Pore characteristics of shale gas reservoirs from the Lower Paleozoic in the southern Sichuan Basin, China

Yuan, Wang; Li, Xianqing; Guo, Man; Peng, Zhao; Xu, Hongwei; Yang, Jie; Wang, Feiyu

doi:10.1016/j.jnggs.2016.07.002

Cited by 33 publications

(33 citation statements)

References 9 publications

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“…Based on IUPAC criteria, all the adsorption curves were divided into six types (types I–VI) and the hysteresis loops were classified into four types (types H 1 –H 4 ) to characterize pore shapes . In addition, the hysteresis loops were reclassified into five types (types A–E) based on criteria developed by Labani et al for precise elaboration of the shapes of pores, which cannot be generated from the blind holes. , In the present study, these two schemes were integrated and produced a novel hysteresis loop of the closed pores classified as type F.…”

Section: Resultsmentioning

confidence: 90%

“…37 In addition, the hysteresis loops were reclassified into five types (types A−E) based on criteria developed by Labani et al 67 for precise elaboration of the shapes of pores, which cannot be generated from the blind holes. 62,68 In the present study, these two schemes were integrated and produced a novel hysteresis loop of the closed pores classified as type F.…”

Section: Energy and Fuelsmentioning

confidence: 99%

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Characterization of Full-Sized Pore Structure and Fractal Characteristics of Marine–Continental Transitional Longtan Formation Shale of Sichuan Basin, South China

Wei

Sun

et al. 2017

Energy Fuels

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Despite the recent significant progress reviewed in marine and continental shale gas reservoirs, there is no general investigation concerning marine−continental transitional shales, especially in the research of the pore structure and fractal characteristics of marine−continental shale reservoirs. In this study, the pore structure characteristics of 12 typical marine− continental transitional shale samples of the Upper Permian Longtan Formation collected from Southern Sichuan Basin were analyzed, combining techniques of total organic carbon (TOC) content determination, X-ray diffraction, field emission scanning electron microscopy, high-pressure mercury intrusion porosimetry, and low-pressure N 2 /CO 2 adsorption. And the pore fractal characteristics of shales were also analyzed using the Frenkel−Halsey−Hill model with N 2 adsorption data. Not only the effects of TOC content and mineralogical compositions for pore structure parameters and fractal dimensions were analyzed but also the relationships between pore structure parameters and fractal dimensions were discussed. The results showed that the macropores (>50 nm) mainly develop within or between clay minerals, while the micropores (<2 nm) and mesopores (2−50 nm) commonly develop within intraparticle pores and organic matter (OM) pores. Marine−continental Longtan shales develop with the characteristic of various pore types, complicated pore structure, and obvious heterogeneity, which mainly consist of silt-shaped pores and ink bottleneck pores. Micropores provide the dominant specific surface area (SSA), whereas meso-and macropores occupy the majority of the pore volume. Both uni-and multimodal pore-size distributions (PSDs) in shales were analyzed; the PSDs of macropores increase rapidly to above 5 μm or below 30 nm, but a flat trend is present within the range of 30 nm to 5 μm; the PSDs of mesopores develop with a peak around 4 nm; and the PSDs of micropores develop with a minor peak around 0.35−0.40 nm and two major peaks around 0.45−0.50 and 0.55−0.60 nm. Micropores and macropores were the most important storage space for shale gas, and the micropores play a pivotal role in shale gas adsorption by providing the dominated SSAs. Two fractal dimensions (D 1 , 2.523−2.696; D 2 , 2.754−2.886) are positively associated with the pore volumes and SSAs of shales, and the micropores are the dominant factor for controlling the pore structure heterogeneity. The small pores of marine−continental shales mainly consist of OM pores, which are considerably affected by TOC content; large pores are mainly produced in clay minerals. TOC content has a significant positive relationship not only with the pore volumes and special surface areas of micropores but also with the fractal dimensions; and the enrichment of the clay minerals will contribute to the production of macropores (including fractures) while the brittle ones play the reverse role.

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Section: Resultsmentioning

confidence: 90%

Section: Energy and Fuelsmentioning

confidence: 99%

Characterization of Full-Sized Pore Structure and Fractal Characteristics of Marine–Continental Transitional Longtan Formation Shale of Sichuan Basin, South China

Wei

Sun

et al. 2017

Energy Fuels

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“…The Longtan shales in the Sichuan Basin suffer from strong OM pores are developed within the OMs, which are closely associated with the formation and enrichment of shale gas and provide the major space for the occurrence and accumulation of shale gas. 12,13,23,29,43,46 Previous studies have suggested that OM pores are developed from kerogen in shale during hydrocarbon generation. 12,13,23,29,43,46 The investigated coal-bearing shale samples are abundant in OMs, and the mass of organic particles is relatively regular, which is more likely to develop OM pores compared with amorphous OMs.…”

