Intraparticle Pores Research Articles

Geological and geochemical characteristics of marine-continental transitional shale from the Lower Permian Taiyuan Formation, Taikang Uplift, southern North China Basin

Abstract In recent years, extensive studies have been conducted on conventional shale gas resources, but little work has been performed on the resource potential of marine-continental shales. This paper takes the Lower Permian Taiyuan shale in the Taikang Uplift of the southern North China Basin as an example to characterize a transitional shale reservoir. The results indicate that the Taiyuan shale has high TOC values (averaging 2.67%) and contains type III gas-prone organic matter; the shale has high Ro values (averaging 3.44%), and Tmax ranges from 424 °C to 601 °C. With respect to fracability or brittleness, the content of brittle minerals in the Taiyuan shale ranges from 21% to 71% (averaging 45.55%), and the average content of clay minerals is 44.1%. Based on SEM and SEM with Ar-ion milling observation, interparticle pores, intraparticle pores, and microfractures are developed in the Taiyuan shale, which can provide reservoir space for the accumulation of shale gas. Organic matter pores rarely appear due to the organic type and high maturity. The results of this study can guide the shale gas exploration of Taiyuan Formation in the Taikang Uplift of the southern North China Basin.

Geologic characterization of a lower Cambrian marine shale: Implications for shale gas potential in northwestern Hunan, South China

We have investigated the geologic features of the lower Cambrian-aged Niutitang Shale in the northwestern Hunan province of South China. Our results indicate that the Niutitang Shale has abundant and highly mature algal kerogen with total organic carbon (TOC) content ranging from 0.6% to 18.2%. The equivalent vitrinite reflectance (equal-Ro) value is between 2.5% and 4.3%. Mineral constituents are dominated by quartz and clay. The average quartz content (62.8%) is much higher than that of clay minerals (26.1%), and this suggests a high brittleness index. Organic-matter pores, interparticle pores, intraparticle pores, interlaminated fractures, and structural fractures are all well developed. The porosity ranges from 0.6% to 8.8%, with an average of 4.8%, whereas the permeability varies from 0.0018 to [Formula: see text] (microdarcy) (averaging [Formula: see text]). The porosity of TOC- and clay-rich shale samples is generally higher than that of quartz-rich shale samples. The gas adsorption capacity of the Niutitang Shale varies from 2.26 to [Formula: see text], with a mean value of [Formula: see text]. The TOC content appears to significantly influence gas adsorption capacity. In general, TOC-rich samples exhibit a much higher adsorption capacity than TOC-poor samples.

Pore network characteristics of lacustrine shales in the Dongpu Depression, Bohai Bay Basin, China, with implications for oil retention

Abstract Pore development and the location of retained hydrocarbons are key topics to understand the shale oil system. In an attempt to investigate pore network characteristics and oil retention in lacustrine shales, 24 samples from the Es3 shales in the Dongpu Depression, Bohai Bay Basin were subjected to mineralogical, petrological, geochemistry and pore structure investigations using X-ray diffraction (XRD), thin section, field emission-scanning electronic microscope (FE-SEM), N2 adsorption-desorption. After removing retained oil by solvent extraction, 12 selected samples were again analyzed by Rock-Eval pyrolysis and N2 adsorption-desorption experiment. According to the mineral compositions and petrological characteristics, six types of lithofacies are identified in the Es3 shales in the Dongpu Depression: laminated calcareous shales, lenticular calcareous shales, laminated argillaceous shales, massive argillaceous shales, laminated siliceous shales, and massive siliceous shales. Geochemical characteristics of these shales are quite different, as calcareous/laminated shales have higher TOC contents than massive argillaceous and siliceous shales. Interparticle pores, intraparticle pores, organic matter pores and fracture pores are observed in the studied samples, while bitumens were found retaining in well-connected pore network. The N2 adsorption-desorption experiments on samples before and after solvent extraction reveal the different pore structure characteristics in six lithofacies and the occurrence of oil in lacustrine shales. In general, pore volumes within pore diameter range of 1.7–10nm and 10–200nm of samples show increase after solvent extraction, indicating that large and small pores in shales both play important roles in oil retention. Oil retained in shales can be divided as free and heavy fractions, as from the pyrolysis results. In lacustrine shales, larger pores are main storage space for hydrocarbon. Larger pores in different lithologies have similar capacity for free oil retention, while those in calcareous and argillaceous shales are more efficient for heavy oil retention. For both free and heavy oil, small pores in argillaceous shales are efficient for their storage.

