Pore Space Of Rocks Research Articles

Pore‐scale intermittent velocity structure underpinning anomalous transport through 3‐D porous media

AbstractWe study the nature of non‐Fickian particle transport in 3‐D porous media by simulating fluid flow in the intricate pore space of real rock. We solve the full Navier‐Stokes equations at the same resolution as the 3‐D micro‐CT (computed tomography) image of the rock sample and simulate particle transport along the streamlines of the velocity field. We find that transport at the pore scale is markedly anomalous: longitudinal spreading is superdiffusive, while transverse spreading is subdiffusive. We demonstrate that this anomalous behavior originates from the intermittent structure of the velocity field at the pore scale, which in turn emanates from the interplay between velocity heterogeneity and velocity correlation. Finally, we propose a continuous time random walk model that honors this intermittent structure at the pore scale and captures the anomalous 3‐D transport behavior at the macroscale.

Diagenesis and kerogen release in oil- and gas-bearing shales

The microstructure of pore space in sedimentary rocks and its evolution during reaction with pore- or fracture-contained fluids is a critically important factor controlling fluid flow properties in geological formations, including the migration and retention of water, gases and hydrocarbons. The size, distribution and connectivity of these confined geometries (pores, fractures, grain boundaries), collectively dictate how fluids of various chemistries migrate into and through these micro- and nano-environments, wet, and ultimately react with the solid surfaces. In order to interpret the time-temperature-pressure-fluid flow history of any geological system, the physical and chemical "fingerprints" of this evolution preserved in the rock must be fully explored over widely different length scales from the nanoscale to the macroscale. We are experimentally investigating these reaction-controlled changes in rock microstructure by conducting in-situ heating experiments on samples of the Garfield oil shale. Oil shale, an organic-rich fine-grained sedimentary rock, contains significant amounts of kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be extracted. Pyrolysis (heating shale in the absence of oxygen) converts the kerogen in the oil shale to shale oil (synthetic crude oil) and oil shale gas and a solid residue. Through SANS, we clearly observe these kerogen and oxidation release at lower temperatures followed by pore structure reordering and finally enlargement at higher temperatures. These results are compared with preliminary results tracking the natural diagenesis of the commercially-important Eagle Ford shale formations across the oil/gas boundary.

Application of positron spectroscopy for investigation of threshold space of oil-gas rocks

Abstract This article considers the possibility of applying the positron annihilation spectroscopy method for investigating the pore space of rocks from oil-gas and methane-coal deposits. The diagnostics of the structure was performed using the method of spectrometry of angular correlation of annihilation rays (ACAR). Using the samples of porous silicon, the authors have shown the applicability of the ACAR method for determination of the average dimensions of spherical and cylindrical nanosized objects and their concentration

What laboratory-induced dissolution trends tell us about natural diagenetic trends of carbonate rocks

Abstract The pivotal idea of this study is to unravel the processes that control heterogeneity in the attributes of the pore space in carbonate rocks (i.e. stiffness, connectivity and tortuosity), and, in turn, in the transport and elastic properties. We use starting rocks of variable fabric (i.e. a depositional-dependent microstructure) to induce a specific process (e.g. chemical dissolution under stress) and then observe the development of the microstructure, permeability, porosity and velocity due to the induced chemomechanical processes. We find that the changes in the two end members of the analysed rock types (mudstones and packstones) can lead to two different evolutionary trends of permeability and velocity, depending on the effectiveness of dissolution with respect to compaction. The balance between the two depends on: (a) the fraction of the carbonate phases characterized by large surface area; and (b) the pore stiffness of the rock. Packstones are characterized by low pore stiffness and compact significantly upon dissolution. This behaviour leads to a decrease in velocity because of a reduction in the stiffness at the grain contacts and a slight increase in permeability. The latter is curbed by the ongoing compaction. Mudstones are characterized by higher pore stiffness, experiencing minimal or negligible compaction. This behaviour leads to a slight change in porosity and velocity. However, large permeability changes are observed, related to enhanced connectivity or decreased tortuosity of the pathways.

