Pore Space Of Rocks Research Articles

Representative elementary volume for [formula omitted] simulations based on X-ray microtomography of sedimentary rock

In porous systems like natural rocks, many phenomenological models have been developed in order to study the correlations between physical properties and the pore structure of these systems. The high resolution obtained with X-ray microtomography (μCT) images (micro or nanometer scales) has allowed exploring in details the complex morphology of the pore space in natural rocks. This has promoted the development of numerical simulations at the pore-scale level aiming to improve our comprehension about the correlations between pore structure and macroscopic physical properties. In this respect, simulations of nuclear magnetic resonance properties performed directly on μCT images are very important, since petrophysical properties can be predicted using a realistic model for the heterogeneous porous structure. Also these simulations can include a specific morphology of the pore geometry, which can be controlled in order to verify the different hypotheses introduced during NMR interpretation of physical properties, like for example, permeability predictions and/or fluid typing. In addition, NMR simulations allow to study the existence of a representative volume of the whole system, whose experimental determination is a major challenge. In this work, nuclear magnetic relaxations are simulated on a pore geometry obtained from microtomography of a natural rock formation, localized in the southeast of Brazil. The simulations were performed through a discrete random-walk algorithm computed at the pore scale. In the simulations bulk relaxation was not considered, while the relaxation rate at the surface of the pores was assumed constant. Our results indicate that the relaxation curves can be considered representatives of the whole system for volumes above a representative volume with dimensions of some cubic millimeters. In addition, this representative elementary volume seems to be of the same order that the one found from the analyses of the porosity on the same digital rock. In summary, this study points out to the importance of verifying the existence of this characteristic volume during NMR simulations directly on images obtained from tomography, in order to ensure the reliability of the information obtained from the numerical simulations.

Balancing the amount and composition of gas contained in the pore space of cupriferous rocks

From the perspective of economy and safety, balancing gas contained in the pore space of rocks is extremely essential, predominantly to establishments dealing with extraction of mineral resources. One of the main methods of evaluating the amount and composition of gas contained in the pore space of a rock is releasing the gas as a result of comminuting the investigated rock material. In the case of cupriferous rocks, effective comminution is a very difficult task, due to the strength properties of these rocks. The present paper discusses the results of studies into the gas content of cupriferous rocks, obtained by means of an original device named the GPR analyzer. The research was done on 41 samples of dolomites and anhydrites from various areas of two copper mines located in Poland: “Rudna” and “Polkowice-Sieroszowice.” For all samples, on the basis of microscope analyses performed on cuts and polished sections, the open porosity, closed porosity, and total porosity were determined. In the case of the dolomite samples, the total porosity variability fell in the range of 4.75–23.05%, and in the case of the anhydrite samples—in the range of 3.87–16.60%. The maximum gas content of the dolomite samples was 166.67 cm3/kg, and of the anhydrite samples—84.66 cm3/kg. In some of the studied samples, the presence of methane was confirmed. Toxic gases, such as H2S, were not found. The main gas in the pore space of the investigated rocks was nitrogen. Knowing the amount of the released gas and the value of the closed porosity in the investigated samples, the authors were able to estimate the pore pressure of the gas, whose maximum value was 0.583 MPa.

Analyzer for measuring gas contained in the pore space of rocks

In the present paper, the authors discussed the functioning of their own analyzer for measuring gas contained in the pore space of high strength rocks. A sample is placed inside a hermetic measuring chamber, and then undergoes impact milling as a result of colliding with the vibrating blade of a knife which is rotationally driven by a high-speed brushless electric motor. The measuring chamber is equipped with all the necessary sensors, i.e. gas, pressure, and temperature sensors. Trial tests involving the comminution of dolomite and anhydrite samples demonstrated that the constructed device is able to break up rocks into grains so fine that they are measured in single microns, and the sensors used in the construction ensure balancing of the released gas. The tests of the analyzer showed that the metrological concept behind it, together with the way it was built, make it fit for measurements of the content and composition of selected gases from the rock pore space. On the basis of the conducted tests of balancing the gases contained in the two samples, it was stated that the gas content of Sample no. 1 was (0.055 ± 0.002) cm3 g−1, and Sample no. 2 contained gas at atmospheric pressure, composed mostly of air.

