successful implementation of foam for mobility control in carbonate reservoirs will depend on a good understanding of the rock pore structure.

Optimized rock physics model implementation to characterize the heterogeneous B-interval reservoir facies in the petro-elastic domain, mubarak block, lower indus basin, Pakistan

Rock physics abridges geological and reservoir parameters to quantify the heterogeneous hydrocarbon reservoir facies in the petro-elastic domain. The widely distributed Lower Goru sands across the Lower Indus Basin are proven hydrocarbon reservoirs and exhibit heterogeneity due to their complex depositional environment. Diagenetic detrital quartz overgrowth cementation, sand, shale intercalation, and various fluids add more challenges to characterize facies in the petro-elastic domain. For precise petro-elastic relationship establishment, an extended cemented sandstone rock physics model for B-Interval sands of the Lower Goru Formation was developed. It produced conclusive elastic properties by optimizing the density log and synthesizing the missing shear sonic log. The accuracy of the selected model was authenticated by statistical measures, i.e., good prediction quality, high correlation coefficient, along with less normalized root mean square error for modeled Vp, Vs and density. This comprehensive approach adheres to the interrelationship between pores, minerals, cementation effects and fluids to address reservoir heterogeneity, facies classification and tight sand. Furthermore, these parameters are translated in a ubiquitous way in the petro-elastic domain, illuminating the sweet spots within the reservoir.

In memoriam Klaus Kubitzki (1933–2022)

In memoriam Klaus Kubitzki (1933–2022)

Effects of mineralogical composition on uniaxial compressive strengths of sedimentary rocks

Figuring out rock strength plays essential roles in the sub ground mining activities, such as oil and gas well drilling and hydraulic fracturing, coal mining, tunneling, and other civil engineering scenarios. To help understand the effects of the mineralogical composition on evaluating the rock strength, this research tries to establish indirect prediction models of rock strength by specific input mineral contents for common sedimentary rocks. Using rock samples collected from the outcrops in the Sichuan Basin, uniaxial compression tests have been conducted to sandstone, carbonate, and shale cores. Combining with statistical analysis, the experimental data prove it true that the mineralogical composition can be utilized to predict the rock strength under specific conditions but the effects of mineralogical composition on the rock strength highly depend on the rock lithologies. According to the statistical analysis results, the predicted values of rock strengths by the mineral contents can get high accuracies in sandstone and carbonate rocks while no evidences can be found in shale rocks. The best indicator for predicting rock strength should be the quartz content for the sandstone rocks and the dolomite content for the carbonate rocks. Especially, to improve the evaluation accuracy, the rock strengths of sandstones can be obtained by substituting the mineral contents of quartz and clays, and those of carbonates can be calculated by the mineral contents of dolomite and calcite. Noticeably, the research data point out a significant contrast of quartz content in evaluating the rock strength of the sandstone rocks and the carbonate rocks. Increasing quartz content helps increase the sandstone strength but decrease the carbonate strength. As for shale rocks, no relationship exists between the rock strength and the mineralogical composition (e.g., the clay fractions). To provide more evidences, detailed discussion also provides the readers more glances into the framework of the rock matrix, which can be further studied in the future. These findings can help understand the effects of mineralogical composition on the rock strengths, explain the contrasts in the rock strength of the responses to the same mineral content (e.g., the quartz content), and provide another indirect method for evaluating the rock strength of common sedimentary rocks.

Application of Non-Destructive Test Results to Estimate Rock Mechanical Characteristics—A Case Study

Accurately determining rock elastic modulus (EM) and uniaxial compressive strength (UCS) using laboratory methods requires considerable time and cost. Hence, the development of models for estimating the mechanical properties of rock is a very attractive alternative. The current research was conducted to predict the UCS and EM of sandstone rocks using quartz%, feldspar%, fragments%, compressional wave velocity (PW), the Schmidt hardness number (SN), porosity, density, and water absorption via simple regression, multivariate regression (MVR), K-nearest neighbor (KNN), support vector regression (SVR) with a radial basis function, the adaptive neuro-fuzzy inference system (ANFIS) using the Gaussian membership (GM) function, and the back-propagation neural network (BPNN) based on various training algorithms. The samples were categorized as litharenite and feldspathic litharenite. By increasing the feldspar% and quartz% and decreasing the fragments%, the static properties increased. The results of the statistical analysis showed that the SN and porosity have the greatest effect on the UCS and EM, respectively. Among the Levenberg–Marquardt (LM), Bayesian regularization, and Scaled Conjugate Gradient training algorithms using the BPNN method, the LM achieved the best results in forecasting the UCS and EM. The ideal obtained BPNN, using a trial-and-error process, contains four neurons in a hidden layer with eight inputs. All five models attained acceptable accuracy (correlation coefficient greater than 70%) for estimating the static properties. By comparing the methods, the ANFIS showed higher precision than the other methods. The UCS and EM of the samples can be determined with very high accuracy (R2 > 99%).

