摘要
四川盆地威荣地区在3 500～4 500 m的深层取得了重大突破.含气特征对页岩储层评价具有重要影响,为揭示威荣地区深层页岩气富集特征以及主控因素,以威荣地区龙马溪组页岩为研究对象,利用XRD组分、TOC含量、RO含量分析实验、低温氮气吸附、等温吸附实验及现场含气量测试等方法,对深层页岩的有机地球化学特征、孔隙结构特征和含气特征系统分析,进一步探讨含气性主控因素.结果表明:威荣地区发育低碳—富碳页岩,处于高—过成熟阶段.整体的平均总含气量为 2.78 m3/t,现场解析气以游离气为主,平均游离气含量为 2.25 m3/t,平均吸附气含量为0.53 m3/t.不同岩相的含气性差异较大,其中富碳混合硅质页岩含气性最好,平均总含气量为5.28 m3/t,平均游吸比(K)为4.20,为优质岩相类型,利于页岩气开采.页岩含气性受多种地质因素控制,TOC含量为主要控制因素,孔隙结构为直接因素.TOC含量促进了有机质孔的发育,孔体积和比表面积增大,进一步为页岩气提供储存空间和吸附点位.此外,黏土矿物的充填使孔隙空间减小,导致其与各含气量之间呈负相关,矿物质中绿泥石因其层状结构且遇水膨胀在一定程度上阻碍了游离气的赋存,石英抗压实作用较强,与各含气量之间呈正相关;随着RO值增加,烃类吸附能力及游离气赋存能力增强.研究结果可对未来深层页岩气勘探开发提供地质依据.
Abstract
Significant breakthroughs were made in the exploration and development of the Weirong area.Taking the Longmaxi shale as the object,we analyzed its gas-bearing characteristics and main controlling factors by means of XRD and on-site gas content test.The results are as follows:the area develops low-carbon-carbon rich shale,which is at the high-over-mature stage.The average total gas content is 2.78 m3/t,and the present de-sorption gas is mainly free gas,with an average of 2.25 m3/t,and the average adsorption gas is 0.53 m3/t.Car-bon-rich mixed siliceous shale is the dominant lithology.There is a positive correlation between the TOC con-tent,pore structure,and their respective gas contents,and at the same time the TOC content affects the pore structure,so that the TOC content is the main controlling factor.Therefore,TOC content is the main control-ling factor and pore structure is the direct factor.Clay content is negatively correlated with gas content,and RO content is positively correlated with gas content.
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