洛河地区高自然伽马砂岩识别及主控因素

Identification and main controlling factors of method high Gamma sandstone in Luohe Area

为识别洛河区延长组长6与泥岩、凝灰质泥岩具有类似常规测井响应特征的高自然伽马砂岩,分析高自然伽马砂岩的成因与主控因素。综合分析高自然伽马砂岩的岩性、物性特征及对应测井响应特征,优选测井曲线敏感参数进行曲线重叠处理,快速识别高自然伽马砂岩,通过多敏感测井参数组合构建新指示参数进行交会,验证高自然伽马砂岩。结果表明:与常规砂岩相比高自然伽马砂岩中钍元素含量相对较高,铀和钾元素含量正常;高自然伽马砂岩纵向随机分布于三角洲前缘水下分流河道沉积旋回砂体的任何部位;高自然伽马砂岩平面展布整体与三角洲前缘水下分流河道砂体平面展布特征基本一致,受沉积微相控制。洛河区高自然伽马砂岩为同沉积期火山事件沉积的凝灰质叠加在三角洲前缘水下分流河道沉积中形成,高放射性主要来自高含量钍元素。

In order to effectively identify the sandstone with high gamma ray in the Triassic Yanchang Chang 6 Member,which have similar conventional well logging response characteristics to the surrounding argillaceous rocks and tuffaceous rocks deposited by volcanic events from conventional well logging response characteristics in Luohe Area,are analyzed the possible genesis and main control factors of the sandstone with high gamma ray.A comprehensive study has been made of the lithology,physical property characteristics and their variations,with well logging curves optimized to quickly identify the sandstone with high gamma ray.And the cross plots of the well logging response characteristics of the sandstone with high gamma ray,the overlapping processing of sensitive new indicator parameters constructed according to the combination of multi sensitive well logging parameters are compiled to verify the sandstone with high gamma ray.Further,an analysis of the radioactive elements,vertical distribution and plane distribution characteristics of the sandstone with high gamma ray shows that:compared with conventional sandstone,the sandstone with high gamma ray has high thorium content,normal uranium and potassium.Sandstone with high gamma ray is vertically distributed in any part of the underwater distributary channel cycle sand body in the delta front.The plane distribution of the sandstone with high gamma ray is basically consistent with that of underwater distributary channel sand bodies in delta front,which is controlled by sedimentary microfacies.It is inferred that the sandstone with high gamma ray of Chang 6 Member in Luohe Area may be formed by the superposition of the tuff deposited by the contemporaneous volcanic event in the underwater distributary channel sediments of the delta front,and the high gamma ray comes mainly from the contribution of thorium.