Nanoscale Pore Structure Characterization and Permeability of Mudrocks and Fine-Grained Sandstones in Coal Reservoirs by Scanning Electron Microscopy, Mercury Intrusion Porosimetry, and Low-Field Nuclear Magnetic Resonance

Porosity and permeability of two typical sedimentary rocks in coal bearing strata of underground coal mines in China, i.e., mudrocks and fine-grained sandstones, were comprehensively investigated by multiple experimental methods. Measured porosity averages of the helium gas porosity (φg), MIP porosity (φMIP), water porosity (φw), and NMR porosity (φNMR) of the twelve investigated rock samples range from 1.78 to 16.50% and the measured gas permeabilities (Kg) range from 0.0003 to 2.4133 mD. Meanwhile, pore types, pore morphologies, and pore size distributions (PSD) were determined by focused ion beam scanning electron microscopy (FIB-SEM), mercury intrusion porosimetry (MIP), and low-field nuclear magnetic resonance (NMR). FIB-SEM image analyses showed that the mineral matrix pores including interparticle (interP) and intraparticle (intraP) pores with varied morphologies are the dominant pore types of the investigated rock samples while very few organic matter (OM) pores were observed. Results of the MIP and the full water-saturated NMR measurements showed that the PSD curves of the mudrock samples mostly present a unimodal pattern and nanopores with pore diameter less than 0.1 μm are their predominant pore type, while the PSD curves of the fine-grained sandstone samples are featured by a bimodal distribution. Furthermore, comparison of the full water-saturated and irreducible-water-saturated NMR measurements indicated that pores in the mudrocks are solely adsorption pores (normally pore size < 0.1 μm) whereas apart from a fraction of adsorption pores, a large part of the pores in the sandstone sample with relatively high porosity are seepage pores (normally pore size > 0.1 μm). Moreover, the PSD curves of NMR quantitatively converted from the NMR T2 spectra by T2Pc and weighted arithmetic mean (WAM) methods are in good agreement with the PSD curves of MIP. Finally, the applicability of three classic permeability estimation models based on MIP and NMR data to the investigated rock samples was evaluated.

Geochemical and geological characterization of marine–continental transitional shales from Longtan Formation in Yangtze area, South China

Abstract Although previous research has provided useful insights into unconventional shale gas resources in recent years, the geochemical and geological characteristics of marine–continental transitional shale have not been studied systematically. During the Late Permian, Longtan Formation shales were widely deposited in the Yangtze area of South China. These shales clearly indicate the need to deepen our understanding of marine–continental transitional shales. This study describes the various characteristics of black shales from the Longtan Formation in this area on the basis of a field investigation and relevant laboratory analyses. Longtan shale reservoirs, with a thickness and burial depth range of 20–650 and 800–2400 m, respectively, are usually interbedded with coal and compact sandstone reservoirs due to their special sedimentary environment. Geochemical analysis of the samples of Longtan shales from seven wells in the Yangtze area indicates the presence of high organic matters (OMs), with a total organic carbon content in the range of 0.85%–35.7% (average of 7.33%) but low hydrocarbon genetic potential (S2) with a value below 3 mg HC/g rock. The analysis of carbon isotopes and organic macerals demonstrates that the investigated samples mainly contain type III kerogen. Data from gas chromatography and gas chromatography-mass spectrometry analyses illustrate a weakly oxidizing to a weakly reducing environment, with most organic materials originating from algal-bacterial organisms and terrestrial plants. The terrestrial plants contribute significantly to the OM. The Longtan shales are thermally over-matured, and they have entered the dry-gas generation window according to Ro, production index data, and biomarker maturity ratios. X-ray diffraction analyses show that the content of brittle minerals of the Longtan shales is generally lower than that of marine shales in North America. The Longtan shales show a high clay content averaging 60.32 wt% and low calcite mineral content averaging 3.73 wt%. Field emission scanning electron microscopy shows that various types of nanometer-to micrometer-scale pores, including interparticle and intraparticle pores, OM pores, and microfractures, are well developed in the shales. Generally, high OM abundance, thermal evolution degree, clay mineral content, and pore space (porosity of 0.56%–10.6%) positively influence shale gas content (1.0%–3.8%). However, high clay content and variable reservoir thickness hinder the successful production of shale gas.

