Pore Space Properties Research Articles

An X-ray micro-tomographic study of the pore space, permeability and percolation threshold of young sea ice

Abstract. The hydraulic permeability of sea ice is an important property that influences the role of sea ice in the environment in many ways. As it is difficult to measure, so far not many observations exist, and the quality of deduced empirical relationships between porosity and permeability is unknown. The present work presents a study of the permeability of young sea ice based on the combination of brine extraction in a centrifuge, X-ray micro-tomographic imaging and direct numerical simulations. The approach is new for sea ice. It allows us to relate the permeability and percolation properties explicitly to characteristic properties of the sea ice pore space, in particular to pore size and connectivity metrics. For the young sea ice from the present field study we obtain a brine volume of 2 % to 3 % as a threshold for the vertical permeability (transition to impermeable sea ice). We are able to relate this transition to the necking of brine pores at a critical pore throat diameter of ≈0.07 mm, being consistent with some limited pore analysis from earlier studies. Our optimal estimate of critical brine porosity is half the value of 5 % proposed in earlier work and frequently adopted in sea ice model studies and applications. By placing our results in the broader context of earlier studies, we conclude that the present threshold is more significant in that our centrifuge experiments and high-resolution 3D image analysis enable us to more accurately identify the threshold below which fluid connectivity ceases by examining the brine inclusion microstructure on finer scales than were previously possible. We also find some evidence that the sea ice pore space should be described by directed rather than isotropic percolation. Our revised porosity threshold is valid for the permeability of young columnar sea ice dominated by primary pores. For older sea ice containing wider secondary brine channels, for granular sea ice and for the full-thickness bulk permeability, other thresholds may apply.

Cyclic Subcritical Water Injection into Bazhenov Oil Shale: Geochemical and Petrophysical Properties Evolution Due to Hydrothermal Exposure

In situ shale or kerogen oil production is a promising approach to developing vast oil shale resources and increasing world energy demand. In this study, cyclic subcritical water injection in oil shale was investigated in laboratory conditions as a method for in situ oil shale retorting. Fifteen non-extracted oil shale samples from Bazhenov Formation in Russia (98 °C and 23.5 MPa reservoir conditions) were hydrothermally treated at 350 °C and in a 25 MPa semi-open system during 50 h in the cyclic regime. The influence of the artificial maturation on geochemical parameters, elastic and microstructural properties was studied. Rock-Eval pyrolysis of non-extracted and extracted oil shale samples before and after hydrothermal exposure and SARA analysis were employed to analyze bitumen and kerogen transformation to mobile hydrocarbons and immobile char. X-ray computed microtomography (XMT) was performed to characterize the microstructural properties of pore space. The results demonstrated significant porosity, specific pore surface area increase, and the appearance of microfractures in organic-rich layers. Acoustic measurements were carried out to estimate the alteration of elastic properties due to hydrothermal treatment. Both Young’s modulus and Poisson’s ratio decreased due to kerogen transformation to heavy oil and bitumen, which remain trapped before further oil and gas generation, and expulsion occurs. Ultimately, a developed kinetic model was applied to match kerogen and bitumen transformation with liquid and gas hydrocarbons production. The nonlinear least-squares optimization problem was solved during the integration of the system of differential equations to match produced hydrocarbons with pyrolysis derived kerogen and bitumen decomposition.

Explaining the large variability in empirical relationships between magnetic pore fabrics and pore space properties

SUMMARYThe magnetic anisotropy exhibited by ferrofluid-impregnated samples serves as a proxy for their pore fabrics, and is therefore known as magnetic pore fabric (MPF). Empirically, the orientation of the maximum susceptibility indicates the average pore elongation direction, and predicts the preferred flow direction. Further, correlations exist between the degree and shape of magnetic anisotropy and the pores’ axial ratio and shape, and between the degrees of magnetic and permeability anisotropies. Despite its potential, the method has been rarely used, likely because the large variability in reported empirical relationships compromises interpretation. Recent work identified an additional contribution of distribution anisotropy, related to the arrangement of the pores, and a strong dependence of anisotropy parameters on the ferrofluid type and concentration, partly explaining the variability. Here, an additional effect is shown; the effective susceptibility of the ferrofluid depends on the measurement frequency, so that the resulting anisotropy depends on measurement conditions. Using synthetic samples with known void geometry and ferrofluids with known susceptibility (4.04 SI and 1.38 SI for EMG705 and EMG909, respectively), magnetic measurements at frequencies from 500 to 512 kHz are compared to numerical predictions. Measurements show a strong frequency-dependence, especially for EMG705, leading to large discrepancies between measured and calculated anisotropy degrees. We also observe artefacts related to the interaction of ferrofluid with its seal, and the aggregation of particles over time. The results presented here provide the basis for a robust and quantitative interpretation of MPFs in future studies, and allow for re-interpretation of previous results provided that the ferrofluid properties and measurement conditions are known. We recommend that experimental settings are selected to ensure a high intrinsic susceptibility of the fluid, and that the effective susceptibility of the fluid at measurement conditions is reported in future studies.

