Quantitative study on hydrocarbon expulsion mechanism based on micro-fracture

Geoscience Frontiers

Yong Li¹  Wen Qiu²  Jungang Lu³  Shijia Chen³  Zhenglu Xiao⁴  Kaiming Su⁵  Meimei Han⁵  Huanxu Zhang⁵ 

[1] Corresponding author. State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu, 610500, China.;Power and Environmental Energy Research Institute of California, San Francisco, 94101, United States;School of Geoscience and Technology, Southwest Petroleum University, Chengdu, 610500, China;Shandong Provincial Key Laboratory of Depositional Mineralization and Sedimentary Minerals, Qingdao, 266590, China;State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu, 610500, China;

关键词: Quantitative study;    Primary migration;    Hydrocarbon generation micro-fractures;    Mechanical analysis;    Thermal evolution simulation;    Ordos basin;   

DOI  :  

来源: DOAJ

【 摘 要 】

The significance of source rocks for oil and gas accumulation has been indisputably acknowledged. Moreover, it has been gradually realized that there is difference between hydrocarbon generation capacity and hydrocarbon expulsion capacity, and this has prompted research on hydrocarbon expulsion efficiency. However, these studies dominantly highlight the results of hydrocarbon expulsion, and investigation into the corresponding process and mechanism is primarily from a macroscopic perspective. Despite its wide acceptance as the most direct hydrocarbon expulsion mode, hydrocarbon expulsion through micro-fractures is still not sufficiently understood. Therefore, this study obtains observations and performs experiments on two types of source rocks (mudstones and shales) of the Chang 7 oil group of the Yanchang Formation in Ordos Basin, China. Microscopy reveals that organic matter is non-uniformly distributed in both types of source rocks. Specifically, mudstones are characterized by a cluster-like organic matter distribution, whereas shales are characterized by a layered organic matter distribution. Thermal evolution simulation experiments demonstrate that the hydrocarbon generation process is accompanied by the emergence of micro-fractures, which are favorable for hydrocarbon expulsion. Moreover, based on the theories of rock physics and fracture mechanics, this study establishes micro-fracture development models for both types of source rocks, associated with the calculation of the fracture pressure that is needed for the initiation of fracture development. Furthermore, the relationship between the fluid pressure, fracture pressure, and micro-fracture expansion length during micro-fracture development is quantitatively explored, which helps identify the micro-fracture expansion length. The results indicate that the development of micro-fractures is commonly impacted by the morphology and distribution pattern of the organic matter as well as the mechanical properties of the source rocks. The micro-fractures in turn further affect the hydrocarbon expulsion capacity of the source rocks. The results of this study are expected to provide theoretical and practical guidance for the exploration and exploitation of tight oil and shale oil.

【 授权许可】

Unknown