Rock Porosity Research Articles

Factors аffecting mineralization of groundwater in deep oil and gas bearing horizons in the western part of the West Siberian megabasin

The purpose of this study was to identify the causes of the observed hydrogeochemical situation and the factors contributing to its formation within the Middle Jurassic hydrogeological complex in the western part of the West Siberian megabasin, using the Talinskoye oil field as an example. The research primarily involved constructing dependencies between mineralization (y) and various factors including porosity, reservoir pressure, modern and paleotemperature of the foundation, and depth of the foundation (x). The study evaluated the degree of connection between each parameter and mineralisation. The results showed that the initial hydrochemical state in the area is heterogeneous, with significant variations in mineralisation levels within a single reservoir. The closest dependencies have been revealed between mineralization and porosity of reservoir rocks (an inverse dependence), mineralization and reservoir pressure (a direct dependence). The practical significance of the study is justified by the need to understand the nature of the formation of the hydrogeochemical environment in order to preserve it, control changes, as well as solve issues related to the forecasting, preservation, and destruction of oil deposits.

Evaluation of Grain Size Effects on Porosity, Permeability, and Pore Size Distribution of Carbonate Rocks Using Nuclear Magnetic Resonance Technology

Evaluation of Grain Size Effects on Porosity, Permeability, and Pore Size Distribution of Carbonate Rocks Using Nuclear Magnetic Resonance Technology

Diagenesis and lateral sealing types of fault zones in the Lishu Depression, Songliao Basin, NE China

The Lishu Depression in the Songliao Basin is characterized by well-developed faults, and the accumulation of oil and gas is closely related to fault sealing. However, there remains a dearth of comprehensive investigation into the diagenesis of fault zones and their influence on lateral sealing. This study employed electron probe analysis, cathodoluminescence, and carbon and oxygen isotope techniques to investigate the diagenetic processes in fault zones. This research also reconstructed the evolution of porosity and displacement pressure of fault rocks, and identified the lateral sealing characteristics of fault zones and their impact on oil and gas accumulation. The majority of faults in the study region formed earlier, and the fault zones experienced intricate diagenesis, characterized by compaction, cementation, replacement, and dissolution. The displacement pressure of fault rocks is higher during fault intermittent and static periods compared to active periods, and it is influenced by diagenesis. Late-stage calcite and pore-filling chlorite were deposited subsequent to the period of fault activity, filling dissolution pores. This led to relatively higher displacement pressure and improved lateral sealing of fault zone. The kaolinite cement exhibits a relatively elevated potassium concentration, due to its connection with the dissolution of feldspar, resulting in lower displacement pressure and poor sealing of fault zone. Based on the evolutionary characteristics of displacement pressure in fault rock and reservoir during various transportation stages, this study identified six types of lateral sealing of fault zones. Notably, the sealing types characterized by "fault core and damage zone sealing during static periods" and "fault core and damage zone sealing during intermittent and static periods" exhibit superior lateral sealing properties, effectively controlling the accumulation of oil and gas in the sand bodies on either side of the fault zone.

Competitive adsorption-diffusion coupling process of helium-nitrogen mixture in shale kerogen nano-slit

Helium, as a probe gas with low adsorption capacity, is widely used for measuring porosity, permeability, and specific surface area in reservoir rocks of unconventional gas such as shale and coal. The pretreatment duration of these rock samples determines the amount of residual nitrogen in their pores, and the competitive adsorption and diffusion of residual nitrogen with the probe gas has a significant impact on the measurement results of their physical properties. This work aims to reveal the mechanisms involved in the competitive adsorption-diffusion coupling process of nitrogen-helium mixtures. Brief experiments were conducted to demonstrate the competitive adsorption between nitrogen and helium in shale. Subsequently, molecular dynamics simulation was employed to investigate this process and provide necessary details. Meanwhile, a theoretical model was developed to describe the diffusion of gas molecules in this process. Our results indicate that helium rapidly permeates shale samples and reaches an equilibrium distribution. However, the competitive adsorption between nitrogen and helium can slow down the helium permeation process, which can be attributed to the main adsorption sites occupied by nitrogen. The agreement between FEM computations and MD simulations validates our model for various mechanisms. Furthermore, our model can be applied to a wider range of porous materials and gas mixtures in related fields.