Multiscale Smoothed Particle Hydrodynamics Model Development for Simulating Preferential Flow Dynamics in Fractured Porous Media

AbstractWe present our new multiscale pairwise‐force smoothed particle hydrodynamics (PF‐SPH) model for the characterization of flow in fractured porous media. The fully coupled multiscale PF‐SPH model is able to simulate flow dynamics in a porous and permeable matrix and in adjacent fractures. Porous medium flow is governed by the volume‐effective Richards equation, while the flow in fractures is governed by the Navier‐Stokes equation. Flow from a fracture to the porous matrix is modeled by an efficient particle removal algorithm and a virtual water redistribution formulation to enforce mass and momentum conservation. The model is validated by (1) comparison to a finite‐element model (FEM) COMSOL for Richards‐based flow dynamics in a partially saturated medium and (2) laboratory experiments to cover more complex cases of free‐surface flow dynamics and imbibition into the porous matrix. For the laboratory experiments, Seeberger sandstone is used because of its well‐known homogeneous pore space properties. The saturated hydraulic conductivity of the permeable matrix is estimated from a pore size and grain size distribution analysis. The developed PF‐SPH model shows good correlation with the COMSOL model and all types of laboratory experiments. We employ the proposed model to study preferential flow dynamics for different infiltration rates. Here, flow in the fracture is associated with the term “preferential flow,” providing rapid water transmission, while flow within the adjacent porous matrix enables only slow and diffuse water transmission. Depending on the infiltration rate and water inlet location, two cases can be distinguished: (1) immediate preferential/fracture flow or (2) delayed preferential flow. In the latter case, water accumulates at the surface first (ponding), then the fracture rapidly transmits water to the bottom system outlet. For the immediate fracture flow response, ponding only occurs once the fracture is fully saturated with water. In all cases, preferential flow is much more rapid than diffuse flow even under saturated porous medium conditions. Furthermore, infiltration dynamics in rough fractures adjacent to an impermeable or permeable matrix for different infiltration rates are studied as well. The simulation results show a significant lag in arrival times for small infiltration rates when a permeable porous matrix is employed, rather than an impermeable one. For higher infiltration rates, water rapidly flows through the fracture to the system outlet without any significant delay in arrival times even in the presence of the permeable matrix. The analysis of the amount of water stored in permeable fracture walls and in a fracture void space shows that for small infiltration rates, most of the injected water is retarded within the porous matrix. Flow velocity is higher for large infiltration rates, such that most of the water flows rapidly to the bottom of the fracture with very little influence of matrix imbibition processes.

Using digital rock physics to investigate the impacts of diagenesis events and pathways on rock properties

Digital rock physics (DRP) has shown promising performance and more realistic results in predicting rock properties and investigating flow mechanisms in geomaterials. However, the application of DRP for studying the effects of diagenesis on rock properties using a systematic and accurate model has not been reported. During the formation of the sedimentary rocks, they may undergo various diagenesis events (e.g., cementation and dissolution), and such events may occur along different pathways, which both make a significant effect on rock properties. With the aid of the DRP techniques, we present a comprehensive investigation of the effects of diagenesis events and diagenesis pathways on rock properties. In this paper, the original digital rock with multicomponent and irregular particles is constructed using the discrete element method (DEM). Then, the original model similarly undergoes four diagenesis events (two cementations and two dissolutions) along with two different diagenesis pathways for generating new models. The cementation and dissolution are simulated using a dilation operation and quartet structure generate set algorithm (QSGSA), respectively. Finally, some properties of pore space, transport, and elastic of all the models are analyzed and compared to investigate the effects of diagenesis events and pathways. The comparisons indicate that the final rock which experiences the cementation and then dissolution exhibits larger porosity, fractal dimension, aperture, coordination number, and permeability, and smaller tortuosity, formation factor, and elastic moduli than the one that undergoes the dissolution and then cementation. Thus, the study will help us to better understand the variations of the flow and mechanical properties of rocks without conducting extensive experiments if rocks experience different diagenesis processes along different pathways.

