Pore Geometry Characteristics Research Articles

Theoretically derived pore geometry in carbonates using the extended biot theory

Carbonates typically display a large scatter in velocity-porosity cross plots that is caused by the difference in stiffness that the highly variable pore geometry produces in carbonate rocks at a given porosity. In recent years, digital image analysis (DIA) made it possible to capture objective, quantifiable parameters of the pore geometry to explain the scatter in carbonate velocity-porosity cross plots. The geometrical parameters most influential for acoustic velocity are Perimeter over Area (measuring the complexity of the pore space) and Dominant Size (measuring pore sizes as equivalent diameter). Most theoretical models of acoustic wave propagation in porous media, however, do not incorporate those geometrical characteristics of the natural pore spaces? In contrast, the frame flexibility and coupling factors (fk and γk) embedded in the Extended Biot Theory capture the geometrical characteristics using poroelastic data. Here, these theoretically derived parameters are tested and validated with experimental data. In 95 limestone samples, Extended Biot Theory parameters fk and γk can be derived reliably from measured acoustic data. Both parameters correlate well to Perimeter over Area (r = 0.702, p < 0.0001), and Dominant Size (r = 0.792, p < 0.0001) derived using digital image analysis of thin section photographs. These correlations confirm the existence and the strength of the relationship between theoretical parameters from the Extended Biot Theory and quantitative pore geometry parameters. Thus, this study illustrates that: (1) estimating porosity from acoustic data can be substantially improved by incorporating information on quantitative pore space geometry; and (2) in cases where good estimates of porosity are available (e.g. from well-log data or seismic with extensive well control) quantitative pore geometric characteristics can be estimated directly from acoustic data. These quantitative pore geometry characteristics can be used to estimate permeability indirectly from acoustic data. For example, permeability estimates based on a Kozeny-Carman type function incorporating geometrical information derived from the topological Extended Biot Theory parameters fk and γk, yield a statistically significant, high Pearson correlation coefficient of r = 0.713 (p < 0.0001).

Soil pore structure mediates the effects of soil oxygen on the dynamics of greenhouse gases during wetting–drying phases

The timing and magnitude of greenhouse gas (GHG) production depend strongly on soil oxygen (O2) availability, and the soil pore geometry characteristics largely regulate O2 and moisture conditions relating to GHG biochemical processes. However, the interactions between O2 dynamics and the concentration and flux of GHGs during the soil moisture transitions under various soil pore conditions have not yet been clarified. In this study, a soil-column experiment was conducted under wetting–drying phases using three pore-structure treatments, FINE, MEDIUM, and COARSE, with 0 %, 30 %, and 50 % coarse quartz sand applied to soil, respectively. The concentrations of soil gases (O2, nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4)) were monitored at a depth of 15 cm hourly, and their surface fluxes were measured daily. Soil porosity, pore size distribution, and pore connectivity were quantified using X-ray computed microtomography. The soil O2 concentrations were found to decline sharply as soil moisture increased to the water holding capacities of 0.46, 0.41, and 0.32 cm cm−3 in the FINE, MEDIUM, and COARSE, respectively. The dynamic patterns of the O2 concentrations varied across the soil pore structures, decreasing to anaerobic in FINE (<0.01 %) and MEDIUM (0.02 %), and to hypoxic (4.42 %) in COARSE. Correspondingly, the soil N2O concentration was the highest in FINE (101 μL L−1) and the lowest in COARSE (10 μL L−1), whereas the highest surface N2O flux was observed in MEDIUM (131 μg N m−2 h−1). As soil CO2 concentrations declined, CO2 fluxes increased from FINE to MEDIUM to COARSE. Most pores of FINE, MEDIUM, and COARSE were 15–80 μm, 85–100 μm, and 105–125 μm, respectively, in terms of diameter. The X-ray CT visible (>15 μm) porosity in FINE, MEDIUM and COARSE were 0.09, 0.17, and 0.28 mm3 mm−3, respectively. The corresponding Euler-Poincaré numbers were 180,280, 76,705, and −10,604, respectively, indicating higher connectivity in COARSE than in MEDIUM or FINE. In soil dominated by small air-filled porosity which limits gas diffusion and result in low soil O2 concentration, N2O concentration was increased and CO2 flux was inhibited as the moisture content increased. The turning point in the sharp decrease in O2 concentration was found to correspond with a moisture content, and a pore diameter of 95–110 μm was associated with the critical turning point between holding water and O2 depletion in soil. These findings suggest that O2-regulated biochemical processes are key to the production and flux of GHGs, which in turn are dependent on the soil pore structure and a coupling relationship between N2O and CO2. Improved understanding of the intense effect of soil physical properties provided an empirical foundation for the future development of mechanistic prediction models for how pore-space scale processes with high temporal (hourly) resolution up to GHGs fluxes at larger spatial and temporal scales.

