Identification of organic matter components and organic pore characteristics of marine shale: A case study of Wufeng-Longmaxi shale in southern Sichuan Basin, China

Chen, Zhiyuan; Yan, Song; Jiang, Zhenxue; Liu, Shaobo; Li, Zhuo; Shi, Dishi; Yang, Wei; Yang, Youdong; Song, Jianan; Gao, Fei; Zhang, Kun; Guo, Xingwei

doi:10.1016/j.marpetgeo.2019.06.002

Cited by 35 publications

(24 citation statements)

References 41 publications

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“… 17 However, the supporting effects of mineral particles contribute to the preservation of OM pores when exposed to tectonic compression. 49 Consequently, the close packing of pyrite particles was beneficial to the preservation of OM pores. However, when the accumulation of pyrite particles becomes closer with increasing lithostatic pressure, the morphology of OM pores changes ( Figures 4 B and 7 C).…”

Section: Discussionmentioning

confidence: 99%

“… 40 Thereafter, the internal OM nanopores of migrated bitumen barely develop if gas hydrocarbon generation does not occur again after bitumen migration. 49 The formation of OM nanopores cannot offset the destruction of OM nanopores in the autochthonous and secondary OM from 2.63 to 2.82% Ro owing to strong lithostatic pressure. Conversely, OM-hosted nanopores increasingly developed until 3.5% Ro in an open simulation system without lithostatic pressure.…”

Section: Discussionmentioning

confidence: 99%

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Pore Structure of Organic Matter in the Lacustrine Shale from High to Over Mature Stages: An Approach of Artificial Thermal Simulation

2022

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The pore structure of organic matter (OM) is affected by the maturity and type of OM, and these exert an important control on the development of OM pores. However, it is often challenging to distinguish between autochthonous and secondary OM. In this study, different types of OM were distinguished by means of morphology and the form of its occurrence under scanning electron microscopy (SEM) observation. Pyrolyzed samples were used to obtain pore structures of autochthonous and secondary OM from a lacustrine shale from high to over mature stages. The SEM observations indicated that the secondary OM is porous, whereas the autochthonous OM is nonporous. Further, nitrogen adsorption data showed that nanopores in the autochthonous OM are blocked in non-extracted samples and reoccurred after extraction, whereas nanopores in the secondary OM remain open from high to over mature stages. Moreover, the pore structure, i.e., pore type and pore size, differed for autochthonous and secondary OM in the lacustrine shale. For instance, nanopores in the autochthonous OM were micropores (smaller than 1.5 nm); nanopores in the secondary OM were mesopores (ranging from 5 to 20 nm) and micropores. Nanopores in the autochthonous OM were formed at reflectance values (Ro) of 1.50%, but they were slightly destroyed at the over mature stage. Nanopores in the secondary OM were formed at 2.00% Ro and were preserved. Therefore, the development of OM nanopores in the lacustrine shale was synchronously affected by the type of OM and maturity. Furthermore, nanopores in the secondary OM were more developed than those in the autochthonous OM; thus, the OM nanopores at the high mature stage belonged to the autochthonous OM, and those at the over mature stage mainly belonged to the secondary OM. Besides, the nanopores in the autochthonous OM are easily blocked. Therefore, the secondary OM is important to the development of OM nanopores in the lacustrine shale at the over mature stage.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Pore Structure of Organic Matter in the Lacustrine Shale from High to Over Mature Stages: An Approach of Artificial Thermal Simulation

2022

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“…Therefore, interP pore shape determines the filled solid bitumen shape, as well as OM pore distribution. The solid bitumen has a size generally smaller than 10 μm and uniform internal structures [58,59], which can significantly increase shale pore complexity. OM pores develop within solid bitumen are circular and elliptical (Figures 6(a)-6(d)), and they are more developed than other types of OM.…”

Section: Resultsmentioning

confidence: 99%

Marine Shale Gas Occurrence and Its Influencing Factors: A Case Study from the Wufeng-Longmaxi Formation, Northwestern Guizhou, China

