沉积盆地地层古埋深的恢复

Restoration of the paleoburial depth of strata in deposition basin.

在盆地模拟中，利用“回剥”技术恢复古埋深，关键在于确定地层古孔隙度演化关系式。确定古孔隙度的传统方法（等效深度法）仅适用于无间断匀速沉积的地层，对于埋藏史复杂的地层计算结果误差较大。为此，提出同时考虑地层埋藏时间和埋藏深度对孔隙度演化的影响，即采用孔隙度埋藏时间、孔隙度埋藏深度关系式作为计算孔隙度的函数，并利用数值积分法，计算出地层的骨架厚度值，然后利用回剥技术，计算地层古埋深。在进行数值积分时，可以根据研究精度的需要，确定合适的步长。此方法在东营凹陷的应用表明，计算结果的准确度、可信度要高于传统的计算方法。

The key to restoring the paleoburial depth of the strata in a basin is to get the accurate paleoporosity of the strata. Backstripping process has become a comparatively good technique to restore the paleoburial depth of strata in a depositional basin. It has been known that the age of a stratum has an influence on the evolution of its porosity. Due to various reasons, for a long time, even nowadays the variation of porosity as a function of strata's depth, which is called the equivalentdepth method, has still been used to get the paleoburial depth of a stratum. In the paper, the relationship simultaneously considering the effects of age and burial depth of a stratum on the evolution of its porosity has been presented to obtain the paleoburial depth, a reasonable algorithm is proposed in backstripping process. The application in Dongying depression shows that there is a relatively apparent difference between the results of using the presented relation and that of using traditional method. The eroded thickness of Dongying formation is got by means of geometric mapping. The effect of extra pressure and diagenesis on the evolution is not included. If a stratum in a certain basin is buried deeply and under a apparently extra high pressure and/or has experienced lots of diagenetic changes, the calculated paleoburial depth of the stratum may deviated from the real one and should be further modified.