Experimental study on strength and failure characteristics of sandstone rock mass with complex cataclastic structure using 3D printing models

A cataclastic rock mass is a poor type of engineering geological rock mass. The determination of the shear failure characteristics and shear strengths of cataclastic rock masses can provide key basis for the design and construction of infrastructure. Physical model samples of a sandstone cataclastic rock mass were first produced by a combination of three-dimensional (3D) printing technology and manual pouring. Shear tests were conducted with respect to the shear stresses parallel to the trace line plane and perpendicular to the trace line plane of the cataclastic rock mass model. Based on an extensive analysis of the shear failure characteristic, shear stress evolution characteristic curve and shear strength. When the shear stress was parallel to the trace line plane, and when the rock block that was cut and confined by the trace line exhibited a significant tip, the end stress concentration effect of the cataclastic rock mass was more significant during the shear process with the anisotropy of the rock block increased. In addition, the shapes of the rock blocks that were confined and cut by the joints were the main influencing factors of the strength of the cataclastic rock mass. When the shear stress was perpendicular to the trace line plane, the structure of the rock wall was the main influencing factor of the deformation and failure process of the shear failure plane and the shear strength. The physical and mechanical properties of the shear failure plane of the cataclastic rock mass were found to be closely related to the joint–rock wall system characteristics of the cataclastic rock mass. Therefore, when determining the shear strength of cataclastic rock mass, the shape and combination form of the rock block, shear direction, and structural failure characteristics of the rock wall should be comprehensively considered during the shear process.

Experimental Investigation of the Synergistic Effect of Two Nonionic Surfactants on Interfacial Properties and Their Application in Enhanced Oil Recovery.

In chemically enhanced oil recovery (EOR), surfactants are conventionally used to lower the interfacial tension (IFT) at the water-oil interface, alter the rock wettability, and help in the emulsification of trapped oil after primary and secondary modes of recovery. A mixture of surfactants is usually more effective than a single surfactant with enhanced surface or interfacial properties. The primary objective of this study is to examine the synergistic effects of two nonionic surfactants (Tergitol 15-S-12 and PEG 600) on surface properties, such as surface tension, IFT, and wettability alteration, in the context of EOR. The optimum composition of the surfactant mixture was obtained by surface tension measurement, and it has been found that the Tergitol 15-S-12 and PEG 600 mixture shows better synergistic effect with a minimum surface tension value of 30.3 mN/m at 225 ppm concentration of Tergitol 15-S-12 and 1 wt % of PEG 600. The surfactant mixture with optimum composition shows an ultra-low IFT of 0.672 mN/m at optimum salinity. The wettability alteration study was conducted in a goniometer by observing the change of the contact angle of an oil-wet sandstone rock in the presence of the formulated chemical slugs at different concentrations, and the results show a shift in the wettability of rock from the oil-wet to the water-wet region. The wettability alteration behavior of oil-wet rock is established using X-ray diffraction analysis of sandstone rock and zeta potential measurements of the chemical slugs. The efficacy of the optimized chemical slug for EOR was checked by a core flooding experiment, and an additional recovery of 17.73% of the original oil in place was observed.

Experimental and numerical investigation of sandstone deformation under cycling loading relevant for underground energy storage

Considering the storage capacity and already existing infrastructures, underground porous reservoirs are highly suitable to store green energy, for example, in the form of green gases such as hydrogen and compressed air. Depending on the energy demand and supply, the energy-rich fluids are injected and produced, which induces cyclic change of state-of-the-stress in the reservoir and its surrounding. Detailed analyses of the geo-mechanical deformations under variable storage conditions i.e., storage frequency and fluid fluctuating pressures, are crucially important for safe and efficient operations. The present work presents an integrated analysis, based on experimental and constitutive modeling aspects, to investigate sandstones’ geomechanical response to cyclic loading relevant to underground energy storage (UES). To this end, sandstone rock samples were subjected to cyclic loading above and below the onset of dilatant cracking under different frequencies and loading amplitudes. Axial strains and Acoustic Emissions (AE) were measured in both regimes to quantify the total deformation (strain) of the rock and its AE characteristics. It is found that the inelastic strain and number of AE events is the highest in the first cycle and reduce subsequently cycle after cycle. Moreover, cyclic inelastic deformations are affected by the mean stress, amplitude, and frequency of the stress waveform. On the one hand, the higher the mean stress and the amplitude, the higher the total inelastic strains. On the other hand, the lower the frequency, the higher the total inelastic strain. From the modeling perspectives, five types of deformation mechanisms were identified based on the governing physics: elastic, viscoelastic, compaction-based cyclic inelastic, inelastic brittle creep, and dilatation-based inelastic deformation. To model elastic, viscoelastic, and brittle creep, the Nishihara model was used. A cyclic modified cam clay model (MCC) and hardening–softening model were applied to capture plastic deformation. The results show a very good fit of the constitutive model with the experimental results, which could help in studying the response of reservoirs to injection and production.

