Geological Media Research Articles

Mixed imbibition controls the advance of wetting fluid in multiscale geological media

Imbibition plays a central role during multiphase flows in geological media; yet, our understanding of imbibition dynamics across the multiscale features of rocks, including fractures, microcracks, and heterogeneous matrices is limited. Here, we deployed a unique combination of micro- and clinical X-ray CT imaging to probe directly the spatiotemporal evolution of imbibition in a natural, multiscale shale sample. The method enabled unraveling of mixed imbibition behavior, with spontaneous imbibition rates in the matrix pores and microcracks driven by capillarity proceeding as ∝t−1/2, whereas pressure-driven flows in the macroscopic fractures yield apparent imbibition rates with ∝t−1 scaling. Regardless of the aperture, we showed that spontaneous imbibition proceeds uniformly away from the fractures. The effects of microcracks are further investigated by comparing the dynamics of the imbibition fronts with and without microcracks. These results highlight the paramount role of microcracks on anomalous front roughening and the need to account for microcracks appropriately in the development of predictive theoretical models.

Improving a geophysical method to determine the boundaries of ore-bearing rocks considering certain tectonic disturbances

Purpose is to improve a geophysical method of determining the boundaries of ore-bearing rocks and tectonic disturbances under complex mining and geological conditions while developing 3D geological models. Methods. 3D geological models of natural objects were developed on the basis of complex structural, geological-geophysical, and lithological facies analysis with the wide use of modern 3D seismic exploration technologies taking into consideration the parameters for prediction and selection of optimal factors for ore deposit development. Findings. The scientifically substantiated result is represented by the increased reliability and efficiency of seismic exploration for singling out the ore horizons and ore bodies as well as tectonic disturbances at different depths by specifying geological structures of the prospective areas and sites under study. Originality. Basing on the carried out studies, methods of the development of 3D geological models to study depth geological inhomogeneities of the ore-bearing complexes under complex mining and geological conditions were improved. Practical implications. The obtained results of 3D modelling of geological media basing on the applied 3D seismic exploration will help increase a confidence factor of scientifically substantiated prediction of ore deposits, provide optimal development of complex ore objects, reduce risks, and increase economic efficiency of solid deposit development under complex mining and geological conditions.

Simulated diffusion spreadability for characterizing the structure and transport properties of two-phase materials

Time-dependent diffusion processes between phases of heterogeneous materials are ubiquitous in a variety of contexts in the physical, chemical, and biological sciences. Examples of such materials include composites, porous materials, geological media, cellular solids, polymer blends, colloids, gels, and biological media. The recently developed diffusion spreadability, S(t), provides a direct link between time-dependent interphase diffusive transport and the microstructure of two-phase materials across length scales (Torquato, 2021); thus making S(t) a powerful dynamic means for classifying all statistically homogeneous microstructures, spanning from anti-hyperuniform to hyperuniform. It was shown that the small-, intermediate-, and long-time behaviors of S(t) are directly determined by the small-, intermediate-, and large-scale structural features of the material. Moreover, the spreadability can be applied as a physical-property based tool for microstructural characterization in the absence of or as supplement to scattering information. In this work, we develop a computationally efficient algorithm for ascertaining S(t) directly from digitized representations of material microstructures via random-walk techniques. Our algorithm yields the time-dependent local walker concentration field c(x,t), a quantity not previously examined in the context of the spreadability, enabling us to compute the entropy production rate ṡ(t) of the associated diffusion process, which is a quantity related to the rate of energy dissipation. We also derive exact analytical expressions for ṡ(t), and find that hyperuniform materials have smaller dissipation than any nonhyperuniform materials. Lastly, we use our algorithm to compute, for the first time, the more general case of the spreadability in which the phase diffusion coefficients are distinct and provide a method for extracting the effective diffusion coefficient of the two-phase material from such data. We apply our algorithm to a variety of two- and three-dimensional simulated model (non)hyperuniform microstructures to assess their large-scale structures and diffusion properties. Given previously identified connections between the spreadability and certain nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) procedures, our algorithm is also pertinent to such experimental studies. Overall, our algorithm has practical use in the discovery and design of heterogeneous materials with desirable time-dependent diffusion properties.

