Origin of organic matter and organic pores in the overmature Ordovician-Silurian Wufeng-Longmaxi Shale of the Sichuan Basin, China

Teng, Juan; Liu, Bei; Mastalerz, María; Schieber, Jüergen

doi:10.1016/j.coal.2022.103970

Cited by 25 publications

(18 citation statements)

References 54 publications

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“…Similar to other types of solid kerogen, pores are poorly developed in the graptolites. It has been suggested that graptolite is composed of aromatic compounds with aliphatic groups, resulting in a weak hydrocarbon generation capacity 28 …”

Section: Resultsmentioning

confidence: 99%

“…Currently, the Upper Ordovician Longmaxi Formation in the Sichuan Basin of China is considered to exhibit the most favorable conditions for shale gas enrichment and production. Several researchers have explored the pore structure characteristics of Longmaxi shale to develop precise development strategies for shale gas reservoirs 12,27–29 . Different shale lithofacies generally display distinct pore structure features, and the development of OM pores is closely related to thermal maturity and OM types 27,30 .…”

Section: Introductionmentioning

confidence: 99%

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Study on the distribution and connectivity of organic matter pores in Longmaxi shale based on 2D and 3D FIB‐SEM

Hui

Zhang²,

Hu³

et al. 2022

Energy Science & Engineering

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Knowledge of shale pore structure characteristics is crucial to understand gas storage and seepage mechanisms. Organic matter (OM) pores are considered the most important pore type in shale, and one of the currently significant research questions focuses on the spatial distribution and connectivity of OM pores. To answer this question, typical OM‐rich siliceous shale samples from the Lower Silurian Longmaxi Formation were comprehensively investigated using focused ion beam scanning electron microscopy. A three‐dimensional model of the OM‐rich region of interest was segmented and reconstructed based on numerous two‐dimensional slices. The types of OM were found to control the development of organic pores, and OM pores including honeycomb‐shaped pores, spongy‐shaped pores, and slit‐like irregular pores are mainly formed in the pyrobitumen. The pore structure parameters of the OM‐rich ROI revealed that the pore size distribution of honeycomb‐shaped OM pores formed in the pyrobitumen was mainly distributed in the range of 10–50 and 80–100 nm, while the throat equivalent diameter distribution demonstrated a unimodal curve with the main peak located at approximately 30 nm. Pore connectivity analysis further indicated that pyrobitumen also contained several isolated nano‐pores, and pores with diameters smaller than 40 nm were poorly connected. Furthermore, permeability simulation revealed clear discrepancies in different directions owing to the heterogeneity of the OM pores. These findings provide experimental evidence for the assessment of shale gas resources and their development potential.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Study on the distribution and connectivity of organic matter pores in Longmaxi shale based on 2D and 3D FIB‐SEM

Hui

Zhang²,

Hu³

et al. 2022

Energy Science & Engineering

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“…The controls of shale organic macerals on organic pores are manifested in three aspects： (1) Residual pores of primary organic matter: the organic matter in shale includes primary organic matter and secondary organic matter, and organic matter pores can also be divided into primary organic matter pores and secondary organic matter pores (Gao et al, 2021(Gao et al, , 2019Hu et al, 2021;Teng et al, 2022). The pores of primary organic matter are mainly distributed in the provitrinite, fusinite and semifusinite.…”

Section: Controls On Organic Pore Developmentmentioning

confidence: 99%

In-situ SEM characteristics of dispersed organic matter in continental shale with its implication for dessert evaluation--A case study of Paleogene shale in the Cangdong Sag, Bohai Bay Basin, China

Xie¹,

Pu²,

Jin³

et al. 2022

E3S Web Conf.

