VOLUME METHOD BASED POTENTIAL EVALUATION ON MINE WATER-BASED GEOTHERMAL RESERVOIR IN ABANDONED COAL MINE

One basic principle of the 'equilibrium mining' theory is the space conservation-based mining damage invariant equation. This paper analogically analyzes the damage patterns between caving and fractured zones in a long-wall coal mining goaf. Specifically,the paper derives linear(caving zone) and logarithmic(fractured zone) functional expressions to capture the vertical expansion and void distribution characteristics of the above two-zones in abandoned Jiahe colliery. On this basis,a multi-stage conceptual model is then proposed to describe the evolution processes of the vertical expansion and void distribution characteristics of the two-zone. After the required void characteristic parameters of the two-zone are obtained,the paper roughly calculates the void/water-storage volume under the hypothesis of inverted trapezoidal shape of the two-zone structure. Accordingly,the potential of the mine water-based low enthalpy geothermal fluid formed in abandoned and thereafter flooded Jiahe coal mine is evaluated using the volume method. The results indicate that the estimated water storage capacity contained in a typical long-wall mining goaf in abandoned Jiahe mine is 3.4~3.8×10⁵ m³. The overlying rock lithology affects the bulking factor and void ratio vertical distribution in the caving and fractured two-zones,and thereby the water volume and geothermal potential of the order of 10%. Moreover,the void-water stored in mining gobs is about two orders of magnitude larger than that in the shafts and tunnels for abandoned coal mines,which need to have more attention in future study. Finally,the total estimated water storage capacity of the abandoned Jiahe colliery is about 2.2×10⁷ m³,corresponding to a static geothermal potential of approximately 127 GWh(~4.6×105 GJ),which may provide guideline for further exploration and exploitation.