可溶有机质对泥页岩储集物性的影响

Influences of soluble organic matter on reservoir properties of shale

可溶有机质是有机质的重要组成部分,为了研究可溶有机质对泥页岩储集物性的影响,对川东北地区龙马溪组和大隆组页岩进行了TOC、岩石热解、扫描电镜、氩离子抛光+扫描电镜等分析,并对页岩进行可溶有机质萃取及开展氮气和甲烷吸附等对比实验。结果表明:(1)可溶有机质在页岩中,特别是在低成熟页岩中主要赋存于干酪根、黏土矿物和草莓体黄铁矿等颗粒的表面及大中孔中;(2)萃取可溶有机质后大隆组页岩比表面积和甲烷吸附量均明显增加,而龙马溪组页岩的比表面积和甲烷吸附量没有明显变化,说明低成熟页岩中可溶有机质能阻碍孔隙的连通和降低对气体的吸附能力,但在高—过成熟阶段可溶有机质很少,对比表面积和甲烷吸附量没有影响;(3)可溶有机质含量与大隆组页岩孔隙分形维数之间具有明显的负相关性,而与龙马溪组页岩孔隙分形维数之间具有正相关性,反映出可溶有机质对低成熟和高成熟页岩孔隙的均匀性方面起相反的作用;(4)萃取可溶有机质后,大隆组与龙马溪组2套页岩的孔隙分形维数均呈降低的趋势,说明可溶有机质被去除后,页岩的孔隙连通性和均匀性变好。通过本次研究,确定了可溶有机质是影响页岩储集物性的重要因素之一,特别是表征低成熟页岩储层物性时要充分考虑可溶有机质的影响。

Soluble organic matter is an important part of organic matter. In order to study the effect of soluble organic matter on shale reservoir properties, the shales of Longmaxi Formation and Dalong Formation in northeastern Si- chuan Basin were analyzed in the aspects of TOC content, rock pyrolysis, scanning electronic microscope, scan-ning electron microscopy combined with argon ion polishing, and the extraction of soluble organic matter and low-pressure N2 and methane adsorption experiments were carried out. The results show that： （ 1 ） Soluble organic matters are mainly existing in the surface and meso-macropore of kerogen, clay minerals and framboid pyrites in shales, especially low-maturity shales. （2） The specific surface area and methane adsorption capacity of extracted shale samples increased obviously compared with raw shale samples from Dalong Formation, while there are no obvious changes of specific surface area and methane adsorption capacity between the extracted shale samples and raw shale samples from Longmaxi Formation, indicating that the soluble organic matters in low-maturity shales could hinder the connectivity of pores and decrease methane adsorption capacity, but it has no obvious effect of soluble organic matter on high-maturity shales due to a low content of soluble matter in these shales. （3） Soluble organic matter content has a significant negative correlation with fractal dimension for Dalong shales, but has a positive correction for Longmaxi shales, indicating that soluble organic matter has an opposite effect on the pore heterogeneity for these two sets of shales with different maturities. （4） After extracting the soluble organic matter, fractal dimension values has a decreasing phenomenon for both extracted Dalong and Longmaxi shales, suggesting that the connectivity and uniformity of the pores are improved due to removing the soluble organic matter exist- ing in shale pores. Therefore, through this study, soluble organic matter is deemed to an important factor of reser- voir properties of shale, and it should be taken into consideration when characterizing the physical properties of the low-maturity shales.