Rock Porosity Research Articles

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

Experimental Investigation of Porosity and Permeability of Reservoir Rock Under the Action of CO2 and Its Oil Displacement Effect

ABSTRACT Background: Core analysis is a key method for directly evaluating the properties of promising or existing reservoirs. Core data can be used to determine the sedimentological and diagenetic characteristics of rocks, which are critical for assessing their filtration and storage properties. This article presents the findings of a core digitization project, including the application of advanced technologies for analysing high-resolution panoramic images of thin rock sections. Aim: Development and implementation of digital technologies for automated core analysis, including determining porosity and grain size composition from panoramic images of thin rock sections, aim to enhance research accuracy and efficiency over traditional methods, aligning with academic standards. Materials and methods: The study describes methods for automated determination of porosity and grain size distribution, as well as their integration with conventional research techniques. Results: The results demonstrate a significant improvement in analysis accuracy and efficiency compared to manual methods, as supported by statistical data from 147 thin rock sections. Conclusion: The analysis of 147 thin rock sections from eight wells confirmed the effectiveness of digital analysis techniques, which significantly enhanced the accuracy of determining porosity and grain size composition of rocks. The data obtained served as the basis for developing detailed petrophysical models. This is critical for geological and hydrodynamic modelling. Future work includes the further expansion of digital core databases and the implementation of machine learning algorithms to predict reservoir properties.

Abstract A numerical sensitivity analysis of a hydrogen pore storage system is carried out on a reservoir-scale geological model of the Ketzin site (Germany) to analyze the influence of uncertainty in geological parameters and fluid properties on storage performance. Therefore, the following physical geological parameters and fluid properties were investigated: Porosity and permeability of the reservoir rock, the brine salinity, relative permeability and capillary pressure and mechanical dispersion. The range of the applied parameters is based on experimental and field data of the chosen location obtained during the former CO2 storage projects at the Ketzin site from 2008 to 2013. Using the open-source reservoir software MUFITS for the numerical simulations, strong differences between the results can be observed. The results were evaluated based on measures to quantify performance, such as the ratio of produced hydrogen mass to produced cushion gas (nitrogen), productivity index and sustainability index. The strongest impact on the performance parameters was observed with variations in the capillary pressure and the relative permeability curves followed by the absolute permeabilities, while the least impact was seen with changes in the porosity and salinity of the brine. This work is not only crucial as a pre-feasibility study for the Ketzin storage site for hydrogen storage but also as a basis for decision-making for other potential storage sites in sedimentary basins.

Abstract Uncertainty in interpretation of the existence and characteristics of each reservoir layer will greatly influence the level of success in the drilling process. Formation evaluation through wireline logging operation can obtain information about reservoir characteristics, one of which is calculating rock porosity, is sometimes not carried out due to limitations in drilling operations which are closely related to drilling costs which are increasingly expensive. The Semberah Field is located in a delta depositional environment which has reservoir layers that have been producing since the 1970s. Drilling activities that produce data in the form of gas drilling ratio and wireline logging have been widely carried out but still have problems in analyzing rock porosity values. To improve level confidence and limitation data affected drilling operation during attempt porosity analysis thorough wireline logging, gas drilling ratio data from 10 wells was taken and then several gas chromatography ratios were calculated, namely wetness, balance, and fluid mobility or estimated potential porosity (FMPP). Then, all these ratios were compared with the effective porosity (phie) from the petrophysical calculation. FMPP apparently has a sensitivity value that matches the phie value from Petrophysical calculations, namely around 70.25%. This gas drilling ratio method is expected to reduce the uncertainty of porosity calculations due to geological environment and in the future can be used as data to determine reservoir characteristics without having to use expensive wireline logging data.