Impact shocked rocks as protective habitats on an anoxic early Earth

AbstractOn Earth, microorganisms living under intense ultraviolet (UV) radiation stress can adopt endolithic lifestyles, growing within cracks and pore spaces in rocks. Intense UV irradiation encountered by microbes leads to death and significant damage to biomolecules, which also severely diminishes the likelihood of detecting signatures of life. Here we show that porous rocks shocked by asteroid or comet impacts provide protection for phototrophs and their biomolecules during 22 months of UV radiation exposure outside the International Space Station. The UV spectrum used approximated the high-UV flux on the surface of planets lacking ozone shields such as the early Earth. These data provide a demonstration that endolithic habitats can provide a refugium from the worst-case UV radiation environments on young planets and an empirical refutation of the idea that early intense UV radiation fluxes would have prevented phototrophs without the ability to form microbial mats or produce UV protective pigments from colonizing the surface of early landmasses.

Wettability Evaluation of a CO2/Water/Bentheimer Sandstone System: Contact Angle, Dissolution, and Bubble Size

The success of CO2 storage in deep saline aquifers and depleted oil and gas reservoirs is largely controlled by interfacial phenomena among fluid phases and rock pore spaces. Particularly, the wettability of the rock matrix has a strong effect on capillary pressure, relative permeability, and the distribution of phases within the pore space and thus on the entire displacement mechanism and storage capacity. Precise understanding of wettability behavior is therefore fundamental when injecting CO2 into geological formations to sequestrate CO2 and/or to enhance gas/oil production. In this study, the contact angles of Bentheimer sandstone/water/CO2 or flue gas have been evaluated experimentally using the captive-bubble technique in the pressure range from 0.2 to 15 MPa. The experiments were conducted using different compositions of aqueous phase with respect to CO2, i.e., unsaturated and fully saturated. It has been shown that a reliable contact-angle determination needs to be conducted using a pre-equilibrat...

Effect of pore structure on the producibility of tight-gas sandstones

The estimated ultimate recovery (EUR) is one of the most significant properties of tight-gas sandstone reservoirs, but it remains difficult to predict. Estimated ultimate recovery is dependent on the success of stimulation by hydraulic fracturing, the existence and connectivity of natural fractures, and as illustrated in this article, the pore structure of the matrix. Here, we analyze the lab measurements that are indicative of the pore structure, and then we predict the effect of pore structure on producibility. We develop a relationship between the EUR of tight-gas sandstones and their petrophysical properties measured by drainage and imbibition tests (mercury intrusion, withdrawal, and porous plate) and by resistivity analyses. We use the ratio of residual mercury saturation after mercury withdrawal ( S gr) to initial mercury saturation ( S gi), which is the saturation at the start of withdrawal, as a measure of gas likely to be trapped in the matrix during production and, hence, a proxy for EUR. A multitype pore space model is required to explain mercury intrusion capillary pressures in these rocks. Implications of this model are supported by other available laboratory measurements. The model comprises a conventional network model and a treelike pore structure (an acyclic network) that mimic the intergranular and intragranular void spaces, respectively. The notion of the treelike pore structure is introduced here for the first time in the context of tight-gas sandstones. Applying the multitype model to porous plate data, we classify the pore spaces of rocks into intergranular dominant, intermediate, and intragranular dominant. This pore space classification is topological and is not based on scale or size. These classes have progressively less drainage and imbibition hysteresis, which leads to the prediction that significantly more hydrocarbon is recoverable from intragranular porosity than intergranular porosity. Available field data (production logs) corroborate the higher producibility of intervals with intragranular porosity, although the data are not sufficient to eliminate the possible contribution of other factors such as size and shape of the volume contacted by hydraulic fractures or the presence and attributes of natural fractures. The superior recovery of hydrocarbon from intragranular-dominant pore structures is despite its inferior initial production rate.

