Geological site selection and evaluation for underground coal gasification

The key technology of underground coal gasification (UCG) has rapidly developed since the 21st century. The modern UCG technology based on directional borehole in the coal seam and moveable gas injection is growing ma-ture and is expected to provide the technical basis for UCG commercialization. The technical process of UCG consists of site selection,gasifier construction,ignition,measurement & control,groundwater pollution control & prevention,shut down of gasifier. Geological site selection for UCG is the most important guarantee condition for UCG project plan,sta-ble operation control,and groundwater pollution prevention. In this paper,typical UCG technical routings were out-lined. Combined with the modern UCG technology,the basic principles for geological site selection were put forward from the aspects of coal reserves,coal seam conditions,geological structure,hydrogeological conditions,roof and bottom rock stability,coal types and coal property. On this basis,taking the Ha Jigobi mining area in Inner Mongolia as an ex-ample,a case study of UCG geological site selection was carried out. Based on the results of 3D seismic interpretation and wave impedance inversion data,the spatial distribution and fault development characteristics of the target coal seam were studied. By analyzing the results of the pseudo-acoustic inversion,the distribution characteristics of the li-thology of the roof and floor of the target coal seam were obtained. Based on seismic attributes and apparent resistivity log curves,a multi-attribute neural network inversion was used to study the water abundance of the target coal seam and the roof and floor. Based on the ant body attribute technique,the fracture development characteristics of the target stratum were analyzed. Finally,the comprehensive evaluation of the geological site selection of the case study area was carried out from the aspects of coal seam distribution and structural characteristics,lithological distribution characteris-tics,water abundance conditions and fracture development law,which was used as the decision-making basis for scien-tific site selection.