Facies-driven correlations based on rock porosity for the assessment of geomechanical properties of carbonate rocks in Santos Basin

Abstract The compressional-to-shear-wave velocity ratio (VP/VS) provides critical insights into rock composition, fluid saturation, porosity, and fault-zone properties. High-resolution imaging is facilitated by in situ VP/VS estimation, which leverages closely located earthquake clusters. However, conventional in situ VP/VS estimation methods, which rely on demeaning differential travel times to mitigate origin time errors, tend to cluster data points near zero, weakening regression constraints and increasing estimation uncertainty. Here, we present an improved method through a two-step grid search that corrects origin time differences while preserving the true distribution of travel-time differences and simultaneously estimates VP/VS. Synthetic tests demonstrate that this approach enhances sensitivity to VP/VS and reduces uncertainty compared with conventional methods. We further validate our method by applying it to three event clusters from the 2021 Ms 6.4 Yangbi earthquake sequence, recorded by a dense seismic array, confirming the method’s robustness under realistic observational conditions. The results reveal spatially variable VP/VS along the fault zone. Our method, optimized for dense array observations, has potential applications in fault zone imaging, earthquake source studies, and seismic hazard assessments.

Analysing the macroscopic and microscopic mechanical properties and damage mechanism of acid-eroded rocks encountered in rock engineering construction in acidic areas is of great significance for the smooth progress of construction. Firstly, this article selects sandstone as the sample and analyses the quality change rate, density change rate, longitudinal wave velocity change rate, microstructure change, and mechanical properties through indoor acid corrosion test, scanning electron microscope observation, and triaxial compression test. Secondly, the changes in porosity of rock before and after acid corrosion are obtained using nuclear magnetic resonance technology to define the microscopic chemical damage variable, and the total damage variable of rocks under the coupling effect of chemical corrosion and confining pressure is derived. Then, based on Lemaitre strain equivalent hypothesis, the microscopic damage evolution equation and constitutive model of rock under the coupling action of chemical corrosion and confining pressure are established by using the theory of continuous damage mechanics and assuming that the rock element strength failure complies with SMP criterion. Finally, the rationality and accuracy of the model are verified by triaxial compression test data of acid-etched rock. The results show that both macro- and micro-mechanical properties of sandstone are degraded by acid etching, resulting in significant damage. The established microscopic damage constitutive model (DCM) can well reflect the stress–strain characteristics of the whole process of acid-eroded rock triaxial compression, and the test curve is in good agreement with the theoretical curve, which verifies the rationality and reliability of the model and the method for determining the model parameters. This model expands the damage model of rock under the coupling effect of chemical corrosion and confining pressure, further revealing the damage mechanism and failure law of rock under the coupling effect of chemical corrosion and confining pressure.

Hydrogen, a genuinely clean energy, is a promising alternative to fossil fuels. Inspired by underground gas storage of methane, establishing underground hydrogen storage (UHS) in depleted oil and gas reservoirs has emerged as a significant research focus. Carbonate reservoirs, where widely-presented fractures can facilitate the high-speed injection and production of gases, are hence ideal candidates for building underground hydrogen storage facilities. During the cyclic injection and extraction processes of UHS, the formation is subjected to stress disturbances, leading to stress sensitivity. Understanding the stress sensitivity patterns of carbonate rocks is crucial for optimizing injection and production strategies. This study reconstructed three-dimensional digital models of fractured carbonate rocks from the L gas field using micro-CT scanning technology. Utilizing the finite element method, we investigated the microscopic permeability characteristics of carbonate rocks and analyzed the impact of stress loading direction and confining stress on stress sensitivity. The findings reveal that the stress loading direction significantly influences the stress sensitivity of fractured carbonate rocks. When a stress of 60 MPa is applied perpendicular to the fracture direction, the permeability reduction ratio can reach 17.32%. In contrast, when the same stress is applied parallel to the fracture direction, the permeability reduction ratio is only 4.82%. Furthermore, a simulation of UHS with cyclic injection and production of H2 in the target block was conducted. When both permeability and porosity stress sensitivity were considered, the working gas volume for UHS decreased by only 3.4%, demonstrating that fractured carbonate reservoirs are feasible candidates for constructing underground hydrogen storage.

