八面河地区原油、烃源岩中甾类化合物的分布特征及其应用

Distribution and Significance of Steroids in Bamianhe Oilfield, East China

对渤海湾盆地八面河地区 31个分别形成于还原性咸化水体和淡水环境的页岩和泥岩样、2 0个油样中甾类化合物进行了剖析 .结果表明该区烃源岩、原油中的甾类化合物异常丰富 ,主要包括C2 7 2 9规则甾烷、C2 8 3 0 4 甲基甾烷、甲藻甾烷以及芳香甾类 ;不同层段烃源岩中甾类化合物的分布各具特色 ,发育于牛庄洼陷南斜坡咸化水体的富藻类沙四段页岩富含 4 甲基甾烷及甲藻甾烷 ,形成于淡水环境的沙三段泥岩中甲藻甾烷不太发育 .烃源岩、原油中规则甾烷的分布型式明显有别于甲基甾烷 ,指示两类化合物可能来源于不同的藻类属种 .甾类化合物的分布特征受控于古环境、生物先质种类及热成熟度等多种因素 .不同层段甾类化合物的特征性分布使其成为该区油源岩确认的关键指标 .结果还表明 ,甲基甾烷在油源岩识别中比规则甾烷具有更好的应用效果 .依据甾类化合物 ,可判断埋深超过 2 70 0m的Es4烃源岩与原油具有较好的相关性 ,发育于牛洼洼陷南斜坡的未熟 -低熟特殊烃源岩—富藻类页岩与原油没有可比性 ,该结论是对近期油源调查结果的进一步确认 .

samples of shales and mudstones developed in reducing hypersaline and freshwater setting and 20 oil samples of Bamianhe oilfield, Bohai Bay basin were collected for a detailed study of petroleum system. Composition and distribution of specific significance of steroids were discussed as a part of the study. Abundant steroidal biomarkers including C_ 27-29 regular steranes, C_ 28-30 4-methyl steranes, dinosteranes and aromatic steranes were detected. The composition and distribution of the steroids in the samples studied were a function of thermal maturity, organic source, paleoenvironment and lithology of potential source rocks. Alga-rich Es_4 shales (brackish water) developed in the south slope of depocenter (Niuzhuang sag) were found particularly rich in steroidal biomarkers including C_ 30 4-methyl steranes and dinosteranes. While Es_3 mudstones (fresh water) displayed devoid of dinosterane, abundant 4-β steranes were only found in argillaceous limestone and calcareous mudstone, clearly distinguished from the other rocks. Distribution patterns of regular steranes are different from methyl steranes completely indicating different origins of specific compound of the fraction. Isomerization of steroids were observed to be determined by paleoenvironment and lithology besides thermal maturity. Methyl steranes were proved much more useful in oil-source rock correlation than regular steranes. It was not possible that alga-rich Es_4 shales located on the south slope were the primary source rock responsible for the oil discovered based on composition and distribution of steroids.