Scrutiny of freeze-thaw cycles effect on physical and dynamic fracture characteristics of cracked sandstone

A series of freeze-thaw (FT) cycle experiments and drop-weight impact tests are performed to explore the dynamic fracture characteristics of fractured sandstone acted upon by FT cycles. To this end, an innovatively cracked sample, a tunnel with a single radial crack (TSRC), made from an intact sandstone rock is implemented. The experimental results reveal that for FT cycles 10, the dynamic elastic modulus and P/S wave velocities of sandstone exhibit the most drastically descending trend. In such a case, the decreasing percentage of the dynamic elastic modulus, P wave velocity, and S wave velocity reach 16.4%, 7.2%, and 8.3%, respectively. The percentage reduction of these three physical parameters is also tapered off as the number of FT cycles reaches 30 and 40. While the porosity of sandstone grows by 1%, the pore distribution substantially alters for the case of 10 cycles of FT. For the number of FT cycles greater than 30, the porosity of sandstone slightly increases. Further, the crack growth velocity generally grows with the number of FT cycles such that the highest crack growth velocity is detected for 40 cycles FT, and the corresponding velocity touches 427.6 m/s. The obtained results demonstrate that the dynamic fracture toughness lessens as the number of FT cycles increases, and the dynamic initiation toughness is less than the average dynamic propagation toughness in sandstone samples subjected to impact loads. The dynamic loading rate calculated from dynamic initiation toughness reduces with the number of FT cycles when the sandstone specimen experiences the same dynamic loading.

Fractal-Based Approaches to Pore Structure Investigation and Water Saturation Prediction from NMR Measurements: A Case Study of the Gas-Bearing Tight Sandstone Reservoir in Nanpu Sag

Pore space of tight sandstone samples exhibits fractal characteristics. Nuclear magnetic resonance is an effective method for pore size characterization. This paper focuses on fractal characteristics of pore size from nuclear magnetic resonance (NMR) of tight sandstone samples. The relationship between the fractal dimension from NMR with pore structure and water saturation is parameterized by analyzing experimental data. Based on it, a pore structure characterization and classification method for water-saturated tight sandstone and a water saturation prediction method in a gas-bearing sandstone reservoir have been proposed. To verify the models, the fractal dimension from NMR of 19 tight sandstone samples selected from the gas-bearing tight sandstone reservoir of Shahejie Formation in Nanpu Sag and that of 16 of them under different water saturation states are analyzed. The application result of new methods in the gas-bearing tight sandstone reservoir of Shahejie Formation in Nanpu Sag shows consistency with experimental data. This paper has facilitated the development of the NMR application by providing a non-electrical logging idea in reservoir quality evaluation and water saturation prediction. It provides a valuable scientific resource for reservoir engineering and petrophysics of unconventional reservoir types, such as tight sandstone, low porosity, and low permeability sandstone, shale, and carbonate rock reservoirs.

Multiphysics Simulations of Microwave Induced Damage Applied to Rock Samples of Varying Strength and Absorptivity

AbstractIn this work, we show the development of a numerical model to investigate the 3D interactions between microwave radiation and basalt, granite, and sandstone rock samples. In particular, we assign sample heterogeneity based on the Weibull statistical distribution, and invoke a damage model for elemental tensile and compressive stresses based on the maximum tensile stress and the Mohr–Coulomb theories, respectively. Model implementation is facilitated by the use of comsol for use in coupling the electromagnetic, thermal, and solid displacement relations. Various parametric studies are conducted related to variable input power and waveguide port alignment, with model validation conducted with respect to damage resulting from a uniaxial compression test. The results indicate that relatively high induced temperatures will promote damage potential, but its impact must be placed within the context of the sample strength to quantify the true potential damage evolution of a given rock mass. As observed herein, a mechanically weaker rock may be prone to mechanical damage; however, it may also possess a relatively large relative permittivity, enabling it to absorb the least amount of microwave radiation thus yielding comparatively low overall damage profiles compared to a more mechanically competent rock mass.