Research status and significance of shale oil micromigration

Abstract

Significance The micromigration of shale oil refers to the phenomenon in which oil is generated in organic-rich layers and expelled at short distances to adjacent, preferable porous and permeable, organic-lean layers in shale systems. Micromigration can effectively improve the oil content and quality of organic-lean layers, even surpassing some organic-rich shale layers based on the exploration practices. Therefore, it is necessary to conduct a systematic study on the micromigration phenomenon of shale oil. Progress Based on the current research progress, this paper first identifies the main tracers of shale oil micromigration, which include rock pyrolysis parameters, hydrocarbon components, biomarkers, NSO compounds, as well as isotopes. The fundamental principle relies on fractionation between migrated hydrocarbons and retained hydrocarbons based on their geochemical properties. Analysis revealed that micromigration can lead to a dispersed distribution of hydrocarbon generation activation energy in organic-lean shale layers, resulting in an earlier hydrocarbon generation threshold. Moreover, the accumulation of light hydrocarbons in a free state in organic-lean layers can further increase the difference of hydrocarbon components between generative units and in-source reservoirs, thereby affecting the oil-bearing and mobility characteristics of shale. Based on the effects of petroleum migration and geological zonation, this paper reveals that micromigration occurs throughout the entire process of hydrocarbon generation, expulsion, and retention. It serves as a bridge connecting all elements of petroleum accumulation within shale systems, influencing the differential enrichment of shale oil. Conclusions and Prospects Comprehensive geochemical and geophysical methods are effective ways to identify micromigration in shale systems and will provide a new perspective for revealing the dynamic differential enrichment of lacustrine shale oil.

Keywords

• shale oil
• micromigration tracing
• geochemistry
• enrichment of shale oil