Resolution-Dependent Multifractal Characteristics of Flow in Digital Rock Twin Simulated Using the Lattice Boltzmann Method

Digital rock twins are widely used to obtain hydraulic properties of porous media by simulating pore-scale fluid flow. Multifractal characteristics of pore geometry and flow velocity distribution have been discovered with two-dimensional (2D) images and three-dimensional (3D) models, whereas the dependency of results on the resolution is not well known. We investigated resolution-dependent multifractal properties of 3D twin models for a sandstone sample with originally 3 μm resolution images. 3D pore-scale water flow was simulated with the lattice Boltzmann method (LBM). As indicated by multifractal analyses, the generalized dimension spectra, the Hölder exponent spectra, and singularity spectra of the flow velocity are similar to that of the pore geometry but different in ranges and sensitivities to the change in the model resolution. Nonlinear dependencies of 2D/3D porosity, holistic/slice permeability, equivalent pore radius squared, and multifractal parameters on the resolution were discussed.

Hardened properties of 3D printed concrete with recycled coarse aggregate

In this paper, a novel extrusion-based 3D printed material was obtained by preparing 3D printed recycled coarse aggregate concrete (3DPRAC) using recycled coarse aggregate (RCA), and the compressive and flexural properties were investigated at different RCA replacement ratios, ages, and construction forms. The porosity, pore volume distribution, pore geometry characteristics were analyzed by X-CT. MIP and SEM were used to analyze the pore structure of the RCA. The results showed that the compressive and flexural strengths have obvious anisotropic characteristics. With increasing replacement ratio, the compressive and flexural strengths generally decreased. Internal pores of 3DPRAC were found to exhibit the geometric characteristics of flat ellipsoidal and uniaxially oriented arrangements along the printing direction. A multiple partition-interface model was proposed to establish the connection between pore structure characteristics and force cracking, and the anisotropic mechanical property mechanism of 3DPRAC was revealed.

A semi-empirical modified geometry model for long-term co-current spontaneous imbibition of porous media based on convoluted, nonuniform and topological pore network

Hydraulic diffusivity or imbibition is a well-known unsaturated hydrodynamics phenomenon in water resources and geosciences study. Currently, there have been numerous analytical or numerical models describing the spontanneous imbibition of porous rock and soil. However, the most existing models do not consider hydrostatic pressure and elaborate pore geometry characteristics. Assuming that the penetration direction is one-dimensional and infinitely continuous, a long-term co-current spontaneous imbibition (SI) model is proposed by average and fractal geometries, respectively accordingly obtaining the general expression of dimensionless comprehensive parameter. The practicability and accuracy of the model are verified by experimental data and compared with other models. The influence mechanisms of tortuosity, pore-throat, fractal, shape and topological characteristics on initial and equilibrium SI behaviors are comprehensively revealed. The new models are applied to inversely predict the dimensionless comprehensive parameters, variations of which with porosity are analyzed along with their influence on long-term SI characteristics. The results are shown as follows. Compared with the existing classical models, the prediction accuracy of the new model consistent with experiment is greatly improved, generalizing the existing models. The dimensionless comprehensive parameters based on average and fractal geometries show the decreasing trend in power-law and increasing trend in linear with the increase of porosity, respectively. The equilibrium height or mass is only related to topology factor, fractal dimension and shape factor, whereas the equilibrium time is also correlated to pore-throat ratio and tortuosity. The sensitivities of fractal dimension, topological factor and shape factor to equilibrium time are stronger than that of equilibrium mass or height. The sensitivities of topological characteristics, pore-throat structure, tortuosity, pore geometry and fractal characteristics to SI reduce successively for porous media. The influences of dimensionless comprehensive parameter on evolution of SI mass with time go through four stages, i. e., no influence at initial stage, increasing influence at initial later stage, weakening influence at later stage and increasing influence at end, whereas on evolution of SI velocity versus time and recovery rate go through two stages, that is, significant influence at initial stage and no influence at later stage.

