涩北二号气田低阻气层成因机理

Genetic mechanism of low-resistivity gas reservoirs in Sebei Ⅱ Gas Field

涩北二号气田第四系七个泉组经证实存在一定数量的低阻气层,复杂的地质条件导致低阻气层的识别难度加大,由于对其成因机制认识不清,导致部分低阻气层被忽略。因此,综合岩心、薄片、物性、扫描电镜、X衍射及测井等资料,在准确识别低阻气层测井响应特征的基础上,深入剖析研究区低阻气层的形成原因。分析结果表明,高地层水矿化度以及由储层岩石粒度细、孔隙结构复杂、构造幅度低所导致的高束缚水含量是研究区低阻气层形成的主要原因,而黏土矿物的附加导电性、导电矿物富集、砂泥岩薄互层和外部钻井液侵入等因素则进一步使气层电阻率降低。

Within the gas reservoirs in the Quaternary Sebei Fm in Sebei Ⅱ Gas Field,it has been confirmed that there are a certain number of low-resistivity gas reservoirs. The complex geological condition however makes it difficult to differentiate from the other gas reservoirs. Not only that,but due to the genesis of low-resistivity which is unclear,this results in some low-resistivity gas reservoirs being ignored. Thus,in combination with the logging responses of low-resistivity gas reservoirs,this article systematically analyzes the genetic mechanisms of the low-resistivity gas reservoirs from cores samples and thin sections observations,petrophysical data,SEM,and X-ray diffraction. The results revealed that the major genesis of the low-resistivity reservoirs in the study area is due to the high salinity of the formation water,high irreducible water saturation formed within the fine grain size,complex pore structure and a low-amplitude structural setting. More to this,the additional conductivity of clay mineral,the enrichment of conductive mineral,the sand shale thin bedded reservoir and the invasion of the drilling fluid further lowered the resistivity of gas reservoirs.