Movable oil content evaluation in low-to-medium maturity lacustrine shale during in-situ conversion

Low-to-medium maturity shale oil resources hold significant potential, but their economic accessibility is limited by low porosity, low permeability, and a low proportion of movable oil. In-situ conversion technology can crack organic matter and in-place oil into lighter molecules, enhancing oil and gas mobility and improving recovery rates. The success of this approach depends on dynamically evaluating the amount of movable shale oil during in-situ conversion. This study targets the lower submember of the fourth member of the Eocene Shahejie Formation (Lower Sha4 Member) in the Damintun Sag, Bohai Bay Basin, China. Through thermal simulation experiments, organic geochemical experiments, and nuclear magnetic resonance experiments, shale residual oil evaluation, organic matter hydrocarbon generation process evaluation, and dynamic evaluation of immovable oil were carried out. By integrating numerical simulations of the temperature field with the experimental results, a dynamic evaluation method for movable resources in shale during in-situ conversion was established. The findings indicate that the conversion rates of kerogen-to-oil and kerogen-to-gas first increase and then gradually stabilize as thermal maturity increases, with oil generation reaching its peak when the vitrinite reflectance reaches 1.0%. Long-term preserved shale samples were identified to contain immovable oil, the content of which increases with maturity before peaking and then declining. In-situ conversion of low-to-medium maturity shale in the upper part of the model can significantly increase movable oil resources in a year, potentially reaching the levels of extractable medium-to-high maturity shale. This work presented a crucial approach for assessing and improving in-situ conversion technology, providing a means of maximizing economic feasibility. Document Type: Original article Cited as: Bai, G., Chen, G., Cai, Z., Yan, H., Lu, S., Radwn, A. E. Movable oil content evaluation in low-to-medium maturity lacustrine shale during in-situ conversion. Advances in Geo-Energy Research, 2025, 16(1): 77-90. https://doi.org/10.46690/ager.2025.04.08