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

【Author】

WU Jin;ZHOU Wen;SUN Shasha;ZHOU Shangwen;SHI Zhensheng;State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology;Research Institute of Petroleum Exploration and Development, PetroChina;National Energy Shale Gas R&D (Experiment) Centre;PetroChina Unconventional Oil & Gas Key Laboratory;

【Institution】

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology;Research Institute of Petroleum Exploration and Development, PetroChina;National Energy Shale Gas R&D (Experiment) Centre;PetroChina Unconventional Oil & Gas Key Laboratory;

【Abstract】

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.

【Keywords】

graptolite;;pore structure;;shale gas;;Wufeng-Longmaxi Formations;;Sichuan Basin

References

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Total: 41 articles

  • [1] WANG Shufang;ZOU Caineng;DONG Dazhong;WANG Yuman;HUANG Jinliang;GUO Zhaojie;The Key Laboratory of Orogenic Belts and Crustal Evolution (MOE),School of Earth and Space Sciences,Peking University;PetroChina Research Institute of Petroleum Exploration and Development;, Biogenic Silica of Organic-Rich Shale in Sichuan Basin and Its Significance for Shale Gas, Acta Scientiarum Naturalium Universitatis Pekinensis,
  • [2] WANG Hong-yan;GUO Wei;LIANG Feng;ZHAO Qun;Langfang Branch,Research Institute of Petroleum Exploration and Development,PetroChina,National Energy Shale Gas Research & Development Center;, BIOSTRATIGRAPHY CHARACTERISTICS AND SCIENTIFIC MEANING OF THE WUFENG AND LONGMAXI FORMATION BLACK SHALES AT WELL WEI 202 OF THE WEIYUAN SHALE GAS FIELD,SICHUAN BASIN, Journal of Stratigraphy,
  • [3] CHEN Xu;FAN Jun-xuan;ZHANG Yuan-dong;WANG Hong-yan;CHEN Qing;WANG Wen-hui;LIANG Feng;GUO Wei;ZHAO Qun;NIE Hai-kuan;WEN Zhi-dong;SUN Zong-yuan;Key Laboratory of Economic Stratigraphy and Palaeogeography,Chinese Academy of Sciences;State Key Laboratory of Palaeobiology and Stratigraphy,Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences;Langfang Branch,PetroChina Research Institute of Petroleum Exploration & Development;School of Earth Science and Engineering,Nanjing University;Research Institute of Petroleum Exploration & Development,PetroChina;Southern Company of SINOPEC Exploration;University of Chinese Academy of Sciences;, SUBDIVISION AND DELINEATION OF THE WUFENG AND LUNGMACHI BLACK SHALES IN THE SUBSURFACE AREAS OF THE YANGTZE PLATFORM, Journal of Stratigraphy,
  • [4] DAI Na;ZHONG Ning-ning;ZHANG Yu;ZHANG Wang;ZHAO Jiang;YAN Wei-han;State Key Laboratory of Petroleum Resource and Prospecting,China University of Petroleum;, Ar ion milling/SEM analysis on graptolitinite macerals, Journal of Chinese Electron Microscopy Society,

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