Geometric 2.5D inversion of marine time domain electromagnetic data with application to hydrocarbon deposits prospecting

To solve the problem of detection and delineation of marine hydrocarbon deposits located at different depths in an inhomogeneous medium, we propose an approach to 2.5D inversion of electromagnetic (EM) data measured in the time domain (TD) using a differentially normalized method of electrical prospecting. The approach is based on geometric inversion, in which block structures are used to parameterize the geological medium. The sizes of blocks in the initial model are set depending on the depth. Bathymetry is taken into account as a 3D surface. As a result of inversion, the coordinates of block boundaries and conductivity inside blocks and layers are determined. The minimized functional is represented as a sum of weighted residuals between computed and practical data and regularizing terms. Adaptive regularization is used to satisfy parameter constraints. To solve a 3D forward problem and calculate derivatives with respect to parameters, the finite element method (FEM) is used. We propose to use a priori data on the depth of the target layers and use various options of block structures with an analysis of possible uncertainties in detecting target bodies and determining their boundaries. We present the results of a 2.5D inversion of field data obtained in one of the areas in the North Sea. Target bodies discovered as a result of inversion are confirmed by well data. Coincidences were obtained both for productive wells and for dry ones. Using synthetic data for various geoelectric models and options of block structures, we justify the proposed approach to the inversion of marine TD EM data and make recommendations for its use.

Cross-Correlation Analysis of the Stability of Heterogeneous Slopes

Geologic material properties of hillslopes are inherently heterogeneous, with complex layering structures due to geological deposition processes. Lacking detailed sampling of the properties’ spatial distribution has led to the stochastic representation of the properties to address uncertainty in the hillslope stability evaluation. This study treats the spatial distributions of the shear strength parameters, the cohesion (c), and the internal friction angle (φ), in a synthetic two-dimensional slope as stochastic random fields characterized by their means, variances, and correlation scales. This study then evaluates the cross-correlation between these parameters and the factor of safety (FS) using unconditional Monte Carlo simulation (MCS). Different from classical sensitivity analyses, the cross-correlation analysis of FS and the stochastic parameter fields stresses the importance of the orientation of the large-scale geological layering, the correlation between the geological media’s cohesion, and the internal friction angle at the local scale on the probability and uncertainty of failure of the heterogeneous hillslope. The analysis further guides the field sampling strategy to reduce uncertainty in the slope stability analysis due to unknown heterogeneity. More importantly, it suggests the location of stability reinforcement measures. The results of this study provide cost-effective tools for geoengineers to deal with field slope stability analysis under uncertainty.

Organic-rich source rock/H2/brine interactions: Implications for underground hydrogen storage and methane production

