Optical characteristics of graptolite-bearing sediments and its implication for thermal maturity assessment

Luo, Qingyong; Hao, Jingyue; Skovsted, Christian B.; Xu, Ying; Yan, Long; Wu, Jin; Zhang, Shuning; Wang, Wanli

doi:10.1016/j.coal.2018.06.019

Cited by 61 publications

(60 citation statements)

References 48 publications

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“…Graptolite has been debated in the literature whether there are a large number of pores (e.g., Ma et al, 2016;Luo et al, 2016Luo et al, , 2018. Almost no pore is ever found in graptolite of this study (Figure 3), although previous studies observed certain micrometer-sized fractures and spindle-shaped pores between cortical fibrils in the cortical of graptolite (Luo et al, 2016(Luo et al, , 2018.…”

Section: Possible Maceral and Om Pores Sourcesmentioning

confidence: 49%

Variation of Organic Pore Structure With Maceral Types in the Longmaxi Shale, Sichuan Basin

Pang

Chaowei

et al. 2021

Front. Earth Sci.

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Organic matter (OM), composed of various macerals, has a strong influence on the enrichment of shale gas. Nevertheless, the connection between OM-hosted pore structure and maceral type is not yet fully understood because of the difficulty to identify the maceral types by traditional scanning electron microscope (SEM). Using a combination of the reflected light microscopy, focused ion beam SEM (FIB-SEM), and Raman spectrum, three maceral types, including alginite, graptolite, and solid bitumen, are identified in the Longmaxi Shale of the Sichuan Basin. The alginate is characterized by the linear arrangement of OM-hosted pores due to the inherited biological structure of benthic algae. Pores in the structureless solid bitumen are randomly distributed with the highest abundance. The graptolite containing pore rarely is unfavorable for the pore generation but can be a good proxy for thermal maturity. Variation in thermal maturity levels accounts for the change of total pore volume in a given marcel type in the Longmaxi Shale obtained from different shale gas fields.

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Section: Possible Maceral and Om Pores Sourcesmentioning

confidence: 49%

Variation of Organic Pore Structure With Maceral Types in the Longmaxi Shale, Sichuan Basin

Pang

Chaowei

et al. 2021

Front. Earth Sci.

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“…Cole (1994) suggested that depositional and/or environmental conditions may affect the graptolite reflectance. Due to the anisotropy of graptolite, maximum or random reflectance was used in various studies (Bertrand, 1990;Bertrand & Malo, 2001;Bustin et al, 1989;Goodarzi & Norford, 1985;Luo et al, 2018;Riediger et al, 1989;Wang et al, 2019).…”

Section: Maturity Evaluation Based On Optical Reflectancementioning

confidence: 99%

“…Laboratory maturity simulations by Bustin et al (1989) and Luo et al (2018) presented correlations between maximum and random reflectance for vitrinite and graptolite. Link et al (1990) stated that the graptolite maximum reflectance was most reliable owing to biaxial optical properties.…”

Section: Maturity Evaluation Based On Optical Reflectancementioning

confidence: 99%

“…The random reflectance data of graptolite will thus be very scattered when direction of polished blocks is not considered, which is problematic for drilling cutting samples or crushed particles. Morga and Pawlyta (2018) conducted graptolite random reflectance measurement on sections cut parallel to bedding, whereas Luo et al (2018) and Wang et al (2019) suggested that the graptolite random reflectance measured perpendicular to the bedding is more precise with smaller standard deviation. Calculated from measured GRo values according to the equation built by Wang et al (2019), the EqVRo values of the four samples range from 2.53 to 2.59%, which are approximately equal to reflectance of pyrobitumen (Table 2).…”

