Abstract
Some major hydrocarbon-bearing basins are rich in shale with terrestrial facies in China, which may provide abundant terrestrial shale oil and gas resources. This work studied the Jurassic Lianggaoshan Formation in the Southeast Sichuan Basin of the upper Yangtze Region. Core samples were chosen for the total organic carbon content and mineral composition analyses to classify shale lithofacies. Afterward, pore connectivity, pore wettability, and shale oil mobility with different lithofacies were characterized by spontaneous imbibition, nuclear resonance, and centrifugation. Conclusions are as follows: the pore connectivity of organic-rich clay shale was mostly between moderate to good with oil-prone wettability and high mobile oil saturation. The organic-rich mixed shale has moderate to good pore connectivity, water-prone wettability, and the highest mobile oil saturation. Organic matter–bearing clay shale has bad to moderate pore connectivity. Meanwhile, its pore wettability covers oil wetting, mixed wetting, oil-prone wetting, and water-prone wetting. Its mobile oil saturation was moderate. Regarding organic matter–bearing mixed shale, the pore connectivity was bad to moderate with mixed-wetting pore wettability and moderate mobile oil saturation.
Highlights
China has achieved major progress in marine shale gas exploration in the Sichuan Basin and its surrounding areas, with shale gas fields built in Jiaoshiba, Weiyuan, Changning, Zhaotong, Luzhou, and other regions (Tan et al, 2014; Liu et al, 2018; Long et al, 2018; Xu et al, 2019; Yi et al, 2019)
Some oil and gas-bearing basins in China, including Sichuan, Junggar, Bohai Bay, Songliao, and Ordos, are home to both marine and terrestrial strata, where terrestrial shale contains a large amount of potential shale oil and gas resources due to the moderate burial depth
This study explored pore structure characteristics of terrestrial shale with different lithofacies types, with the key exploration well TY1 being taken as the research object in the case analysis of terrestrial shale from the Jurassic Lianggaoshan Formation in the southeast Sichuan Basin of the upper Yangtze Region in southern China (Figure 1)
Summary
Huge achievements have been underscored in geological theories about unconventional oil and gas, horizontal drilling, fracturing technologies, and decreasing single-well drilling costs. Shale pores serve as the primary reservoir space and seepage channel of light shale gas, and their connectivity as well as wettability are important research objects in studying a shale reservoir’s characteristics because they affect the difficulty of oil and gas transportation in shale. Jiang et al (2020) studied terrestrial shale experimental tools including scanning electron microscope, Soxhlet extraction, gas adsorption, nuclear magnetic resonance, and centrifugation. They pointed out that pore structure characteristics and mineral composition of shale reservoirs jointly control the mobility of shale oil. Experiments were conducted on shale samples: spontaneous imbibition was adopted to clarify the pore connectivity and wettability of shale with different lithofacies types; nuclear resonance and centrifugation were used to study the mobility of shale oil with different lithofacies types
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