There is increasing global interest in the attainment of a carbon dioxide-free global economy by replacement of carbon-based fossil fuels with clean hydrogen. But huge volume of hydrogen needs to be stored to address the imbalance between energy demand and supply due to low volumetric energy content of H2. Underground Hydrogen Storage (UHS) is an integral part of the hydrogen economy value chain and an appealing technology for the attainment of global decarbonization. The Jordan oil shale (Upper Cretaceous, organic-rich source rock sequence) has been proposed as a promising geological storage medium for hydrogen due to its exceptionally high organic content because methane can be produced from the reaction of trapped hydrogen with the kerogen. However, the extraction of methane from kerogen during hydrogen storage in organic-rich shale has not yet been reported. In this study, pressurized hydrogen was injected into high TOC shale samples for 80 days at 1500 psi and 75 °C to assess the extent of hydrogen-rock reaction and possible methane production. We also measured H2/brine and CH4/brine interfacial tensions (IFT), as well as the contact angles of H2/brine/shale and CH4/brine/shale systems at 75 °C and varying pressure (500–1500 psi) to understand the shale-fluid interaction at subsurface conditions. Results indicate some reaction of H2 with the shale after 80 days. No hydrogen sulfide was detected from gas chromatography analysis at the end of the experiment, but traces of methane (0.018 %) were detected. The reaction between hydrogen and organic matter of the shale yielded only a little methane under the conditions investigated in this research, possibly because the experimental temperature and reaction time was insufficient for copious methane generation. Furthermore, contact angle values of CH4/brine were found to be higher than of H2/brine. This means that under geo-storage conditions, the surface becomes fully CH4-wet condition (131o-149o) but remains only intermediate-wet in the presence of the H2/brine system (94o -106o) with increasing pressure, confirming that the interaction of methane with the shale surface is higher than hydrogen-shale surface interaction at similar conditions. The opposite trend was observed for IFT values. The hydrogen/brine IFT was 69.4 mN/m at 500 psi but decreased to 67.9 mN/m at 1500 psi. Likewise, the methane/brine IFT decreased from 69.7 mN/m to 58.3 mN/m with increasing pressure from 500 to 1500 psi. The findings of this study contribute to a better understanding of the adsorption trapping potential of organic-rich source rocks.

Editorial: Applications of wave propagation simulation in complex geological media

Editorial: Applications of wave propagation simulation in complex geological media

A phase transition in the O’Doherty-Anstey model

In the O’Doherty-Anstey model, the spectrum of a seismic wave transiting and reverberating within a stack of interfaces is estimated in terms of its reflectivity. At the center of the model is a discrete combinatorical calculation, in which the contributing raypaths at each lag are weighted and counted. The model maps naturally into an analysis based on statistical mechanics, with raypaths playing the role of system configurations and lag playing the role of system energy. This leads to an expression for the probability of finding a contribution to the wave at a given lag, determined up to a partition function and a scattering parameter analogous to temperature. The partition function is estimated within the O’Doherty-Anstey model itself, and the scattering parameter can be adjusted to describe geologic media with increased or decreased scattering potential. The average contributing lag deriving from this analysis exhibits a continuous phase transition, separating two distinct scattering regimes, one in which the direct wave dominates and the other in which the scattering dominates. The weighting produced by the reflectivity appears to govern the smoothness of the transition.

Importance of shear dilation to two-phase flow in naturally fractured geological media: A numerical study using zero-thickness interface elements

In this paper, a hydro-mechanical coupling model is proposed to investigate the geomechanical effects on two-phase flow in fractured rocks. The discrete fracture model (DFM) and modified Barton-Bandis's model are used to model two-phase fluid flow and mechanical behavior of fractures, respectively. The coupled problem is solved by a mixed finite volume/finite element method, together with the fixed-stress split algorithm. Our model is able to capture the complex coupled behavior induced by the interaction between pore pressure and in-situ stress loadings. Then the proposed model is applied to investigate the two-phase flow behaviors in the fracture networks with different fracture configurations under various in-situ stress conditions. The results illustrate significant influences of shear dilation on the hydraulic properties of fractured rock. With the increase of differential stress, fracture aperture gradually increases due to shear dilation, which accordingly enhances the equivalent permeability of the fractured medium. The degree of shear dilation is highly dependent on the fracture orientation and length distribution. Consequently, channelized flow is formed through the dilated fractures, which results in early water breakthrough and reduces the water sweep efficiency. This study highlights the necessity of considering hydro-mechanical coupling effect for accurate prediction of saturation distributions in fractured rocks.