Reservoir properties of drill cutting by the nuclear magnetic resonance relaxometry and dielectric spectroscopy data

The purpose of the study is to extend the use of nuclear magnetic resonance relaxometry and dielectric spectrometry methods. This is realized through a complex interpretation of the data by the above methods to timely provide additional petrophysical information about the drill cuttings pore space properties and structure. The relevance of the study is that the data on the drill cuttings obtained by the NMR method can be used as prior information in the logging data interpretation before a detailed petrophysical study of the core sample or in case of the core absence in the sampling interval. The objects of study are the drill cuttings samples from the fields of the West Siberian oil-and-gas province. The samples are saturated with different fluids, and their reservoir properties are determined by the nuclear magnetic resonance and dielectric spectrometry methods. As part of the experimental research, nuclear magnetic resonance investigations of the core samples of different discretization degrees have been carried out to determine the reservoir properties of the samples depending on the degree of their particle size reduction. It has been shown that the obtained results do not depend on the particle size of the measured sample and are consistent with the results of the standard petrophysical studies. The relationship between the porosity and the saturating fluid type has been established. Based on the data obtained by the dielectric spectroscopy method, the study has determined the value of the complex dielectric constant that shows how the degree of saturation changes depending on the fluid, and what happens in the pore space. The complex interpretation of the results obtained by the two methods provides additional information on the drill cuttings reservoir properties that can be used as a priori information on the formation properties.

Computational characterization of nonwoven fibrous media: I. Pore-network extraction and morphological analysis

Nonwoven fibrous materials are a unique class of porous materials that are widely used for filtration and separation applications. The complex pore structure in fibrous media, with high connectivity and low tortuosity, enhances filtration efficiency while preventing filter fouling. The pore size distribution is a key to predicting and improving transport properties by tailoring the microstructure of fibrous media. However, the statistical properties of the pore space are not easily accessible in experiments, and often only effective geometric properties such as hydraulic radius and specific surface area are reported. In this study, we employ a computational framework and generate realistic nonwoven fibrous media with a wide range of porosities. We obtain the pore network by extracting a subnetwork of the watershed segmentation of pore space and analyze the statistical distribution of pore and throat sizes and their connectivity. We find that a random fiber orientation has a pronounced effect on the effective geometric properties and their dependence on porosity. We investigate the influence of processing parameters such as fiber size, orientation, and overlaps between fibers as a prerequisite to predicting transport properties of nonwoven fibrous media. The computational approach can be combined with experimental imaging techniques, which enables rapid characterization of porous microstructures in terms of the statistical pore space properties resulting from specific manufacturing processes.

Geometrical and Topological Analysis of Pore Space in Sandstones Based on X-ray Computed Tomography

The pore geometry and topology properties of pore space in rocks are significant for a better understanding of the complex hydrologic and elastic properties. However, geometry and topology information about the sandstone pore structures is not fully available. In this study, we obtained the topological and geometrical pore parameters from a representative elementary volume (REV) for fluid flow in sandstone samples. For comparison, eight types of sandstones with various porosities were studied based on the X-ray micro-computed tomography technique. In this study, the REV size was selected based on the parameters from the respective pore network models (PNM), not just the porosity. Our analysis indicates that despite different porosity, all the sandstone samples have highly triangular-shaped pores and a high degree of pore structural isotropy. The high porosity group sandstones exhibit wider ranges of pore sizes than the low porosity group sandstones. Compared to the high porosity group sandstones, the low porosity group sandstones samples showing a higher global aspect ratio, indicating some pores exist in the form of bottlenecks. The pore topological properties of different sandstones show a high dependence of the porosity. The high porosity group sandstones obtain large coordination numbers, large connectivity densities and low tortuosities. The results from this study will help better understand the complex pore structure and the fluid flow in sandstone.

