Occurrence and influence of residual gas released by crush methods on pore structure in Longmaxi shale in Yangtze Plate, Southern China

This study is predominantly about the differences in shale pore structure and the controlling factors of shale gas content between Lower Silurian and Lower Cambrian from the upper Yangtze plate, which are of great significance to the occurrence mechanism of shale gas. The field emission scanning electron microscopy combined with Particles (Pores) and Cracks Analysis System software, CO2/N2 adsorption and the high-pressure mercury injection porosimetry, and methane adsorption were used to investigate characteristics of overall shale pore structure and organic matter pore, heterogeneity and gas content of the Lower Paleozoic in southern Sichuan Basin and northern Guizhou province from the upper Yangtze plate. Results show that porosity and the development of organic matter pores of the Lower Silurian are better than that of the Lower Cambrian, and there are four main types of pore, including interparticle pore, intraparticle pore, organic matter pore and micro-fracture. The micropores of the Lower Cambrian shale provide major pore volume and specific surface areas. In the Lower Silurian shale, there are mesopores besides micropores. Fractal dimensions representing pore structure complexity and heterogeneity gradually increase with the increase in pore volume and specific surface areas. There is a significant positive linear relationship between total organic carbon content and micropores volume and specific surface areas of the Lower Paleozoic shale, and the correlation of the Lower Silurian is more obvious than that of the Lower Cambrian. The plane porosity of organic matter increases with the increase in total organic carbon when it is less than 5%. The plane porosity of organic matter pores is positively correlated with clay minerals content and negatively correlated with brittle minerals content. The adsorption gas content of Lower Silurian and Lower Cambrian shale are 1.51–3.86 m3/t (average, 2.31 m3/t) and 0.35–2.38 m3/t (average, 1.36 m3/t). Total organic carbon, clay minerals and porosity are the main controlling factors for the differences in shale gas content between Lower Cambrian and Lower Silurian from the upper Yangtze plate. Probability entropy and organic matter plane porosity of the Lower Silurian are higher than those of Lower Cambrian shale, but form factor and roundness is smaller.

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Pore structure variations across structural deformation of Silurian Longmaxi Shale: An example from the Chuandong Thrust-Fold Belt

Fuel ◽

10.1016/j.fuel.2018.12.108 ◽

2019 ◽

Vol 241 ◽

pp. 914-932 ◽

Cited By ~ 36

Author(s):

Hongjian Zhu ◽

Yiwen Ju ◽

Cheng Huang ◽

Kui Han ◽

Yu Qi ◽

...

Keyword(s):

Pore Structure ◽

Structural Deformation ◽

Fold Belt ◽

Longmaxi Shale

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Impact of de-ionized water on changes in porosity and permeability of shales mineralogy due to clay-swelling

Scientific Reports ◽

10.1038/s41598-021-99523-2 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Di Zhang ◽

Jay N. Meegoda ◽

Bruno M. Goncalves da Silva ◽

Liming Hu

Keyword(s):

Hydraulic Fracturing ◽

Pore Structure ◽

Coordination Number ◽

Gas Permeability ◽

Mineralogical Composition ◽

Nitrogen Adsorption ◽

Gas Production ◽

Pore Network Model ◽

Longmaxi Shale ◽

Laboratory Reactor

AbstractHydraulic fracturing is widely applied for economical gas production from shale reservoirs. Still, the swelling of the clay micro/nano pores due to retained fluid from hydraulic fracturing causes a gradual reduction of gas production. Four different gas-bearing shale samples with different mineralogical characteristics were investigated to study the expected shale swelling and reduction in gas permeability due to hydraulic fracturing. To simulate shale softening, these shale samples were immersed in deionized (DI) water heated to 100 °C temperature and subjected to 8 MPa pressure in a laboratory reactor for 72 hours to simulate shale softening. The low-temperature nitrogen adsorption and density measurements were performed on the original and treated shale to determine the changes in micro and nano pore structure. The micro and nano pore structures changed, and the porosity decreased after shale treatment. The porosity decreased by 4% for clayey shale, while for well-cemented shale the porosity only decreased by 0.52%. The findings showed that the initial mineralogical composition of shale plays a significant role in the change of micro and nano pores and the pore structure alteration due to retained fluid from hydraulic fracturing. A pore network model is used to simulate the permeability of shale used in this study. To define pore structure properties, specific factors such as porosity, pore size, pore throat distribution, and coordination number were used. Furthermore, the anisotropy characteristics of shale were integrated into the model via a coordination number ratio. Finally, the change in permeability due to shale softening was determined and compared with untreated with the progress of shale softening. The simulation showed that the permeability of Longmaxi shale could decrease from 3.82E–16 m2 to 4.71E–17 m2 after treatment.