Pore-scale assessment of subsurface carbon storage potential: implications for the UK Geoenergy Observatories project

The growing importance of subsurface carbon storage for tackling anthropogenic carbon emissions requires new ideas to improve the rate and cost of carbon capture and storage (CCS) project development and implementation. We assessed sandstones from the UK Geoenergy Observatories (UKGEOS) site in Glasgow, UK and the Wilmslow Sandstone Formation (WSF) in Cumbria, UK at the pore scale to indicate suitability for further assessment as CCS reservoirs. We measured porosity, permeability and other pore geometry characteristics using digital rock physics techniques on microcomputed tomographic images of core material from each site. We found the Glasgow material to be unsuitable for CCS due to very low porosity (up to 1.65%), whereas the WSF material showed connected porosity up to 26.3% and permeabilities up to 6040 mD. Our results support the presence of a percolation threshold at 10% total porosity, introducing near full connectivity. We found total porosity varies with permeability with an exponent of 3.19. This provides a reason to assume near full connectivity in sedimentary samples showing porosities above this threshold without the need for expensive and time-consuming analyses. Supplementary material: Information about the boreholes sampled in this study, additional well logs of boreholes and a summary of the supporting data plotted throughout this article from literature are available at https://doi.org/10.6084/m9.figshare.c.5260074 Thematic collection: This article is part of the Geoscience for CO 2 storage collection available at: https://www.lyellcollection.org/cc/geoscience-for-co2-storage

Pore Geometry Characteristics and Fluid–Rock Interaction in the Haynesville Shale, East Texas, United States

Since 2007, the Upper Jurassic marine Haynesville Formation has become one of the leading shale gas plays and is currently the third most prolific producer in the United States. A detailed study ha...

Quantitative pore‐type characterization from well logs based on the seismic petrophysics in a carbonate reservoir

ABSTRACTQuality, availability and consistency of the measured and interpreted well log data are essential in the seismic reservoir characterization methods, and seismic petrophysics is the recommended workflow to achieve data consistency between logs and seismic domains. This paper uses seismic petrophysics workflow to improve well logs and pore geometry interpretations for an oil carbonate reservoir in the Fahliyan Formation in the southwest of Iran. The petrophysical interpreted well logs, rock physics and well‐to‐seismic tie analysis are integrated into the proposed workflow. Our implementation incorporates revising petrophysical well log interpretations and updating pore geometry characteristics to obtain a better well‐tie quality. We first propose an improved pore‐type characterization approach based on both P‐ and S‐wave velocities for quantifying pore geometry. Then, seismic logs are estimated accordingly, and the results are used in the well‐to‐seismic analysis. The quality of the well‐tie is improved, furthermore, by iterating on the petrophysical interpreted well logs as well as the calculated pore geometries. For the intervals with high‐quality data, our workflow improves the consistency between the results of measured and modelled seismic logs. For the intervals with problematic well logs, the application of our proposed workflow results in the successful replacement of the poor data and subsequently leads to an improved wavelet estimation and well‐tie results. In both cases, a higher quantification of pore geometries is achieved, which in turn is confirmed by the core images and formation micro‐imager analysis.

The effects of mineral composition, TOC content and pore structure on spontaneous imbibition in Lower Jurassic Dongyuemiao shale reservoirs

