漫谈前陆逆掩断层带油气勘探的经验教训

前陆盆地是在克拉通之上由被动边缘地台型沉积区转变为造山前渊的陆源碎屑沉积区。伴随挤压变形,在造山带及其前渊产生由厚皮到薄皮的复杂变形构造。因受原始和后期从构造背景、沉积体系到运动条件的控制而具有多样性。虽然前陆盆地是世界上最重要和高产的含油气盆地类型,但油气田只保存于盆地有同造山期沉积盖层的范围内。由于邻造山带一侧,冲断褶皱构造明显,加以地面油气显示,是早期油气勘探的目标。1975年开始的逆掩断层带找油热只是因为三维地震和钻井技术的进步,能识别冲断层下伏的构造面貌和圈闭条件,但当把逆掩断层带的构造现象当作主要因素去找油气聚集时就受到了挫折。实践证明,只有在保持同造山期沉积的现存盆地内,而且下伏有前造山期沉积层序的条件下,才具有找到油气储集的潜力。

An informal discussion on experiences and lessons of petroleum exploration in foreland over-thrust zone

Foreland basin is an orogenic foredeep filled with terrigenous clastics,that has been developed on a craton and has been converted from a passive margin and platform type sedimentary area.Complex structural deformation,from thick skinned to thin skinned structures,has occurred in the orogenic belt and its frontal region along with compressional deformation;and structural styles are varied,due to the control of tectonic settings,sedimentary sequences and movement characteristics.Although foreland basin is the most prolific basin type,hydrocarbon accumulations can only be preserved in regions where there are synorogenic sedimentary covers.Since thrust fold structures are clear,and there are oil and gas seepages in the area neighboring the orogenic zone,thus the mountain front became the main objective area in the early stage of exploration.The exploration campaign in foreland overthrust zone since 1975 has been the result of advances in 3 D seismic survey and drilling technologies which make it possible to recognize structural features and trap conditions beneath the thrusts.Failures often occur in exploration when the thrust zones are taken as the main targets for exploration of hydrocarbon accumulations.Practices have shown that only the basins that have preserved both the synorogenic sediments and underlying pre orogenic sediments would have exploration potentials.