An innovative nitrogen injection assisted in-situ conversion process for oil shale recovery: Mechanism and reservoir simulation study

In-situ conversion process (ICP) can be an effective technique for the development of oil shale and ultra heavy oils, in which kerogen or heavy components will be cracked into light oils and gases via underground heating and pyrolysis, and the retorted oil can be recovered via conventional extraction techniques. Heating of targeted formation can be conducted using electrical heaters installed in vertical or horizontal wells, while a slow heating rate and lack of driving energy for oil production are the main issues of the conventional in-situ conversion process. In this study, an innovative nitrogen injection assisted in-situ conversion process (NAICP) was proposed to increase formation heating rate and improve oil production from oil shale. Reaction models of kerogen pyrolysis at elevated temperature were established, along with models for the evolution of porosity and permeability of oil shale formation during the pyrolysis process. The performance of nitrogen injection on the effectiveness of the ICP was then investigated through reservoir numerical simulation. The simulation results show that additional nitrogen injection can improve the heating rate of the oil shale formation, enhance oil production and energy efficiency in comparison with the conventional ICPs, which can be attributed to enhanced heat convection, pressurization effect and gas driving mechanism. Nitrogen injection assisted in-situ conversion process can be a promising technique for the exploitation of oil shale.