Interpreting correlations in stress‐dependent permeability, porosity, and compressibility of rocks: A viewpoint from finite strain theory

AbstractCharacteristics of stress‐dependent properties of rocks are commonly described by empirical laws. It is crucial to establish a universal law that connects rock properties with stress. The present study focuses on exploring the correlations among permeability, porosity, and compressibility observed in experiments. To achieve this, we propose a novel finite strain‐based dual‐component (FS‐DC) model, grounded in the finite strain theory within the framework of continuum mechanics. The FS‐DC model decomposes the original problem into the rock matrix and micro‐pores/cracks components. The deformation gradient tensor is utilized to derive the constitutive relations. One of the novelties is that the stress‐dependent variables are calculated in the current configuration, in contrast to the reference configuration used in small deformation theory. The model has only a few number of parameters, each with specific physical interpretations. It can be reduced to existing models with appropriate simplifications. Then, model performance is examined against experimental data, including permeability, porosity, compressibility, volumetric strain and specific storage. It proves that the variations of these properties are effectively described by the proposed model. Further analysis reveals the effect of pores/cracks parameters. The validity of the FS‐DC model is examined across a broad range of pressures. The results show that rock properties at high confining pressures (300 MPa) differ from those observed under relatively low pressures (200 MPa). This disparity can be attributed to inelastic behaviors of micro‐structure, wherein the rock skeleton undergoes permanent deformation and breakage.

4D Neutron Imaging of Solute Transport and Fluid Flow in Sandstone Before and After Mineral Precipitation

AbstractIn many geological systems, the porosity of rock or soil may evolve during mineral precipitation, a process that controls fluid transport properties. Here, we investigate the use of 4D neutron imaging to image flow and transport in Bentheim sandstone core samples before and after in‐situ calcium carbonate precipitation. First, we demonstrate the applicability of neutron imaging to quantify the solute dispersion along the interface between heavy water and a cadmium aqueous solution. Then, we monitor the flow of heavy water within two Bentheim sandstone core samples before and after a step of in‐situ mineral precipitation. The precipitation of calcium carbonate is induced by reactive mixing of two solutions containing CaCl2 and Na2CO3, either by injecting these two fluids one after each other (sequential experiment) or by injecting them in parallel (co‐flow experiment). We use the contrast in neutron attenuation from time‐resolved tomograms to derive three‐dimensional fluid velocity field by using an inversion technique based on the advection‐dispersion equation. Results show mineral precipitation induces a wider distribution of local flow velocities and leads to alterations in the main flow pathways. The flow distribution appears to be independent of the initial distribution in the sequential experiment, while in the co‐flow experiment, we observed that higher initial local fluid velocities tended to increase slightly following precipitation. The outcome of this study contributes to progressing the knowledge in the domain of reactive solute and contaminant transport in the subsurface using the promising technique of neutron imaging.

Research on thermal insulation materials properties under HTHP conditions for deep oil and gas reservoir rock ITP-Coring

