A review on upgrading and viscosity reduction of heavy oil and bitumen by underground catalytic cracking

Nowadays, the output of light crude oil is approaching its peak, which has shifted the attentions of petroleum industry to a large quantity of heavy oil and bitumen in order to offset the growing demand of energy and fuels. The heavy oil and bitumen are usually characterized by high viscosity, high density/low API gravity, low yield of low boiling point fuel fraction, and high heteroatom content in comparison with the light oil, requiring in situ upgrading to improve the mobility of heavy oil. before recovery it. One of the methods for upgrading is to add catalysts to the underground reservoir. This paper firstly reviewed various kinds of catalysts, including mineral, water-soluble, oil-soluble, solid acid, ionic liquid (IL) catalysts, and dispersed and super-dispersed catalysts that reported in domestic and foreign literatures, and secondly described their effectiveness in underground catalytic cracking and upgrading of heavy oil. This critical review suggests that it is necessary to develop the catalytic cracking catalysts of low-cost, high activity, high selectivity, and wide adaptability in order to accommodate a wide range of heavy oil with different properties, especially the ultra-dispersed nano-catalysts. The in situ upgrading technology by injecting super-dispersed nano-catalysts is a promising method to improve the quality of the lowest grade heavy oil components and enhance the recovery of heavy oil reservoirs. Moreover, further research is needed to explore the optimal process of catalyst synthesis, catalytic working conditions and the actual mechanisms of heavy oil with catalysts. (C) 2021 The Authors. Published by Elsevier Ltd.