Effect of silica sol on the sealing mechanism of a coalbed methane reservoir: New insights into enhancing the methane concentration and utilization rate

The low efficiency of coalbed methane (CBM) extraction not only causes a great waste of energy resources and environmental pollution but also poses potential safety risks during coal mining. The main reasons for these issues are the weak borehole sealing effect and serious air leakage that occur during CBM extraction. Seeking an effective sealing material is the key to improve the efficiency of CBM extraction and to protect the environment. In this paper, to explore ways to break through this bottleneck, the feasibility of silica sol (S.G325) as a sealing material for the boreholes used in CBM extraction was theoretically demonstrated. Scanning electron microscopy (SEM) was used to compare the surface morphological characteristics of S.G325 and some commonly used sealing materials. The performance of these materials after sealing the pores/fractures in the methane reservoir was also evaluated using mercury intrusion, an helium porosimeter and methane seepage tests. The experimental results indicate that S.G325 has obvious advantages over other materials because of its greater compactness, stability and performance after sealing. Evaluation of the effects of enhancing CBM extraction showed that S.G325 increased the initial concentration of CBM from 60% to 73.5%-82.9%, the amount of time the CBM that can be utilized from 54 d to 99 d -132 d, the volume of utilizable CBM from 3421 m(3) to 4951 m(3) - 5773 m(3), and the utilization rate of CBM increased by 44.7%-62.8% compared with the original utilizable methane volume. In this paper, new insights into the improvement of energy resource utilization and protection of the environment are shown.