Fire-induced damage in tunnels: Thermo-mechanical modeling incorporating support system and geological conditions

The thermo-mechanical response of underground tunnels to fire loads is governed by interactions between the tunnel structure and the surrounding geological formation. Accordingly, for accurate prediction of damages in the tunnel structure subsequent to a fire event, it is critical to incorporate the state of the support system as well as in-situ conditions in the surrounding geology at the time of the fire event. Current tunnel-fire studies are mainly developed adopting beam-spring elements, thus disregarding the intricacies of the surrounding geological formation, its true constitutive behavior, as well as realistic tunnel-rock interactions. Another limitation in current tunnel-fire studies is assuming uniform temperature loads within the tunnel interface using time–temperature curves obtained from design codes, therefore ignoring the spatial nature of fire-induced temperatures along the tunnel interior. Temperature gradients can generate additional damage to the tunnel structure. This paper presents a comprehensive integrated numerical framework aimed to predict fire-induced damages in underground tunnels, incorporating four novel components: (i) detailed design of the tunnel support system and in-situ conditions; (ii) degradation of the original tunnel support system over the years due to presence of chloride and sulfates in nearby environment; (iii) thermal gradients generated along tunnel cross section due to real fire events; (iv) and thermo-mechanical interactions between the tunnel structure and the surrounding geological medium, incorporating thermal-induced strength degradation in the concrete and in the steel support elements following design standards from Eurocode. The numerical framework consists of fire simulation using computational fluid dynamics, and thermo-mechanical modeling of the tunnel response to fire. The proposed numerical framework has been utilized to simulate the Caldecott tunnel fire as the case study in this paper, and to evaluate the impacts from the in-situ stress regime and rock strength parameters on the thermo-mechanical behavior response of tunnel to fire events. Results provide a novel insight into the geomechanical response of horseshoe tunnels to fire. Findings reveal the critical zones prone to damage during a fire event to be highly governed by the in-situ stress field and the strength parameters of the surrounding geological strata.

Strategy to Enhance Geological CO2 Storage Capacity in Saline Aquifer

AbstractGeological CO2 storage is an emerging topic in energy and environmental community, which is, as a commonly accepted sense, considered as the most promising and powerful approach to mitigate the global carbon emissions during the transition to net‐zero. Of the geological media which initially considered cover the saline aquifers, oil and gas reservoirs, coal beds, and potentially basalts, up to now only the first two choices have been proven to be the most capable storage sites and successfully implemented at pilot/commercial scales. Here, two tandem papers propose novel strategies for the first time, by synthesizing and utilizing new high‐dryness CO2 foam, to enhance geological CO2 storage capacity in saline aquifer and oil and gas reservoirs. In this paper, a new high‐dryness CO2 foam is synthesized and injected into the saline aquifers to explore the storage capacity enhancement, with the unique foam‐induced advantages of sweep area expansion and storage efficiency improvement. Such a new idea is specifically evaluated and validated through a series of static analytical and dynamic performance experiments. With the optimum surfactant concentration of 0.5 wt%, the foaming volume and quality are determined to be 521 mL and 80.81%, respectively, which also shows excellent salt tolerance with 45,000 ppm Na+, 25,000 ppm Ca2+, and 25,000 ppm Mg2+. Moreover, the water consumption for CO2 storage decreases from 464.31 g/mol at 25% foam quality to 67.38 g/mol at 85% foam quality by using the new CO2 foam. Overall, the newly synthesized CO2 foam could effectively enhance geological CO2 storage capacity and concurrently diminish water consumption, therefore realizing the win‐win environment and economic benefits.

SOME CLASSES OF RICCATI EQUATIONS INTEGRABLE IN QUADRATURES

As it is known, the second-order ordinary linear differential equation with variable coefficients is solvable in case if related Riccati equation can be integrated by quadratures. This paper considers establishment of correspondence between such equations by the authors’ method which means the second-order equation representation by a chain of the first-order equations. The algorithm of special Riccati equation solving is demonstrated (coefficients of these Riccati equations satisfy special conditions). One more peculiarity of this paper stands in consideration of exact applicational example – the Riccati equation which describes the magnetotellurics impedance behavior in geological media.