Section: Resultsmentioning

confidence: 99%

Characterization of the Full-Sized Pore Structure of Coal-Bearing Shales and Its Effect on Shale Gas Content

Zou

Zhao

et al. 2019

Energy Fuels

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The characterization of the pore structure and shale gas content provides useful information for shale gas reservoir assessment and evaluation and guides the exploration and development of shale gas. Fresh core samples obtained from three different basin formations in China were analyzed by field-emission scanning electron microscopy, low-pressure CO 2 and N 2 gas adsorption−desorption, high-pressure mercury intrusion, and methane adsorption experiments to clarify the pore structure characteristics of coal-bearing shales and their effects on shale gas content. The inter-and intraparticle pores, organic matter pores, and microfractures were well developed in coal-bearing shales. These pores had different geneses, morphologies, and sizes with main diameters of <6.5 and 80−200 nm and the main shape of slit, taper, and ink bottle. Pores with diameters <10 nm dominated the shale pore networks. Shale gas content was directly influenced by shale pores, and small pores had a large surface area, which resulted in the high adsorption capacity of shale gas. Clay mineral and total organic carbon contents positively controlled the pore structures and shale gas adsorption, whereas brittle minerals were counterproductive. Coalbearing shale gas content was lower than marine shale gas content, with an adsorption gas content percentage of 50−85%. The proportion of adsorbed gas decreased with the increase of pore size diameters, whereas the proportion of free gas increased. When the pore size diameter reached approximately 3.5 nm, the free and adsorption gases reached dynamic balance. The adsorption gas content would be slightly low with pore size ranges of >6.5 nm, whereas the free gas content would be stable and merely increase in the range of 100−300 nm.

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“…Deep shale gas reservoirs (deeper than 3500 m) account for more than 65% of the total resources and are a hotspot and alternative for shale gas research in China [2]. However, similar to deep shale gas reservoirs in North America, the gas production of deep shale gas wells in the Weiyuan, Fuling, and Fushun-Yongchuan blocks in China is relatively low after the fracturing [3,4]. The fracturing effect and production of shale gas wells are closely related to the retention, imbibition, and backflow of fracturing fluid.…”

Section: Introductionmentioning

confidence: 99%

Study on the Spontaneous Imbibition Characteristics of the Deep Longmaxi Formation Shales of the Southern Sichuan Basin, China

Qian

Shen

et al. 2021

Geofluids

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Deep shale gas reservoirs are a significant alternative type of shale gas reservoir in China. The productivity of deep shale gas wells is lower than that of shallow shale, and the imbibition characteristics of deep shale have a significant effect on the retention and backflow of fracturing fluid and the productivity of shale gas wells. In this study, the pore structure characteristics of organic-rich deep shale in the Lower Silurian Longmaxi Formation of Weiyuan-Luzhou play were analyzed by low-temperature nitrogen adsorption experiments, and then the imbibition characteristics and factors influencing deep shale were extensively investigated by spontaneous imbibition and nuclear magnetic resonance experiments. The results show that mainly micropores and mesopores are growing in the deep organic-rich shale of the Longmaxi Formation. The spontaneous imbibition curve of deep shale can be divided into an initial spontaneous imbibition stage, an intermediate transition stage, and a later diffusion stage, and the imbibition capacity coefficient of deep shale is lower than that of shallow shale. The transverse relaxation time (T2) spectrum distributions suggest that clay hydration and swelling produce new pores and microcracks, but then some pores and microfractures close. Deep shale reservoirs have an optimal hydration time when their physical properties are optimal. The increasing pore volume and the decreasing TOC content can enhance the imbibition capacity of shale. An inorganic salt solution, especially a KCl solution, has an inhibitory effect on the imbibition of shale. Higher salinity will result in a stronger inhibitory effect. It is crucial to determine the optimal amount of fracturing fluid and soaking time, and fracturing fluid with a high K+ content can be injected into the Longmaxi Formation deep shale to suppress hydration. These results provide theoretical guiding significance for comprehending the spontaneous imbibition and pore structure evolution characteristics of deep shale and enhancing methane production in deep shale gas reservoirs.

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Pore characteristics of shale gas reservoirs from the Lower Paleozoic in the southern Sichuan Basin, China

Cited by 33 publications

References 9 publications

Characterization of Full-Sized Pore Structure and Fractal Characteristics of Marine–Continental Transitional Longtan Formation Shale of Sichuan Basin, South China

Characterization of Full-Sized Pore Structure and Fractal Characteristics of Marine–Continental Transitional Longtan Formation Shale of Sichuan Basin, South China

Characterization of the Full-Sized Pore Structure of Coal-Bearing Shales and Its Effect on Shale Gas Content

Study on the Spontaneous Imbibition Characteristics of the Deep Longmaxi Formation Shales of the Southern Sichuan Basin, China

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