利用等效孔隙度法恢复沉积盆地残余地层古厚度——以济阳坳陷惠民凹陷为例

Paleo-thickness recovery of residual strata in sedimentary basin by equivalent porosity methodcase of Huimin depression

为了进一步提高沉积盆地残余地层古厚度的计算精度,对传统方法进行了改进,以地层压实过程中孔隙度与深度遵循指数关系为前提,提出了适用于中、新生代残余地层古厚度恢复的等效孔隙度法。首先,根据沉积压实原理,以钻井岩心和测井数据为基础,划分各井地层压实单元,并通过测试确定适用于研究区不同岩性地层的压实参数;然后,将地层压实单元等效看作不同岩性地层匀速沉降的均质体,按岩性比例确定各地层压实单元的初始孔隙度、压实系数和偏移常量,并建立其孔隙度一深度关系模型;最后,依据地层骨架厚度不变原理、沉积环境古水深的变化以及压实单元所处地层的相对位置,回剥反演计算残余地层古厚度。将等效孔隙度法应用惠民凹陷沙三段残余地层古厚度恢复,一定程度上校正了岩性差异、构造活动、异常压实作用和古水深的影响,恢复结果明显小于传统方法的结果,与实际地质情况吻合性较好,具有较高的准确性和可信度。

In order to raise the calculation accuracy of the paleothicknesses of residual strata in sedimentary basin,we improve traditional method and provide the method of equivalent porosity for Mesozoic and Cenozoic on the premise of porosity and depth following the exponential relationship in the compressive process of strata.Firstly,according to the principles of sedimentary compaction and the data of cores and well logging,we divide the strata of every well into different compaction units and establish the compaction parameter table of different lithological strata in the study area;then,considering compaction unit beds as the homogeneous mass which came into being from the uniform sedimentation of different lithological strata,and determine initial porosity, compacting factor and offset constant and porosity-depth relationship model in lithological proportion;finally,we retrieve and compute the paleo-thickness of residual strata in the light of the conversion law of solid thickness of strata,the variation of ancient water depth and the relative position of compaction unit.The application to the residual strata of the third member of Shahejie formation (Es_3) in Huimin depression by this method,which regulate the impact of different lithology,tectonic activity,abnormal compaction and paleo-depth to a certain extent,shows significantly smaller results than traditional method and has higher accuracy and reliability.