Review on Surfactant Flooding: Phase Behavior, Retention, IFT, and Field Applications

Surfactant flooding is an important technique used in enhanced oil recovery to reduce the amount of oil in pore space of matrix rock. Surfactants are injected to mobilize residual oil by lowering the interfacial tension between oil and water and/or by the wettability alteration from oil-wet to water-wet. A large number of cationic, anionic, non-ionic, and amphoteric surfactants have been investigated on a laboratory scale under different conditions of temperature and salinity. Selection of the appropriate surfactant is a challenging task, and surfactants have to be evaluated by a series of screening techniques. Different types of surfactants along with their limitations are reviewed with particular emphasis on the phase behavior, adsorption, interfacial tension, and structure–property relationship. Factors affecting the phase behavior, interfacial tension, and wettability alteration are also discussed. Field applications of surfactants for chemical enhanced oil recovery in carbonate and sandstone reservoi...

Pore-scale Analysis of In Situ Contact Angle Measurements in Mixed-wet Rocks: Applications to Carbon Utilization in Oil Fields

Carbon utilization in depleting oil reservoirs is considered as an important component in achieving the widespread commercial deployment of carbon capture and storage (CCS) technology. With absent strong climate policy, CO2 enhanced oil recovery (EOR) process adds a significant revenue stream and makes the subsequent carbon storage process economically feasible. This is reflected in the great majority of CO2 storage projects in oil fields utilizing CO2 for EOR. Therefore, early deployment of subsurface carbon dioxide storage is likely to focus on injection into depleted or producing oil fields. Observations and modelling have shown that capillary trapping of CO2 through capillary forces within the pore space of the water-wet rocks, typical of subsurface saline aquifers, is one of the most significant mechanisms for storage capacity. This important storage process is also a factor determining the ultimate extent of CO2 plume migration within the reservoir, enhancing the security of the storage process. In contrast, carbonate oil reservoirs are characterized by a mixed-wet state in which the capillary trapping of nonpolar fluids have been observed to be significantly reduced relative to trapping in water-wet rocks typical of saline aquifers unaltered by the presence of hydrocarbons. This study discuss the first observations of supercritical CO2 in a mixed-wet carbonate rock. Here we show that residual CO2 trapping of supercritical CO2 in a limestone altered to a mixed-wet state with crude oil is significantly less than trapping in water-wet systems characteristic of saline aquifers. The initial-residual CO2 saturations characteristic curve are reported for each system from core scale observations. While pore scale observations provided the first in situ contact angle measurements of supercritical CO2 in a mixed-wet rock and pore to pore arrangements of CO2 droplets. The measurements were compared with trapping of N2 and was similar in the water-wet rock. After altering the sample's wettability to a mixed-wet, however, trapping of CO2 was much less than N2. Here we provide a theoretical explanation of the different response in trapping between CO2 and N2 in the mixed-wet rock.

Streaming potential during drainage and imbibition

AbstractThe rock pore space in many subsurface settings is saturated with water and one or more immiscible fluid phases. Examples include nonaqueous phase liquids (NAPLs) in contaminated aquifers, supercritical CO2 during sequestration in deep saline aquifers, the vadose zone, and hydrocarbon reservoirs. Self‐potential (SP) and seismoelectric (SE) methods have been proposed to monitor multiphase flow in such settings. However, to properly interpret and model these data requires an understanding of the saturation dependence of the streaming potential. This paper presents a methodology to determine the saturation dependence of the streaming potential coupling coefficient (C) and streaming current charge density (Qs) in unsteady state drainage and imbibition experiments and applies the method to published experimental data. Unsteady state experiments do not yield representative values of C and Qs (or other transport properties such as relative permeability and electrical conductivity) at partial saturation (Sw) because Sw within the sample is not uniform. An interpretation method is required to determine the saturation dependence of C and Qs within a representative elementary volume with uniform saturation. The proposed method makes no assumptions about the pore space geometry. Application of the method to published experimental data from two natural sandstone samples shows that C exhibits hysteresis between drainage and imbibition, can exhibit significant nonmonotonic variations with saturation, is nonzero at the irreducible water saturation, and can exceed the value observed at Sw = 1. Moreover, Qs increases with decreasing Sw but is not given by 1/Sw as is often assumed. The variation in Qs with Sw is very similar for a given sample and a given drainage or imbibition process, and the difference between samples is less than the difference between drainage and imbibition. The results presented here can be used to help interpret SP and SE measurements obtained in partially saturated subsurface settings.