Toward a better understanding of low-frequency electrical relaxation — An enhanced pore space characterization

The relaxation phenomena observed in the electrical low-frequency range (approximately 1 MHz–10 kHz) of natural porous media such as sandstones are often assumed to be directly related to the dominant (modal) pore throat sizes measured, for instance, with mercury intrusion porosimetry. Attempts to establish a universally valid relationship between pore size and peak spectral induced polarization (SIP) relaxation time have failed, considering sandstones from very different origins and featuring great variations in textural and chemical compositions as well as in geometric pore space properties. In addition working with characteristic relaxation times determined in Cole-Cole or Debye decomposition fits to build the relationship have not been successful. In particular, samples with narrow pore throats are often characterized by long SIP relaxation times corresponding to long “characteristic length scales” in these media, assuming that the diffusion coefficients along the electrical double layer were constant. Based on these observations, three different types of SIP relaxation can be distinguished. We have developed a new way of assessing complex pore spaces of very different sandstones in a multimethodical approach to combine the benefits of mercury intrusion porosimetry, micro-computed tomography, and nuclear magnetic resonance. In this way, we achieve much deeper insight into the pore space due to the different resolutions and sensitivities of the applied methods to pore constrictions (throats) and wide pores (pore bodies). We experimentally quantify pore aspect ratios and volume distributions within the two pore regions. We clearly observe systematic differences between three SIP relaxation types identified previously, and we can attribute the SIP peak relaxation times to measured characteristic length scales within our materials. We highlight selected results for a total of nine sandstones. It seems that SIP relaxation behavior depends on the size difference of the narrow pore throats to the wide pore bodies, which increases from SIP type 1 to type 3.

A comprehensive investigation of the effects of Organic-Matter pores on shale properties: A multicomponent and multiscale modeling

Organic-matter (OM) pores play a significant role in the pore systems of shale formations. Numerous studies have analyzed the characteristics of OM pores. However, fewer studies reported the effects of OM pores on shale properties. In this study, a comprehensive pore-scale investigation of the impacts of OM pores on various physical properties of shale samples based on multicomponent and multiscale shale models is presented. To this end, a novel technique for constructing three-dimensional (3D), multicomponent, and multiscale shale models was proposed. Multiple shale models with different fractions of OM pores were then generated using the proposed algorithm. Based on these shale models, the effects of OM pores on the geometric properties, topological properties, correlation functions, and transport properties of pore space were comprehensively evaluated within the physics-based and realistic models. The results show that the addition of more OM pores in a pore system increases its connectivity, decreases its tortuosity, and strengthens the correlation of the voxels in the pore structure. At the same time, it enhances the surface roughness of the pore space, the proportions of small pores, and the number of isolated pores. Besides, the generation of more OM pores into the pore space leads to the increase of the permeability and decrease of the formation factor of the shale models.

On the role of microgeometry in conductivity substitution

Conductivity substitution is the process of predicting the change in the effective electrical conductivity of a rock upon a change in conductivity of the mineral or fluid phase. Conductivity substitution is nonunique — only a range of conductivities can be predicted from knowledge of the initial effective conductivity, the porosity, and the initial and final compositions. The precise change depends strongly on the rock microstructure, which is seldom adequately known. Rigorous bounds on the change in effective conductivity upon changes in the phase conductivities for two-phase isotropic composites are used to gain insights into the roles of microgeometry and phase conductivity contrast. When the conductivity contrast between phases is high, the conductivity substitution predicted by Archie’s law corresponds approximately to the upper bound on the change of conductivity upon substitution. Inclusion modeling suggests that vuggy, highly tortuous, or partially disconnected pore space could account for conductivity changes smaller than those predicted by Archie’s law. Substitution behavior computed analytically for known microgeometries correlates with measures of microgeometry, including the fraction of connected fluid phase and variance of electric field strength in each phase. Comparison of the conductivity substitution bounds with brine-saturated sandstone data reveals that the position of measured data with respect to the conductivity substitution bounds can be indicative of the effective clay content. The bounds provide a template for better prediction of effective conductivity if we have at least some knowledge of the pore microstructure. Similarly, multiple conductivity measurements on the same rock might be used to extract more information about the rock and pore space properties than is possible with only a single measurement.