Spontaneous imbibition (SI) is a capillary-force controlled process, which has been identified as one of the most important mechanisms to affect hydrocarbon recovery from unconventional shale reservoirs. In this work, we focus on the mineral composition, total organic carbon (TOC) content, pore geometry characteristics and fluid imbibition behaviors of the terrestrial Lower Jurassic Dongyuemiao shale reservoirs. The pore morphology is directly imaged and observed via field emission-scanning electronic microscope (FE-SEM). Nitrogen (N2) physisorption and mercury intrusion porosimetry (MIP) are applied to investigate the pore geometry characteristics. The slopes of deionized (DI) water/n-decane imbibition from fluid imbibition experiments are used to evaluate the pore connectivity characteristics of hydrophilic and hydrophobic pore spaces, respectively. Finally, the relationships between shale dominant mineral composition, TOC content and pore structure parameters on fluid imbibition behavior are discussed. Experimental results show that clay and quartz are the two dominant minerals in the Dongyuemiao shales. In this study, four typical lithofacies are identified in the Dongyuemiao shales, including laminated or massive mudstone, silty mudstone, shell limestone and argillaceous siltstone. Organic matter (OM) pores and interP pores are the dominant pore types in the Dongyuemiao shales, and most of the pores with sizes smaller than 50 nm. The imbibition slopes of n-decane are generally higher than that of DI water, indicating better pore connectivity of hydrophobic pores. Due to protection by quartz grains, samples with higher abundances of quartz are beneficial for forming a connected pathway for DI water migration, resulting in a better-connected water-wet pathway. The hydrophobic and hydrophilic pore networks in samples with higher TOC content are better connected, which are speculated to be related to the high volume of connected organic matter in shale matrix. Positive correlations occur between porosity/pore volume and fluid (including DI water and n-decane) imbibition slopes, suggesting that the connectivity of pore networks become better as porosity and pore volume increase, regardless of whether the pores are hydrophobic or hydrophilic.

Separation of Soil Macropore Types in Three‐Dimensional X‐Ray Computed Tomography Images Based on Pore Geometry Characteristics

Core Ideas For preferential flow modeling, different macropore types must be considered. A method was developed for separating biopores and cracks in 3D images from XRCT. The method enabled a more objective determination of structuring element sizes. The voxel‐based approach was found useful for quantification of macropore types. In structured soils, earthworm burrows, root channels, shrinkage cracks, and interaggregate spaces form complex macropore networks. Depending on the type and morphological properties, each macropore surface type is coated with specific organo‐mineral compounds, differently affecting sorption and mass exchange during preferential flow and turnover processes. For a quantitative, macropore type–specific analysis using X‐ray computed tomography (XRCT) with subsequent three‐dimensional (3D) image analysis, a discrimination of biopores from cracks and interaggregate spaces is necessary. We developed a method that allows separating biopores from other larger macropores in 3D images from XRCT of intact soil cores. An image‐processing workflow using the MAVI (Modular Algorithms for Volume Images) software framework ToolIP (Tool for Image Processing) was created to handle XRCT 3D images. Masking steps enabled to retain the surface roughness in the resulting two images of separated biopores and cracks. As a key point, the sizes of the structuring elements used in the spherical opening and dilation were objectively determined. For this purpose, maximum differences in the pore shapes between the 3D images of cylindrical biopores vs. more flat cracks and unregularly interaggregate spaces were focused. At the given resolution of 231‐μm voxel edge length, an optimum size of 2.5 voxels was found for both processing steps. The voxel‐based approach is applicable to XRCT 3D images of different spatial resolution and appears useful for the quantification of physicochemical surface properties of different macropore types for soil volumes, enabling a more precise description of preferential flow and transport.

Comparative pore surface area in primary and secondary porosity in sandstones

Primary and secondary porosity in sandstones possess different pore geometry characteristics, but these are not well quantified. The pore surface area in 2 suites of sandstones exhibiting only primary porosity (Permo-Triassic, Northern Ireland) and only secondary porosity (Cambrian, England) were measured using JMicrovision software. The data show pore surface areas per unit pore volume ∼2.5 times as great in the secondary porosity compared to the primary porosity. This difference is great enough to have a significant impact on properties dependent on pore surface area, including oil production and capacity for microbial colonization in the deep biosphere.