In order to accurately describe the characteristics of each stage of triaxial creep behavior of rock in alkaline environment, the graded loading creep tests are carried out under the chemical corrosion of NaOH solution with different concentrations and pH values. The microscopic pore structure, porosity and phase composition of rocks immersed in different pH solutions are tested. The rock microstructure characteristics of solutions with different pH values are obtained. Based on the damage degradation law of cohesion and internal friction angle and chemical damage theory, a nonlinear creep damage model of rock considering alkali solution corrosion is established. The results show that with the increase of pH value, the porosity shows a gradual upward trend. This indicates that the pore structure of sandstone may change in an alkaline enhanced environment. This leads to the expansion of pore size or the formation of new pores. In the neutral environment, the rock skeleton structure is partially loose. But no obvious cracks and pores appear. In the alkaline environment, some pores and cracks appear. With the increase of pH value, the loss of rock mineral particles is more obvious. The derived constitutive model can well describe the characteristics of each stage of the triaxial creep behavior of rock under the corrosion of alkaline solution. The model can more accurately capture the changes of rock creep characteristics caused by these changes and thus more accurately reflect the creep behavior of rock under actual working conditions. The Nishihara model is relatively traditional. It does not fully consider the influence of the specific factor of alkali solution corrosion, and cannot accurately describe the complex mechanical response of rock after alkali solution corrosion. The research results provide a theoretical basis for further study on the long-term stability of rock engineering under multi-field coupling.

Phosphorus deposits in central Guizhou are typical of global phosphorogenic events after the Neoproterozoic Ice Age. These deposits exhibit a high correlation between weathering characteristics and the ore grade level. To investigate the mechanisms of the process in which phosphate is partially dissolved, phosphorus weathering migration, precipitation, and re-enrichment in the supergene environment, this study uses X-ray diffraction analysis, scanning electron microscopy, energy spectrum analysis, elemental geochemical tests, saturation method rock porosity experiments, and dissolution experiments to compare the primary ore and weathered ore of phosphorus deposits in central Guizhou. It is considered that the weathered phosphate ore is lighter in color and is highly porous. The main gangue mineral, dolomite, is mostly dissolved, and characteristic weathering fabrics are widely observed. The P2O5 content in primary phosphate ore is not strongly correlated with porosity. However, in weathered ores, when the weathering indexes reach the weathering thresholds, there is a strong correlation between the P2O5 content and porosity, with a significant increase in P2O5 content. When the grade reaches around 35%, the correlation between porosity and P2O5 content deteriorates again, and the impact of weathering and leaching on phosphorus enrichment is significantly reduced. REEs may be adsorbed, migrated, and lost by clay minerals, especially the LREEs, which are more prone to loss. The δCe negative anomaly becomes weaker, indicating that the weathering of phosphate ore occurs in a weakly acidic environment. The weathering and enrichment process of phosphorus deposits includes three stages: superimposed weathering conditions, carbonate mineral leaching, and phosphate mineral recrystallization. This study can further enrich the ore-forming theory of weathering-type phosphorus deposits and provide geological evidence of mineral exploration practices.

Abstract Reservoir characteristic analysis through surface data can help in describing subsurface characteristics. Ngrayong Formation is one of the target reservoirs because of its characteristic rocks that have good porosity. Reservoir characterization through surface data can use two parameters, namely outcrop geometry (reservoir thickness) and porosity that can be observed in thin sections. This study aims to determine the characteristics of lithology, outcrop geometry, porosity, and their relationship to depositional facies. The research location is located in Sendangharjo Village, Blora District, Blora Regency, Central Java. Measurement of stratigraphic data in the field uses the rope span method. Rock naming and porosity calculations are determined through petrographic analysis using the point counting method. Based on the results of data collection on 4 tracks in the research area, it was found that the Ngrayong Formation consists of 3 lithologies, namely sandstone, shale, and limestone. The results of the measured stratigraphic analysis indicate that the research area has two depositional environmental systems, namely coastal and reef depositional systems. The porosity of the research area is divided into 6 categories, namely 1 neglected sample, 5 bad, 7 sufficient, 8 good, 3 very good, and 1 special. The facies association with the best porosity is found in the coastal plain. The geometry of the Ngrayong Formation rocks has a thick reservoir rock thickness in the form of sandstone and limestone. Based on the results of thickness measurements, track 4 has the thickest reservoir with a thickness of 36.5 meters.

