Visualization of Shale Oil Occurrence Characteristics and Analysis of Main Controlling Factors Within Microdomains: Insights from Raman Mapping Combined with AFM

Abstract

It is of great significance to visually investigate the occurrence characteristics and controlled factors of shale oil within microdomains to determine its migration and production. However, a significant gap exists in visually investigating the intricate interplay between shale oil, mineral composition and pore structure, which has hindered shale oil production. To address this gap, this study used Raman mapping to intuitively analyze the occurrence characteristics of shale oil and applied Raman mapping combined with atomic force microscopy (AFM) to investigate the interrelationship between shale oil occurrence characteristics, mineral compositions and pore structure of the Permian Fengcheng Formation in the Mahu Sag of the Junggar Basin. The results show that the occurrence of shale oil can be divided into four types. More specifically, microdomains with high total organic carbon (TOC) content and developed pores are most favorable for shale oil occurrence, whereas microdomains with high TOC content and migration pathways are relatively unfavorable. Microdomains with high TOC content and undeveloped pores are unfavorable for shale oil occurrence, whereas microdomains with low TOC content and undeveloped pores are the most unfavorable. The shale oil content was positively correlated with the carbonate, feldspar, pyrite, and reedmergnerite contents. Conversely, the shale oil content was negatively correlated with the quartz content. Furthermore, the AFM phase peaks at the interiors of the elliptical- and slit-shaped pores positively shifted by 11.1% and 54.4% more than at the interface, respectively. The interiors of slit- and elliptical-shaped pores always showed a higher shale oil Raman signal than the exteriors of these pores, both of which indicate that these two types of pores are favorable for shale oil occurrence. These findings improve our understanding of the key factors influencing the oil-bearing properties and occurrence characteristics of shale oil within microdomains and provide a new analytical perspective for the effective exploitation of shale oil.