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Organic matter (OM) in continental shale serves as both the source of oil and gas and the storage space in unconventional petroleum systems. However, directly identifying the types of organic matter under SEM is challenging when simultaneously observing minerals and pores. Kong2 Member(E2k2) of Paleogene in Cangdong sag of Bohai Bay basin is a typical continental shale oil layer in China. Based on the positioning observation technology combining field emission scanning electron microscope (FE-SEM) and fluorescence microscope, the in-situ SEM identification and observation of macerals were carried out, and the identification methods and characteristics of organic macerals were summarized. The results show that: (1) Organic macerals in E2k2 shale are divided into vitrinite, inertinite, liptinite and solid bitumen by external morphology, hardness, brightness, color, protrusion, pore and fracture development of organic matter, and further subdivided into multiple subcategories. Based on the SEM charging effect of the remaining oil, it is further confirmed that the shale movable oil and oil generation potential developed by lipoid group is the largest, while the shale movable oil and oil generation potential developed by vitrinite group and inertinite group is the worst; (2) The organic pores include primary pores and secondary pores. The pores of primary organic matter are derived from the biological structure of primary organic matter, and the secondary organic pores are developed during the thermal maturation of oily organic matter. Clay mineral catalysis, difference of hydrocarbon generation potential and residual pores of primary organic matter control the development of organic pores; (3) Calcareous-dolomitic shale and felsic shale are typical lithology formed in relatively dry and humid climate respectively, and the types of organic macerals are significantly different. Although the former has weak total hydrocarbon generation, it has stronger oil generation potential and is worthy of attention in dessert prediction and exploration.

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“…Recently, great progress in shale gas exploration and development has been made in China, especially in revealing the mechanisms of shale gas generation and accumulation (Guo and Zhang., 2014;Borjigin et al, 2017;Guo et al, 2017;Wang et al, 2019;Shu et al, 2020;Xi et al, 2022), the formation and preservation of organic matter (OM) pores in shales (Liang et al, 2017;Dong et al, 2021;Ma et al, 2022;Teng et al, 2022;, and the characteristics of shale gas in China (Zou et al, 2010;Zou et al, 2016;Zou et al, 2019; OPEN ACCESS EDITED BY 2021; Feng et al, 2022;Nie et al, 2022). Shale gas production in China exceeded 230×10 8 m 3 by the end of 2021, most of which was distributed in marine Longmaxi shale reservoirs in the Sichuan Basin and its surrounding area.…”

Section: Introductionmentioning

confidence: 99%

Pore characteristics and preservation mechanism of over-6000-m ultra-deep shale reservoir in the Sichuan Basin

Guoliang

Jiao²,

Deng³

et al. 2023

Front. Earth Sci.

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Investigation of pore characteristics and their preservation mechanism of over 6000 m ultra-deep shale reservoirs is of significance for shale gas exploration and development in the Sichuan Basin. In this study, the pores structure and multifractal characteristics of pores for the Longmaxi shale and Qiongzhusi shale in the Sichuan Basin are well studied by using field emission scanning electron microscopy (FE-SEM), gas adsorption and multifractal analysis. The results show that: (1) Extremely strong mechanical compaction resulting from ultra-deep burial depth can lead to the homogenization of pore structure, which is characterized by the change of bubble-like OM pores to silt or fracture shape pores and the higher average pore diameter (APD) value. (2) The Longmaxi shale and Qiongzhusi shale reservoirs have the obvious multifractal nature for different pore sizes. Samples from the Longmaxi shale and Qiongzhusi shale in well CS#1 demonstrate the higher average H values and smaller average ΔD values compared with those samples in well MS#1, indicating that shale reservoir in over-pressure condition has higher connectivity and less heterogeneity. The pore preservation in over 6000 m ultra-deep shale reservoirs are influenced by several geological factors, including 1) quartz is beneficial for the preservation of pores especially for OM pores due to its supporting effect; 2) the shale reservoirs in over-pressure show many more OM pores and higher surface porosity than those in normal pressure; 3) the direct floor of Qiongzhusi shale is likely the critical geological factor affecting the pores preservation. Therefore, the Longmaxi shale with both over-pressure condition and high quartz content is likely the best target zone for deep shale gas exploration in the Sichuan Basin.

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Origin of organic matter and organic pores in the overmature Ordovician-Silurian Wufeng-Longmaxi Shale of the Sichuan Basin, China

Cited by 25 publications

References 54 publications

Study on the distribution and connectivity of organic matter pores in Longmaxi shale based on 2D and 3D FIB‐SEM

Study on the distribution and connectivity of organic matter pores in Longmaxi shale based on 2D and 3D FIB‐SEM

In-situ SEM characteristics of dispersed organic matter in continental shale with its implication for dessert evaluation--A case study of Paleogene shale in the Cangdong Sag, Bohai Bay Basin, China

Pore characteristics and preservation mechanism of over-6000-m ultra-deep shale reservoir in the Sichuan Basin

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