CO2 storage potential of basaltic rocks in Iceland and the oceanic ridges

Abstract Iceland is the largest landmass found above sea level at the mid-ocean ridges, about 103,000 km2 mostly made of basaltic rocks (∼90%). Theoretically much of Iceland could be used for injection of CO2, fully dissolved in water. Most of the pore space in the older rocks is filled with secondary minerals, thus the young and porous basaltic formations, found within the active rift zone and covering about one third of Iceland, are the most feasible for carbon storage onshore. Studies on mineral storage of CO2 in basaltic rocks are still at an early stage. Therefore, natural analogues are important for gaining a better understanding of CO2 fixation in basaltic rocks. Volcanic geothermal systems serve as an applicable analogue since the systems receive considerable amounts of CO2 from magma in the roots of the systems. Wiese et al. [1] quantified the amount and spatial distribution of CO2 stored as calcite within the bedrock of three active geothermal systems in Iceland. The results from this study reveal a large storage potential of basaltic rocks and can be used as a guideline for the theoretical potential of CO2 storage in basaltic formations. The largest storage potential lies offshore, with long-term advantages for safe and secure CO2 storage in the mid-ocean ridges. The theoretical mineral CO2 storage capacity of the ocean ridges, using the Icelandic analogue, is orders of magnitude larger than the anticipated release of CO2 caused by burning of all fossil fuel on Earth.

Numerical simulation on hydromechanical coupling in porous media adopting three-dimensional pore-scale model.

A novel approach of simulating hydromechanical coupling in pore-scale models of porous media is presented in this paper. Parameters of the sandstone samples, such as the stress-strain curve, Poisson's ratio, and permeability under different pore pressure and confining pressure, are tested in laboratory scale. The micro-CT scanner is employed to scan the samples for three-dimensional images, as input to construct the model. Accordingly, four physical models possessing the same pore and rock matrix characteristics as the natural sandstones are developed. Based on the micro-CT images, the three-dimensional finite element models of both rock matrix and pore space are established by MIMICS and ICEM software platform. Navier-Stokes equation and elastic constitutive equation are used as the mathematical model for simulation. A hydromechanical coupling analysis in pore-scale finite element model of porous media is simulated by ANSYS and CFX software. Hereby, permeability of sandstone samples under different pore pressure and confining pressure has been predicted. The simulation results agree well with the benchmark data. Through reproducing its stress state underground, the prediction accuracy of the porous rock permeability in pore-scale simulation is promoted. Consequently, the effects of pore pressure and confining pressure on permeability are revealed from the microscopic view.

The application of well logging and seismic modeling to assess the degree of gas saturation in Miocene strata (Carpathian Foredeep, Poland)

The presence of natural gas in the pore space of reservoir rocks results in a significant decrease in P-wave velocity. Even low gas saturation can generate seismic anomalies (DHI) and false image of gas accumulation of economic importance. This article presents an attempt to evaluate gas saturation from 2D seismic section in the Miocene sandstone strata in the south-eastern part of the Carpathian Foredeep. The ESTYMACJA program and the Biot-Gassmann model were used to study the dependence between elastic parameters and saturating fluids (water and gas) recorded in wells. Series of calculations was carried out using a method of fluid substitution for various gas saturation. The applicability of seismic data for evaluating gas saturation of reservoir beds was assessed with the use of 1D modelling (synthetic seismograms) and 2D modelling (theoretical seismic section) calculated for different gas saturation. The proposed methodology can be used to identify low and high gas-saturated zones and contour the reservoir.