Characteristics and control mechanism of nanoscale pores in lacustrine tight carbonates: Examples from the Jurassic Da'anzhai Member in the central Sichuan Basin, China

Compared with the studies of nanoscale pores in shale, coal, and tight sandstone, studies associated with lacustrine tight carbonate nanoscale pores and their control mechanisms, particularly quantitative studies combining reservoir evaluation and geochemistry, remain scarce. To address this disparity, lacustrine tight carbonate samples collected from the Jurassic Da'anzhai Member in the central Sichuan Basin of China were quantitatively investigated.Similar to other unconventional reservoirs, lacustrine tight carbonate reservoirs contain well-developed intraparticle pores, interparticle pores, and micro-cracks with nanoscale storage spaces that dominate the full-scale reservoirs. The relatively small pores (3–5 nm) make a dominant contribution to the nanoscale storage space. Isotherms and hysteresis loops are Type II and Type H3, respectively, indicating wedge-shaped pores. However, the hysteresis loops indicate more dead-end pores, larger pores, and more complex microstructures than those found in other unconventional reservoirs.The mineral in lacustrine carbonate provides a link between the reservoir and the formation environment. Strong paleo-weathering, low salinity, a humid (rainy) paleo-climate and poor hydrodynamic conditions are favorable to improve the storage spaces and terrestrial mineral contents but harmful to the formation of authigenic minerals. Terrestrial minerals, including primarily quartz, clay, and dolomite, have well-developed nanoscale pores and are positively correlated with the nanoscale storage space, whereas authigenic minerals, primarily calcite, have strong cementation and filling effects and are negatively correlated with the nanoscale storage space.

Effect of Shale Lithofacies on Pore Structure of the Wufeng–Longmaxi Shale in Southeast Chongqing, China

Total organic carbon (TOC), optical microscopy (OPM), field emission scanning electron mi-croscopy (FE-SEM), X-ray diffraction (XRD) and nitrogen gas adsorption (N2GA) analyses were performed on shale samples from the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation (Wufeng-Longmaxi Formation) in order to explore the effect of shale lithofacies on pore structure. The results show that the Wufeng-Longmaxi shale consists of four types of pores: organic matter pores, interparticle pores, intraparticle pores and micro-fracture pores. A total of 8 kinds of shale lithofacies were identified on the basis of TOC and the ternary diagram of siliceous minerals (quartz and feldspar), clay and carbonate. The geological properties have substantial heterogeneity in these shale lithofacies. The volumes of organic matter (OM), clay-related and brittle mineral-related pores are 0.00119-0.01262 cm3/g, 0.00080-0.00260 cm3/g, and 0.00122-0.00215 cm3/g, with an average proportion of 51.85 %, 26.44 % ...

Impact of tectonism on pore type and pore structure evolution in organic-rich shale: Implications for gas storage and migration pathways in naturally deformed rocks

Tectonism significantly affects the pore type and pore structure evolution of organic-rich shale. The Lower Cambrian Lujiaping Shale in the northeastern of the upper Yangtze area is a significant marine shale being studied for shale gas exploration in South China. Here, we use two groups of Lujiaping Shale samples, such as brittle deformation shales (BDS) and ductile deformation shales (DDS), to investigate the relationship between tectonism and pore structure using a combination of mineralogy, organic geochemistry, low-pressure nitrogen adsorption, low-field nuclear magnetic resonance (NMR), optical microscopy, and high-resolution scanning electron microscopy (SEM). Results indicate that the samples are quartz, carbonate, and clay rich. Total organic carbon (TOC) content ranges between 2.27% and 5.88%, and vitrinite reflectance (Ro) measured between 2.95% and 4.11%. Helium porosity lies between 3.02% and 4.66% in BDS and 3.16%-4.29% in DDS. In addition, four major pore types can be identified and classified by their formation mechanism, location, geometry, and connectivity, which we named type I (pore within or between organic and mineral particles), type II (pore in admixtures), type III (micro-channel), and type IV (micro-fracture). Under the BDS, the interparticle (interP) pores, micro-channels, and micro-fractures are more developed, the macropores (＞50 nm) increase, the connectivity and porosity are enhanced. The intraparticle (intraP) pores, micro-channels, and micro-fractures are dominant in DDS, the micropores (< 2 nm) increase and the connectivity is enhanced, whereas the porosity decreases. Meanwhile, pore network within the admixtures of organic matter (OM) and clays can also contribute to gas storage and migration pathways in both BDS and DDS, in addition to other pore types. However, OM pores are poorly-developed in samples. Our findings provide a key component for further evaluation of the exploration and development potential of the Lujiaping Shale in the complex tectonic areas of South China.

