Natural fractures and their influence on shale gas enrichment in Sichuan Basin, China

Zeng, Lianbo; Lyu, Wenya; Li, Jian; Zhu, Lei; Weng, Jianqiao; Yuan, Feng; Zu, Kewei

doi:10.1016/j.jngse.2015.11.048

Cited by 142 publications

(52 citation statements)

References 16 publications

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“…Fractal dimension correlates well with the pore volume and surface area (Bu et al, 2015;Sun et al, 2015Sun et al, , 2016Yang et al, 2014Yang et al, , 2016. The Longmaxi and Qiongzhusi are the extensively studied shale formations in southern China Sun et al, 2016;Tian et al, 2015;Xue et al, 2016;Yan et al, 2016;Yang et al, 2016;Zeng et al, 2016;Zhang et al, 2015). The study of rich organic matter shale in the late Paleozoic marine-terrigenous facies in Qinshui Basin, northern China, is relatively new and there exists only few studies.…”

Section: Introductionmentioning

confidence: 99%

Pore characteristics of organic-rich shale in the Carboniferous-Permian coal-bearing strata in Qinshui Basin

Gao

Wei

Song

et al. 2017

Energy Exploration & Exploitation

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The study of shale pore has always been an important aspect of nonconventional shale reservoir analysis. However, there are relatively few studies on shale that is deposited in transitional environment in the Qinshui Basin. X-ray diffraction, field-emission scanning electron microscopy, N 2 , and CO 2 adsorption experiments were used for shale samples from the Taiyuan and Shanxi Formations. Sample pore characteristics based on field-emission scanning electron microscopic photographs were quantitatively characterized by pore fracture characteristics analysis software and fractal characteristics were discussed based on the nitrogen adsorption curve. Results show that sample pores were primarily composed of inter-granular and intra-granular pores. The proportion of micropores (<2 nm) is 25.84-91.65% of the total pore space, with an average of 58.65%. Micropores show three peaks, which occur near 0.38 nm, 0.5 nm, and 0.85 nm. Mesopores (2-50 nm) account for 6.74-56.11% of the total pore space, with an average of 31.20%. The ratio of macropores (>50 nm) less than 100 nm is 1.61-20.64% with an average of 9.17%. The volume of micropores increases with increase in the total organic carbon and clay mineral contents, decreases with the increase of carbonate and quartz mineral contents, and has weak correlation with other factors. The micropore volume per unit organic matter decreases with increase in maximum vitrinite reflectance (R o,max ) in a binomial relationship. The correlations between meso-macropore volume and each factor are rather weak. Form factor, fractal dimension, and probability entropy all correlate well with the depth. Pore structure complexity gradually increases with the increase in the burial depth. The deeper the rock layer increases with the pore size, the more slowly the pore complexity increases. The larger pore diameter, the more smooth journals.sagepub.com/home/eea the pore wall surface, and the rougher surface is more favorable for gas adsorption. The directionality of pore development increases first and then decreases with increase in the depth.

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Section: Introductionmentioning

confidence: 99%

Pore characteristics of organic-rich shale in the Carboniferous-Permian coal-bearing strata in Qinshui Basin

Gao

Wei

Song

et al. 2017

Energy Exploration & Exploitation

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“…The iron monosulfide were eventually transformed into framboidal pyrite which precipitated on the graptolite periderm (Briggs et al 1991(Briggs et al , 1996Schieber, 2002;Wilkin, 1997;Baliński and Sun 2013). In addition, due to the degradation of the soft tissues, a reducing microenvironment was formed around the graptolites, which was beneficial to the formation of framboidal pyrite (Yang et al, 2011;Li et al, 2016). With the dissolution or shedding of the pyrite crystals, honeycomb-like pyrite moulage pores were formed on the graptolite-derived OM, which were found to be very common under the SEM (Fig.…”

Section: Framboidal Pyrite Moulage Poresmentioning

confidence: 99%

“…When compared with the internal pores in the graptolite-derived OM, these intricated microfractures were observed to not only provide larger storage space, but also more importantly supplied interconnections between the pores to form effective shale gas flow channels (Ma et al, 2016;Zhou et al, 2017;Nie et al, 2015Nie et al, , 2018. The organic-rich shale was found to be characterized by highly developed lamellation (Zeng et al, 2016). The lamellation plane was a mechanically weak surface, which was easily induced to form lamellation fractures during the diagenesis (Zhu et al, 2015;.…”

Section: Contribution Of the Graptolites To The Shale Gas Reservoirsmentioning

confidence: 99%

Graptolite‐Derived Organic Matter and Pore Characteristics in the Wufeng‐Longmaxi Black Shale of the Sichuan Basin and its Periphery

