大宁-吉县区块山西组煤储层微观孔隙结构特征

Microscopic pore structure characteristics of Shanxi Formation coal reservoir in Daning-Jixian Block

煤储层微纳米孔隙精准描述对煤层气的储集和产气能力评价发挥着重要的作用,以鄂尔多斯盆地东缘大宁-吉县地区6个连续取样的高阶煤样品为研究对象,采用高压压汞、低温N_(2)吸附和低压CO_(2)吸附实验联合表征微纳米孔隙结构特征,旨在深入了解全尺寸孔隙大小分布,并探讨煤储层孔隙结构的影响因素。研究结果表明:研究区煤样孔体积、比表面积随孔径分布存在明显差异,煤样微孔对总孔体积和总比表面积的贡献率显著,尤其是直径<1.5 nm的微孔,为大部分吸附气提供了存储空间;而介孔和宏孔对孔体积和比表面积的贡献相对较小,不利于煤层气的渗流;研究区煤样的镜质组含量与孔体积、比表面积呈较好的正相关关系,对孔隙发育有重要贡献;惰质组含量与孔体积、比表面积间关系不明显;随着空气干燥基水分含量增加煤样中有更多吸附孔的发育,而孔体积、比表面积与干燥基灰分产率呈负相关关系,表明灰分产率的增加会导致孔体积和比表面积的降低。

Accurate description of micro and nano pores in coal reservoir plays an important role in evaluating the reservoir and gas production capacity of coalbed methane,we used 6 continuous samples of high rank coal in Daning-Jixian area on the eastern margin of Ordos Basin as the research object,and combined with high pressure mercury injection,low temperature N_(2) adsorption and low pressure CO_(2) adsorption experiments to characterize the pore structure characteristics.The aim of this study is to have an indepth understanding of the full-size pore size distribution and explore the influencing factors of coal reservoir pore structure.The results show that the pore volume and specific surface area of coal sample in the study area have obvious differences with the pore size distribution,and the contribution rate of coal sample micropores to pore volume and specific surface area is significant,especially the diameter less than 1.5 nm micropore provides storage space for most of the adsorptive gas.The contribution of mesoporous and macroporous to pore volume and surface area is relatively small,which is not conducive to coalbed methane seepage.The vitrinite content of coal samples in the study area is positively correlated with pore volume and specific surface area,which contributes signific-antly to pore development.The relationship between inertinite content and pore volume and surface area is not obvious.With the increase of Mad,more adsorption pores are developed in coal samples,and pore volume and specific surface area are negatively correlated with Ad,indicating that the increase of Ad will lead to the decrease of pore volume and specific surface area.