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Paper No. 217-16
Presentation Time: 4:45 PM

EFFECTS OF THERMAL EVOLUTION OF ORGANIC MATTER ON THE GENESIS OF SHALE GAS AND THE DEVELOPMENT OF ORGANIC MATTER PORES: A CASE STUDY OF MARINE SHALE IN THE UPPER YANGTZE REGION, SOUTH CHINA


ZHANG, Kun1, PENG, Jun2, WANG, Xin3, XUE, Zixin4, WEN, Ming5, HUANG, Yizhou6, LIU, Xiaoxue4, YANG, Yiming2, ZENG, Yao2, JI, Xin2, LI, Xiang2 and YANG, Peng2, (1)School of Geoscience and Technology, Southwest Petroleum University, Chengdu, 610500, China; State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, 610500, China, (2)School of Geoscience and Technology, Southwest Petroleum University, Chengdu, 610500, China, (3)State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, Beijing, 102249, China; Unconventional Natural Gas Institute, China University of Petroleum, Beijing, China, China University of Petroleum-Beijing, 18 Fuxue Road, Changping, Beijing China, Beijing, 102249, China, (4)Unconventional Natural Gas Institute, China University of Petroleum, Beijing, Beijing, 102249, China; State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, Beijing, 102249, China, (5)State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, Beijing, 102249, China; Unconventional Natural Gas Institute, China University of Petroleum, Beijing, Beijing, 102249, China, (6)Organic Geochemistry Unit, University of Bristol, Bristol, BS8 1TS, United Kingdom

The Marine shale in southern China has undergone complex tectonic evolution with high thermal evolution degree. Excessive thermal evolution brings certain risks to shale gas exploration and development. With the advancement of experimental methods, the evolution process of shale reservoirs can be better understood from the the micro-nano scale. This work takes the Ordovician-Silurian Wufeng and the first member of Longmaxi Formation in the Sichuan Basin and Lower Cambrian Niutitang Formation in Outer Margin of the Sichuan Basin to study the impact of maturity upon the genesis of shale gas and development features of the reservoir. A series of geochemical research methods, including TOC, gas component and gas isotope, were adopted to study the impact of different thermal evolution stages of organic matter upon the genesis of shale gas. The nanoscale micro-imaging technique, such as FIB-SEM and FIB-HIM, was used to analyze the development of OM-hosted pores. As shown from the results, when Ro=1.2%~3.5%, the marine shale gas is dominated by the methane and other hydrocarbon gases, since the mixture of cracking gas from liquid hydrocarbons and kerogen-cracking gas cause the carbon isotope reversal. Besides, the pyrobitumen pores characterized by the strong connectivity and storage capacity were primarily developed. When Ro>3.5%, the organic matter is at the graphitization stage. The shale gas is mainly composed by nitrogen at this stage. The nitrogen is originated from the atmosphere and the thermal evolution process, and the OM-hosted pores (pyrobitumen and kerogen pores) characterized by the bad connectivity and storage capacity are developed. Finally, the main component of shale gas, the genesis of shale gas and pattern of OM-hosted pores under different thermal evolution stages of organic matter are summarized, which provides technical support for the exploration and development of shale gas.

Session No. 217

T221. The Unconventional Shale Systems: From Source-Rocks to Reservoirs II
Thursday, 29 October 2020: 1:30 PM-5:30 PM
Geological Society of America Abstracts with Programs. Vol 52, No. 6
doi: 10.1130/abs/2020AM-350924
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