Characterization of LIBS emission lines for the identification of chlorides, carbonates, and sulfates in salt/basalt mixtures for the application to MSL ChemCam data

AbstractAncient environmental conditions on Mars can be probed through the identification of minerals on its surface, including water‐deposited salts and cements dispersed in the pore space of sedimentary rocks. Laser‐induced breakdown spectroscopy (LIBS) analyses by the Martian rover Curiosity's ChemCam instrument can indicate salts, and ChemCam surveys aid in identifying and selecting sites for further, detailed in situ analyses. We performed laboratory LIBS experiments under simulated Mars conditions with a ChemCam‐like instrument on a series of mixtures containing increasing concentrations of salt in a basaltic background to investigate the potential for identifying and quantifying chloride, carbonate, and sulfate salts found only in small amounts, dispersed in bulk rock with ChemCam, rather than concentrated in veins. Data indicate that the presence of emission lines from the basalt matrix limited the number of Cl, C, and S emission lines found to be useful for quantitative analysis; nevertheless, several lines with intensities sensitive to salt concentration were identified. Detection limits for the elements based on individual emission lines ranged from ~20 wt % carbonate (2 wt % C), ~5–30 wt % sulfate (1–8 wt % S), and ~5–10 wt % chloride (3–6 wt % Cl) depending on the basaltic matrix and/or salt cation. Absolute quantification of Cl, C, and S in the samples via univariate analysis depends on the cation‐anion pairing in the salt but appears relatively independent of matrices tested, following normalization. These results are promising for tracking relative changes in the salt content of bulk rock on the Martian surface with ChemCam.

Geologic influence on induced seismicity: Constraints from potential field data in Oklahoma

AbstractRecent Oklahoma seismicity shows a regional correlation with increased wastewater injection activity, but local variations suggest that some areas are more likely to exhibit induced seismicity than others. We combine geophysical and drill hole data to map subsurface geologic features in the crystalline basement, where most earthquakes are occurring, and examine probable contributing factors. We find that most earthquakes are located where the crystalline basement is likely composed of fractured intrusive or metamorphic rock. Areas with extrusive rock or thick (>4 km) sedimentary cover exhibit little seismicity, even in high injection rate areas, similar to deep sedimentary basins in Michigan and western North Dakota. These differences in seismicity may be due to variations in permeability structure: within intrusive rocks, fluids can become narrowly focused in fractures and faults, causing an increase in local pore fluid pressure, whereas more distributed pore space in sedimentary and extrusive rocks may relax pore fluid pressure.

Use of scanning electron microscopy for the classification of rocks of oil and gas reservoirs

With the development of electron microscopy-based porosity measurement techniques, it is possible to devise new oil and gas reservoir rock classification schemes that would take the geometrical features of the pore space into account. This is associated with the fact that the structure of the pore space of reservoir rocks has a significant effect on the recovery of hydrocarbons upon reservoir processing. For several years, we have carried out microstructural studies of rocks from the productive strata of various fields using cathodoluminescence scanning electron microscopy (SEM) and porometric software for the analysis of SEM images. The investigations show that it is possible to classify reservoirs by the connectivity of pores and pore channels in reservoir rocks.

Емкостное пространство пород высокоуглеродистой формации (на примере доманиковой толщи Южно-Татарского свода)

Емкостное пространство пород высокоуглеродистой формации (на примере доманиковой толщи Южно-Татарского свода)

A Pore-Scale Simulation on Thermal-Hydromechanical Coupling Mechanism of Rock

Thermal-hydromechanical (THM) coupling process is a key issue in geotechnical engineering emphasized by many scholars. Most existing studies are conducted at macroscale or mesoscale. This paper presents a pore-scale THM coupling study of the immiscible two-phase flow in the perfect-plastic rock. Assembled rock matrix and pore space models are reconstructed using micro-CT image. The rock deformation and fluid flow are simulated using ANSYS and CFX software, respectively, in which process the coupled physical parameters will be exchanged by ANSYS multiphysics platform at the end of each iteration. Effects of stress and temperature on the rock porosity, permeability, microstructure, and the displacing mechanism of water flooding process are analyzed and revealed.