Analysis of heterogeneity and permeability anisotropy in carbonate rock samples using digital rock physics

The heterogeneity of a carbonate reservoir exists at all scales and always presents a challenge because it cannot be studied visually during laboratory measurements. Permeability is an important parameter and plays a key role in enhanced oil recovery operations. However, permeability anisotropy is observed at different scales of hydrocarbon production, especially in carbonate reservoirs, and complicates reservoir characterization and description. Digital rock physics (DRP) uses digitized images of reservoir rocks to compute their properties, such as porosity and directional permeability, and provide a better view of the internal structure of the rock sample, which can be used to study the heterogeneity and permeability anisotropy in carbonate rocks and reservoirs.In this study, we processed and used images of five carbonate rock samples obtained from three-dimensional (3D) computed tomography (CT) scans to calculate porosity and directional permeability. Subsamples taken at three positions along each original core plug image were processed to segmented images using image processing methods. Porosities were calculated by the voxel statistics method based on a segmented image. Absolute permeabilities of these subsamples in the three main perpendicular directions (one axial, z, and two transverse, x and y) were calculated by applying the parallel lattice Boltzmann method (PLBM) in our high-performance computing cluster (HPCC). The heterogeneity and permeability anisotropy were analyzed by combining the experimental results, the rock images, and simulated results, which included visualization of the velocity field and calculated parameter values. By analyzing these data, we found that these carbonate rock samples had strong heterogeneity and clear permeability anisotropy. In addition, we also found a close relationship between the measured values of the whole core samples and the maximum (minimum) values of the simulations for porosity (permeability). We verified that the characteristics of pore geometry, flow velocity distribution, and transport properties can be captured using DRP.

Pore facies analysis: incorporation of rock properties into pore geometry based classes in a Permo-Triassic carbonate reservoir in the Persian Gulf

Pore facies analysis is a useful method for the classification of reservoir rocks according to pore geometry characteristics. The importance of this method is related to the dependence of the dynamic behaviour of the reservoir rock on the pore geometry. In this study, pore facies analysis was performed by the quantification and classification of the mercury injection capillary pressure (MICP) curves applying the multi-resolution graph-based clustering (MRGC) method. Each pore facies includes a limited variety of rock samples with different depositional fabrics and diagenetic histories, which are representative of one type of pore geometry. The present pore geometry is the result of the interaction between the primary rock fabric and its diagenetic overprint. Thus the variations in petrographic properties can be correlated with the pore geometry characteristics. Accordingly, the controlling parameters in the pore geometry characteristics were revealed by detailed petrographic analysis in each pore facies. The reservoir rock samples were then classified using the determined petrographic properties which control the pore system quality. This method is proposed for the classification of reservoir rocks in complicated carbonate reservoirs, in order to reduce the incompatibility of traditional facies analysis with pore system characteristics. The method is applicable where enough capillary pressure data is not available.

Quantification of pore structure and its effect on sonic velocity and permeability in carbonates

Carbonate rocks commonly contain a variety of pore types that can vary in size over several orders of magnitude. Traditional pore-type classifications describe these pore structures but are inadequate for correlations to the rock's physical properties. We introduce a digital image analysis (DIA) method that produces quantitative pore-space parameters, which can be linked to physical properties in carbonates, in particular sonic velocity and permeability. The DIA parameters, derived from thin sections, capture two-dimensional pore size (DomSize), roundness (), aspect ratio (AR), and pore network complexity (PoA). Comparing these DIA parameters to porosity, permeability, and P-wave velocity shows that, in addition to porosity, the combined effect of microporosity, the pore network complexity, and pore size of the macropores is most influential for the acoustic behavior. Combining these parameters with porosity improves the coefficient of determination (R2) velocity estimates from 0.542 to 0.840. The analysis shows that samples with large simple pores and a small amount of microporosity display higher acoustic velocity at a given porosity than samples with small, complicated pores. Estimates of permeability from porosity alone are very ineffective (R2 = 0.143) but can be improved when pore geometry information PoA (R2 = 0.415) and DomSize (R2 = 0.383) are incorporated. Furthermore, results from the correlation of DIA parameters to acoustic data reveal that (1) intergrain and/or intercrystalline and separate-vug porosity cannot always be separated using sonic logs, (2) P-wave velocity is not solely controlled by the percentage of spherical porosity, and (3) quantitative pore geometry characteristics can be estimated from acoustic data and used to improve permeability estimates.