Microstructural characterization of pores in marine shales of the Lower Silurian Longmaxi Formation, southeastern Sichuan Basin, China

Abstract Understanding the complexities of sedimentary pore systems is the key to understanding the mechanisms that lead to shale gas accumulation. In this study, the microstructures, networks, and connectivity of pores in marine shales of the Longmaxi Formation in the southeastern Sichuan Basin are investigated using a combination of qualitative and quantitative methods. 2D and 3D characterizations of the formation provide an opportunity to describe the types of pores, pore networks and pore connectivity in these shales. The study's results show that nearly all pores are nanosized and that organic matter (OM) pores are the most common but also include interparticle (InterP) pores, intraparticle (IntraP) pores and micro-fracture pores. Reconstructed 3D models show that there is limited connectivity of pores. Gas adsorption analysis and statistical results indicate that nearly 95% of the pores are micro-to meso-scale and account for approximately 23% and 73% of the pore space, respectively. A combination of image processing and calculations also shows that OM pores account for approximately 87% of all pores, and as such, the pore networks are dominated by OM pores. OM pores are associated with discontinuous occurrences of organic matter, which results in relatively poor connectivity.

Pore characteristics and dominant controlling factors of overmature shales: A case study of the Wangyinpu and Guanyintang Formations in the Jiangxi Xiuwu Basin

Because of the great potential for hydrocarbon generation, the Lower Cambrian Wangyinpu and Guanyintang Formations of the Jiangxi Xiuwu Basin have become the most important targets for shale-gas exploration in the Jiangxi province. We investigate the pore characteristics and main controlling factors of overmature shale using field emission-scanning electron microscopy, image-processing software (i.e., the Particles [Pores] and Crack Analysis System), X-ray diffraction, and gas-adsorption experiments. The results show that the shales have a high abundance of organic matter (OM), over maturity, and highly siliceous mineral content. The kerogen type is identified as type I. OM pores are the most developed, followed by interparticle (interP) pores and intraparticle (intraP) pores. We combine complementary image processing and gas-adsorption methods to reveal that micropores are mainly from OM pores; mesopores are from OM pores and interP pores; and macropores are from OM pores, interP pores, and intraP pores. Although the number of micropores is at a maximum, the total contribution of mesopores and macropores to the pore volume (PV) is larger than that of micropores. However, the specific surface area (SSA) is mainly from the micropores. OM content and maturity are the main controlling factors for the development of pore structures. Because of overmaturity, OM loses its potential for hydrocarbon generation and new pores cannot be produced. Gas loss leads to reservoir pressure drop, and the pores generated during the mature stage collapse and even disappear because they lack support. Therefore, PV, SSA, and porosity decrease when the OM content is more than 10%. When the OM content is less than 10%, most of the OM pores are preserved because they are protected by the skeleton particles.

Porosity classification from thin sections using image analysis and neural networks including shallow and deep learning in Jahrum formation

The porosity within a reservoir rock is a basic parameter for the reservoir characterization. The present paper introduces two intelligent models for identification of the porosity types using image analysis. For this aim, firstly, thirteen geometrical parameters of pores of each image were extracted using the image analysis techniques. The extracted features and their corresponding pore types of 682 pores were used for training two intelligent models, BPN (back-propagation network) and SAE (stacked autoencoder). The trained models take the geometrical properties of pores to classify the type of six porosity types including intra-particle, inter-particle, vuggy, moldic, biomoldic, and fracture. The MSE values for the BPN and SAE models were found to be 0.0042 and 0.0038, respectively. The precision, recall, and accuracy of the intelligent models for classifying the types of pores were calculated. The BPN model was able to correctly recognize 193 intra-particle pores out of 197 ones, 45 inter-particle pores out of 50 ones, 7 vuggy pores out of 9 ones, 10 moldic pores out of 12 ones, 2 biomoldic pores out of 3 ones, and 6 fractures out of 7 ones. Also the SAE model was able to correctly classify 193 intra-particle pores out of 197 ones, 46 inter-particle pores out of 50 ones, 8 vuggy pores out of 9 ones, 10 moldic pores out of 12 ones, 3 biomoldic pores out of 3 ones, and 7 fractures out of 7 ones. The results obtained showed that the SAE model carried out a bit more accuracy for classification of the inter-particle, vuggy, biomoldic, and fracture pores.

