Study on site selection of underground gasification in deep coal seam: a case study of J148 area in Dongsheng Gas Field

Abstract

The feasibility of underground gasification of Yan 9 coal seam of the middle-lower Jurassic Yan ′an Formation in J148 area of Dongsheng gas field is systematically studied from the perspectives of geological structure, hydrogeology and coal gasification characteristics, and the prospects of carbon sequestration by using the pore layer, aquifer layer and tight gas layer in the deep coal gasification cavity are discussed.The results show that the coal seam of Yan 9 in this area is stable when the buried depth is 1 264~1 285 m and the dip angle is less than 1°.In the interior of the gasification target constituency, the structural faults are not developed, the joint cracks are not developed, there are occasional cracks but the section is fresh and closed, and the cavity of the coal seam after gasification has a good tightness, which has little influence on the construction and expansion of coal gasification furnace, and can meet the implementation of large-scale coal gasification projects.There is a continuous water barrier layer on the top and bottom of Yan 9 coal seam, which can prevent the influence of groundwater on the direct water filling of coal seam, and is conducive to the layout of underground gasifier.The thickness of the roof water-barrier layer is less than the height of the water-conducting fissure zone, there is a risk of indirect water filling through the roof aquifer, but the roof aquifer is a weak water-rich aquifer, and the risk of small water inflow is controllable.The thickness of the floor water barrier layer is greater than the safe thickness of the floor water barrier layer, which can effectively prevent the risk of direct water filling to the coal seam.In general, Yan 9 coal seam has moderate thickness, little waste, low ash, low sulfur, high calorific value non-stick coal, high coke reactivity, and has a good development prospect.In view of the large amount of CO2 emission from large-scale gasification mining of deep coal seam, the feasibility of CO2 safe geological storage by using coal seam burning and caving area, top and bottom aquifer and lower tight natural gas layer was discussed.The analysis shows that 60.8 % ~88.2 % of CO2 produced by coal seam gasification can be stored in the pore layer and the top and bottom aquifer in the gas-burning and air-burning zone of Yan 9 coal seam.Combined with the development of tight natural gas in the Upper Paleozoic of Dongsheng gas field, it is expected to achieve near-zero carbon emissions in the process of deep coal seam gasification mining by using CO2 generated by coal gasification for natural gas displacement and storage.

Keywords

• deep coal seam
• underground coal gasification
• site selection
• carbon dioxide storage