Terrestrial shale oil has emerged as a crucial area for enhancing China’s oil and gas reserves and output. In recent years, the establishment of demonstration zones has marked the entry of China's terrestrial shale oil into a phase of scaled exploration and development. In 2023, China’s total shale oil output exceeded 4 million tons, becoming a vital supplement to stable crude oil production. Currently, most of the output comes from medium to high-maturity formations, primarily tight-oil-type shale, where oil is found in interbedded tight sandstones adjacent to organic-rich shale.

Research on terrestrial shale oil is deepening, and we recently interviewed Professor Zhao Wenzhi, Academician of the Chinese Academy of Engineering and former Director of CNPC’s Research Institute of Petroleum Exploration and Development, who offered insights into shale oil recovery challenges and solutions.

Key Takeaways from the Academician
China’s terrestrial shale oil is characterized by high contents of colloids and asphaltenes, as well as heavier fractions among saturated hydrocarbons. These features negatively impact oil mobility and cumulative recovery—especially in pure shale layers, where strong clay adsorption and confinement within nano-scale pores further reduce flow potential. Without sufficient light and intermediate hydrocarbons, the economic recoverability of shale oil significantly decreases.

Shale oil mainly resides in ultra-tiny nano-scale pores, coexisting with a high proportion of clay minerals, which strongly adsorb oil molecules and hinder their mobility. Oil quality and composition vary greatly by region, and these differences significantly affect flowability and recovery. A key, yet underexplored issue is the concept of "component flow"—a new approach to evaluating the mobility of shale oil and its impact on economic recoverability.

What Is Component Flow?
"Component flow" refers to the phenomenon where multiple oil components—light, intermediate, and heavy hydrocarbons—form a miscible phase during initial flow, based on the "like dissolves like" principle. This enhances the mobility of heavier components like resins and asphaltenes, allowing them to flow alongside lighter molecules.

In this process, heavier molecules are suspended in lighter hydrocarbons, increasing cumulative oil recovery. Without adequate light and intermediate hydrocarbons, heavy fractions struggle to move through nano-scale pores—similar to heavier individuals trying to exit through a narrow door behind faster, slimmer people.

Mechanism and Production Implications
During early production, higher reservoir energy facilitates component flow. As lighter components are gradually depleted, heavier fractions accumulate and block pores, reducing output. Post-cleaning, production often temporarily rebounds due to renewed miscibility and energy restoration, but the effect is short-lived. Studies from certain basins show that light and intermediate hydrocarbons are essential solvents, dissolving and mobilizing heavier molecules to enhance output.

Research Objective: Maximizing Recovery
The ultimate goal of studying component flow is to maximize shale oil recovery. The challenge lies in breaking down large aggregates of heavy hydrocarbons into smaller, more flowable units using in-situ light/intermediate hydrocarbons as solvents, which lowers viscosity and enhances flow.

Typically, shale pores show strong interaction between pore walls and fluid molecules, resulting in multi-layer adsorption and quasi-solid layers. With adequate light/intermediate hydrocarbons, heavy molecules can form suspended aggregates, facilitating flow and boosting cumulative recovery.

Development Strategy
A proper ratio among components is critical. The higher the content of light hydrocarbons, the more favorable the component flow. Avoiding premature depletion of these lighter fractions is crucial to maintain steady flow and high recovery.

Efficient development requires balancing production rate and reservoir pressure to sustain component flow. Over-enlarged choke diameters and aggressive production pressure drops can destabilize the flow regime—leading to early depletion of light components and pore clogging by heavy fractions, causing sharp production declines.

A well-managed development approach preserves in-situ compositional balance and energy, enabling sustained and stable component flow and maximizing output.

Case Study: Cretaceous Gulong Shale Oil in Songliao Basin
This high-maturity shale oil, rich in gas and light hydrocarbons, exhibits over 90% saturated and aromatic hydrocarbons, with less than 10% colloid/asphaltene. In production, lighter components flow first, while heavier fractions accumulate and eventually hinder flow. Thus, maintaining sufficient light/intermediate hydrocarbons in the reservoir is essential for prolonged and efficient production.

Conclusion
Research on shale oil has entered the micro-scale domain, revealing that not all shale oil is recoverable due to complex pore structures and compositions. Component flow—a concept still under-recognized—is vital to maximizing economically recoverable shale oil. By understanding and managing the miscibility and flow conditions of multi-component hydrocarbons, producers can significantly enhance recovery rates and ensure the commercial viability of terrestrial shale oil development in China.