Evaluation of formation pore pressure behind the casing using borehole gravity data

Reliable estimates of the fluid pressure in the pore space of rocks are critical for different aspects of petroleum exploration and production including injection operations and scenarios of water flooding. Numerous approaches are available for formation pore pressure evaluation, however, these measurements become a challenge inside a cased borehole, and a list of possible options is short: either the casing is to be perforated, or the production tubing needs to be disconnected to perform the pressure tests. We present a method for through-casing evaluation of formation pore pressure without shutting down production. We suggest equipping an observation well with a borehole gravimeter and acquiring time variations of the vertical component of the gravity field. Changes in gravity occur during gas production and are related to time variations of formation pore pressure. Gravity changes obtained in the observation well are supposed to be inverted for time-dependent formation pore pressure variations beyond the casing. Our results and recommendations are based on numerical modeling of pore pressure spatial distribution during gas field exploitation and relevant changes in borehole gravity. Benchmark models were elaborated in order to consider a dynamic process of pressure changes in time and space under conditions similar to those in the Medvezhye gas field (Russia). Different modeling scenarios are considered for early and late stages of gas field exploitation. The sensitivity analysis was performed to estimate quantitatively a sensitivity of borehole temporal gravity changes to variations in formation pore pressure behind the casing. Based on resolution analysis we justify the possibility to extract the gravity measurements directly related to changes in pore pressure from the total changes in the gravity field due to reservoir exploitation. The impact of pore pressure on the gravity field measured in boreholes during the water flooding is also evaluated, and obtained results are discussed.

Experimental investigations on the explosivity of steam-driven eruptions: A case study of Solfatara volcano (Campi Flegrei).

Steam‐driven eruptions, both phreatic and hydrothermal, expel exclusively fragments of non‐juvenile rocks disintegrated by the expansion of water as liquid or gas phase. As their violence is related to the magnitude of the decompression work that can be performed by fluid expansion, these eruptions may occur with variable degrees of explosivity. In this study we investigate the influence of liquid fraction and rock petrophysical properties on the steam‐driven explosive energy. A series of fine‐grained heterogeneous tuffs from the Campi Flegrei caldera were investigated for their petrophysical properties. The rapid depressurization of various amounts of liquid water within the rock pore space can yield highly variable fragmentation and ejection behaviors for the investigated tuffs. Our results suggest that the pore liquid fraction controls the stored explosive energy with an increasing liquid fraction within the pore space increasing the explosive energy. Overall, the energy released by steam flashing can be estimated to be 1 order of magnitude higher than for simple (Argon) gas expansion and may produce a higher amount of fine material even under partially saturated conditions. The energy surplus in the presence of steam flashing leads to a faster fragmentation with respect to gas expansion and to higher ejection velocities imparted to the fragmented particles. Moreover, weak and low permeability rocks yield a maximum fine fraction. Using experiments to unravel the energetics of steam‐driven eruptions has yielded estimates for several parameters controlling their explosivity. These findings should be considered for both modeling and evaluation of the hazards associated with steam‐driven eruptions.

Modelling karst aquifer evolution in fractured, porous rocks

The removal of material in soluble rocks by physical and chemical dissolution is an important process enhancing the secondary porosity of soluble rocks. Depending on the history of the soluble rock, dissolution can occur either along fractures and bedding partings of the rock in the case of a telogenetic origin, or within the interconnected pore space in the case of eogenetic origin. In soluble rocks characterised by both fractures and pore space, dissolution in both flow compartments is possible.We investigate the dissolution of calcite both along fractures and within the pore space of a limestone rock by numerical modelling. The limestone rock is treated as fractured, porous aquifer, in which the hydraulic conductivity increases with time both for the fractures and the pore spaces.We show that enlargement of pore space by dissolution will accelerate the development of a classical fracture-dominated telogenetic karst aquifer, breakthrough occurs faster. In the case of a pore-controlled aquifer as in eogenetic rocks, enlargement of pores results in a front of enlarged pore spaces migrating into the karst aquifer, with more homogeneous enlargement around this dissolution front, and later breakthrough.

Flood characteristic and fluid rock interactions of a supercritical CO2, brine, rock system: South West Hub, Western Australia

Chemical and/or physical interactions between the storage rock and injected and in-situ created solutes are expected to occur during many underground CO2 storage projects. The intensity of the reactions, however, depends on the abundance of susceptible minerals (e.g. carbonates, clays) in the pore space of the host rock. Such interactions may impact on the multiphase flow characteristics of the underground fluids-rock system over short as well as long time frames.In this research the in-situ multiphase flow characteristics of four sandstone samples have been investigated using a set of laboratory measurements. The samples tested were taken from the Wonnerup Member of the Triassic Lesueur Sandstone which is under consideration as a storage formation in the South-West Hub CO2 geo-sequestration site in Western Australia.All the samples tested show favourable characteristics in terms of storage capacity in the form of residual capillary trapping with residual CO2 saturation varying between 23% and 43%. They underwent a degree of alteration to their petrophysical characteristics which was most significantly pronounced in the case of their absolute gas permeability which showed drops of 25%–60% in the post-flood samples. Formation damage by fines migration is proposed as a mechanism for the observed reduction in permeability. The fines are believed to have originated from the kaolinite particles present in the pore space of the samples.