This research was initiated to study the groundwater potential zones using the Fuzzy logic technique at Lembangan Kadamaian, Kota Belud, Sabah, and its surroundings. The lithological units of this study mainly focus on the sedimentary rock of Wariu Formation, Crocker Formation, and Trusmadi Formation, including the quaternary alluvium deposition unit of Kota Belud. Based on the structural geology analysis results, the deformation trends are in the northwest-southeast direction. The interpretation of groundwater potential zones was made by using the ArcGIS Pro, R-studio Global Mapper, and several other mappingrelated software. Ten thematic maps that have been produced are lithological map, lineament density map, rainfall map, distant from river map, distant from lineament map, drainage density map, landform, and land cover map, Topographic Wetness Index (TWI) map, rock porosity map, curvature map, and slope steepness map. GIS techniques were used during the spatial analysis stage. All thematic maps have their class values and are based on field data, relevant department data, and remote sensing data. Further processes were done using R-studio, Fuzzy Toolset, and Raster Calculator. This process afterward will produce the groundwater potential map of the study area. The final result has been supported by the data of tube wells from the Department of Minerals and Geosciences, Sabah, and was validated using the ROC and AUC curve validation technique.

Excavating water-saturated rock strata inevitably induces slippage and alters effective stress, significantly affecting the rock’s strength and deformation capacity. Understanding the hydro-mechanical coupling characteristics of these strata is essential for the safe excavation of vertical shafts. This study employs triaxial compression tests on water-saturated sandstone using the MTS-815 rock mechanics test system to investigate these characteristics. Tests were conducted at confining pressures (σ3) of 10, 20, and 30 MPa, with pore water pressures set at 0%, 20%, 40%, 60%, and 80% of the respective confining pressures. The effective stress coefficient (α) was analyzed concerning the rock’s deformation and strength. A novel method for calculating the effective stress coefficient, based on the effective stress principle and the Mohr–Coulomb criterion, is proposed, leading to several key conclusions. The results indicate: (1) A positive linear correlation exists between the peak strength attenuation coefficient of sandstone specimens and the effective stress coefficient, with a correlation coefficient of 0.82. (2) The effective stress coefficient α is a bilinear function of pore water pressure p and volumetric stress Θ, with a fitting analysis correlation coefficient of 0.986. Furthermore, α is positively linearly correlated with p and negatively linearly correlated with Θ. (3) Under hydro-mechanical coupling, rock porosity is positively exponentially correlated with the effective stress coefficient. At constant confining pressure, the effective stress coefficient is positively linearly correlated with Poisson’s ratio and negatively linearly correlated with the elastic modulus. This criterion addresses the limitations of pore elasticity theory in determining the effective stress coefficient for the peak strength of rocks and significantly enhances the prediction of the mechanical properties of aquifer rocks.

Summary The pressure pulse decay (PPD) method is widely used for measuring permeability in tight porous media. However, it can overestimate the permeability of salt rocks to hydrogen due to gas leakage at the rock-sleeve interface, caused by hydrogen’s high diffusivity. In addition to this, the method is time-consuming, particularly for tight materials such as salt rocks, and the error in permeability measurements can be as high as 60%, making it less reliable for accurate assessments. We present a modified experimental setup and analytical approach for fast and more accurate determination of permeability and porosity of salt rocks with hydrogen. Our results demonstrate that this modified experimental configuration significantly improves the accuracy by at least 10 times and reduces the duration of experiments 4 times for measuring permeability and porosity compared with the conventional PPD method. We validated our experimental and analytical methodology through permeability and porosity measurements on salt rock samples sourced from the Lotsberg Formation (LSF) in Fort Saskatchewan, Alberta, Canada.

