Large-scale 3D experimental study on in-situ pyrolysis of tar-rich coal (I): Heat transfer behavior and product characteristics under conductive heating

Conductive heating is a key method for in-situ pyrolysis of tar-rich coal. However, the temperature and pressure characteristics, oil and gas production mechanisms, and reaction zone characteristics under high-pressure, large-scale conditions remain poorly understood. This study focuses on tar-rich coal from the eastern Ordos Basin in China and develops an experimental apparatus for in-situ high-temperature, high-pressure pyrolysis. Conductive heating experiments were performed, and the temperature, pressure, and oil and gas products were analyzed. CT scanning, Rock-Eval pyrolysis, and XRD analysis were also conducted on the post-pyrolysis rock samples. The results show that due to the low thermal conductivity of tar-rich coal, the heat injection capacity is inadequate, with the heater power efficiency reaching only 1.73%. After 482 h of experiment, the oil recovery is 1.97%, and the gas recovery is 27.86%. The oil consists of light components, and the gas primarily consists of CH₄. Because the temperature near the production well remains low, pyrolysis products migrating there cause heavy components to condense and accumulate, reducing local porosity to 0.25%. Furthermore, gaseous and light pyrolysis products preferentially migrated upward and accumulated near the top of the physical model. Therefore, arranging the production wells above the heating wells is recommended. This study offers theoretical support and experimental evidence for the in-situ pyrolysis of tar-rich coal using conductive heating.