济阳坳陷低位古潜山成藏条件分析

济阳坳陷富台油田位于埕南陡坡带下降盘二台阶上,具有“坡下山”的成藏特点。研究发现,在二台阶潜山带上发育2种古潜山类型,即以“两洼之古梁”为背景的古梁低位古潜山和发育于生油洼陷中心的隐伏低位古潜山。前者其上被新生界下第三系沙河街组沙三、四段所覆盖,古潜山顶部以石炭一二叠系为盖层,古潜山主体以奥陶系、寒武系为储层,以前震旦系片麻岩为基底。形成多层古潜山内幕块状油气藏;后者以新生界下第三系沙河街组沙三段底部和奥陶系顶部之间的不整合面为盖层,以寒武系、奥陶系为主要储层,形成新生古储古潜山内幕油气藏。其中,寒武系是近期发现的区域性新高产含油层系。据此认为,在济阳坳陷箕状断陷湖盆陡坡带一侧寻找类似的古潜山油气藏将取得一定的勘探突破。

Reservoir forming conditions in low buried hill of Jiyang depression

Futai oilfield is located in the second step on the downthrow of Chengnan steep slope belt in Jiyang depression, showing "hill below slope" feature. There are two types of buried hills developed on the second step buried hill zone, i.e. Guliang low buried hill between two sags and the low subtle buried hill in hydrocarbon kitchen. The former was covered by s_3 and s_4 of Shahejie formation, Palaeogene, Cenozoic, with Carboniferous-Permian as caprock on the top, Ordovician-Cambrian as reservoirs, and Sinian gneiss as basement, forming multi-layer inner buried hill block reservoir. The latter has the unconformity between the bottom of s_3 and the top of Ordovician as caprock, and Cambrian and Ordovician as main reservoirs, forming inner buried hill reservoirs with oil generated in a later time and preserved in ancient formation. Among which, Cambrian is a newly discovered regional prolific oil system. Hence, to look for similar buried hill reservoirs on the steep slope of Jiyang half fault depression will achieve certain exploration breakthrough.