Groundwater beneath earth’s surface is stored in pores and rock fractures.Weathering and diagenesis plays vital roles in the enhancement or decrease of rock porosity. To that extent, argillaceous rocks ordinarily considered impervious could earn fracture porosity,enhancing the permeability and substantial storage of water through interconnected matrix channels. Alex Ekwueme University Ndufu-Alike and Gregory University, Uturu are growing universities faced with challenges of good groundwater for domestic uses. Preliminary geophysical studies were carried out within the campuses using electrical resistivity method. Thereafter, the group recommended drilling at five points ,three at Ndufu-Alike and two at Uturu. The very low resistivity data obtained from the survey confirmed that the lithology of the area is predominantly shale of moderate to high plasticity. The pumping test of drilled boreholes were carried out according to the Cooper-Jacob’s(1946) method. Test results showed that Transmissivity (T) varied from 18.23m2/day to 37.44m2/day at Ndufu-Alike and from 22,85m2/day to 23.04m2/day at Uturu. Storativity (S) was determined to range from 0.22 to 0.32. These values suggest intermediate class associated with confined aquifers. The study shows that fractured shale aquifers hold a promise for domestic water supply and that the shales can be counted as groundwater prospects to be harnessed after careful site-specific geophysical studies.

Case-hardening processes that develop in monuments reduce the porosity of rocks while increasing surface hardness. This situation may contribute to the transfer of cultural stone heritage markers to future generations by limiting the penetration into the rock structure of water, which is the most destructive agent in atmospheric weathering processes. This study focused on the Fraktin relief monument, which was created by the Hittites in the 13th century BCE by carving into the rock surface. The site was investigated to reveal the case-hardening mechanism and its effects on the physical properties of the rock. The geochemical formation mechanism of the surface-hardening process, which contributed to the survival of the Fraktin relief monument, was examined by use of scanning electron microscope–energy dispersive spectrometry (SEM-EDS) and analysis by an inductively coupled plasma–mass spectrometer (ICP-MS). In addition, the effect of the hardening on the physical properties of the rock was investigated with nondestructive tests applied both in situ and in a laboratory. The SEM-EDS and ICP-MS analyses revealed that amorphous silica filled the pores of the rock and created surface hardening. This situation has increased the geotechnical properties of the unit in which the monument was carved, making it more resistant to atmospheric processes.

Abstract The ABAQUS software was used to simulate the triaxial compression test of rocks. Using Python programming scripts to achieve random deletion of units, thereby obtaining loading models with different porosities. Based on actual triaxial compression test data, numerical simulations are conducted to analyze the mechanical properties and energy dissipation evolution of rocks during loading. The results show that: ① With the increase of porosity, the elastic modulus, peak stress, and their corresponding internal energy and elastic strain energy all decrease linearly. ② When the pore volume in the rock is small, shear failure occurs, forming a distinct strain localization band. After the peak stress, the stress in the rock rapidly decreases, exhibiting brittle failure. Rocks with more pores exhibit multiple localized strain bands during failure, making them more fragmented. The stress after peak strength slowly decreases, exhibiting ductile failure characteristics. With the increase of porosity, the internal energy and elastic strain energy gradually decrease. After reaching the peak stress, the internal energy and plastic dissipation energy steadily increase, and the elastic strain energy is partially released. The release amount and release rate decrease due to the increase in rock porosity, and the severity of rock failure weakens. At the initial stage of loading, elastic deformation of the rock is the main cause, and at this time, the plastic dissipation energy is close to zero. When the stress reaches a certain value, the plastic dissipation energy slowly increases and rapidly increases near the peak stress until the rock fails.

