基于低温液氮吸附实验的沁南无烟煤孔隙结构特征

Pore structure characteristics of anthracite coal in Southern Qinshui basin based on low-temperature nitrogen adsorption method

为实现沁南地区煤层气井高产稳产,以沁南地区无烟煤为研究对象,采集不同煤矿3^(#)煤层的5个煤样,采用低温液氮吸附实验并结合扫描电子显微镜(scanning electron microscope,SEM)研究煤储层孔隙结构特征。结果表明:变质孔和溶蚀孔在沁南无烟煤中尤为常见,可见较多微裂隙,张裂隙和剪裂隙均有发育;孔隙以微孔为主,大多为吸附孔,渗流能力较差,平均比表面积为1.34185 m^(2)/g,平均孔容为0.00720 cm^(3)/g,平均孔径为29.24 nm;低温液氮吸附回线可以划分为3种类型,HX1型和HX2型孔隙形态以狭窄缝隙形孔为主,但HX2型存在部分两端开口透气性孔和少量墨水瓶形孔;HX3型孔隙形态由2个部分组成,在孔径<4.5 nm范围主要为狭窄缝隙形孔,在孔径>4.5 nm范围主要为狭窄缝隙形孔和墨水瓶形孔;以相对压力0.5为分界点,低压段和高压段具有不同的孔隙结构分形特征,分形维数D_(1)和D_(2)与吸附回线类型具有明显相关性。

To achieve high and stable production of CBM wells in Qinnan area,takeing anthracite coal in Qinnan area as the research object,five coal samples from the 3#coal seams of different coal mines were determined by low-temperature nitrogen adsorption experiment and scanning electron microscope(SEM)for the study of coal reservoir pore structure.The results show that metamorphic pores and dissolution pores are particularly developed.Many micro-cracks are also seen,and both tension and shear fractures are developed.The average specific surface area is 1.34185 m^(2)/g,the average pore volume is 0.00720 cm^(3)/g,and the average pore size is 29.24 nm.The pores are mainly micropores,most of which are adsorption pores,with poor seepage capacity.The low-temperature liquid nitrogen adsorption loops can be divided into three types.HX1 and HX2 pores are mainly narrow slit-shaped holes,but HX2 also has some open air-permeable holes at both ends and a small number of ink bottle-shaped holes;HX3 pore morphology consists of two parts,in the smaller pore size range(<4.5 nm)mainly narrow slit-shaped pores,in the larger pore size range(>4.5 nm)mainly narrow slit-shaped holes and ink bottle-shaped holes.With a relative pressure of 0.5 as the dividing point,the low-pressure section and the high-pressure section have different fractal characteristics of pore structure.The fractal dimension has a clear correlation with the type of adsorption loop.