声波时差测井资料识别层序地层单元界面的方法、原理及实例

结合济阳坳陷古近系层序地层研究,在地震、岩芯、录井等资料综合分析基础上,探讨了运用声波时差测井识别层序地层单元界面的方法和原理。在正常埋藏压实条件下,泥页岩的声波时差对数与其深度的关系曲线为一条直线(回归线),由于沉积作用形成的不整合造成地层缺失、风化层和致密的湖侵泥岩层形成等,将使不整合面(层序界面)上下的声波时差对数与深度的回归线出现错开、斜率不同、异常值等异常响应。生油岩密集段(CS段)在湖盆洼陷带对应于泥岩、页岩沉积,有机质含量高,声波时差值也高,并且同一层序内在最大湖泛面位置声波时差值达到最大,向上、向下均逐渐减小,在层序界面附近达到最小。

Method, Principle and Example of Identifying Sequence Stratigraphical Boundary Using Sonic Logging

On the base of the comprehensive analysis of seismic data, core and logging , we have discussed the method and principle of identifying sequence stratigraphical boundary with sonic logging, and its application in the study of sequence stratigraphy of Paleogene in Jiyang depression. The sequence boundary and the maximal lacustrine flooding surface (MLFS) are the key boundaries in the sequence strata. The sequence boundary corresponds to the unconformity surface or its corresponding conformity surface, and MLFS is the division surface between transgressive systems tract (TST) and high systems tract (HST), and condensed section (CS) can form near the MLFS. The regression line of the logarithm of interval transit-time of mud rocks versus its depth is a straight line in the basin under the normal imbedding and compacting conditions, but the unconformity usually leads to the formation of stratigraphical break, weathered crust and TST mud, and these characteristics also lead to the anomaly of the regression line, such as, the dislocation and different slope of the regression line above or below the unconformity surface and some anomaly of interval transit time below the unconformity surface, and they are the important identifying signs of sequence boundaries. The lithology of the CS is usually depth-water shale or mudstone, and it has high content of the organic substance and high interval transit time. The interval transit time is the highest at the location of the maximal lacustrine flooding surface, and becomes lower upward and downward in a sequence, and reach the lowest value at the location of the sequence boundary