Comparison of Air and Water Permeability between Disturbed and Undisturbed Soils

Although soil structure and pore geometry characteristics largely control flow and transport processes in soils, there is a general lack of experiments that study the effects of soil structure and pore‐space characteristics on air and water permeability. Our objective was to determine the dependency of soil permeability on fluid content for both water and air, and compare results for both disturbed (D) and undisturbed (UD) soils. For that purpose, we first measured the water permeability (kw) and air permeability (ka) for several intact UD soil samples. Subsequently, the same samples were crushed and repacked into the same soil cores to create the D equivalent for the same soil material. Measurements showed large differences between D and UD samples, confirming the enormous impact of soil structure and pore‐space characteristics on flow. The permeability of both fluid phases (air and water) was greatly reduced for the D samples, especially for soil air permeability due to its greater dependency on soil aggregation and structure. Soil water retention and permeability data were fitted to Campbell's and Mualem's pore‐size distribution model, respectively. Regardless of soil disturbance, we showed that the tortuosity–connectivity parameter, l, for the water permeability (l1) and air permeability (l2) were different. This is in contrast to the general practice of using the same parameter value for both functions. The relation between l1 and l2 was largely controlled by soil structure and associated macroporosity properties.

Prediction of In-Situ Permeability: Significance of Rock Type Identification in Resevoir Characterization of Tight Gas Sandstones: ABSTRACT

The accurate prediction of in-situ permeability is fundamentally important in reservoir characterization. Analyses of several thousand core samples from low permeability ([open quotes]tight[close quotes]) gas sandstones of the Travis Peak, Cotton Valley and Frontier Formations reveal that the rate of permeability decrease is a function of Rock Type (interval of rock characterized by unique pore geometry). These tight gas sandstones consist of alternations of several Rock Types, depending on changes in environment of deposition and diagenesis. In such complex sequences, in-situ permeability cannot be successfully predicted using only an initial value of permeability. A knowledge of both the initial permeability (at minimum net effective stress) and pore geometry are required to predict in-situ permeability at any given value of net effective stress. Pore geometry characteristics that control in-situ permeability include size and shape aspects of both the pore throats and the pore bodies. These can be, in part, a function of mineral composition. In some instances, they are independent of composition. SEM-based pore image analysis of pore bodies and pore throats allows for the identification of different Rock Types. This information, when coupled with an initial value of permeability, allows for the prediction of permeability at any given value ofmore » net effective stress in the Travis Peak, Cotton Valley and Frontier Formations of Texas and Wyoming.« less

Pore Geometry Characteristics of the Lunde and Statfjord Reservoirs in the Snorre Field, North Sea: ABSTRACT

Pore Geometry Characteristics of the Lunde and Statfjord Reservoirs in the Snorre Field, North Sea: ABSTRACT

The Use of Alternating Flow to Characterize Porous Media Having Storage Pores

Abstract Storage porosity has been considered one of the important pore geometry characteristics of heterogeneousporosity limestones. Storage pores are only containers for fluids, in contrast to flow channel pores which both contain fluids and provide continuity for fluid flow. The concept of another geometry characteristic, "porostriction", is presented as a second pertinent variable in describing limestone pore space. In simple terms, porostriction is a measure of the flow resistance between storage and flow channel pores. Alternating-flow core-testing theory provides flow relationships which can be used to divide the pore space of heterogeneous-porosity media into flow channel and storage pores and to measure the "porostriction" of the latter. Experimental application of this theory to naturally occurring heterogeneous limestones shows that "porostriction" and the ratio of storage to flow channel pores can be estimated. Porostriction and porosity ratio are microscopic characteristics which should influence oil-recovery efficiencies during certain types of displacement processes. A knowledge of pore geometry should be valuable in designing or selecting the most effective oil-recovery process for heterogeneous limestones containing storage porosity. Introduction The primary and secondary recovery of oil from limestone (carbonate) reservoirs has been and will continue to be a major source of the world's supply of petroleum. Oil recovery from this type of formation is strongly influenced by the size, shape and arrangement of the pore spaces which hold the formation fluids. Therefore, it is expected that better knowledge of pore geometry would lead to design of more effective recovery processes. The concept of storage and flow channel pores has been presented as an important characteristic of limestone porosity. In this concept, storage pores are only containers for fluids, whereas flow channel pores are those pores which both contain and transmit the fluids. The work reported herein involves the concept of an additional pore characteristic called "porostriction".