지중저장 조건에서 초임계CO2에 의한 포항분지 사암과 이암의 지화학적 풍화반응 연구

국내 이산화탄소 지중저장 후보지인 포항분지의 심부 대수층 구성하고 있는 사암과 이암을 대상으로 초임계<TEX>$CO_2$</TEX> 반응에 의한 암석의 지화학적/광물학적 풍화를 규명하는 실험을 실시하였다. 고압셀 장치를 사용하여 실험실 규모의 <TEX>$CO_2$</TEX> 지중저장 조건을 모사하였으며, 시추한 포항분지 암석이 미고결 상태임을 감안하여 암석시료는 입자상으로 분쇄하여 시료 30 g과 지하수 100 ml를 고압셀(200 ml 용량)에 넣고 100 bar, <TEX>$50^{\circ}C$</TEX> 조건에서 총 60일 동안 반응시켜, 초임계<TEX>$CO_2$</TEX> 주입 시 포항분지 심부 사암층과 이암층 내에서 발생하는 초임계<TEX>$CO_2$</TEX>-암석-지하수반응을 재현하였다. 반응 후 10일, 30일, 60일 간격으로 시료를 회수하여 암석의 지화학적 풍화 정도를 정량화하기 위한 XRD(X-Ray Diffractometer), BET(Brunauer-Emmett-Teller) 분석을 실시하였고, 암석 슬랩(<TEX>$15mm{\times}40mm{\times}5mm$</TEX>)을 같은 지중 조건에서 반응시켜 반응시간에 따른 지하수시료의 용존 이온 농도 변화를 ICP/OES로 분석하였다. XRD 분석결과, 초임계<TEX>$CO_2$</TEX>-암석-지하수반응에 의해 사암과 이암을 구성하는 광물 중 사장석과 정장석(기질의 장석류 포함)의 비율이 가장 크게 감소한 것으로 나타났다. 사암의 경우 점토광물인 일라이트, 스멕타이트, 황철석 비율이 증가하였으며, 이암의 경우 일라이트, 카오리나이트, 칼슘을 함유한 불소인회석 비율이 증가하였다. 반응시간에 따른 지하수 이온 농도 분석결과, 사암과 이암에서 방해석과 장석류의 용해가 가장 활발히 일어나 지하수 내 <TEX>$Ca^{2+}$</TEX>, <TEX>$Na^+$</TEX>농도가 증가하였다. <TEX>$K^+$</TEX>, <TEX>$Si^{4+}$</TEX>, <TEX>$Mg^{2+}$</TEX> 같은 이온들의 농도는 반응시간 동안 증가와 감소를 반복하였는데, 이는 암석의 용해와 2차 광물의 침전이 함께 일어나고 있음을 의미한다. 사암과 이암 입자의 비표면적은 반응 60일 후까지 각각 <TEX>$27.3m^2/g$</TEX>과 <TEX>$19.6m^2/g$</TEX>에서 <TEX>$28.6m^2/g$</TEX>과 <TEX>$26.6m^2/g$</TEX>으로 증가하였으며, 미세공극의 평균 크기는 각각 <TEX>$72.6{\AA}$</TEX>, <TEX>$96.7{\AA}$</TEX>에서 <TEX>$68.4{\AA}$</TEX>과 <TEX>$75.8{\AA}$</TEX>으로 지속적으로 감소하여, 초임계<TEX>$CO_2$</TEX>-암석-지하수반응에 의해 입자 표면이 용해되면서 미세 공극들이 추가로 형성되어 비표면적이 증가하는 것으로 나타났다. 본 연구를 통하여 포항분지 사암에 <TEX>$CO_2$</TEX>를 지중 주입하는 경우, 암석의 용해 및 침전반응에 의한 대상암석의 물성변화가 지중저장의 효율성과 안정성에 큰 영향을 미칠 수 있다는 것을 입증하였다. Laboratory experiments for the reaction with supercritical <TEX>$CO_2$</TEX> under the <TEX>$CO_2$</TEX> sequestration condition were performed to investigate the mineralogical and geochemical weathering process of the sandstones and mudstones in the Pohang basin. To simulate the supercritical <TEX>$CO_2$</TEX>-rock-groundwater reaction, rock samples used in the experiment were pulverized and the high pressurized cell (200 ml of capacity) was filled with 100 ml of groundwater and 30 g of powdered rock samples. The void space of the high pressurized cell was saturated with the supercritical <TEX>$CO_2$</TEX> and maintained at 100 bar and <TEX>$50^{\circ}C$</TEX> for 60 days. The changes of mineralogical and geochemical properties of rocks were measured by using XRD (X-Ray Diffractometer) and BET (Brunauer-Emmett-Teller). Concentrations of dissolved cations in groundwater were also measured for 60 days of the supercritical <TEX>$CO_2$</TEX>-rock-groundwater reaction. Results of XRD analyses indicated that the proportion of plagioclase and K-feldspar in the sandstone decreased and the proportion of illite, pyrite and smectite increased during the reaction. In the case of mudstone, the proportion of illite and kaolinite and cabonate-fluorapatite increased during the reaction. Concentration of <TEX>$Ca^{2+}$</TEX> and <TEX>$Na^+$</TEX> dissolved in groundwater increased during the reaction, suggesting that calcite and feldspars of the sandstone and mudstone would be significantly dissolved when it contacts with supercritical <TEX>$CO_2$</TEX> and groundwater at <TEX>$CO_2$</TEX> sequestration sites in Pohang basin. The average specific surface area of sandstone and mudstone using BET analysis increased from <TEX>$27.3m^2/g$</TEX> and <TEX>$19.6m^2/g$</TEX> to <TEX>$28.6m^2/g$</TEX> and <TEX>$26.6m^2/g$</TEX>, respectively, and the average size of micro scale void spaces for the sandstone and mudstone decreased over 60 days reaction, resulting in the increase of micro pore spaces of rocks by the dissolution. Results suggested that the injection of supercritical <TEX>$CO_2$</TEX> in Pohang basin would affect the physical property change of rocks and also <TEX>$CO_2$</TEX> storage capacity in Pohang basin.