Applications of critical path analysis to uniform grain packings with narrow conductance distributions: II. Water relative permeability

Accurate estimation of water relative permeability has been of great interest in various research areas because of its broad applications in soil physics and hydrology as well as oil and gas production and recovery. Critical path analysis (CPA), a promising technique from statistical physics, is well known to be applicable to heterogeneous media with broad conductance or pore size distribution (PSD). By heterogeneity, we mean variations in the geometrical properties of pore space. In this study, we demonstrate that CPA is also applicable to packings of spheres of the same size, known as relatively homogeneous porous media. More specifically, we apply CPA to model water relative permeability (krw) in mono-sized sphere packs whose PSDs are fairly narrow. We estimate the krw from (1) the PSD and (2) the PSD and saturation-dependent electrical conductivity (σr) for both drainage and imbibition processes. We show that the PSD of mono-sized sphere packs approximately follows the log-normal probability density function. Comparison with numerical simulations indicate that both the imbibition and drainage krw are estimated from the PSD and σr data more accurately than those from the PSD. We show that CPA can estimate krw in mono-sized sphere packs precisely.

A linear constitutive model for unsaturated poroelasticity by micromechanical analysis

SummaryThis paper extends the Biot theory of poroelasticity from the saturated to unsaturated case. The Biot phenomenological model uses parameters that are easily observable, such as the deformation of porous frame, total stress, pore pressure, and fluid specific discharge. Such model is preferred for engineering applications. At this macroscopic level, the extension of Biot theory from saturated to unsaturated is straightforward. The constitutive constants, however, are combined properties of solid, pore space, and fluids. In the unsaturated case, the constants are functions of the degree of saturation. Their measurements and tabulation over a range of saturation is generally not feasible for practical applications. In this work, a Biot‐Willis type analysis is performed for the unsaturated case to provide a theory that the bulk material constants can be evaluated using laboratory measurable micromechanical constants under saturated condition, plus a capillary pressure curve (saturation versus suction pressure) typically available for unsaturated porous medium, without the need of measurement at each state of saturation. In particular, it is demonstrated that the surface energy contained in the meniscus interface manifests as a “capillary modulus,” given by the negative inverse slope of the capillary pressure curve. A rigorous analysis based on the thermodynamic variational energy approach is also conducted to lend theoretical support to the phenomenological approach. The presented model can bring a closure to the practical engineering modeling of the deformation of partially saturated porous medium that lacks the information of material constants over the range of saturation.

Pore-scale modeling of carbonates

Abstract Carbonate rocks display complex pore textures with heterogeneities that extend over several length scales. Identifying and capturing the significant pore space properties in a computationally tractable model is therefore nontrivial. Pore-scale models bridge predictions of transport properties from sub-pore to core scale and attempts have been made to render such methods cost-effective. This chapter reviews several methods for fabricating pore-scale models of carbonate rocks and discusses approaches to simulating their fluid flow and solute transport properties. The advantages and limitations of each method in reducing the reservoir development uncertainties are explained. We argue that pore-scale models can play an important role in predicting the petrophysical properties of carbonate rocks. Even more importantly, they provide sensitivity analyses of pore-scale features on macroscopic transport observations and offer explanations for anomalous flow behaviors.

Pore space properties in carbonate fault rocks of peninsular Italy

The fault cores of extensional faults in Mesozoic limestones and dolostones are examined by mean of combined microstructural, ultrasonic and petrophysical analyses. Grain-supported fault rocks commonly localize in the outer fault cores, whereas matrix-supported fault rocks in their inner portions. Cemented fault rocks, if present, surround the main slip surfaces. All dolomite-rich fault rocks, include elongated pores that show a preferential orientation only in the inner fault core. On the contrary, the pore network of calcite-rich fault rocks is made up of elongated pores in the outer fault core, and of sub-spherical pores in the inner fault core. Despite their different pore network characteristics, the petrophysical values of both grain-supported and matrix-supported fault rocks are quite similar one another, with effective porosity up to 10–12%, and permeability up to 2–5 mD. Differently, these values drop down to host rock values, porosity ~5% and permeability ~10−3 mD, in the cemented fault rocks. Experimental data are discussed to establish, for the first time, the relative control exerted by individual cataclastic and diagenetic processes on the present day pore characteristics, and to decipher the fault core permeability structure at depth.