Zhou

Sun

et al. 2019

Acta Geologica Sinica (Eng)

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A key target of shale gas exploration and production in China is the organic‐rich black shale of the Wufeng Formation‐Longmaxi Formation in the Sichuan Basin and its periphery. The set of black shale contains abundant graptolites, which are mainly preserved as flattened rhabdosomes with carbonized periderms, is an important organic component of the shale. However, few previous studies had focused on the organic matter (OM) which is derived from graptolite and its pore structure. In particular, the contributions of graptolites to gas generation, storage, and flow have not yet been examined. In this study, focused ion beam‐scanning electron microscope (FIB‐SEM) was used to investigate the characteristics of the graptolite‐derived OM and the micro‐nanopores of graptolite periderms. The results suggested that the proportion of OM in the graptolite was between 19.7% and 30.2%, and between 8.9% and 14.4% in the surrounding rock. The total organic carbon (TOC) content of the graptolite was found to be higher than that of the surrounding rock, which indicated that the graptolite played a significant role in the dispersed organic matter. Four types of pores were developed in the graptolite periderm, including organic gas pores, pyrite moulage pores, authigenic quartz moldic pores, and microfractures. These well‐developed micro‐nano pores and fractures had formed an interconnected system within the graptolites which provided storage spaces for shale gas. The stacked layers and large accumulation of graptolites resulted in lamellation fractures openning easily, and provided effective pathways for the gas flow. A few nanoscale gas pores were observed in the graptolite‐derived OM, with surface porosity lie in 1.5%–2.4%, and pore diameters of 5–20 nm. The sapropel detritus was determined to be rich in nanometer‐sized pores with surface porosity of 3.1%–6.2%, and pore diameters of 20–80 nm. Due to the small amount of hydrocarbon generation of the graptolite, supporting the overlying pressure was difficult, which caused the pores to become compacted or collapsed.

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“…Diagenetic shrinkage joints are generally found in shale with high silicon content, formed by a shrinkage effect due to chemical changes during diagenesis. Additionally, vertical shearing fractures and interlayer lamellation seams could form abundant reticular fracture systems (as shown in Figure 7c), which could greatly enhance the reservoir space and permeability, forming crucial pathways for shale gas migration from the source to the reservoir [17,36,37].…”

Section: Reservoir Storage-space Typesmentioning

confidence: 99%

A New Insight into Shale-Gas Accumulation Conditions and Favorable Areas of the Xinkailing Formation in the Wuning Area, North-West Jiangxi, China

Li¹,

Zeng²,

Wang³

et al. 2017

Energies

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Abstract:In north-west Jiangxi, China, most shale-gas exploration has been focused on the Lower Cambrian Hetang and Guanyintang formations, whereas the Upper Ordovician Xinkailing formation shale has been ignored for years due to heavy weathering. This study systematically analyzed gas source conditions, reservoir conditions and gas-bearing ability in order to reveal the shale-gas accumulation conditions of the Xinkailing formation. The results show that the Xinkailing formation is characterized by thick deposition of black shale (10-80 m), high organic content (with total organic carbon between 1.18% and 3.11%, on average greater than 2%), relatively moderate thermal evolution (with vitrinite reflectance between 2.83% and 3.21%), high brittle-mineral content (greater than 40%), abundant nanopores and micro-fractures, very good adsorption ability (adsorption content between 2.12 m 3 /t and 3.47 m 3 /t, on average about 2.50 m 3 /t), and strong sealing ability in the underlying and overlying layers, all of which favor the generation and accumulation of shale gas. The Wuning-Lixi and Jinkou-Zhelin areas of the Xinkailing formation were selected as the most realistic and favorable targets for shale-gas exploration and exploitation. In conclusion, the Wuning area has great potential and can provide a breakthrough in shale gas with further investigation.

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Natural fractures and their influence on shale gas enrichment in Sichuan Basin, China

Cited by 142 publications

References 16 publications

Pore characteristics of organic-rich shale in the Carboniferous-Permian coal-bearing strata in Qinshui Basin

Pore characteristics of organic-rich shale in the Carboniferous-Permian coal-bearing strata in Qinshui Basin

Graptolite‐Derived Organic Matter and Pore Characteristics in the Wufeng‐Longmaxi Black Shale of the Sichuan Basin and its Periphery

A New Insight into Shale-Gas Accumulation Conditions and Favorable Areas of the Xinkailing Formation in the Wuning Area, North-West Jiangxi, China

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