鄂尔多斯盆地中央隆起带奥陶系风化壳古油藏与靖边大气田关系

Paleo-oil Reservoir and Jingbian Natural Gasfield of Ordovician Weathering Crast in Ordos Basin

大量岩石薄片分析表明,中央隆起带淳探1井、富探1井和陕54井区奥陶系风化壳储层中存在次生充填状沥青或炭屑,其成熟度高(RO≈2.0%),光性和生物标志物特征显示为石油裂解的残余物,是古油藏(田)的证据。古油藏位于靖边大气田的下倾方向,其西侧和南侧地层下倾方向的中奥陶统平凉组笔石页岩有机质含量丰富,可能是古油藏的烃源岩。J2—K1期的埋深加大和古地温升高,导致古油藏石油裂解形成古气藏;K2—E期燕山和喜马拉雅运动形成陕北斜坡,中央隆起带天然气向斜坡高部位运移,受岩性封堵形成靖边气田。

Rock thin section analysis data show that pack bitumen exists in the reservoir of Ordovician weathering crast of Chuntan1,Futan1 and Shan54 wellblocks in central uplift belt.The pack bitumen with high maturity is proved to be remnant of oil pyrolysis by the optical feature,which proves the existence of paleo-oil reservoir.The paleo-oil reservoir is located in the downdip direction of the Jingbian gasfield and the shale of the Middle Ordovician Pingliang Formation with abundant organic matter might be the source rock of the paleo-oil reservoir.The increasing of its buried depth and palaeogeotherm in the stage of J2-K1 caused Paleo-oil reservoir to turn into Paleo-gas reservoir.Shanbei slope was formed by the Yanshan movement during K2-E.The gas in central Paleo-uplift zone migrated to the high place of slope and formed Jingbian gas field by lithology sealing.