柴达木盆地西部尕斯库勒油田原油地球化学特征及成因

GEOCHEMICAL CHARACTERISTICS AND GENESIS OF CRUDE OILS FROM GASKULE OILFIELD IN WESTERN QAIDAM BASIN

尕斯库勒油田是柴达木盆地最大的油田,对于该大型油藏的形成机理一直是研究的重要课题。对尕斯库勒油田E31和N1-N2油藏原油的地球化学特征进行综合研究,结果表明:原油的正构烷烃呈偶奇优势,具有低的P r/Ph比值,含β-胡萝卜烷,反映它们形成于强还原环境;含丰富的伽玛蜡烷和>C30藿烷,指示它们形成于咸水-超咸水环境,但是,N1-N21原油的成油环境古盐度略高于E31原油;具有高含量的C27甾烷、规则甾烷、4-甲基甾烷、长链三环萜烷和低含量的二环倍半萜、烷基环已烷,说明它们母质主要为菌藻类,但是,两个油藏原油母质略有不同,E31原油较多的来自细菌,N1-N21油藏原油则较多的来自浮游生物;原油具有低的C29甾烷20S/20S+20R和ββ/ββ+αα比值及T s/Tm比值和低丰度的重排甾烷,反映了它们都为未成熟-低成熟度原油,但是,E31油藏原油的成熟度略高于N1-N21油藏原油。油源研究表明E31和N1-N21油藏原油由第三系盐湖相生油岩中生物脂类与可溶有机质和干酪根一起在低成熟阶段所生成。

The mechanism of hydrocarbon accumulation in Gasqule oilfield,which is the largest one in Qaidam basin, has not been well known. In this paper,the geochemical characteristics of crude oils in E3^1 and N1-N2 reservoirs of Gaskule oilfield were synthetically studied,and genetic environments, matrix types, maturity, and genesis for these studied oils were discussed. The results show that the rude oils have even-odd carbon predominance for n alkanes,low Pr/Ph ratios and certain amount of β-carotane,indicating that they were originated from high anoxic environments. High abundance of gammacerane and 〉C30 hopanes in the rude oils reflect that they were derived from saline-hypersaline lacustrine environment and the ancient salinity of sedimentary en vironment generating N1-N2 crude oils is slightly higher than that of E3^1 crude oils. The rude oils have high abundance of C27 steranes,regular steranes, 4-methyl steranes and long chain tricyclic terpanes,and low abundance of bicyclic sesquiterpanes and alkylcyclohexanes ,indicating that their matrixes are mainly bacteria and algae. However,E3^1 crude oils were mostly originated from bacteria and N1-N2 crude oil were mostly derived from plankton. Low C29 sterane 20S/（20S＋20R） and ββ/（ββ＋αα） ratios and Ts/Tm ratios as well as low abundance of rearranged steranes in the rude oils show that they are immature or low mature. However,maturity of N1-N2 crude oils is slightly higher than that of E3^1 crude oils. The results of oil source study indicated that N1-N2 and E3^1 crude oils were originated from organism lipids,soluble organic matters and kerogen in Tertiary low mature source rocks deposited under saline-hypersaline conditions.