沧东凹陷孔二段高伽马砂岩成因探讨及识别

Genesis and Identification of Sandstones with High Gamma Values in the Second Member of Kongdian Formation, Cangdong Sag

针对沧东凹陷孔二段致密砂岩具有高自然伽马的测井响应特征,基于岩心观察和薄片鉴定,结合全岩X射线衍射分析和测井曲线分析等方法研究认为,沧东凹陷孔二段二亚段(Ek_2~2)致密砂岩段因方沸石含量普遍较高、钍富集,导致Ek_2~2致密砂岩段自然伽马普遍较高;孔二段四亚段(Ek42)致密砂岩段局部层段因白云母含量较高、铀相对富集,导致Ek_2~4致密砂岩段局部呈高自然伽马的特征。通过常规测井曲线声波时差、自然伽马—声波时差关联分析和深感应电阻率—自然伽马关联分析的综合使用,可有效识别出高方沸石含量所致的高伽马致密砂岩。

Regarding high natural gamma values in logging response of the sandstones in the second member of Kongdian formation in Cangdong sag,based on the core observation and thin section identification and combined with whole?rock X?ray diffraction analysis and well logging analysis,it is considered that the relatively high content of analcite and enrichment of thorium(Th)are commonly noted in the Ek22tight sandstones of Cangdong sag,which leads to the high natural gamma value of the tight sandstone interval;relatively high content of white mica and enrichment of uranium(U)in some local areas in the Ek42tight sandstones result in the high natural gamma value of the sandstone interval locally.The integrated use of AC logging curves,AC?GR correlation and GR?RILD correlation allows effective identification of tight sandstones with high gamma value caused by high content of analcite.