Deep oil and gas reservoirs are under high-temperature conditions, but traditional coring methods do not consider temperature-preserved measures and ignore the influence of temperature on rock porosity and permeability, resulting in distorted resource assessments. The development of in situ temperature-preserved coring (ITP-Coring) technology for deep reservoir rock is urgent, and thermal insulation materials are key. Therefore, hollow glass microsphere/epoxy resin thermal insulation materials (HGM/EP materials) were proposed as thermal insulation materials. The materials properties under coupled high-temperature and high-pressure (HTHP) conditions were tested. The results indicated that high pressures led to HGM destruction and that the materials water absorption significantly increased; additionally, increasing temperature accelerated the process. High temperatures directly caused the thermal conductivity of the materials to increase; additionally, the thermal conduction and convection of water caused by high pressures led to an exponential increase in the thermal conductivity. High temperatures weakened the matrix, and high pressures destroyed the HGM, which resulted in a decrease in the tensile mechanical properties of the materials. The materials entered the high elastic state at 150 °C, and the mechanical properties were weakened more obviously, while the pressure led to a significant effect when the water absorption was above 10%. Meanwhile, the tensile strength/strain were 13.62 MPa/1.3% and 6.09 MPa/0.86% at 100 °C and 100 MPa, respectively, which meet the application requirements of the self-designed coring device. Finally, K46-f40 and K46-f50 HGM/EP materials were proven to be suitable for ITP-Coring under coupled conditions below 100 °C and 100 MPa. To further improve the materials properties, the interface layer and EP matrix should be optimized. The results can provide references for the optimization and engineering application of materials and thus technical support for deep oil and gas resource development.

Cohesive approach for determining porosity and P-impedance in carbonate rocks using seismic attributes and inversion analysis

AbstractThe assessment of hydrocarbon flow through seismic and well-log data presents a persistent challenge in determining porosity. The acoustic impedance section provides a visual representation of the layers, while the raw seismic data showcase the subsurface reflectors that exist within the rock layers. The accuracy of acoustic impedance is widely acknowledged to surpass that of seismic data as a representation of reality. The primary objective of this study is to convert seismic reflector data into acoustic impedance values, which provide insights into the layer properties based on lithology. This approach enhances the accuracy of seismic inversion results by aligning them more closely with actual geological conditions. Seismic inversion is employed to ascertain the physical characteristics of the rock, including acoustic impedance and porosity. Carbonate reservoirs are recognised for their complex pore structures and heterogeneity, which present difficulties in their characterisation. The objective of this research is to predict the porosity and identify the reservoir within the dense carbonate reservoirs in Central Luconia, Sarawak. These objectives are achieved by employing a porosity and acoustic impedance cross-plot and improved precision and predictability through the integration of seismic attribute interpretation and deterministic seismic inversions. The uniqueness of our approach stems from the incorporation of various geophysical techniques to detect reservoirs that have hydrocarbon deposits. A correlation is observed between seismic inversion acoustic impedance and porosity within the zone of interest, indicating an estimated porosity range of 10–35%. The analysed area demonstrates the possibility of containing a hydrocarbon based on the observed relationship between porosity and impedance, as well as the outcomes of the inversion analysis.

Laboratory Hydraulic Tensile Strength Correlation with Strength-Based Brittleness Indices for Carbonate Reservoirs

Hydraulic fracturing (HF) is the primary choice for stimulating petroleum reservoirs. Rock tensile strength and brittleness are crucial parameters required for screening candidate reservoirs and in designing successful HF operations. However, in situ and laboratory determinations of the hydraulic tensile strength (HTS) of rock can prove problematic. Alternatively, the HTS could be estimated from the rock brittleness once a reliable relationship has been established between them. Accordingly, this paper investigates the correlations between the HTS, as measured using laboratory hydraulic fracture tests, and ten strength-based brittleness indices (BIs) selected from the research literature. The primary inputs for computing these BIs are uniaxial compressive strength (UCS) and the Brazilian tensile strength (BTS), which are typically measured for most projects using standard laboratory rock mechanics tests or obtained from log data. For the purposes of this experimental investigation, intact rock core samples were obtained from a carbonate–dolomite formation in Iran, comprising eight distinct geomechanical units, with measured values of UCS, BTS, and HTS ranging 29.7–162.2, 1.93–12.23, and 7.20–20.63 MPa, respectively. The measured HTS was found to directly correlate with the UCS, BTS, and Young’s modulus, and inversely correlated with the rock porosity. Seven of the ten investigated BIs correlated with the measured HTS over 69% (R2 ≥ 0.69). In particular, the BI expressions developed by Yagiz and Gokceoglu, Ghadernejad et al., and Khandelwal et al. exhibited relatively strong correlations with the measured HTS (producing R2 values of 0.94, 0.87, and 0.86, respectively), suggesting that these three HTS–BI correlations could be used to provide preliminary HTS estimates for the investigated carbonate–dolomite formation in Iran. This work adds to a database that can be expanded to include other geographical regions for providing useful information about the selection of a suitable site or reserve for conducting HF operations.