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Pore structure characteristics and its effect on adsorption capacity of Niutitang marine shale in Sangzhi block, southern China

Interpretation ◽

10.1190/int-2019-0044.1 ◽

2019 ◽

Vol 7 (4) ◽

pp. T843-T856

Author(s):

Xinghua Wang ◽

Arash Dahi Taleghani ◽

Wenlong Ding

Keyword(s):

Organic Matter ◽

Pore Structure ◽

Adsorption Capacity ◽

Southern China ◽

Quartz Content ◽

Isothermal Adsorption ◽

Structure Characteristics ◽

Marine Shale ◽

Lp Formula ◽

Organic Pores

Characteristics of shale pore structures may play an important role in natural gas accumulation and consequently estimating the original gas in place. To determine the pore structure characteristics of Niutitang marine shale in the Sangzhi block, we carried out [Formula: see text] adsorption-desorption (LP-[Formula: see text]GA), [Formula: see text] adsorption (LP-[Formula: see text]GA), and methane isothermal adsorption on shale samples to reveal the pore size distribution (PSD) and its impact on the adsorption capacity. Results indicate that the Niutitang Shale is in stages of maturity and overmaturity with good organic matter, and they also indicate well-developed interparticle, intraparticle, and organic pores. Quartz and clay are found to be the main minerals, and the high illite content means that the Niutitang Shale is experiencing the later stage of clay mineral transformation. Various-sized shale pores are well-developed, and most of them are narrow and slit-like. For pores with diameters of 2–300 nm measured with LP-[Formula: see text]GA, mesopores (2–50 nm) contribute most of the total specific surface area (SSA) and total pore volume (TPV) in comparison to macropores (50–300 nm). For micropores ([Formula: see text]) tested by LP-[Formula: see text]GA, the PSD appears to be multimodal; shale pores of 0.50–0.90 nm diameter contribute most of the SSA and TPV. [Formula: see text]-SSA and [Formula: see text]-SSA indicate positive correlations with their corresponding TPV. The total organic matter (TOC) has good correlation with the SSA and TPV of micropores. The Langmuir volume positively correlates with the total SSA. Additionally, the TOC content has a good correlation with the Langmuir volume, which is consistent with the observation of well-developed fossils of diatoms and organic pores. As an important source of organic matter, more diatoms mean more organic matter, larger TOC values and quartz content, larger SSA and TPV of micropores, and, of course, stronger shale adsorption capacity. The results provide important guidance for the exploration and development of shale gas existing in the Sangzhi block.

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Full-scale pore structure and its controlling factors of the Wufeng-Longmaxi shale, southern Sichuan Basin, China: Implications for pore evolution of highly overmature marine shale

Journal of Natural Gas Science and Engineering ◽

10.1016/j.jngse.2019.04.020 ◽

2019 ◽

Vol 67 ◽

pp. 134-146 ◽

Cited By ~ 14

Author(s):

Yang Wang ◽

Luofu Liu ◽

Shanshan Zheng ◽

Zehua Luo ◽

Yue Sheng ◽

...

Keyword(s):

Pore Structure ◽

Sichuan Basin ◽

Controlling Factors ◽

Full Scale ◽

Marine Shale ◽

Longmaxi Shale ◽

Pore Evolution

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Brittleness evaluation of the Lower Silurian marine shale reservoirs: A case study of Longmaxi shale in Fenggang block, Southern China

Interpretation ◽

10.1190/int-2020-0142.1 ◽

2020 ◽

pp. 1-55

Author(s):

Yang Gu ◽

Sheng Xu ◽

Chao Fang ◽

Wei Zhang ◽

Bairen Zhang ◽

...

