Study on the Microscopic Oil Content Characteristics of Gulong Shale

Micro-nano pores and their oil-bearing properties are important information for shale oil exploration and development, and the core of the study of shale oil reservoir characteristics is the pore structure of the reservoir and the occurrence form of shale oil in the pores. Gulong shale has abundant reservoir space and diverse pore types, and the characteristics of hydrocarbon occurrence and enrichment in shale are the problems we need to solve urgently. In order to fully understand the microscopic distribution characteristics of shale oil, this study used field emission electron microscopy (FESEM) and environmental scanning electron microscopy (ESEM) to qualitatively describe and observe the occurrence state of shale oil in micro-nano pores. It is found that shale oil can exist in various types of pores and pore sizes, such as intergranular pores, particle dissolution pores, organic pores, clay mineral intergranular pores, pyrite intergranular pores, fractures and foliation fractures. Laser confocal analysis shows that shale oil can be enriched in both matrix pores and micro-fractures. With the help of nuclear magnetic analysis technology, two-dimensional nuclear magnetic analysis before and after chloroform oil washing shows that shale oil occurrence pore size is 3–5000 nm, mainly 3–300 nm. This discovery breaks through the traditional understanding that the lower pore diameter of shale oil is greater than 20 nm, indicating that there is no lower pore diameter of oil in Gulong shale. In order to further verify that shale oil can exist in nano-sized pores, nitrogen adsorption experiments before and after oil washing of multiple shale samples are compared. The results show that pore volumes in the 2 nm–8 nm range after oil washing show a significant increase trend, and it is also confirmed that shale oil can be distributed in small pore sizes between 2 nm–8 nm, indicating that shale small pores contain a large amount of crude oil. The volume of 8nm-16nm and 16 nm–32 nm pore also increased after oil washing, and the increasing trend was weaker than that of 2 nm–8 nm pore. By comprehensive application of a variety of experimental techniques and analysis results, this study clarified that Gulong shale oil has the characteristics of oil and gas enrichment in various types of pores and pores of various sizes and pore sizes, providing reliable technical support for the theory of shale oil source origin storage.