scholarly journals Pore Structure and Fractal Characteristics of Different Shale Lithofacies in the Dalong Formation in the Western Area of the Lower Yangtze Platform

Minerals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 72 ◽  
Author(s):  
Longfei Xu ◽  
Jinchuan Zhang ◽  
Jianghui Ding ◽  
Tong Liu ◽  
Gang Shi ◽  
...  
Keyword(s):  
Pore Structure ◽  
Fractal Dimensions ◽  
Upper Permian ◽  
Hydrocarbon Generation ◽  
Yangtze Platform ◽  
Dalong Formation ◽  
Fractal Characteristics ◽  
Lower Yangtze ◽  
Siliceous Shale ◽  
Organic Pores

The purpose of this article was to quantitatively investigate the pore structure and fractal characteristics of different lithofacies in the upper Permian Dalong Formation marine shale. Shale samples in this study were collected from well GD1 in the Lower Yangtze region for mineral composition, X-ray diffraction (XRD), and nitrogen adsorption–desorption analysis, as well as broad-ion beam scanning electron microscopy (BIB-SEM) observation. Experimental results showed that the TOC (total organic carbon) content and vitrinite reflectance (Ro) of the investigated shale samples were in the ranges 1.18–6.45% and 1.15–1.29%, respectively, showing that the Dalong Formation shale was in the mature stage. XRD results showed that the Dalong Formation shale was dominated by quartz ranging from 38.4% to 54.3%, followed by clay minerals in the range 31.7–37.5%, along with carbonate minerals (calcite and dolomite), with an average value of 9.6%. Based on the mineral compositions of the studied samples, the Dalong Formation shale can be divided into two types of lithofacies, namely siliceous shale facies and clay–siliceous mixed shale facies. In siliceous shale facies, which were mainly composed of organic pores, the surface area (SA) and pore volume (PV) were in the range of 5.20–10.91 m2/g and 0.035–0.046 cm3/g, respectively. Meanwhile, the pore size distribution (PSD) and fractal dimensions were in the range 14.2–26.1 nm and 2.511–2.609, respectively. I/S (illite-smectite mixed clay) was positively correlated with SA, PV, and fractal dimensions, while illite had a negative relationship with SA, PV, and fractal dimensions. I/S had a strong catalytic effect on organic matter for hydrocarbon generation, which was beneficial to the development of organic micropores, so I/S was conducive to pore structure complexity and the increase in SA and PV, while illite easily filled organic pores, which was not beneficial to the improvement of pore space. In clay–siliceous mixed shale facies, which mainly develop inorganic pores such as intergranular pores, SA and PV were in the range of 6.71–11.38 m2/g and 0.030–0.041 cm3/g, respectively. Meanwhile, PSD and fractal dimensions were in the range of 14.3–18.9 nm and 2.563–2.619, respectively. Quartz and I/S showed weak positive correlations with SA, PV, and fractal dimensions. The various compact modes between quartz particles and the disorder of I/S were conducive to the complexity of pore structure and the improvement of SA and PV. The research findings can provide a reference for the optimization and evaluation of shale gas favorable area of the Lower Yangtze Platform.

scholarly journals Coupling between Source Rock and Reservoir of Shale Gas in Wufeng-Longmaxi Formation in Sichuan Basin, South China

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2679
Author(s):  
Yuying Zhang ◽  
Shu Jiang ◽  
Zhiliang He ◽  
Yuchao Li ◽  
Dianshi Xiao ◽  
...  
Keyword(s):  
Source Rock ◽  
Shale Gas ◽  
Sichuan Basin ◽  
Gas Content ◽  
Potential Zone ◽  
Hydrocarbon Generation ◽  
Gas Generation ◽  
Longmaxi Formation ◽  
Siliceous Shale ◽  
Organic Pores

