建南地区飞仙关组三段白云岩分布与成因--基于三维地震、岩石学和地球化学综合分析

建南地区飞三段是现今研究区重要的产气层,储层类型主要为致密颗粒灰岩和细晶白云岩,然而,相对优质储层均发育于白云岩中。因此,对飞三段白云岩分布规律的研究是预测优质储层的基础。本研究基于录井、测井、岩芯和三维地震等资料,在构建单井白云石含量曲线的基础上,利用多属性转换分析建立三维地震属性与白云石含量曲线的关系,反演白云石含量在平面和剖面上的分布,结合岩石学、地球化学和沉积相对白云岩化流体的性质与来源进行了分析。建南地区飞三段白云岩以细晶、平面自形-半自形为主,非平面它形晶少量分布。阴极发光下白云石为暗红色,无或少量环带状结构。利用多属性转换方法建立地震属性与白云石含量的关系,当选取5个地震属性组合时对白云石含量的预测最佳,预测误差为9%。五个属性分别为 Amplitude Weighted Frequency、Amplitude Weighted Cosine Phase、Derivative Instantaneous Amplitude、Quadrature Trace 和 Integrate。将预测的白云岩分布与沉积相叠合显示白云岩主要分布于台内洼地的两侧,向台地内部规模和厚度逐渐减小。综合地球化学数据和白云岩的分布特征说明,白云岩化流体主要来源于台内洼地的泥灰岩和泥晶灰岩的压实海源流体。随埋深的加大,洼地沉积物中的富Mg流体优先侧向运移至洼地两侧的孔隙性颗粒滩中并发生白云岩化作用。因此,洼地边缘颗粒滩是优质白云岩储层的有利勘探区。

Distribution and Origin of the Third Member of Feixianguan Formation in the Jiannan Area : Comprehensive analysis from three-dimensional seismic,petrography, and geochemistry

The third member of Feixianguan Formation (T₁f3) is an important gas reservoir in the Jiannan area which consists mainly of tight grainstones and crystalline dolostones. However, the high quality reservoir is limited in the dolostones. Therefore, understanding the distribution mechanism of dolostones is prerequisite to predict the distribution of high-quality reservoir. In this study, the dolomite-content logs were firstly constructed based on the well logs and cores. Secondly, the correlation between dolomite-contents and seismic attributes derived from 3-D seismic volume were defined using the method of multiattribute transforms to predict the distribution of dolomite in the Jiannan area. At last, the predicted dolomite distribution and paleogeography were integrated to explain the source and nature of the dolomitizing fluid.The dolostone of T₁f3 in the Jiannan area consist mainly of fine-grained, planar-e to planar-s crystals, and minor nonplanar crystals. Under CL, dolomite crystals show zoned to uniform dull red luminescence. Five most effective attributes were selected based on the method of multiattribute transforms. These attributes are Amplitude Weighted Frequency, Amplitude Weighted Cosine Phase, Amplitude Envelope, Quadrature Trace and Instantaneous Phase. Integration dolomite distribution and paleogeography indicates that dolomites mainly occur along the opposing margins of a trough. During progressively burial, owing to the increase in pore pressure and different compactability of sediments, Mg-rich, seawater-derived, compaction flow from trough sediments moved laterally and preferentially through less rapidly compacting, trough-margin shoals, which caused extensive dolomitization in shoals. Shoals along margins of the trough can be recognized as important exploration targets.