Linking capillary and mechanical seal capacity mechanisms

Mechanical fault reactivation is a mechanism where high fluid pressures generated within a fault zone can change the effective stress such that an optimally orientated fault segment will rupture. This style of strain has been recognized in three settings: (1) deep crustal locations at greenschist and higher-grade metamorphism with fluid generation; (2) active plate boundaries where tectonic stresses can result in seismicity; and (3) hydrocarbon column buoyancy pressure reactivation of critically stressed fault-bound traps. This paper examines category 3 in the context of mechanical fault reactivation and capillary processes. For water-wetting fault rock, mechanical reactivation may be reached prior to the capillary seal capacity. However, the non-wetting fluid cannot access the fault rock pore space until the hydrocarbon column height reaches the capillary threshold pressure. At the threshold pressure, the non-wetting fluid enters the fault rock imparting a buoyancy pressure in excess of the mechanical reactivation threshold causing rupture. This suggests that in certain circumstances the mechanical fault reactivation by buoyancy pressure is more accurately predicted by the capillary threshold pressure than mechanical reactivation pressure.

Changes in composition and pore space of sand rocks in the oil water contact zone (section YU13-4, Klyuchevskaya area, Tomsk region)

The article provides an analysis of specific features in changes of rocks in the oil water contact zone. The object of study is the formation YU13-4 (J3o1) of Klyuchevskaya oil deposit (West Siberian oil-gas province, Tomsk region). The research data allow the authors to determine vertical zoning of the surface structure and identify the following zones: oil saturation (weak alteration), bitumen-content dissolution, non-bitumen-content dissolution, cementation, including rocks not affected by hydrocarbon deposit. The rocks under investigation are characterized by different changes in composition, pore space, as well as reservoir filtration and volumetric parameters. Detection of irregularity in distribution of void- pore space in oil-water contact zones is of great practical importance. It helps to avoid the errors in differential pressure drawdown and explain the origin of low-resistivity collectors.

Printing out the pores

Rock Mechanics The diversity of three-dimensional (3D) printing applications now includes fabricating porous rocks. The organization of pore space in rocks strongly influences their strength and fluid flow through them. Head and Vanorio constructed virtual 3D images of rocks by using x-ray tomography, which they followed with a series of pore microgeometry modifications and 3D printing of samples. Measurements of fluid flow through the samples brings deeper understanding to how processes such as mineral precipitation and compaction clog up the pore network. This technique helps reverse-engineer how rocks get their pore structure and offers a method for measuring flow properties through delicate samples. Geophys. Res. Lett. 10.1002/2016GL069334 (2016).

Pre-Quaternary rocks and sediments with a high level of radioactivity in Denmark

The pre-Quaternary sediments and rocks in Denmark generally have a low content of radioactive minerals and elements. Uranium, thorium and radium are built into mineral structures or are, for example, adsorbed on the surface of clay minerals, Fe-minerals or organic material. Radon (222Rn) is a radioactive noble insoluble gas with a half-life of 3.8 days. It belongs to the uranium (238U) decay chain where radon is formed from radium (226Ra). When Rn is formed by radioactive decay from Ra, the emanation process sends part of the radon produced into the pore spaces of rocks and soils. From here, the radon can enter and accumulate in buildings. The source of the radioactive materials in Danish sediments and rocks is primarily from weathered Precambrian crystalline rocks from Norway, Sweden, Finland and the Danish island of Bornholm. Physical and chemical weathering disintegrates these rocks and rivers transport the material into the Danish–Norwegian and Danish–Polish sedimentary basins.

Adsorbed oil of gas condensate fields

The pore space of reservoir rocks has a lot of active centers capable to form different types of bonds (from hydrogen to chemical). Therefore, almost any hydrocarbon can be adsorbed to a particular extent on the internal pore surface and form an adsorbed layer, which has a definite spatial configuration and makes contact with a certain part of the rock surface. Study of gas condensate reservoirs brings up the question of the composition of adsorbed hydrocarbons. The properties of such hydrocarbons in many giant gas condensate fields are of special interest as these compounds can serve as an additional source of resources after production of mobile-gas reserves. The performed study of gas condensate reservoirs of the Karachaganak, Astrakhan, and Yamburg fields has shown that their adsorbed hydrocarbons (adsorbed oil) have polar components with sulfur and oxygen atoms.