Quantitative geophysical pore‐type characterization and its geological implication in carbonate reservoirs

ABSTRACTThis paper discusses and addresses two questions in carbonate reservoir characterization: how to characterize pore‐type distribution quantitatively from well observations and seismic data based on geologic understanding of the reservoir and what geological implications stand behind the pore‐type distribution in carbonate reservoirs. To answer these questions, three geophysical pore types (reference pores, stiff pores and cracks) are defined to represent the average elastic effective properties of complex pore structures. The variability of elastic properties in carbonates can be quantified using a rock physics scheme associated with different volume fractions of geophysical pore types. We also explore the likely geological processes in carbonates based on the proposed rock physics template. The pore‐type inversion result from well log data fits well with the pore geometry revealed by a FMI log and core information. Furthermore, the S‐wave prediction based on the pore‐type inversion result also shows better agreement than the Greensberg‐Castagna relationship, suggesting the potential of this rock physics scheme to characterize the porosity heterogeneity in carbonate reservoirs. We also apply an inversion technique to quantitatively map the geophysical pore‐type distribution from a 2D seismic data set in a carbonate reservoir offshore Brazil. The spatial distributions of the geophysical pore type contain clues about the geological history that overprinted these rocks. Therefore, we analyse how the likely geological processes redistribute pore space of the reservoir rock from the initial depositional porosity and in turn how they impact the reservoir quality.

Reasonably Water Injection Time about Abnormal Pressure of Low Permeability Reservoir

Abnormal pressure of low permeability reservoirs is a special reservoir, which have some characteristic : low permeability, strong stress sensitivity, complex pore structure, abnormal pressure. with the pressure decreasing about bottom-hole and reservoir, the formation of the rock pore space and permeability will decrease, and reservoir stress-sensitive phenomenon of serious. All these have brought greater difficulty for developing. in order to reasonable development of those reservoirs, maintain the formation energy is important, choose the reasonable injection timing is an important aspect. In this paper, taking abnormal pressure of low permeability reservoir as an example, studies variation law of abnormally pressure reservoir rock compressibility, porosity, stress sensitivity by experimental, Associated with the nature of the reservoir to determine a reasonable water injection time, and demonstrated by numerical simulation, finally proposed reasonable water injection timing about abnormal pressure of low-permeability reservoirs.

