层序地层分析在裂谷盆地油气勘探中的应用

裂谷盆地演化可分为裂谷初始期、深陷期、后裂谷早期和后裂谷晚期阶段.反映构造阶段演化的关键界面为前裂谷期不整合面、水进面、最大洪泛面和后裂谷早期沉积顶部不整合面.最大洪泛期的沉积物可能是烃源岩最发育的层段.关键界面作图与烃源岩的确定对裂谷盆地的油气勘探有着重要意义.裂谷盆地的成藏组合类型为前裂谷期潜山油气藏;裂谷初始期低水位体系域河流、三角洲和水下扇砂砾岩体油气藏;裂谷深陷期水进体系域重力流水道砂体和浊积扇体油气藏;后裂谷早期高水位体系域扇三角洲、辫状河三角洲、三角洲和河流砂体油气藏;具断—坳叠合结构盆地的坳陷阶段发育下切谷、河流—三角洲和滨岸砂岩油气藏.在21世纪我国油气勘探实践中,应加强含油气大区层序地层学、陆相层序成因与高分辨率层序地层学研究,为寻找新的含油气凹陷与含油气层系、寻找隐蔽圈闭与老区挖潜服务.

APPLICATION OF SEQUENCE STRATIGRAPHIC ANALYSIS TO HYDROCARBON EXPLORATION OF RIFT BASINS

Evolution of rift basins is divided into rift initiation,rift climax,immediate post-rift,and late post-rift stages.The key surfaces, which reflect the tectonic evolutionary stages, are pre-rift unconformity surface, transgressive surface, maximum flooding surface,and top unconformity surface of immediate post-rift sediments.Maximum flooding deposits are most developed intervals of possible source rocks.Mapping of the key surfaces and defining of source rocks are important for hydrocarbon exploration of rift basins.Play types of rift basins are:(1)buried-hill pools of pre-rift stage; (2)fluvial,delta,and subaqueous fan sandstone and conglomerate pools of lowstand systems tract deposited during rift initiation stage; (3)gravity flow channel sandstone and turbidite fan pools of rift-climax transgressive systems tract;and (4)fan delta,braid delta,delta and fluvial sand stone pools of immediate post-rift highstand systems tract.Play types of depression stage of faulted-depression stacked basins are incised valley,fluvial-delta,and shoreface sandstone pools.Sequence stratigraphic study of petroliferous provinces,genesis of nonmarine sequences,and high-resolution sequence stratigraphic study should be enhanced in hydrocarbon exploration practices of China in the 21st century,in order to serve for discovering new petroliferous sags and strata and finding subtle traps and new reserves in“matured”exploration regions.