Section: Maturity Evaluation Based On Optical Reflectancementioning

confidence: 99%

“…Other geochemical parameters, for example, Rock-Eval Tmax (Bertrand & Malo, 2001;Petersen et al, 2013), biomarker parameters (Radke & Welte, 1983), fluorescence photometry (Haeri-Ardakani & Sanei, 2015;Wilkins et al, 1995), the conodont colour alteration index (CAI; Epstein et al, 1977;Rejebian et al, 1987), and kerogen atomic ratio (H/C) (Buchardt & Lewan, 1990;Hartkopf-Fröder et al, 2015) are ineffective in such shales with over-maturity stage. Fortunately, the reflectances of solid bitumen and graptolite have been analysed in such kind of source rocks, and have been regarded as the effective indicator for maturity evaluation (Bertrand & Malo, 2001;Bustin et al, 1989;Luo et al, 2018;Petersen et al, 2013;Wang et al, 2019). The maturity assessment of Wufeng-Longmaxi Shale has been carefully studied, and the conversion from graptolite reflectance to equal vitrinite reflectance has been proposed in our earlier study with Raman analysis (see Wang et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

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Maturity and thermal evolution differences between two sets of Lower Palaeozoic shales and its significance for shale gas formation in south‐western Sichuan Basin, China

et al. 2021

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The Lower Cambrian Qiongzhusi shale and the Upper Ordovician-Lower Silurian Wufeng-Longmaxi shale are major source rocks and important shale gas exploration targets in the Sichuan Basin. Cutting and core samples from two shale gas wells in south-western Sichuan Basin have been selected for organic matter (OM) reflectance measurement and Raman spectra analysis with the aim to determine maturity. The results were incorporated for basin modelling to construct the thermal evolution of this area. Graptolite fragments and pyrobitumens are the dominant form of OM in

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Enrichment characteristics and exploration potential of the Permian marine shale gas in the Wujiaping Formation, Sichuan Basin, SW China

Nie,

Li,

Ding

2023

Geological Journal

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Shale gas exploration has achieved global success in marine shales. This study analysed geochemical, mineralogical, porosity, permeability and gas‐bearing parameters of organic‐rich shales in the Permian Wujiaping Formation in the Sichuan Basin. A comprehensive comparison was conducted with the Longtan Formation transitional shales and typical commercially developed marine shales. The results showed that: (1) siliceous shale within the Wujiaping Formation exhibits total organic carbon content ranging from 0.60% to 9.53% (average 4.45%) and vitrinite reflectance (Ro) ranging from 1.83% to 2.14% (average 1.98%), indicating an overmature stage of hydrocarbon generation. Porosity varies from 0.48% to 11.8% (average 4.94%), with an average content of 51.4% brittle minerals (quartz+calcite+dolomite) and calculating gas content exceeding 3 m3/t based on logging data. Effective sealing is achieved by the overlying carbonate of the Changxing Formation and the underlying carbonate of the Maokou Formation. (2) The primary storage space of the siliceous shale in the Wujiaping Formation encompasses diverse organic matter pores, clay mineral pores and microfractures. The porosity and permeability of the Wujiaping Formation marine shale ranges from 0.48% to 11.8% and 0.0053 to 0.8450 mD. Total gas content was estimated between 3 to 12 m3/t averaging 6 m3/t. (3) By comparing Permian Wujiaping Formation shales with Longtan Formation transitional shales, Wufeng Formation‐Longmaxi Formation shales and the typical North American marine gas shales (such as Barnett, Ohio, Antrim, New Albany, etc.), we conclude that marine siliceous shales within the Wujiaping Formation exhibit enrichment conditions comparable to established marine shales and superior to Permian transitional shales. The favourable upper and lower seals of the Wujiaping Formation resemble those of the Barnett shale gas reservoirs. In conclusion, the marine shale in Wujiaping Formation holds potential for substantial shale gas reservoirs and is poised for strategic exploration and development breakthroughs in the northeast and east Sichuan Basin.

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Optical characteristics of graptolite-bearing sediments and its implication for thermal maturity assessment

Cited by 61 publications

References 48 publications

Variation of Organic Pore Structure With Maceral Types in the Longmaxi Shale, Sichuan Basin

Variation of Organic Pore Structure With Maceral Types in the Longmaxi Shale, Sichuan Basin

Maturity and thermal evolution differences between two sets of Lower Palaeozoic shales and its significance for shale gas formation in south‐western Sichuan Basin, China

Enrichment characteristics and exploration potential of the Permian marine shale gas in the Wujiaping Formation, Sichuan Basin, SW China

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