The Relationship of Physical Properties of Rock to The Slope Stability of The Progo River Cliff in Sentolo-Sedayu, Kulon Progo, Yogyakarta, Indonesia

To support the increasingly advanced development of the Kulon Progo area, road access via the Progo River bridge needs to be maintained in instability. To support this, an engineering geological survey was carried out to find out the relationship between the physical properties of rocks and the stability of slopes on the cliffs of the Progo River. The research method begins with a field survey to obtain lithology and slope geometry data. Scanlines at selected locations were carried out to determine discontinuity areas and interpret rock weathering using a Schmidt hammer. Physical laboratory tests are useful for determining the bulk density and porosity of rocks, while from rock mechanical tests (shear strength) cohesion and friction angle values are obtained. The results of the safety factor analysis using the Slide program show that the slopes generally have a medium-high level of severity (Fk 1.2), supported by quite a lot of joint areas, varying porosity (4.12 – 25.10%) and the level of weathering is at level III-IV. Rock porosity is less related to slope strength, while weathering generally reduces slope stability.

Stability Deterioration Analysis of Toppling Dangerous Rock Mass under the Combined Effect of Vibration and Freeze-Thaw Cycles

To investigate the degree of stability deterioration in toppling dangerous rock mass under different action times, firstly, the vibration load generated by train travel in a single action and its decay law were studied, and the theoretical relational equation of rock strength deterioration under the action of vibration loading was obtained by analyzing the increase in half axle expansion of micro fissures inside the rock. Secondly, the freezing stress of the microfissures was determined according to the rock freezing and swelling theory, and the theoretical relational equation of rock strength deterioration under the action of freeze-thaw cycles was obtained by integrating the rock confinement and moisture migration conditions of the fissures wall. The stability coefficient of the toppling dangerous rock mass exhibited a rapid and then slow decreasing trend with increasing number of actions, which was non-linearly negatively correlated with the train running speed and the initial porosity of the rock, and non-linearly positively correlated with the freezing temperature. Controlling the freezing temperature and initial porosity of rock can significantly reduce the degree of deterioration in the stability of dangerous rock mass.

3D Quantification of Pore Networks and Anthropogenic Carbon Mineralization in Stacked Basalt Reservoirs.

Basalt formations are promising candidates for the geologic storage of anthropogenic CO2 due to their storage capacity, porosity, permeability, and reactive geochemical trapping ability. The Wallula Basalt Carbon Storage Pilot Project demonstrated that supercritical CO2 injected into >800 m deep Columbia River Basalt Group stacked reservoir flow tops mineralizes to ankerite-siderite-aragonite on month-year time scales, with 60% of the 977 metric tons of CO2 converted within 2 years. The potential impacts of mineral precipitation and consequent changes in the rock porosity, pore structure, pore size, and pore size distributions have likely been underestimated hitherto. Herein, we address these knowledge gaps using X-ray microcomputed tomography (XMT) to evaluate the pore network architecture of sidewall cores recovered 2 years after CO2 injection. In this study, we performed a detailed quantitative analysis of the CO2-reacted basalt cores by XMT imaging. Reconstructed 3D images were analyzed to determine the distribution and volumetric details of porosity and anthropogenic carbonate nodules in the cores. Additional mineralogic quantification provided insight into the overall paragenesis and carbonate growth mechanisms, including mineralogic/chemical zonation. These findings are being used to parametrize multiphase reactive transport models to predict the fate and transport of subsurface CO2, enabling scale-up to commercial-scale geologic carbon storage in basalts and other reactive mafic-ultramafic formations.