In order to analyze the main factors controlling shale gas accumulation and to predict the potential zone for shale gas exploration, the heterogeneous characteristics of the source rock and reservoir of the Wufeng-Longmaxi Formation in Sichuan Basin were discussed in detail, based on the data of petrology, sedimentology, reservoir physical properties and gas content. On this basis, the effect of coupling between source rock and reservoir on shale gas generation and reservation has been analyzed. The Wufeng-Longmaxi Formation black shale in the Sichuan Basin has been divided into 5 types of lithofacies, i.e., carbonaceous siliceous shale, carbonaceous argillaceous shale, composite shale, silty shale, and argillaceous shale, and 4 types of sedimentary microfacies, i.e., carbonaceous siliceous deep shelf, carbonaceous argillaceous deep shelf, silty argillaceous shallow shelf, and argillaceous shallow shelf. The total organic carbon (TOC) content ranged from 0.5% to 6.0% (mean 2.54%), which gradually decreased vertically from the bottom to the top and was controlled by the oxygen content of the bottom water. Most of the organic matter was sapropel in a high-over thermal maturity. The shale reservoir of Wufeng-Longmaxi Formation was characterized by low porosity and low permeability. Pore types were mainly <10 nm organic pores, especially in the lower member of the Longmaxi Formation. The size of organic pores increased sharply in the upper member of the Longmaxi Formation. The volumes of methane adsorption were between 1.431 m3/t and 3.719 m3/t, and the total gas contents were between 0.44 m3/t and 5.19 m3/t, both of which gradually decreased from the bottom upwards. Shale with a high TOC content in the carbonaceous siliceous/argillaceous deep shelf is considered to have significant potential for hydrocarbon generation and storage capacity for gas preservation, providing favorable conditions of the source rock and reservoir for shale gas.

scholarly journals The Impacts of Matrix Compositions on Nanopore Structure and Fractal Characteristics of Lacustrine Shales from the Changling Fault Depression, Songliao Basin, China

Minerals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 127 ◽  
Author(s):  
Zhuo Li ◽  
Zhikai Liang ◽  
Zhenxue Jiang ◽  
Fenglin Gao ◽  
Yinghan Zhang ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Pore Structure ◽  
Fractal Dimensions ◽  
Organic Medium ◽  
Songliao Basin ◽  
Sem Images ◽  
Fractal Characteristics ◽  
Inorganic Mineral ◽  
Nanopore Structure ◽  
High Fractal Dimension

The Lower Cretaceous Shahezi shales are the targets for lacustrine shale gas exploration in Changling Fault Depression (CFD), Southern Songliao Basin. In this study, the Shahezi shales were investigated to further understand the impacts of rock compositions, including organic matters and minerals on pore structure and fractal characteristics. An integrated experiment procedure, including total organic carbon (TOC) content, X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), low pressure nitrogen physisorption (LPNP), and mercury intrusion capillary pressure (MICP), was conducted. Seven lithofacies can be identified according to on a mineralogy-based classification scheme for shales. Inorganic mineral hosted pores are the most abundant pore type, while relatively few organic matter (OM) pores are observed in FE-SEM images of the Shahezi shales. Multimodal pore size distribution characteristics were shown in pore width ranges of 0.5–0.9 nm, 3–6 nm, and 10–40 nm. The primary controlling factors for pore structure in Shahezi shales are clay minerals rather than OM. Organic-medium mixed shale (OMMS) has the highest total pore volumes (0.0353 mL/g), followed by organic-rich mixed shale (ORMS) (0.02369 mL/g), while the organic-poor shale (OPS) has the lowest pore volumes of 0.0122 mL/g. Fractal dimensions D1 and D2 (at relative pressures of 0–0.5 and 0.5–1 of LPNP isotherms) were obtained using the Frenkel–Halsey–Hill (FHH) method, with D1 ranging from 2.0336 to 2.5957, and D2 between 2.5779 and 2.8821. Fractal dimensions are associated with specific lithofacies, because each lithofacies has a distinctive composition. Organic-medium argillaceous shale (OMAS), rich in clay, have comparatively high fractal dimension D1. In addition, organic-medium argillaceous shale (ORAS), rich in TOC, have comparatively high fractal dimension D2. OPS shale contains more siliceous and less TOC, with the lowest D1 and D2. Factor analysis indicates that clay contents is the most significant factor controlling the fractal dimensions of the lacustrine Shahezi shale.