Keyword(s):

Shale Gas ◽

Seismic Data ◽

Strain Energy ◽

Southern China ◽

Strain Energy Release ◽

Lower Silurian ◽

Data Inversion ◽

Fracture Development ◽

Longmaxi Shale ◽

Shale Reservoirs

The brittleness of shale determines the fracturability of shale reservoir and has a great influence on the exploration and development of shale gas. Therefore, prediction of brittleness and evaluation of fracturability of shale are very important in finding favorable areas for shale gas. We used the mineral composition, rock mechanics experiment, logging evaluation, two-dimensional seismic data inversion and fracture development degree to evaluation and analysis the vertical and plane brittleness characteristics and main controlling factors of the Longmaxi shale. In addition, we established the fracturability index (FI) of shale based on the brittleness index, critical strain energy release rate and fracture toughness. The results indicate that the brittle mineral content of Longmaxi shale in Fenggang block is between 69% and 90%, shale samples are prone to brittle deformation by microscopic observation. Brittle deformation has a positive effect on the porosity and percolation ability of shale; the fractures in the upper and lower parts of Longmaxi shale are relatively developed, and the degree of core fracture development is consistent with rock brittleness. The brittleness distribution of two-dimensional seismic data inversion is in good agreement with the brittleness predicted by well logging; shale reservoirs with low fracture toughness, low critical strain energy release rate and high brittleness index have high fracturability. Therefore, the research on shale brittleness and fracturability of Lower Silurian Longmaxi shale is expected to have important guiding significance for shale gas exploration and development in Southern China.

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

Journal of Chemistry ◽

10.1155/2015/303164 ◽

2015 ◽

Vol 2015 ◽

pp. 1-12 ◽

Cited By ~ 8

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.

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Comparative analysis of shale reservoir characteristics in the Wufeng-Longmaxi (O3w-S1l) and Niutitang (Є1n) Formations: A case study of wells JY1 and TX1 in the southeastern Sichuan Basin and its neighboring areas, southwestern China

Interpretation ◽

10.1190/int-2018-0024.1 ◽

2018 ◽

Vol 6 (4) ◽

pp. SN31-SN45 ◽

Cited By ~ 10

Author(s):

Ruyue Wang ◽

Zongquan Hu ◽

Chuanxiang Sun ◽

Zhongbao Liu ◽

Chenchen Zhang ◽

...

Keyword(s):

Comparative Analysis ◽

Pore Structure ◽

Sichuan Basin ◽

Tectonic Deformation ◽

Hydrocarbon Generation ◽

Reservoir Characteristics ◽

Longmaxi Shale ◽

Methane Sorption ◽

Shale Reservoir ◽

Southeastern Sichuan Basin

A systematic comparative analysis of shale reservoir characteristics of the Wufeng-Longmaxi (O3 w-S1 l) and Niutitang (Є1 n) Formations in southeastern Sichuan Basin and its neighboring areas was conducted with respect to mineralogy, organic geochemistry, pore structure, methane sorption, brittleness, and fractures. Results indicate that (1) organic matter (OM)-hosted pores that are hundreds of nanometers to micrometers in size in the Longmaxi shale are well-developed in migrated OM rather than in the in situ OM, and they are the dominant reservoir spaces. Furthermore, the total organic carbon (TOC), brittleness, organic pores, and bedding fractures have good synergistic development relationships. However, there are fewer OM-hosted pores in the Niutitang shale; they are smaller in size, usually less than 30 nm, and have a more complicated pore structure. The intergranular pores in cataclastic organic-inorganic mineral fragments are the dominant reservoir spaces in the Niutitang shale and are coupled with stronger methane sorption and desorption capacities. (2) The piecewise correlation between TOC and brittleness indicates the significant differences in pore and fracture characteristics. When the TOC [Formula: see text], the TOC, brittleness, organic/inorganic pores, and fractures synergistically develop; when the TOC [Formula: see text], even though the increase in ductility reduces the number of fractures, the lower cohesive strength, internal friction angle, and weaker surfaces of interlayer fractures and cataclastic minerals promote the development of slip fractures, which significantly improves the fracture effectiveness and reservoir spaces for free and absorbed shale gas. (3) The Longmaxi, Wufeng, and Niutitang shales formed and evolved in different evolutionary stages. With the evolution of hydrocarbon generation, diagenesis, tectonic deformation, and pressure, the size and proportion of OM-hosted pores gradually decrease. At the same time, the complexity of the pore-fracture structure, the methane adsorption/desorption capacity, and the proportion of inorganic pores and fractures increase.

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