Electrical resistivity, seismic velocity, and porosity of crustal rocks from the Oman ophiolite under brine-saturated ocean floor conditions

In order to examine the effects of crack properties on electrical resistivity and seismic velocity, we conducted simultaneous measurements of electrical resistivity, seismic velocity and porosity at brine-saturated hydrostatic pressures using mafic crustal rocks from the Oman ophiolite. The resistivity and velocity of the samples increase systematically with increasing confining pressure owing to the closure of cracks, as monitored by changes in porosity. Apparent formation factors of each sample are related to the porosity, but nonlinear relationships on logarithmic plots indicate that Archie's law cannot explain these experimental data. We evaluated the effect of crack porosity and aspect ratio for the measured velocity based on the effective medium theory, and the electrical resistivity was inferred from the crack porosity and connectivity according to the percolation model. The experimental velocity and resistivity results are consistent with the model calculations in terms of crack density, aspect ratio and connectivity. We applied a combined velocity-resistivity model to the geophysical logging and borehole data for the oceanic crust in Hole 504B. Our inversion results indicate that the seismic layer 2/3 transition is primarily caused by an alteration front controlled by interconnected cracks and fluid flow in the oceanic crust.

Introducing standardized field methods for fracture-focused surface process research

Abstract. Rock fractures are a key contributor to a broad array of Earth surface processes due to their direct control on rock strength as well as rock porosity and permeability. However, to date, there has been no standardization for the quantification of rock fractures in surface process research. In this work, the case is made for standardization within fracture-focused research, and prior work is reviewed to identify various key datasets and methodologies. Then, a suite of standardized methods is presented as a starting “baseline” for fracture-based research in surface process studies. These methods have been shown in pre-existing work from structural geology, geotechnical engineering, and surface process disciplines to comprise best practices for the characterization of fractures in clasts and outcrops. This practical, accessible, and detailed guide can be readily employed across all fracture-focused weathering and geomorphology applications. The wide adoption of a baseline of data collected using the same methods will enable comparison and compilation of datasets among studies globally and will ultimately lead to a better understanding of the links and feedbacks between rock fracture and landscape evolution.

ФОРМИРОВАНИЕ И РЕДУКЦИЯ БАЗЫ ЗНАНИЙ ДЛЯ ОЦЕНКИ ЦЕЛЕСООБРАЗНОСТИ БУРЕНИЯ СКВАЖИН НА НЕФТЯНЫХ МЕСТОРОЖДЕНИЯХ

The article discusses the issues of forming and reducing a fuzzy knowledge base designed to assess the feasibility of drilling wells in oil fields as part of a decision support system. The initial knowledge base was formed using a specially developed software package that implements neuro-fuzzy modeling technology based on a group of fuzzy neural networks. To train them and form a knowledge base, initial data were required that described the dependence of the influence of the characteristics of producing wells on their efficiency in terms of the production rate of oil produced. The initial data for the analysis of 3187 records were presented for 46 oil field objects with carbonate reservoirs. Each record was characterized by the values of the input parameters “absolute rock permeability”, “rock porosity”, “average flow rate of neighboring wells” and “minimum water cut of neighboring wells”. The output parameter determined the efficiency of the well as the average oil flow rate for the first 3 years of operation. When training a team of 5 fuzzy neural networks, 5 gradations of input parameters were selected. The total number of fuzzy rules in the original knowledge base was 319. To assess its classification ability, the values of the Accuracy, Precision, Recall and F1-Score metrics were calculated. To reduce the knowledge base, a specially developed software package was used that implements 2 stages of genetic optimization: structural-parametric transformations of the fuzzy rules of the original knowledge base to obtain an intermediate knowledge base and minimizing the composition of the fuzzy rules of the intermediate knowledge base to obtain the desired (reduced) knowledge base. As a result of the reduction, the quantitative composition of knowledge bases, as well as the values of classification quality metrics, changed. The number of rules in the intermediate knowledge base was 131, and in the reduced one - 33. The overall reduction in the volume of the knowledge base was 89.66%. After the 1st stage of reduction, the values of the Accuracy, Precision, Recall and F1-Score metrics on the test data set increased, respectively, by 7.88%, 6.8%, 0.34% and 0.53%. After the 2nd stage of reduction, the overall increase in the values of these metrics was, respectively, 9.02%, 7.55%, 1.58% and 1.68%. The results obtained were tested at Tatneft and used to form and optimize the knowledge base when developing a decision support system for assessing the feasibility of drilling wells in oil fields.