Nano-Pore Structure and Fractal Characteristics of Shale Gas Reservoirs: A Case Study of Longmaxi Formation in Southeastern Chongqing, China

2021 ◽  
Vol 21 (1) ◽  
pp. 343-353
Author(s):  
Wei-Dong Xie ◽  
Meng Wang ◽  
Xiao-Qi Wang ◽  
Yan-Di Wang ◽  
Chang-Qing Hu
Keyword(s):  
Fractal Dimension ◽  
Pore Structure ◽  
Shale Gas ◽  
Fractal Dimensions ◽  
Gas Reservoirs ◽  
Longmaxi Formation ◽  
Shale Gas Reservoirs ◽  
Fractal Characteristics ◽  
Temperature Liquid ◽  
Menger Sponge

Pore structure and fractal dimensions can characterize the adsorption, desorption and seepage characteristics of shale gas reservoirs. In this study, pore structure, fractal characteristics and influencing factors were studied of the Longmaxi formation shale gas reservoir in southeastern Chongqing, China. Scanning electron microscopy was used to describe the characteristics of various reservoirs. High pressure mercury intrusion and low temperature liquid N2 and CO2 adsorption experiments were used to obtain pore structure parameters. V–S model, FHH model and Menger sponge model were selected to calculate the micropore, mesopore and macropore fractal dimensions, respectively. The results show that organic matter pores, inter-granular pores, intra-granular pores and micro-fractures are developed within the shale, and the pore morphology is mostly ink pores and parallel plate pores with aperture essentially in the 1–2 nm and 2–50 nm ranges. Moreover, macropores are the most complex in these samples, with mesopores being less complex than macropores, and the micropores being the simplest. D1 (micropore fractal dimension) ranges from 2.31 to 2.50, D2 (mesopore fractal dimension) ranges from 2.74 to 2.83, D3 (macropore fractal dimension) ranges from 2.87 to 2.95, and Dt (comprehensive fractal dimension) ranges from 2.69 to 2.83 of fractal characteristics. D1 and D2 are mainly controlled by TOC content, while D3 and Dt are mainly controlled by brittle and clay mineral content. These results may be helpful for exploration and the development of shale gas in southeastern Chongqing, China.

scholarly journals An Investigation of Fractal Characteristics of Marine Shales in the Southern China from Nitrogen Adsorption Data

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Jian Xiong ◽  
Xiangjun Liu ◽  
Lixi Liang
Keyword(s):  
Fractal Dimension ◽  
Pore Structure ◽  
Southern China ◽  
Fractal Dimensions ◽  
Nitrogen Adsorption ◽  
Mean Value ◽  
Relative Pressure ◽  
Pore Surface ◽  
Adsorption Sites ◽  
Fractal Characteristics

We mainly focus on the Permian, Lower Cambrian, Lower Silurian, and Upper Ordovician Formation; the fractal dimensions of marine shales in southern China were calculated using the FHH fractal model based on the low-pressure nitrogen adsorption analysis. The results show that the marine shales in southern China have the dual fractal characteristics. The fractal dimensionD1at low relative pressure represents the pore surface fractal characteristics, whereas the fractal dimensionD2at higher relative pressure describes the pore structure fractal characteristics. The fractal dimensionsD1range from 2.0918 to 2.718 with a mean value of 2.4762, and the fractal dimensionsD2range from 2.5842 to 2.9399 with a mean value of 2.8015. There are positive relationships between fractal dimensionD1and specific surface area and total pore volume, whereas the fractal dimensionsD2have negative correlation with average pore size. The larger the value of the fractal dimensionD1is, the rougher the pore surface is, which could provide more adsorption sites, leading to higher adsorption capacity for gas. The larger the value of the fractal dimensionD2is, the more complicated the pore structure is, resulting in the lower flow capacity for gas.

FRACTAL CHARACTERISTICS OF NANOSCALE PORES IN SHALE AND ITS IMPLICATIONS ON METHANE ADSORPTION CAPACITY

Fractals ◽  
2019 ◽  
Vol 27 (01) ◽  
pp. 1940014 ◽  
Author(s):  
YU LIU ◽  
YANMING ZHU ◽  
YANG WANG ◽  
SHANGBIN CHEN
Keyword(s):  
Adsorption Capacity ◽  
Rough Surface ◽  
Large Scale ◽  
Fractal Theory ◽  
Fractal Dimensions ◽  
Methane Adsorption ◽  
Small Scale ◽  
Sem Images ◽  
Fractal Characteristics ◽  
Organic Pores

