利用流体包裹体计算地层剥蚀厚度——以东海盆地3个凹陷为例

CALCULATION OF DENUDED STRATA THICKNESS BY FLUID INCLUSION DATA—A CASE STUDY OF THREE DEPRESSIONS IN THE EAST CHINA SEA BASIN

刘斌

LIU Bin

同济大学, 地下工程系, 上海, 200092

Department of Geotechnical Engineering, Tongji University, Shanghai 200092, China

绘制包裹体形成温度对埋藏深度的关系曲线,从明显的温度跃变之处可以确定侵蚀不整合面;把剥蚀面以下的深度、温度(或压力)对应数值的点用回归方法联结成的直线,向上延伸至古地表温度的坐标处,这一坐标也就是古地表面。对于浅埋藏阶段还未压实地层捕获的包裹体,必须经过压实系数校正才能进行。由剥蚀面至古地表面的距离就是地层剥蚀厚度,计算出东海盆地3个凹陷不同的地层剥蚀厚度。结果表明,本区第三系地层(E2、E3)大多数埋深刚刚达到或者完全进入主成熟高峰期门限,今后勘探应着重寻找沉积间断以前的有利构造圈闭;对于K、E1和N1地层,沉积间断以后比间断以前热演化稍微充分一些,因此对沉积间断以后的构造部位也应该加以重视。

On the plotted graphs of formation temperature of fluid inclusions vs.burial depth,the point with distinct change of temperature corresponds to the erosion surface of unconformity.So,on the diagram of temperature (or pressure) vs.depth a straight line passing through the data points recording the temperature (or pressure) and the depth below the denudation surface can be constructed by the regression method.This line is then extended upward to the point with the coordinate defining the ancient surface temperature,and the corresponding depth is inferred as the ancient surface.The distance between the denudation surface and the ancient surface is the denuded strata thickness.It is essential that strata thickness is corrected by coefficient of compaction when fluid inclusions are trapped in shallow burial conditions.This method has been applied to calculate the denuded thickness of the Tertiary (E1,E2,E3 and N1) and the Cretaceous (K) strata in the three depressions of the East China Sea Basin.The results show that the burial depth of most Tertiary ( E2,E3) strata has just reached or fully entered the thresholds of main peak maturation periods of oil.In the future,the exploration work should be focused on searching for the favorable structural traps prior to the depositional break.For the strata of K,E1 and N1,however,the thermal evolution history prior to the depositional break is unknown while that after the depositional break is much clear.Therefore,attention should also be paid to the structures after the depositional break.

国家自然科学基金项目(40173029).

https://doi.org/10.11781/sysydz200202172