Mineral compositional controls on the porosity of black shales from the Wufeng and Longmaxi Formations (Southern Sichuan Basin and its surroundings) and insights into shale diagenesis

The effects of brittle minerals in shale diagenesis on shale pores remain controversial and it is difficult to quantify directly. However, the relationship between brittle minerals and shale pores could provide indirect guidance regarding diagenesis processes in post-mature marine shales. In this study, the pore size distribution was determined, and the relationship between pore volume and shale composition was examined in shale samples with different total organic carbon contents from the Wufeng and Longmaxi Formations, with the objective of distinguishing pore size ranges in organic matter and inorganic minerals, respectively, and studying shale diagenesis. The samples of the Wufeng and Longmaxi shales are composed of clay minerals, calcite, dolomite, quartz, feldspar, and some minor components. The pore size distributions, which were determined using nitrogen adsorption isotherm analysis of shale and kerogen, show similar trends for pore sizes less than approx. 6.5 nm but different trends for larger pore sizes. Mercury injection saturation shows that macropores account for 14.4–22% of the total pore volume. Based on a series of crossplots describing the relationships between shale composition and pore volume or porosity associated with different pore sizes as well as on scanning electron microscopy observations, organic matter pores were found to comprise most of the micro-mesopores (pore diameters &lt; 6.5 nm). Organic matter pores and intraparticle pores associated with carbonate constitute the majority of mesopores (pore diameters 6.5–50 nm). Finally, interparticle pores associated with quartz comprise the majority of the macropores. The mesopores associated with carbonate were formed by dissolution during diagenesis, whereas the macropores associated with quartz are the remainders of the original interparticle pores. Mesopore volumes increase with increasing carbonate content while macropore volumes decrease due to the ‘pore size controlled solubility’ effect, which causes dissolved calcium carbonate to precipitate in larger macropores.

Capacitive deionization with wire-shaped electrodes

Capacitive deionization is a desalination technology to remove ions from aqueous solution in a cyclic manner by applying a voltage between pairs of porous electrodes. We describe the dynamics of this process by including a possible rate limitation in the transport of ions from the interparticle pore space in the electrode into intraparticle pores, where electrical double layers are formed. The theory includes the effect of chemical surface charge located in the intraparticle pores, which is present in the form of acidic and basic groups. We present dynamic data of salt adsorption for electrodes with and without coated ion-exchange membranes. Experiments were conducted in a CDI cell geometry based on wire-shaped electrodes placed together. The electrodes consisted of graphite rods coated with a layer of porous carbon. To fabricate this layer, we examined two procedures that involve the use of different solvents: acetone and N-methyl-2-pyrrolidone (NMP). We found that electrodes prepared with acetone had a lower salt adsorption compared to electrodes prepared with NMP. At equilibrium, the theory is in agreement with data, and this agreement underpins the effect of chemical surface groups on electrode performance. Under dynamic conditions, our theory describes reasonably well desalination cycles.

Understanding Model Crude Oil Component Interactions on Kaolinite Silicate and Aluminol Surfaces: Toward Improved Understanding of Shale Oil Recovery

Shale oil is currently of interest for unconventional resource exploration and development. Understanding the mechanism of interaction between the complex mixture of organic compounds in shale oil and minerals making up the reservoir rock–oil interface will assist recovery. In this study, molecular dynamics simulation is used to study the adsorption characteristics of a model oil mixture within nanoscale intraparticle pores of kaolinite minerals, which form pore-filling structures in shale rock. To better understand the effects of oil composition, temperature, and pressure on the adsorption properties of the model oil mixture, a range of temperatures (298, 323, 348, and 373 K) and pressures (1, 50, 100, and 200 bar) representing up to reservoir conditions were used. This study shows that adsorption and arrangement of oil molecules is dependent on the surface of kaolinite and the distance away from it. The simulations show polar compounds are likely to be adsorbed on aluminol kaolinite basal surfaces, whil...

