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

Overpressure systems in the Qingshankou Formation of the Gulong Sag have a significant impact on unconventional shale oil accumulation, but their distribution and genesis are unknown. This study uses a comparative analysis of three primary pressure prediction methods—the equivalent depth method, the Eaton method, and the Bowers method—to investigate the genetic mechanisms of overpressure and their controlling factors. The study clarifies the link between overpressure and hydrocarbon distribution. The key findings are as follows. (1) The Eaton method is identified as the best approach for estimating current formation pore pressure. The Qingshankou Formation exhibits mild overpressure development, with a maximum pressure coefficient of 1.44. (2) Hydrocarbon-generating overpressure, driven by source rock maturation, is confirmed as the dominant mechanism through integrated acoustic velocity–density cross plots and logging analysis. (3) Tectonic-sedimentary factors, such as burial depth, source rock thickness, sand-mud ratio, and faults, collectively control the spatial variability of overpressure. (4) The distribution of the Gulong shale oil and the Fuyu tight oil is influenced by overpressure, with the northwestern part of the sag and the adjacent sand bodies being the respectively favorable areas. These results lay the groundwork for accurately reconstructing paleopressure and better understanding the hydrocarbon accumulation potential of shale oil and Fuyu tight oil. They also provide guidance on the exploration and development of unconventional resources.