Pore structure in shale controls the gas storage mechanism and gas transport behaviors. Since nanoscale pores in shale matrix have fractal characteristics, fractal theory can be used to study its structure. In addition, fractal method has its own advantages to investigate nanopores in shale, especially for the heterogeneity and irregularity of nanopores in shale. In this work, fractal features of nanoscale pores and the implication on methane adsorption capacity of shale were investigated by employing low pressure nitrogen adsorption, scanning electron microscopy (SEM), and methane adsorption experiments. Frenkel–Halsey–Hill (FHH) model was also used to calculate the fractal parameters of nanoscale pores in shale. The results showed that nanoscale pores in 12 shale samples have obvious fractal features. All the fractal curves of these shale samples can be divided into two segments, which are cut off by [Formula: see text], and the fractal dimensions of these two segments vary from 2.48 to 2.92 [Formula: see text] and 2.42 to 2.80 [Formula: see text], respectively. Based on SEM images, it is found that self-similarity of organic pore systems in shales refers to two aspects. One is that relatively large-scale and small-scale pores have similar formation properties and types, which are of elliptical shape with rough surface. The other is that some small-scale pores are formed by rough surface of relatively large pores. The results also demonstrate that methane adsorption capacity of shale samples increase with increasing total organic carbon (TOC) contents. This is mainly because organic matter is rich in pores and has relatively large fractal dimension values. Larger fractal dimensions indicate rougher pore surfaces and could form more small-scale organic pores. These organic pores would provide more space for methane adsorption.

scholarly journals Nanoscale pore characteristics and fractal characteristics of organic-rich shale: An example from the lower Cambrian Niutitang Formation in the Fenggang block in northern Guizhou Province, South China

2018 ◽  
Vol 37 (1) ◽  
pp. 273-295 ◽  
Author(s):  
Yang Gu ◽  
Wenlong Ding ◽  
Min Yin ◽  
Baocheng Jiao ◽  
Siyu Shi ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Pore Structure ◽  
Carbon Content ◽  
South China ◽  
Fractal Dimensions ◽  
Nitrogen Adsorption ◽  
Organic Carbon Content ◽  
Structure Parameters ◽  
Pore Characteristics ◽  
Fractal Characteristics

Organic-rich marine shale in South China has great potential for gas generation, and the pore structure has a considerable influence on the enrichment of shale gas. The nanoscale pore characteristics and fractal characteristics of the Niutitang shales in the Fenggang block were studied by means of methane adsorption and low-pressure nitrogen adsorption experiments, porosity and permeability tests, X-ray diffraction analyses, organic geochemical analyses, and field emission scanning electron microscopy. The fractal geometry of the pore structure was assessed, and the factors influencing the pore structure were determined. We used a fractal Frenkel–Halsey–Hill-based method to obtain the fractal dimensions D1 and D2 by nitrogen adsorption at relative pressures of 0–0.5 and 0.5–1, respectively. The relationships between the shale pore structure parameters and the fractal dimensions, the mineral composition, the total organic carbon content, and the pore structure parameters of shale are discussed. In addition, the significance of D1 and D2 and the implications of the fractal dimension for the adsorption capacity of shale are investigated. The results show that the two fractal dimensions are positively correlated with total organic carbon content and specific surface area, negatively correlated with quartz content and average pore diameter, but have a weak relationship with clay mineral content and total pore volume. The Niutitang shale samples are dominated by mesopores, and the pore structure is complicated. The results presented here indicate that fractal analyses represent an effective method of characterizing the complexity of pore structure.

Study on Porous Structure and Fractal Characteristics of Oil Shale and Semicoke

2013 ◽  
Vol 868 ◽  
pp. 276-281
Author(s):  
Li Mei Zhao ◽  
Jie Liang ◽  
Lu Xin Qian
Keyword(s):  
Porous Structure ◽  
Pore Structure ◽  
Oil Shale ◽  
Fractal Dimensions ◽  
Isothermal Adsorption ◽  
The Matrix ◽  
Fractal Characteristics ◽  
Adsorption Desorption ◽  
Desorption Method ◽  
Skeleton Structure

In order to find the change rule of porous structure of oil shale during pyrolysis, the Huadian oil shale samples were heated to final temperature of 300°C400°C500°C600°C700°C. The pore structure and pore size distribution of oil shale and produced semi-cokes were measured by N2 isothermal adsorption/desorption method. The fractal characteristics and other parameters of porous structures were then analyzed in detail. The results indicate that the pores in oil shale were open at one direction while the pores in semi-cokes could be observed from two or even four directions. The pore sizes of semi-cokes were mostly between 3-5 nm; and the pore volume increased at a quickest rate when pyrolysis temperature increased from 400 to 600 °C. Oil shale and its semi-cokes all showed obvious fractal characteristics, whereas oil shale and the semi-coke from 600 °C gave the lowest fractal dimensions; this means that the matrix of oil shale tended to keep its original skeleton structure and the pore structure of semi-cokes from high temperatures became regular after devolatilization during the pyrolysis.