Justification of geotechnology for nonuniform geomechanical medium of Dzhamgyr gold ore deposit

The uncertain discontinuity and concentration of the mineralization at Dzhamgyr deposit govern the errors in the appraisal of the commercial ore reserves and in the choice of the optimal mining system parameters. In particular, the ore occurrence discontinuity is different when determined using the ore content coefficient in exploration blocks (observations along the block perimeter at a step of 3.5 m along the dip and strike) or the operational exploration data at a regular grid 3.5×(4–5) m. The accomplished research substantiates the geotechnology based on the geological medium discreteness. It is shown that the extraction-purpose delineation of ore and no-ore and generation of pillars allows using the mixed-type stoping flow chart in enlarged extraction panels. Feasibility of lumpiness-conditioned grading, screening and sensor-based calibration of gold-andquartz ore makes it possible to increase the minimum stoping thickness to 2.5–3 m at the high ore dilution of 70%. This enables using mechanized stoping in larger extraction panels (160×(120–160 m) in combination with shrinkage stoping and /or overhand stoping slicing of very rich (bonanza) ore. With the proposed geotechnology introduced, it is possible to implement planning of investment and economic development of production at the doubled mining output and annual ore extraction of 60 thousand tons at the reduced cost of stoping.The authors appreciate contribution of the Geotechnical Engineering Department Head E. A. Babkin, Vertex Gold Company, to preparation of this article.

Adsorption of methane and carbon dioxide by water-saturated clay minerals and clay rocks

Understanding the effects of water on gas adsorption in geological media is of high importance in order to efficiently control numerous subsurface engineering process operating at gas/rock interfaces. Due to preferential interaction with clay surfaces, water fills their porous body, greatly reducing CH4 and CO2 adsorption capacity. In order to quantitatively describe CH4 and CO2 adsorption by hydrated clay minerals, this work proposes to rely on the mechanism of gas uptake by dissolution in pre-adsorbed pore water. This approach was employed to characterise water-saturated porous media of increasing complexity: mesoporous silica SBA-15 and silica gel with different pore sizes and geometry, isolated illite and montmorillonite and natural clay-rich rock (the Callovo-Oxfordian formation – COx, France) in powdered and crushed states. It was found that the solubility in water can reliably explain the CO2 uptakes by hydrated pore systems regardless of their nature as well as the CH4 uptakes, but only for solids with large mesopores and montmorillonite mineral. A so called “adsorption enhanced gas uptake in pore water” for CH4, exceeding its solubility in bulk water by a factor of 5–8, was observed for the systems with narrow pore sizes, highlighting the impact of surface energy on gas uptake and the occurrence of the interaction of weakly-soluble methane with the surface, promoting its uptake in comparison to pure dissolution.

Dynamic Borehole Pressure of Geological Material Finite in Radial Extent

In recent years, the construction of tunnels and subways has increased significantly. Current researches related to the underground engineering always focus on quasi-static force analysis of semi-infinite media, thus it is of great significance to analysis the borehole pressure during tunnel construction. In this paper, a finite cavity expansion model in finite diameter geological media is proposed considering the influence of finite radial extent of geological media and drilling velocity, and theoretical and computational analysis is carried out.

The Use of Convolutional Neural Networks to Search for Fractures in the Geological Media

The Use of Convolutional Neural Networks to Search for Fractures in the Geological Media

Выявление природных и техногенных разуплотненных зон в подработанном массиве по данным высокоточных гравиметрических наблюдений