Pore Characteristics Analysis of Shale from Sichuan Basin, China

Pore characteristics are significant for shale gas exploration and production. In this paper, the method of field emission scanning electron Microscopes (FE-SEM) was applied to qualitatively describe minerals and pore structures of shale samples. Low pressure nitrogen adsorption-desorption and carbon dioxide adsorption were applied to analyse meso-pores and micro-pores respectively. Inter-particle pores are always associated with rigid mineral grains and intra-particle pores are mainly located in unstable minerals. The BET (Brunauer–Emmett–Teller) surface area of Longmaxi Formation (LMX) is 5.47m 2 /gr and 16.33m 2 /gr of Wufeng Formation (WF). N 2 and CO 2 adsorption shows that the diameter of micro-pores in the LMX and WF formation is approximately 1nm. Most meso-pores in WF formations range from 2nm - 20nm, while meso-pores existing in LMX formations range from 2nm - 30nm.

Quantitative Analysis of Nanopore Structural Characteristics of Lower Paleozoic Shale, Chongqing (Southwestern China): Combining FIB-SEM and NMR Cryoporometry

Characterizing nanopore structure is one of the most important factors in understanding gas storage and transport in shale reservoirs, but remains a significant challenge. In this work, we combine the benefits of Focused Ion Beam Scanning Electron Microscopy (FIB-SEM) and Nuclear Magnetic Resonance Cryoporometry (NMR-C) to characterize the nanopore structure of lower Paleozoic shales from Chongqing, southwestern China. Mineral composition is qualified through X-ray Energy Dispersive Spectroscopy (EDS) and Field-Emission Scanning Electron Microscopy (FE-SEM). Voids in 2D micrographs are classified into types of meso- and/or microfractures, inter particle pores (InterP pores), intraparticle pores (IntraP pores), and pores in organic matter (OM pores). An Otsu thresholding algorithm and an edge detection algorithm (in Avizo) are used to segment OM, InterP, and IntraP pores and to establish 3D pore structure for pore-network modeling (PNM). The pore size distribution (PSD) is measured via PNM and compared to ...

Insight into the Pore Structure of Tight Gas Sandstones: A Case Study in the Ordos Basin, NW China

A wide spectrum of pore size distributions (PSD) exists in tight gas sandstones, ranging from several nanometers to several hundred micrometers in radius, which controls both the physical rock-flow capacity and storage capacity. Thin-section, scanning electron microscope (SEM), field emission scanning electron microscope (FE-SEM), high-pressure mercury intrusion (HPMI), constant-rate mercury intrusion (CRMI) and micro-CT scanning experiments are performed on tight sandstone samples from the eighth member of the Middle Permian Shihezi Formation (P2h8) in the Ordos Basin to better understand the pore-system characteristics of a tight gas sandstone. The results of this case study show that various types of pores exist in the P2h8 sandstones: residual intergranular pores, intraparticle dissolution pores, intercrystalline pores, and small micro-cracks are observed. We combine HPMI and CRMI to determine the PSD; the pore sizes range from 3.7 nm to 600 μm in radius. The multimodal PSD is characterized by two bro...

Investigation of the pore structures and fractal characteristics of marine shale reservoirs using NMR experiments and image analyses: A case study of the Lower Cambrian Niutitang Formation in northern Guizhou Province, South China

