基于液氮吸附法的淮南煤田晚石炭世太原组灰岩孔隙结构特征研究
Study on Pore Structure Characteristics of Limestone of Late Carboniferous Epoch Taiyuan Formation in Huainan Coalfield Based on Liquid Nitrogen Adsorption Method
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摘要: 灰岩孔隙发育特征是认识灰岩中吸附气储集和运移的重要因素。以淮南煤田晚石炭世太原组含煤岩系典型钻孔剖面为研究对象,按地层层序由上而下依次采集不同层段灰岩样品,采用低温液氮吸附法,结合扫描电子显微镜(SEM),联合观察灰岩样品的比表面积和孔径分布特征。研究成果表明:不同层段灰岩孔隙类型主要以次生晶间微溶孔为主,其次为超晶微溶孔、溶解晶洞和溶蚀裂缝;不同层段灰岩样品比表面积、总孔容与氮气吸附总量呈正相关,即随着样品比表面积、总孔容增大,氮气吸附能力增强,孔隙发育程度增大;各样品平均孔隙半径随着外表面积的增加而减少;各样品孔隙结构以中孔为主,次之为微孔,含少量大孔;良好的孔隙之间连通性,有利于油气、水的储集和运移作用。Abstract: The pore development characteristic of limestone is an important factor in understanding the adsorption gas reservoir and migration in limestone. In this paper, the typical geological section of coal-bearing series of the late Carboniferous epoch Taiyuan formation in Huainan coalfield is taken as the research object; the samples of different layers of limestone are collected from the upper and lower layers according to the stratigraphic sequence. The specific surface area and pore size distribution characteristics of limestone samples are observed by using the low temperature nitrogen adsorption method combined with scanning electron microscope (SEM). The results show that: the pore types of limestone in different layers are mainly secondary intergranular micro-pores, followed by super micro-pores, dissolved geodes and dissolution cracks; the specific surface area and total pore volume of limestone samples in different intervals are positively correlated with the total nitrogen adsorption, i.e., with the increase of specific surface area and total pore volume, the nitrogen adsorption capacity is enhanced and the porosity development degree is increased; the average pore radius decreases with the increase of the outer surface area; the pore structure of each sample is dominated by mesopores, followed by micropores and contains a small amount of macropores; good connectivity between pores, is conducive to oil and gas, water storage and migration.
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