Underground coal gasification modelling in deep coal seams and its implications to carbon storage in a climate-conscious world

As a clean coal technology, underground coal gasification (UCG) boasts a prospect in tapping worldwide deep coal seams, with a tremendous potential to be linked with following carbon storage and sequestration. Therefore, UCG ought to play a vital role as a sustainable technological alternative in a climate-conscious world. However, the world has very limited experience in deep UCG development because most of the tests were on shallow coals. This paper aims to bridge the knowledge gap to shed light on the development of UCG cavities in deep coal seams. A large-scale 3D UCG model was constructed with an improved Controlled Retraction Injection Point (CRIP) method, which is more suitable to deep UCG. In addition, the effect of double-diffusive natural convection was included. Modelling results show that the improved method contributed to a favourable development of UCG cavities in deep coal seams with a good gas production. Compared to a shallow UCG, pore variations exhibited a similar pattern but with distinct characteristics owing to the effects of a high pressure. Furthermore, double-diffusive natural convection was revealed to play an important role in the development of cavities and the general UCG performance. The relevant findings will help enhance the knowledge base of UCG operations in world deep coal seams, promote the clean utilization of world coal resources, and if linked to carbon dioxide storage and sequestration, contribute to the reduction of carbon dioxide emissions in a climate-conscious world.