北部湾盆地高放射性储层地质成因分析与评价

Geological Origin Analysis and Evaluation on High-radioactive Reservoirs in the Beibuwan Basin

针对北部湾盆地高放射性储层测井评价中存在的困难,基于自然伽马能谱和成像测井,参考各种岩心分析资料,分析了储层的宏观、微观特征以及矿物组分与测井曲线之间的关系。分析表明:地层具有高放射性的主要原因是富含钾长石,结合区域构造和沉积特征,进一步指出这是近物源、短距离搬运和快速沉积的结果;针对高放射性储层的测井响应特征,根据电阻率、孔隙度曲线以及录井资料对其进行综合识别;在定量评价方面,采用多矿物最优化模型与中子—密度交会相结合的方法,计算出地层的泥质含量和孔隙度;也可得到地层中主要矿物组分的体积含量。最终的解释成果经过岩心资料的标定和取样的证实,表明所用的方法是有效和可靠的。

It is difficult to make well logging evaluation for high- radioactive reservoirs in the Beibuwan Basin. In this regard,based on the spectroscopy gamma ray( SGR) and imaging logging,and using various core analysis data,this paper analyzes the macroscopic and microscopic features of reservoirs and the relation between mineral components and logs,indicating that the leading cause for such high radioactivity lies in its abundance of K- feldspar. Then,combined with regional structure and sedimentary features,this paper points out that high radioactivity is the result of proximal material source,short distance transportation and rapid deposition. The log response characteristics of high- radioactive reservoirs are synthetically recognized using resistivity and porosity logs as well as mud logging data. As for quantitative evaluation,the multi- mineral optimal model is combined with the neutron-density crossplot to obtain the shale content and porosity of formation,or the volume content of principal mineral components in the formation. After the final interpretation results are calibrated and verified by core data,it is confirmed that the method proposed in this paper is effective and reliable.