et al. 2022

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Organic-rich shales were found in the Ordovician to Silurian Wufeng-Longmaxi Formation in northwestern Guizhou province, China, which has high shale gas content revealed by field measurement. Shale gas occurrence, free gas/sorbed gas ratio, and their influencing factors are crucial for shale gas exploitation strategy. Results indicated that the Wufeng-Longmaxi shales are dominated by type I kerogen, with total organic carbon (TOC) and equivalent vitrinite reflectance (eqvRo) of 0.77%–6.98% and 2.37%–2.53%, respectively. The total porosity and permeability are in the range of 1.23%–8.43% and 3 × 10 − 4 – 2.23 × 10 − 1 mD, respectively. FE-SEM observation and correlation analysis show shale porosity is dominated by organic matter (OM) pores, followed by interparticle (interP) pores related to brittle minerals. CH4, derived from oil cracking, is the main component of shale gas, but its proportion is lower than that in Fuling and Weiyuan areas, probably due to the weak preservation condition. Desorption gas and lost gas determined by in situ desorption test are 0.42–1.54 cm3/g and 1.9–7.14 cm3/g, respectively, and Langmuir volume ( V L ) from isothermal adsorption experiment is 1.63–4.78 cm3/g. Shale gas content is positively correlated with micropore volume, mesopore volume and TOC content but negatively correlated with macropore volume and clay mineral content, indicating that methane is preferentially stored in micropores (<2 nm) and mesopores (2–50 nm) related to OMs. By comparing actual total gas content with theoretical gas content, shale gas is considered to exist primarily in sorbed state, and the free gas proportion can increase with increased TOC content, due to that OM pores with larger sizes are also main space for free gas. Combined with the two methods, it can result in accurate calculations of shale gas reserves and free/sorbed gas ratio. Based on this understanding, a model of shale gas occurrence was proposed, which can provide a reference for shale gas exploitation in normal pressure areas.

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“…Accordingly, a multitude of hydrocarbon-generating pores and complex organic matter structures were formed, greatly increasing the shale adsorption capacity. Hu et al (2016) and Chen et al (2019) reported that a high TOC generally corresponds to a high porosity, pore volume and specific surface area, which is especially beneficial to the development of mesopores and indicates that the higher the TOC value, the stronger the shale adsorption capacity [33,34]. Similarly, as depicted in Figure 5a, the TOC value of sample Y1-4 is only 0.31, and its V L value also approaches 0.…”

Section: The Impact Of Toc and Mineral Composition On V Lmentioning

confidence: 87%

Adsorption Characteristics and Controlling Factors of CH4 on Coal-Measure Shale, Hedong Coalfield

2021

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Adsorbed gas is one of the crucial occurrences in shale gas reservoirs; thus, it is of great significance to ascertain the adsorption capacity of shale and the adsorption characteristics of CH4. In this investigation, the Taiyuan–Shanxi Formations’ coal-measure shale gas reservoir of the Carboniferous–Permian era in the Hedong Coalfield was treated as the research target. Our results exhibit that the shale samples were characterized by a high total organic carbon (TOC) and over to high-over maturity, with an average TOC of 2.45% and average Ro of 2.59%. The mineral composition was dominated by clay (62% on average) and quartz (22.45% on average), and clay was mainly composed of kaolinite and illite. The Langmuir model showed a perfect fitting degree to the experimental data: VL was in the range of 0.01 cm3/g to 0.77 cm3/g and PL was in the range of 0.23–8.58 MPa. In addition, the fitting degree depicted a linear negative correlation versus TOC, while mineral composition did not exhibit a significant effect on the fitting degree, which was caused by the complex pore structure of organic matter, and the applicability of the monolayer adsorption theory was lower than that of CH4 adsorption on the mineral’s pore surface. An apparent linear positive correlation of VL versus the TOC value was recorded; furthermore, the normalized VL increased with the growth of the total content of clay mineral (TCCM), decreased with the growth of the total content of brittle mineral (TCBM), while there was no obvious correlation of normalized VL versus kaolinite, illite and quartz content. The huge amount of micropores and complex internal structure led to organic matter possessing a strong adsorption capacity for CH4, and clay minerals also promoted adsorption due to the development of interlayer pores and intergranular pores.

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Identification of organic matter components and organic pore characteristics of marine shale: A case study of Wufeng-Longmaxi shale in southern Sichuan Basin, China

Cited by 35 publications

References 41 publications

Pore Structure of Organic Matter in the Lacustrine Shale from High to Over Mature Stages: An Approach of Artificial Thermal Simulation

Pore Structure of Organic Matter in the Lacustrine Shale from High to Over Mature Stages: An Approach of Artificial Thermal Simulation

Marine Shale Gas Occurrence and Its Influencing Factors: A Case Study from the Wufeng-Longmaxi Formation, Northwestern Guizhou, China

Adsorption Characteristics and Controlling Factors of CH4 on Coal-Measure Shale, Hedong Coalfield

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