В связи с истощением резервов традиционно добываемой нефти как в России, так и во всем мире разработка нефти из низкопоровых коллекторов актуальна и перспективна. Приведен статистический анализ распределения величины пористости в отложениях основных нефтегазоносных бассейнов (НГБ) России - Волго-Уральском, Тимано-Печорском, Северо-Кавказском и Западно-Сибирском. Эти бассейны обладают большими резервами трудноизвлекаемой нефти из сложнопостроенных низкопоровых пластов. Представлены компьютерные карты размещения месторождений с низкопоровыми коллекторами. В Западно-Сибирском НГБ выявлено 15 таких месторождений, в Тимано-Печорском - 13, в Северо-Кавказском - 63, самое большое количество месторождений находится в Волго-Уральском НГБ - 82. Показана большая роль низкопоровых пород в нефтегазовом потенциале бассейнов, в Волго-Уральском НГБ сосредоточено 80 % российских запасов низкопоровых отложений. По литологическим характеристикам низкопоровые коллекторы в основном относятся к карбонатным отложениям, но пористость терригенных пород выше по сравнению с последними. Установлена приуроченность коллекторов к различным стратиграфическим отделам от кайнозоя до палеозоя, но большинство пород относится к палеозойскому возрасту. Проанализировано распределение низкопоровых коллекторов с возрастанием глубин. Показано, что пористость уменьшается на больших глубинах (более 5000 м) в 2-3 раза, при этом доля низкопоровых отложений по сравнению со средне- и высокопористыми породами с глубиной увеличивается. В перспективе на больших глубинах роль низкопоровых коллекторов как источника добычи трудноизвлекаемой нефти будет только расти. Oil production from low-permeable reservoirs is an urgent and promising issue because of the depleted reserves of oil extracted using traditional procedures, both in Russia and abroad. The statistical analysis of porosity distribution in the sediments of the main oil and gas basins (OGB) of Russia is presented: the Volga-Ural, Timan-Pechora, North Caucasus and West Siberian. These basins have large reserves of hard-to-recover oil from complex formations with low porosity. Computer maps of the deposits with low-pressure reservoirs are presented. In the West Siberian basin, 15 deposits of this kind have been identified, 13 deposits in the Timan-Pechora basin, 63 in the North Caucasus, and the largest number of deposits is located in the Volga-Ural basin - 82. The great role of low-porosity rocks in the oil and gas potential of basins is shown, 80 % of the Russian reserves of low-porosity sediments are concentrated in the Volga-Ural basin. According to lithological characteristics, low-permeable reservoirs mainly belong to carbonate sediments, but the porosity of terrigenous rocks is higher, compared to carbonate deposits. The presence of reservoirs in various stratigraphic layers has been established, starting from the Cenozoic and ending with the Paleozoic, but most rocks belong to the Paleozoic age. The distribution of reservoirs with low porosity is analysed as the depths increase. It is shown that porosity decreases at great depths (over 5000 m) by a factor of 2-3, while the proportion of low-porosity sediments increases with depth, compared to medium-pored and highly porous rocks. In the future, at great depths, the role of low-permeable reservoirs as the sources of hard-to-recover oil will only increase.

Oil production from low-permeable reservoirs is an urgent and promising issue because of the depleted reserves of oil extracted using traditional procedures, both in Russia and abroad. The statistical analysis of porosity distribution in the sediments of the main oil and gas basins (OGB) of Russia is presented: the Volga-Ural, Timan-Pechora, North Caucasus and West Siberian. These basins have large reserves of hard-to-recover oil from complex formations with low porosity. Computer maps of the deposits with low-pressure reservoirs are presented. In the West Siberian basin, 15 deposits of this kind have been identified, 13 deposits in the Timan-Pechora basin, 63 in the North Caucasus, and the largest number of deposits is located in the Volga-Ural basin - 82. The great role of low-porosity rocks in the oil and gas potential of basins is shown, 80 % of the Russian reserves of low-porosity sediments are concentrated in the Volga-Ural basin. According to lithological characteristics, low-permeable reservoirs mainly belong to carbonate sediments, but the porosity of terrigenous rocks is higher, compared to carbonate deposits. The presence of reservoirs in various stratigraphic layers has been established, starting from the Cenozoic and ending with the Paleozoic, but most rocks belong to the Paleozoic age. The distribution of reservoirs with low porosity is analysed as the depths increase. It is shown that porosity decreases at great depths (over 5000 m) by a factor of 2-3, while the proportion of low-porosity sediments increases with depth, compared to medium-pored and highly porous rocks. In the future, at great depths, the role of low-permeable reservoirs as the sources of hard-to-recover oil will only increase.