Radial-symmetric well design to optimize coal yield and maintain required safety pillar width in offshore underground coal gasification

Underground coal gasification (UCG) enables utilization of coal seams, currently not economically extractable due to complex geological boundary conditions. The technical and economic feasibility of onshore UCG operation has been extensively investigated in the past decades, while studies on offshore UCG operations are rare. We propose a radial-symmetric well design and validate it by means of geomechanical simulations. Our calculations and simulation results demonstrate that a coal yield of 46% can be achieved with safety pillar widths of 100 m. For an extracted coal seam thickness of 11 m, seabed level subsidence amounts to 0.16 m.