Case Study on the Application of In-Situ Combustion for Ultra-Low Permeability Oil Shale from Natih B Formation (Oman): Synthetic Oil Generation and Micro-Scale Pore Structure Changes

Abstract

Oil shale is considered as the world's second largest solid fossil fuel resource. Oil shale is an extremely ash-rich sedimentary rock loaded with organic matter. Most of the organic matter is rich in kerogen and a small amount of bitumen, which can be converted into synthetic oil using different thermal treatment methods. In-situ combustion (ISC) is a promising thermal enhanced oil recovery (EOR) method for the conversion of kerogen contained in oil shale to synthetic oil by oxidation. However, its field application is still limited due to difficulty in ignition, low combustion efficiency, and low rock permeability, etc. The main goal of this work was to determine the optimal conditions for synthetic oil generation and changes in the properties of oil shale. In this work, a self-designed combustion tube was developed to evaluate the effect of catalyst and water, including improving combustion front propagation and shale oil recovery. Copper (II) stearate (0.1 wt% by metal) was used as an oil-soluble catalyst to improve the process of ISC. The performance of ISC was evaluated in terms of material balance, recovery factor, composition of evolved gases, and produced synthetic oil quality. In addition, the changes in the properties of oil shale rock were also investigated using 3D computed tomography. According to the results of the combustion tube experiments, the presence of both water and catalysts is favorable for reactions that produce synthetic oil, sufficient heat generation (according to CO2 release) and hydrocarbon gases. The temperature profile and pressure profile indicate a successful ignition and successful establishment of combustion front for Natih B oil shale. The catalysts and water together improved the stability of combustion front and increase the efficiency of ISC process. The permeability was increased about 4 times higher after combustion. Generally, these promising results technically prove the potential for the development of shale oil from Natih B Formation (Oman) by ISC process. The use of ISC can allow the conversion of oil shale into light synthetic oil with hydrocarbon gas production. Moreover, based on the obtained results the in-situ combustion can occur in ultra-low permeability reservoirs.