低阶煤储层微观孔隙结构多尺度联合表征

Multi-scale joint characterization of micro-pore structure of low-rank coal reservoir

多尺度微观孔隙结构对低阶煤储层煤层气吸附/解吸过程的研究具有重要意义。以黄陇侏罗系煤田和陕北侏罗系煤田低阶煤为研究对象,采用压汞、液氮吸附和CO2吸附等测试手段表征低阶煤储层的孔径分布、孔隙类型等参数,联合核磁共振测试定量分析低阶煤阶段孔径和多尺度孔径分布特征。结果表明,低阶煤孔隙以微孔为主,大孔次之。微孔、大孔、介孔对比表面积的贡献率依次减小。低阶煤储层孔隙类型以两端开口的“柱状孔”和“墨水瓶孔”为主,孔隙连通性较好。核磁共振法获取样品的T2 c截止值为1.4~155.2 ms,变化较大,束缚流体饱和度(BVI)为79.21%~96.96%,可动流体饱和度低。低阶煤储层的孔隙结构复杂多样,单一测试技术与联合计算表征方法在表征低阶煤储层的孔隙结构时差异较大。

The multi-scale micro-pore structure is of great significance to the study of the adsorption/desorption process of coalbed methane in low rank coal reservoirs.Taking Jurassic Huanglong coalfield and Shaanbei coalfield as examples,the pore size distribution andpore types of low-rank coal reservoirs were measured by mercury injection,liquid nitrogen adsorption and CO2 adsorption.Combined with nuclear magnetic resonance,the pore size and multi-scale pore size distribution characteristics of low-rank coal were quantitatively analyzed.The results show that the pores of low-rank coal are mainly micropores,followed by macropores.The contribution rate of micropores,macropores and mesoporous pores to specific surface area decreased in turn.The pore types of low-rank coal reservoirs are mainly“columnar pore”and“ink bottle hole”,which have good pore connectivity.The T2 c cut-off value of the samples obtained by NMR method is 1.4-155.2 ms,which varies greatly.The bound fluid saturation(BVI)is 79.21%-96.96%,and the movable fluid saturation is low.The pore structure of low-rank coal reservoirs is complex and diverse,and there are great differences between single test technique and combined computing characterization method in the characterization of pore structures of low-rank coal reservoirs.