Digital rock physics benchmarks—Part I: Imaging and segmentation

The key paradigm of digital rock physics (DRP) “image and compute” implies imaging and digitizing the pore space and mineral matrix of natural rock and then numerically simulating various physical processes in this digital object to obtain such macroscopic rock properties as permeability, electrical conductivity, and elastic moduli. The steps of this process include image acquisition, image processing (noise reduction, smoothing, and segmentation); setting up the numerical experiment (object size and resolution as well as the boundary conditions); and numerically solving the field equations. Finally, we need to interpret the solution thus obtained in terms of the desired macroscopic properties. For each of these DRP steps, there is more than one method and implementation. Our goal is to explore and record the variability of the computed effective properties as a function of using different tools and workflows. Such benchmarking is the topic of the two present companion papers. Here, in the first part, we introduce four 3D microstructures, a segmented Fontainebleau sandstone sample (porosity 0.147), a gray-scale Berea sample; a gray-scale Grosmont carbonate sample; and a numerically constructed pack of solid spheres (porosity 0.343). Segmentation of the gray-scale images by three independent teams reveals the uncertainty of this process: the segmented porosity range is between 0.184 and 0.209 for Berea and between 0.195 and 0.271 for the carbonate. The implications of the uncertainty associated with image segmentation are explored in a second paper.

Measuring effective radium concentration with large numbers of samples. Part I – experimental method and uncertainties

Effective radium concentration ECRa, product of radium concentration and radon emanation, is the source term for radon release into the pore space of rocks and the environment. To measure ECRa, we have conducted, over a period of three years, more than 5500 radon-222 accumulation experiments in the laboratory with scintillation flasks, and about 700 with integrating solid state nuclear track detectors, leading to experimental values of ECRa for more than 1570 rock and soil samples. Through detailed systematic checks and intercomparison between various repeated experiments, the experimental uncertainty has been assessed, and ranges from 30% (1 σ) for ECRa values smaller than 0.2 Bq kg−1 to about 8–10% for ECRa values larger than 50 Bq kg−1. The detection limit, defined as the 90% probability for obtaining a non-zero experimental ECRa value at 68% confidence level, depends on the mass of the sample with respect to the volume of the accumulation volume, and typically varies between 0.04 and 0.09 Bq kg−1. To measure ECRa from large numbers of samples with sufficient accuracy and uncertainty for our purpose, i.e. for the most natural objects encountered in the environment, the accumulation method with scintillation flask emerged as particularly useful and robust. Properties of ECRa and interpretations inferred from this large data set are presented in the companion paper.

Measuring effective radium concentration with large numbers of samples. Part II – general properties and representativity

Effective radium concentration ECRa, product of radium concentration and radon emanation, is the source term for radon release into the pore space of rocks and the environment. Over a period of three years, we performed more than 6000 radon-222 accumulation experiments in the laboratory with scintillation flasks and SSNTDs and we obtained experimental ECRa values from more than 1570 rock and soil samples. With this method, which allowed the measurement of ECRa from large numbers of samples with sufficient accuracy and uncertainty, as detailed in the companion paper, the dependence of the emanation factor on temperature and moisture content is revisited. In addition, with such a large ECRa dataset, dispersion of ECRa can be studied at sample-scale (cm to dm) and at scarp-scale (m to tens of m). Furthermore, we are able to discuss the representativity of obtained ECRa values at field-scale, and to investigate the spatial variations of ECRa over kilometric scales, within geological formations and across formations and faults. This experimental study opens new perspectives in the understanding of radium geochemistry and illustrates the importance of studying the radon source term with large numbers of samples for the modelling of geological and environmental processes, and also for the assessment of the radon health hazard.

Pore space in source rock during the generation of hydrocarbons

Modern technical facilities for laboratory experiments allow carrying out the step-by-step description of HC generation from the organic rich rocks and its reflection in rock structure in an undisturbed rock sample. A clayeycarbonate rock sample of the Domanik Horizon (D3fr) with high content of organic matter and its low maturation grade was heated in nitrogenatmosphere and alterations in its pore space structure was monitored. That was shown that pores in the initial rock are small and isolated. When the rock is heated, the pores are first bound with each other due to the propagation of fractures along bedding, resulting in the formation of isolated filtration intervals. At a certain stage of organic matter maturity further heating provokes the formation of bedding-perpendicular fractures that connect the isolated filtration intervals into a single system, promoting filtration in the low permeable media. Experimental works described in the paper can serve as a basis for the development of new methods for the successful prediction of nontraditional reservoir zones.