The structure of the pore space of Tournaisian reservoir rocks in the southeast of Tatarstan Republic

The article shows the main types of structures of the porosity of the Tournaisian reservoirs from the southeast of Tatarstan. The main type of pore space is intergrain porosity, while the fractures have a subordinate significance. They are analyzed in detail main factors of the origin of the pore space of the Tournaisian reservoir rock. There are include depositional, diagenetic, structural and tectonically factors. The depositional factor is the selectivity of rock types as reservoirs, only two lithological types of limestone have industrially significant reservoir properties and represented by peloidal and crinoid-peloidal packstones. The diagenetic factor realizes via secondary leaching of carbonate rocks during burial diagenesis of rocks. Leaching processes provide the main increase in rock porosity. On the one hand, the structural and tectonic factor provides the possibility of oil charge in the structure, on the other hand, it shows the heterogeneity of the distribution of porosity depending on the position of the reservoir rocks on the structure. The highest porosity values are characteristic for the crest part, lower for the flanks and minimal for the deflections of the oil-bearing structures.

ВИЗНАЧЕННЯ ЕФЕКТИВНОЇ ПОРИСТОСТІ ПОРІД-КОЛЕКТОРІВ ЗА ДАНИМИ СТРУКТУРИ ЇХ ПУСТОТНОГО ПРОСТОРУ У ВІЗЕЙСЬКИХ І ТУРНЕЙСЬКИХ ВІДКЛАДАХ БЕРЕЗІВСЬКОГО РОДОВИЩА

Background. Currently, it is quite important to track the patterns of the internal structure of reservoirs with their physical properties. The analysis of well-logging data in the well 203 of the Berezivske field of the Dnipro-Donetsk depression is necessary to assess the prospectivity of complexly structured reservoirs. Methods. The methodology for studying the void space structure in complexly structured reservoirs involved several stages: interpretation of well logging data; determination of parameters for the initial mathematical model of the reservoir; inversion of data from acoustic surveys into a curve of the distribution of different void formats; evaluation of reservoir rock types with determination of their effective porosity. Results. Based on the data of compressional and shear wave velocities, as well as density, three distinct rock groups were identified: compacted sandstone, calcareous sandstone and limestone. The initial approximation was obtained for each rock sample, including the set of void formats and their concentration within the reservoir layers. Direct analysis of the resulting data by the authors revealed that the most optimal void formats for the investigated intervals are: for intergranular voids – 0.07 to 0.9; for transitional voids and microcracks – 0.05 to 0.077; for microcracks – 0.007 to 0.0019; for caverns – 4 to 8. Based on the research results, it has been established that granular-cavernous porosity (39,2 %) and fracturedcavernous-granular porosity (29,5 %) are prevailing types of reservoirs. Conclusions. The calculated values of the void formats were used for these formations to quantitatively assess effective porosity based on the obtained data and specific electrical resistivity values at different depths of investigation. The resulting approximation of α = 0.6996 was selected, which reduced the error in calculating the effective porosity of reservoir rocks. The obtained results have demonstrated that the proposed methodologies are essential for understanding and quantitatively assessing the void space structure and filtration-capacitive properties of reservoir rocks, particularly when we are facing with a limited well logging data and restrictive core sampling.