The pore structures and fractal characteristics of the organic-rich marine shales of the Lower Cambrian Niutitang Formation in northern Guizhou Province were investigated using nuclear magnetic resonance (NMR) and field emission scanning electron microscopy (FE-SEM). In this paper, the NMR fractal dimensions and pore morphology fractal dimensions were calculated based on NMR T2 spectra and SEM image analyses. The relationships among the total organic carbon (TOC) contents, mineral compositions, porosities, permeabilities, CH4 adsorptions and NMR fractal dimensions (DN1 and DN2) of the shales are discussed, and the properties of the different pores are quantitatively analyzed using pore extraction based on SEM images. Moreover, the geological significances of fractal dimensions are discussed. The results reveal that DN1 is positively correlated with TOC contents, whereas DN2 does not have an apparent relationship with TOC contents. The quartz content presents a positive linear correlation with DN1 and DN2, whereas the clay content is positively correlated with DN1 but is not correlated with DN2. DN1 increases with decreases in porosity and permeability, and DN2 increases with increases in porosity but is not correlated with permeability. The organic matter (OM) pores are smaller in size and have a larger number than the interparticle pores and intraparticle pores. The interparticle pores have the smallest average roundness values, implying that their roundness is the worst. Moreover, the fractal dimension of the OM pores is the largest, whereas the fractal dimension of the intraparticle pores is the smallest. The pore morphology fractal dimension has no apparent relationship with the roundness but shows a negative correlation with pore size. Shale samples with larger surface fractal dimensions have higher methane adsorption capacities.

Multiscale modeling of fixed-bed reactors with porous (open-cell foam) non-spherical particles: Hydrodynamics

An accurate numerical model is proposed to simulate flow through cylindrical fixed-bed reactors with randomly packed porous non-spherical particles. The length scale for flow outside the porous particles (made of open-cell foam) is O(102) higher than the size of the internal micro-pores of the particles. To capture the flow at these two different length scales, a multiscale modeling approach, derived using volume averaging theory (VAT), is developed. The flow through and around the porous particles is computed as a single hydrodynamic field in a Cartesian computational domain. The flow within the inter-particle space is fully resolved, whereas, flow at the scale of the intra-particle micro-pores is not resolved and instead represented by closure terms. Random packings of cubic and cuboid particles in cylindrical columns of different diameter are generated using a glued-sphere Discrete Element Method (DEM) approach. The packing structures for different particle-column combinations are analysed. The effects of particle size/shape, column diameter and internal porosity of the particles on the overall pressure drop and flow distribution are investigated. The macroscopic Reynolds number (based on the particle equivalent diameter and the superficial velocity of the bed) is varied from 0.1 to 400. The effect of Reynolds number on pressure drop is analyzed, as well as the reduction in pressure drop due to the presence of the intra-particle pores. In addition, our numerical simulations have helped to elucidate the detailed fluid-solid interaction in complex bi-disperse, dual porosity porous media.

Geological and geochemical characterization of lacustrine shale: A case study of the Jurassic Da'anzhai member shale in the central Sichuan Basin, southwest China

Although numerous progresses have been achieved in characterizing marine shales, studies that are associated with lacustrine shales are limited. To study lacustrine shales, samples were collected from the Jurassic Da'anzhai Member in the central Sichuan Basin of China, and their mineralogical, reservoir, OM, and paleoenvironmental characteristics were determined, as well as the relationships between them. Analysis of trace elements reveals that the shales formed in paleoenvironments that were oxic to suboxic, dry to humid, had moderate to strong weathering, and were characterized by fresh to salt water conditions. These environments are more variable than those of marine shales. The paleoenvironmental conditions and mineralogy of the shales, particularly the oxic to suboxic paleo-redox conditions, resulted in the relatively low levels (0.11–2.18%, average 0.97%). However, based on evaluation criteria for continental source rocks, the OM is of high quality because of its high level of maturity (Ro: 0.95–1.43; Tmax: 428–500 °C) and favorable kerogen type (II2). There are well-developed intraparticle pores, interparticle pores, and microcracks. The SBET (5.42–10.69 m2/g, average 6.92 m2/g) and VBJH (1.19–4.10 mL/100 g, average 2.97 mL/100 g) values also indicate good nanoscale storage space. Terrestrial minerals (i.e., quartz and clay) and authigenic carbonate minerals (i.e., calcite) are, respectively, positively and negatively correlated with the nanoscale storage space,. Small pores (3–5 nm) dominate the nanoscale storage space. The isotherms and hysteresis loops are of Type Ⅱ and Type H3, respectively, which indicates wedge-shaped pores. However, the hysteresis loops indicate that the lacustrine shale has more dead-end pores and larger pores with more complex microstructures than other lacustrine reservoirs. In general, the Da'anzhai lacustrine shale has the potential for unconventional oil and gas exploration. The lacustrine shale's mineralogy, reservoirs, and OM are closely related to each other, and their differences are mainly caused by the paleoenvironmental conditions in which the shale formed.