Combined Analytic Hierarchy Process and Weighted Interval Method Models for the Geological Evaluation of CO2 Storage in Coal Goaf

The increasing concentration of CO2 in the atmosphere is a major factor contributing to climate change. CO2 storage in coal goaf is a convenient, effective, and economical solution. Methods to quickly and effectively evaluate geological conditions are urgently required. The main influencing factors are geological safety, storage potential, economics, and environmental protection; these include 4 aspects, 38 indexes, and 4 index levels that can be quantified using classification levels. We established a geological evaluation model, using analytic hierarchy process (AHP) and weighted interval methods. AHP was used to determine its elements, indicators, and inter-layer relationships, as well as to clarify its structural relationships. The weight interval method is used to evaluate unstable elements, reducing their difficulty, and constant values are used to assign weights of stable elements to increase accuracy. This model was applied to assess the suitability of the goaf in Yaojie mine for geological CO2 storage. The results revealed that this goaf is an above average CO2 storage space, which was consistent with previous research. This geological CO2 storage evaluation model may also be used to assess the CO2 storage suitability of other coal goafs.