A STUDY OF THE THERMAL EVOLUTION OF PERMEABILITY AND POROSITY OF POROUS ROCKS BASED ON FRACTAL GEOMETRY THEORY

The temperature effect on the permeability of porous rocks continues to be a considerable controversy in the area of reservoirs since the thermal expansion of mineral grains exhibits complicated influence on pore geometries in them. To investigate the degree of effect of pore structures on the hydro-thermal coupling process, a study of the thermal evolution of permeability and porosity of porous rocks is performed based on fractal theory and on thermal as well as stress effects. This work can provide a general physical explanation on some arguments in this area. The proposed models for permeability and porosity can be associated with temperature and the pore-structural parameters as well as physical parameters of porous rocks, such as the initial porosity ([Formula: see text], the initial fractal dimension ([Formula: see text], the fractal dimension for tortuosity ([Formula: see text] and the thermal expansion coefficient of pore volume ([Formula: see text]. The validity of the proposed models for temperature-dependent permeability and temperature-dependent porosity is validated by comparing them with the available experimental results. The investigations are performed in detail considering the essential effects of pore-structural parameters and physical parameters of porous rock on the dimensionless temperature-dependent permeability and temperature-dependent porosity as well as the fractal dimensions for pore areas and tortuosity. It is found that the pore distribution scale range ratio ([Formula: see text], and pore thermal expansion coefficient ([Formula: see text] have significant effects on the dimensionless temperature-dependent permeability and temperature-dependent porosity of porous rock as well as the fractal dimensions for pore areas and tortuosity. The proposed models may provide a fundamental understanding of the coupled hydro-thermal process of rocks.

The influence of alteration and fractures on gas permeability and mechanical properties of the sedimentary and volcanic rocks of the Acoculco Caldera Complex (México)

Petrophysical and mechanical properties of limestones and volcanic altered and unaltered rocks were estimated by a series of laboratory measurements. The aim of this work was to study the changes in matrix permeability and the influence of an induced vertical fracture. The phenomenon was studied by direct comparison of different properties (porosity, UCS, permeability) and by a multiple linear regression analysis. Porosity, UCS, and matrix permeability of limestones and non-altered volcanic rocks showed homogeneous values. However, the permeability increased from poor to moderate after fracture induction (10–17 to 10–14 m2). Altered volcanic specimens showed a more complex pore system. Thus, considerable variations in all measured properties were identified. For example, porosity ranged from 6 to 50% and Permeability ranged from 10–14 to 10–12 m2. Comparison plots including UCS, porosity, and matrix permeability showed a good fitting (R2=0.75). Multiple linear regression analysis in fractured specimens has a moderate R2 (0.55) The model that better explains the permeability evolution of fractured specimens has the fracture permeability as the response variable and the porosity values as independent variables. The usage and repeatability of these equations in other zones should include more singularities of every single specimen as pore size, pore distribution, and fractures.

Air permeability measurements in low porosity clayey rocks

The paper describes the development of a high-pressure isotropic cell for studying the environmental degradation of low porosity clayey rocks. Air permeability measurements are used in this device as a tool to evaluate rock degradation in unsaturated rock specimens caused by mechanical, hydraulic and chemical paths. A modified equation, based on the air pressure decay method proposed by Yoshimi and Osterberg (1963), is presented. The proposed method is applied to an Australian clayey shale. Estimated values of air permeability are compared against those calculated using the original method which, in the case of low porosity rocks, seems to provide unrealistic values when the air pressure in the vessel decays beyond 50%.