Rock Mechanics Parameters Calculation of the Fractured Rock Based on the Effective Media Theory with Well Logging

Fractured rocks are the main oil and gas exploration objects offshore in China in recent years, which include the fractured sandstone, carbonate, volcanic rock, coal methane bed, shale gas and so on. The accurate calculation of the rock mechanics parameters (elastic modulus and Poisson’s ratio) play remarkable role in petroleum engineering operations, such as borehole stability, mud density window determination, perforation, EOR, in-situ stress predication and so on. Now the applications show that the in-situ stress estimation based on the rock parameters obtained by acoustic logging is much different from the downhole measurement with wireline formation tester. The pore space of the fractured rock contains fracture and cave and it is different from sandstone. In the paper a novel method based on the effective media theory with well logging for the rock mechanics parameters calculation of the fractured rock is introduced, and some problems and potential application are also discussed.

Pore-scale imaging and modelling

Pore-scale imaging and modelling – digital core analysis – is becoming a routine service in the oil and gas industry, and has potential applications in contaminant transport and carbon dioxide storage. This paper briefly describes the underlying technology, namely imaging of the pore space of rocks from the nanometre scale upwards, coupled with a suite of different numerical techniques for simulating single and multiphase flow and transport through these images. Three example applications are then described, illustrating the range of scientific problems that can be tackled: dispersion in different rock samples that predicts the anomalous transport behaviour characteristic of highly heterogeneous carbonates; imaging of super-critical carbon dioxide in sandstone to demonstrate the possibility of capillary trapping in geological carbon storage; and the computation of relative permeability for mixed-wet carbonates and implications for oilfield waterflood recovery. The paper concludes by discussing limitations and challenges, including finding representative samples, imaging and simulating flow and transport in pore spaces over many orders of magnitude in size, the determination of wettability, and upscaling to the field scale. We conclude that pore-scale modelling is likely to become more widely applied in the oil industry including assessment of unconventional oil and gas resources. It has the potential to transform our understanding of multiphase flow processes, facilitating more efficient oil and gas recovery, effective contaminant removal and safe carbon dioxide storage.

Low pore connectivity in natural rock

As repositories for CO2 and radioactive waste, as oil and gas reservoirs, and as contaminated sites needing remediation, rock formations play a central role in energy and environmental management. The connectivity of the rock's porespace strongly affects fluid flow and solute transport. This work examines pore connectivity and its implications for fluid flow and chemical transport. Three experimental approaches (imbibition, tracer concentration profiles, and imaging) were used in combination with network modeling. In the imbibition results, three types of imbibition slope [log (cumulative imbibition) vs. log (imbibition time)] were found: the classical 0.5, plus 0.26, and 0.26 transitioning to 0.5. The imbibition slope of 0.26 seen in Indiana sandstone, metagraywacke, and Barnett shale indicates low pore connectivity, in contrast to the slope of 0.5 seen in the well-connected Berea sandstone. In the tracer profile work, rocks exhibited different distances to the plateau porosity, consistent with the pore connectivity from the imbibition tests. Injection of a molten metal into connected pore spaces, followed by 2-D imaging of the solidified alloy in polished thin sections, allowed direct assessment of pore structure and lateral connection in the rock samples. Pore-scale network modeling gave results consistent with measurements, confirming pore connectivity as the underlying cause of both anomalous behaviors: imbibition slope not having the classical value of 0.5, and accessible porosity being a function of distance from the edge. A poorly connected porespace will exhibit anomalous behavior in fluid flow and chemical transport, such as a lower imbibition slope (in air–water system) and diffusion rate than expected from classical behavior.