双界面地震层拉平的古地貌恢复技术及应用——以鄂尔多斯盆地天环坳陷为例

Palaeo-geomorphology restoration with double-interface seismic layer leveling:an example of Tianhuan Depression in Ordos Basin

为了落实古地貌形态、研究古地貌与油气成藏的关系,提出一种利用双界面地震层拉平技术恢复生烃关键期的古地貌的新方法,主要步骤有:①判断地震层拉平技术的适用性,确定生烃关键期和填平补齐结束期对应的地震拉平层位;②先拉平生烃关键期对应的地震反射层位,去除后期构造变形对古地貌形态的影响,计算拉平层至古地貌填平补齐结束期对应的层位之间的地层厚度;③再拉平填平补齐结束期对应的地震反射层位,恢复该时期的古地貌形态,计算该拉平层与不整合面(古地貌)之间的地层厚度;④将以上两次计算的地层厚度值相加,即为生烃关键期时的古地貌形态。应用该方法恢复了鄂尔多斯盆地天环坳陷中部前侏罗纪的古地貌形态,提高了古地貌恢复的精度;同时,指明了该区侏罗系成藏规律,即古地貌填平补齐结束期层位相对宽缓的构造形态控制了石油运移的方向,古地貌的局部隆起是石油成藏的有利部位。该方法将对类似区古地貌研究起指导作用。

In order to identify the palaeogeomorphology and study the relationship between the hydrocarbon accumulation and the palaeo-geomorphology,a new approach for palaeo-geomorphology restoration in the critical period of hydrocarbon generation with double-interface seismic layer leveling is proposed.The approach includes four steps.First,the applicability of seismic layer leveling technology is analyzed,and the seismic layers in the critical period of hydrocarbon generation and the end period of filling-leveling up are determined.Second,in order to eliminate the influence of late tectonic deformation on the palaeo-geomorphology,the seismic layer of the critical period is flattened,then the stratum thickness between the seismic leveling layer and the seismic layer representing the end period of filling-leveling up is calculated.Third,the seismic layer representing the end period of filling-leveling up is flattened in order to restore the palaeo-geomorphology of this period,and the stratum thickness between the two seismic leveling layers is calculated.Finally,by adding up the above the two strata thickness values,the palaeo-geomorphology at the critical period of hydrocarbon generation is described.The proposed approach is applied to restore the pre-Jurassic palaeo-geomorphology in the middle part of Tianhuan Depression,Ordos Basin,and the accuracy of palaeo-geomorphology restoration is improved.At the same time,the Jurassic reservoir-forming regularity in this area is found out,that is,relatively gentle structures of palaeogeomorphology at the end period of filling-leveling up control the oil migration direction,and the local uplift of palaeo-geomorphology in the critical period of hydrocarbon generation is the favorable part of oil accumulation.This proposed approach may provide a reference in the study of palaeo-geomorphology in similar areas.