尤因塔盆地P.R.泉始新统油砂成藏条件及成藏模式

Reservoir forming condition and model of P.R. spring of Eocene oil sand in Uinta Basin

尤因塔盆地P.R.泉位于美国犹他州东北部,油砂资源丰富,油砂矿藏面积约650 km2,油砂储量约6.76×108t,储层为始新统绿河组湖泊三角洲相砂体。晚白垩世到古近纪拉拉米运动使盆地由海相转变为陆相盆地。古新世末—始新世,尤因塔湖在盆地内分布广泛,并沉积了两套巨厚的绿河组烃源岩。其中绿河组上部的中始新统烃源岩厚达150 m,有机质丰富,且仍处于低熟阶段,约30 Ma以来,产生了大量的低熟油。P.R.泉油砂矿藏为斜坡降解型成藏模式,发育5套广布的三角洲砂体,储层物性好。绿河组上部烃源岩生成的低熟油沿着深入烃源岩中的连续砂体经过长距离的运移,进入P.R.泉绿河组三角洲的砂岩储层中,经过生物降解和水洗作用最终形成油砂矿藏。

Uinta Basin was located in the northeastern Utah State of U.S.A,which was rich in oil sand resources.The area of P.R.spring oil sand deposit was 650 km2 and the resource was 6.76×108 t,whose reservior was Eocene lacustrine delta sand body in Green River Formation.The laramide orogeny changed the basin environment from marine facies to continent facies during Late Cretaceous and Paleogene.From the latest Paleocene to Eocene,the Uinta lake was widespread in the basin,and two sets of thick source rocks of Green River Formation were deposited.The middle Eocene source rock in upper Green River Formation was about 150 m thick,with rich organic matter in low maturity,so that abundant immature oil was generated since 30 Ma ago.P.R.spring oil sand deposit was degradation on slope type,which developed five sets of delta sandstone with good physical properties.After long-distance migration along continuous sand body,the immature oil generated from the upper source rock of Green River Formation entered the sandstone reservoir of lacustrine delta in Green River Formation of P.R.spring,and formed oil sand deposit eventually through biodegradation and water washing.