渤海海域新近系稠油油藏原油特征及形成机制

近10余年来,在渤海海域新近系发现了一系列大中型油气田及一批小型油气田和含油构造,累计各级石油地质储量达20多亿方。其中,绝大部分油田属稠油油田。研究表明:1)渤海地区稠油油藏的分布与其埋藏深度有明显的负相关关系,稠油油藏分布的深度下限约为2 000 m;2)渤海地区已发现稠油油藏原油的性质明显具有"三高两低"的特点,即高密度、高粘度、高沥青胶质含量、低凝固点和低气油比,地下原油粘度普遍在70～500 mPa·s范围,胶质含量是制约稠油粘度的关键因素;3)渤海地区新近系油藏均为下生上储型,原油主要来自生烃凹陷中的古近系沙河街组烃源岩,部分地区有古近系东营组三段烃源岩的贡献,断裂活动、晚期成藏、多期充注、微生物降解等特点突出;4)油藏内部近油源通道附近和油藏高部位是原油密度和粘度相对较低区域,与油藏后期的油气充注以及近油藏底部水体的氧化等综合作用有关。

Crude features and origins of the Neogene heavy oil reservoirs in the BohaiBay

During the past10years，a number of oil/gas fields of various scale and oil/gasˉbearing structures have been found in the Neogene of the Bohai Bay.The initial oil in place is as high as2billion cubic meters.Most of them are heavy oil fields.A detailed research of these fields gives the following conclusions.（1）The distribution of these heavy oil reservoirs is in apparent negative correlation with their burial depth.Their lower lim it ofoccurrence is at about2000m.（2）The crude samples from these reservoirs are high in density，viscosiˉty（inˉsitu oil viscositywithin70-500mPa•s）and bitumenˉcolloid content（a key factor controlling viscosiˉty），but low in freezing point and gas oil ratio.（3）Oilwasmainly generated by the sources rocks of the Palaeoˉgene Shahejie Formation in the hydrocarbon kitchen.In some areas，source rocks in the third member of the Palaeogene Dongying Formation also contributed some oil to the reservoirs.The generated oilm igrated upwards to and accumulated in the reservoirs above the source rocks.These reservoirs feature in active faulting，late pooˉling，multipleˉstage charging，and m icrobiological degradation.（4）Crude density and viscosity are relatively low at the top of these reservoirs and near them igration paths，a phenomenon closely related to late oil charging and oxidation ofwater bodies at the bottom of the reservoirs.