Effect of pressure on the oil shale convection heating in-situ conversion process

Abstract

In-situ conversion technology represents the developmental trend for large-scale commercial exploitation of oil shale. High-pressure geological conditions significantly influence the pyrolysis kinetics of oil shale and the in-situ extraction process. This study conducted pyrolysis experiments on Qingshankou Formation oil shale from the Songliao Basin under varying nitrogen pressures, analyzing temperature fields, pressure fields, and oil production. Concurrently, CMG software was employed to simulate the in-situ extraction process through high-temperature nitrogen injection, evaluating the impact of pressure variations on extraction effectiveness from perspectives of reservoir properties, product yield, and energy utilization efficiency. Laboratory results indicated that increased pressure led to higher reaction temperatures and thermal losses, which would be expected to reduce the oil yield, but higher pressure reduced the risk of reservoir plugging, so that the observed oil yield was higher at higher pressure. Numerical simulations revealed distinct pyrolysis kinetics under high pressure compared to atmospheric conditions, showing elevated activation energy and reduced conversion rates with pressure increase. During high-temperature nitrogen injection, cumulative oil production and energy efficiency decreased under higher pressures. Consequently, the simulation indicates that excessive pressure inhibits the effectiveness of convection.