原煤孔隙拓扑特征对CO_(2)-ECBM过程的影响机制

Impact mechanism of pore topological characteristics to CO_(2)-ECBM

为了研究原煤孔隙拓扑特征对CO_(2)-ECBM过程的影响,选取羊场湾矿褐煤、胜利矿肥煤、阳泉无烟煤,基于X-ray CT扫描技术三维重构了原煤孔隙空间拓扑结构,同时利用受载原煤注气置驱甲烷THM耦合实验台,进行了不同条件下原煤注CO_(2)置驱CH_(4)分步实验。结果表明:羊场湾褐煤、胜利肥煤、阳泉无烟煤的孔隙发育程度、空间分布、连通性依次变差;原煤CO_(2)-ECBM过程经历3个阶段,早期阶段置换作用占主导,中期阶段置换、载携、稀释作用并存,后期阶段载携、稀释作用占主导;对于孔隙发育均匀且连通性较好的羊场湾褐煤,置驱过程以早期阶段为主;地应力和注气压力能够显著影响甲烷置驱效率,煤孔隙空间拓扑性质是重要影响因素,但阳泉无烟煤的强吸附性能够在一定程度上改善渗流通道缺失引起的甲烷置驱缺陷。

In order to study the impact of pore topological characteristics to CO_(2)-ECBM process in raw coal,YCW lignite,SL fat coal and YMY anthracite samples were selected,and the topological structure of raw coal pore space was reconstructed based on X-ray CT scanning technology.And the THM coupling experimental platform for methane displacement by gas injection of loaded raw coal was established,and the experiment of CH_(4) displacement by CO_(2) injection in raw coal under different conditions was conducted.Results show that:the porosity development degree,spatial distribution and connectivity of YCW lignite,SL fat coal and YMY anthracite become worse in turn.The CO_(2)-ECBM process in raw coal goes through three stages:the replacement is dominant in the early stage;the replacement,carrying and dilution coexist in the middle stage;the carrying and dilution are dominant in the later stage.Stress and gas injection pressure can significantly affect methane displacement efficiency,and the topological property of coal pore is an important influencing factor.However,the strong adsorption of YMY anthracite can improve the methane displacement defect caused by the lack of seepage channel to a certain extent.