The paper presents the results of gravimetric studies at the potassium salt deposit in order to obtain information on the development of negative engineering-geological processes in the rock mass caused by subsoil development. A methodology was developed for high-precision monitoring gravimetric observations, which makes it possible to determine the change in the field over time. A physico-geological model of gravimetric monitoring, representing a homogeneous geological medium with an isolated area in which rock density changes have occurred, has been created. For the purposes of gravimetric monitoring, a method for processing and interpreting dynamic gravity anomalies based on the synthesis of qualitative and quantitative methods for extracting geological information from gravimetric data has been adapted. The result of the interpretation is the area of distribution, the probable interval of depths of rock decompaction, as well as the magnitude of the change in rock density, which characterizes the intensity of the process of decompaction. Examples are given of testing the developed technology for dividing decompressed zones into natural and man-made zones at the Verkhnekamskoye potash deposit in order to improve the safety of its operation. It is shown that the results of monitoring gravimetric observations can predict areas of dangerous geological processes and control subsidence of the earth's surface.

Sustainable carbon-dioxide storage assessment in geological media using modified Pythagorean fuzzy VIKOR and DEMATEL approach

In a developing country like India, the primary source of power generation is fossil fuels. The lion's share of India's electricity production is from fossil fuels leading to massive greenhouse gas emissions (GHG) like CO2, which causes global warming. To deal with climate change and control global warming, the carbon capture utilization and storage (CCUS) project in geological formation is a practical, comparatively secure, inevitable and emergent method to be materialized. However, CO2 storage in deep geological structures in the sedimentary basin has a risk of leakage due to the geological formation of different seams, which might harm human beings, including different underground, terrestrial, and aquatic species. It could affect the energy sources of our environment also. Therefore the selection of CO2 storage site in geological media is based on some criteria, and therefore it is a multi-criteria decision-making (MCDM) problem. The multi-criteria group decision-making (MCGDM) method is proposed to get a more impartial result, using the soft computing methodology Pythagorean fuzzy VIKOR (“VIekriterijumsko KOmpromisno Rangiranje”, a Serbian term for “multi-criteria optimization and compromise solution”) modified with a novel divergence called Pythagorean fuzzy Jensen-Shannon Song (PJSS). The fuzzy DEMATEL (DEcision MAking Trial and Evaluation Laboratory) method is introduced to evaluate the criteria weights. A Comparative Study and Sensitivity analysis are also presented in this article. Finally, the outcomes of the work show that the proposed methodology is feasible.

Wavelet Transforms for the Simulation of Flow Processes in Porous Geologic Media

Wavelet Transforms for the Simulation of Flow Processes in Porous Geologic Media

Effect of heat-treatment on the pure- and mixed-mode fracture properties of a homogeneous sandstone

Fracture-mechanical properties of the sedimentary rocks at elevated temperature strongly control hydraulic fracturing in rocks, geothermal energy extraction, deep tunnelling, and spent fuel disposal in geological medium. This paper investigates the relationship between the strength properties (e.g. tensile strength, brittleness index and Young’s modulus) and the pure-mode and mixed-mode fracture toughness of Dholpur sandstone at temperatures ranging from room temperature to 500 °C. A suitable brittleness index definition was identified to quantify the deformational changes. Additionally, evolution of the stress–strain behaviour, change in the degradation degree (DD), peak strain, and evolution in porosity values were closely studied to comment on the potential brittle–ductile transition of the rock. The fracture toughness remained unchanged between 25–150 °C, sharply increased 3%–28% between 150–200 °C, and followed by a 75%–80% decrease from 200–500 °C. All the pure- and mixed-mode fracture toughness were found to maintain an exponential relationship with the Young’s modulus, tensile strength, and brittleness index of the heat-treated rocks across all the temperatures. A potential brittle to quasi-brittle/semi-ductile transition temperature of 225 °C was identified for Dholpur sandstone. Additionally, mixed mode fracture behaviour of the heat-treated rock was investigated using generalized maximum tangential stress (GMTS) criterion. It was noticed that GMTS is far better at predicting the KII/KI ratio of mode-II fractures than the conventional maximum tangential stress (MTS) criterion. Statistical analysis of the test data indicate that a 3-parameter Weibull function can be successfully employed to predict the mode-II fracture toughness of heat-treated sandstone in terms of the mode-I data.