Study on the pore structure and fractal characteristics on shale rock and isolated organic matter in lacustrine shales from the Changling fault depression in the Songliao Basin, China

2021 ◽  
pp. 1-67
Author(s):  
Zhikai Liang ◽  
Zhenxue Jiang ◽  
Zhuo Li ◽  
Fenglin Gao ◽  
Chengxi Wang ◽  
...  
Keyword(s):  
Organic Matter ◽  
Pore Structure ◽  
Higher Plants ◽  
Fractal Dimensions ◽  
Close Correlation ◽  
Songliao Basin ◽  
Thermal Maturity ◽  
Significant Difference ◽  
Fractal Characteristics ◽  
Shale Reservoir

The stock of shale gas in the Shahezi shale reservoir in Changling fault depression, Songliao basin is believed to be worth exploring. To conduct an in-depth study on the pore structure and fractal characterization of organic matter (OM) can help better understand the pore system of shale reservoir, which has implications for the exploration of lacustrine shale. In order to demonstrate the nanoscale pore structure and irregularity of the isolated OM, we collected a large number of samples and then conducted a series of laboratory experiments, such as the XRD, SEM, CO2, and N2 adsorption experiments conducted to determine the pore structure parameters and reveal their heterogeneity according to FHH theory. As suggested by the experimental results, the pore volume of the isolated OM ranges between 0.034 and 0.056 cm3/g, which is approximately 0.90-3.06 times that of bulk shale samples. As for the fractal dimensions D1 (2.594 on average) and D2 (2.657 on average) of bulk shale, they are larger as compared to isolated OM, indicating that inorganic minerals can make a significant difference to the heterogeneity of shale pores. The fractal dimensions (D1 and D2) of bulk shales show a close correlation with the parameters of pore structure, while there is no significant correlation observed between the dimensions of isolated OM and its parameters. In addition, thermal maturity and solid bitumen have only limited impact on the OM pore structure of isolated OM samples. Then, we conducted a further research to reveal that the insoluble OM macerals derived from terrestrial higher plants can be used to explain the difference in pore structure and heterogeneity between isolated OM samples. Therefore, we arrived at the conclusion that the composition of macerals depends on the exact pore structure and fractal characteristics of isolated OM samples with similarity in thermal maturity

Pore Size Distribution and Fractal Characteristics of the Nanopore Structure in Organic-Rich Shales Using the Neimark-Kiselev Fractal Approach

2021 ◽  
Vol 21 (1) ◽  
pp. 646-658
Author(s):  
Mingming Wei ◽  
Li Zhang ◽  
Yongqiang Xiong ◽  
Ping’an Peng ◽  
Yiwen Ju
Keyword(s):  
Pore Structure ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Shale Gas ◽  
Fractal Dimensions ◽  
Clay Content ◽  
Scientific Basis ◽  
Fractal Approach ◽  
Fractal Characteristics

Shale gas has been playing an increasingly important role in meeting global energy demands. The heterogeneity of the pore structure in organic-rich shales greatly affects the adsorption, desorption, diffusion and flow of gas. The pore size distribution (PSD) is a key parameter of the heterogeneity of the shale pore structure. In this study, the Neimark-Kiselev (N-K) fractal approach was applied to investigate the heterogeneity in the PSD of the lower Silurian organic-rich shales in South China using low-pressure N2 adsorption, total organic carbon (TOC) content, maturity analysis, X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) measurements. The results show that (1) the fractal dimension DN-K obtained by N-K theory better represents the heterogeneity of the PSD in shale at an approximately 1–100 nm scale. The DN-K values range from 2.3801 to 2.9915, with a mean of 2.753. The stronger the PSD heterogeneity is, the higher the DN-K value in shale is. (2) The clay-rich samples display multimodal patterns at pore sizes greater than 20 nm, which strongly effect the PSD heterogeneity. Quartz-rich samples display major peaks at less than or equal to a 10 nm pore size, with a smaller effect on the PSD heterogeneity in most cases. In other brittle mineral-rich samples, there are no obvious major peaks, and a weak heterogeneity of the PSDs is displayed. (3) A greater TOC content, maturity, clay content and pore size can cause stronger heterogeneity of the PSD and higher fractal dimensions in the shale samples. This study helps to understand and compare the PSD and fractal characteristics from different samples and provides important theoretical guidance and a scientific basis for the exploration and development of shale gas resources.

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