鄂尔多斯盆地彭阳地区延长组、延安组原油地球化学特征与油源对比

GEOCHEMICAL CHARACTERISTICS OF CRUDE OIL FROM YANCHANG AND YAN’AN FORMATIONS IN PENGYANG AREA OF ORDOS BASIN AND THEIR IMPLICATIONS FOR OIL-SOURCE

鄂尔多斯盆地彭阳地区的中生界延长组、延安组油源还存在一定的不确定性,应用分子地球化学的手段和方法,对彭阳地区延长组、延安组的原油及长7烃源岩样品和盆地内部长7优质烃源岩样品开展生物标识化合物地球化学定量分析,并进行油源对比研究。结果表明:鄂尔多斯盆地天环坳陷彭阳地区延长组、延安组原油形成于淡水、微咸水且还原性较强的环境;生物标志化合物地球化学特征相似,属于同一成因类型,具有相同的油源;原油母质类型为低等水生生物和陆生高等植物构成的混合型母质,原油已经成熟。彭阳地区原油在成熟度、母源性质和沉积环境方面与盆地内部长7优质烃源岩具有相似的特征,二者具有较好的亲缘关系,彭阳地区原油不是本地长7泥岩产物,主要来自盆地内部长7优质烃源岩。

Researches have been devoted to the uncertainties of sources of oil from the Yan'an and Yanchang Formations in the Pengyang area of the Ordos Basin.Using the methods of GC-MS,biomarkers are analyzed,upon which correlation of oil-sources is made for the crude oil samples from the Yanchang and Yan'an Foi-mations with those from the Chang-7 high quality source rock in both the Pengyang area and the area within the basin.Results show that the crude oils produced from the Yanchang Formation and Yan?an Formation of the Pengyang area came from the west Tianhuan Depression and was formed under a deoxidized lake environment of freshwater and mildly brackish water.Biomarker characteristics suggest that the crude oils o Yanchang Formation and Yan'an Formation come from the same oil source,of which the parent materials are mainly from aquatic organisms and higher plant,and the crude oil is mature.Facts show that the maturity,parent materials and sedimentary environment of crude oil from the Pengyang area are similar with the Chang-7 source rock formed within the basin center.It is thus concluded that the crude oil is coming from the Chang-7 mudstone in the basin center,but not the local Chang-7 deposits in the Pengyang area.