On the effect of pore-space properties and water saturation on explosive spalling of fire-loaded concrete

In this paper, the influence of concrete properties such as permeability and environmental conditions (water content) on the spalling behavior of concrete subjected to fire loading is investigated. For this purpose, a special fire-test setup is presented, allowing an improved reproduction of temperature histories observed, e.g., in tunnel fires. Moreover, the developed test setup enables a continuous monitoring of spalling, giving access to the spalling history and the final level of damage of concrete specimens.The obtained results, considering different water/cement-ratios and saturation degrees, are related to the required initial tensile strength determined by means of a numerical assessment tool. Finally, correlations between the identified parameters governing fire-spalling were established and allowed an evaluation of the spalling risk of concrete mixtures. These correlations revealed that – in contrast to requirements given in national and international standards – the combination of water content and permeability may serve as proper key and design parameter, defining the risk of spalling.

Estimating irreducible water saturation and permeability of sandstones from nuclear magnetic resonance measurements by fractal analysis

Abstract Understanding the relationships between the pore structure and bulk properties such as irreducible water saturation (Swir) and permeability (k) of rocks is a crucial problem in geoscience. In this study, two types of fractal dimension were determined from nuclear magnetic resonance (NMR) T2 relaxation time distribution and models for estimating Swir and k using fractal theory were proposed. In view of the data of sandstone samples from upper Paleozoic formation in China, we found a good agreement between the predicted Swir values based on fractal analysis and the experimental measurements, and the estimated k values based on the proposed model are within one order of magnitude of measured k. Additionally, another four frequently used k estimation models were compared with our proposed model, and the result support that the proposed approach has great potential in investigating k while certain limitation still exists. This procedure was applied on another set of sandstone samples collected from a different location, and the predicted permeability values are reliable. Our study suggests that the proposed Swir estimation model using NMR T2 data and fractal dimensions provides useful insights into characterizing the pore space properties of sedimentary rocks. Our work demonstrates that we can use NMR data to infer Swir directly, and the estimated Swir value can be well integrated in permeability prediction model, which improves the applications of NMR in characterizing the properties related to rock pores.

Application of microstructure classification for the assessment of the variability of geological-engineering and pore space properties in clay soils

Abstract The performed investigations were focused on analysing the variability of geological-engineering properties in clay soils from central-eastern Europe with regard to microstructures. Thirty-nine soils differing in origin, lithology and microstructure type were selected for analysis. Results of studies on lithological and physical and mechanical parameters were analysed, coupled with quantitative microstructural parameters based on microstructure images. The relationships between lithological, physical and mechanical and pore space parameters were determined with regard to microstructure types. Sediment origin and diagenesis, and soil microstructure and pore space parameters had influence on the geological-engineering properties. Such approach allows for predicting engineering parameters based on soil microstructure types and their pore space parameters.

Comparison between mercury intrusion porosimetry and nuclear magnetic resonance relaxometry to study the pore size distribution of limestones treated with a new consolidation product

Pore-space properties, such as pore-size distribution and connected porosity, are relevant factors in the evaluation of the performance of a consolidation treatment. In this study, two different techniques – Mercury Intrusion Porosimetry (MIP) and Nuclear Magnetic Resonance Relaxometry (NMRR) – were adopted to study the compatibility and the efficacy of a new consolidation product for limestones. This work aims at comparing and combining data obtained by MIP and NMRR; to confirm the relationship between the quantitative results of MIP and the qualitative ones of NMRR, a calibration which leads to correlate T2 distribution and pore size distribution has been applied. Experimental results showed that, in most cases, NMRR results agree with MIP data. Therefore, NMRR technique can be considered a powerful tool to evaluate the change in pore size distribution due to the application of a consolidating agent on stone, especially in cases when sampling should be avoided.

THE CHARACTERISTICS OF PORE SPACE IN LOWER TRIASSIC SANDSTONES OF THE WARSAW REGION

Reservoir and sealing properties of Lower Triassic sandstones from seven boreholes of the central part of the Koszalin-Zamość Synclinorium were investigated in terms of potential levels for underground storage of carbon dioxide. Extensive petrographic studies, image analysis, and investigations of petrophysical properties of rocks and pore space were carried out. The research shows that diagenetic processes both variously affected the intensity of alteration and variously shaped the pore space. Not only primary but also secondary porosity, resulting from diagenetic alteration and dissolution, is observed in the rocks. Microscopic observations revealed that the pore space in studied samples is dominated by macropores. The results obtained indicate a poor suitability of the Lower Triassic deposits for the purpose of carbon dioxide sequestration.