川西北地区飞仙关组原油的发现及地质意义

The Discovery and Geological Significance of Petroleum of Triassic Feixianguan Formation in Northwest Sichuan Basin

采用色谱(GC)、色谱—质谱(GC-MS)和同位素分析等技术方法,以广元长江沟剖面为例,系统分析了川西北地区飞仙关组原油地球化学特征,并初步分析了其成因。结果表明,长江沟剖面飞一段灰岩缝洞中原油的δ13C值和各族组成δ13C值都小于-30‰,族组分之间的碳同位素分馏效应较小,原油没有遭受细菌分解、淡水淋滤等次生同位素分馏效应;正构烷烃为前高后低的单峰型,主峰碳为C22,Pr/Ph值为0.75,姥姣烷和植烷均较相应正构烷烃(nC17和nC18)优势;芳烃色谱呈现驼峰,总体上组成比较复杂,以菲系列为主,经过MPI1折算该原油成熟度RO=0.94%;三环萜分布在C19—C30之间,以C23为主峰;霍烷以C30为主峰,伽马蜡烷含量较高,表明其母源为还原—弱还原的咸水环境;规则甾烷以C29优势,呈C29>C27>C28的"V"字型分布,甾烷成熟度参数C2920S/(20S+20R)值和C29ββ/(ββ+αα)值分别为0.39和0.31,均未达到平衡值。结合区域地质背景、飞一段烃源岩特征、原油地球化学特征,认为飞仙关组原油是寒武系烃源岩进入生烃高峰期的产物,现今灰岩洞缝中原油的分布状态是原油早期充注以后遭受构造运动破坏的结果。

Several techniques, including GC, GC MS and GC-IRMS, are used to study the molecular geochemistry and origin of oil （filled joint and cavern in limestone） of T1f1 in the Changjianggou profile of the northwest of the Sichuan basin. The data show that the petroleum δ^13C values for bulk oil and group compositions are less than -30 ‰. The crude oil has not suffered the secondary change such as bacterial decomposition, water leaching and so on. The isotope fractionation effect for the group compositions is small. The distribution of normal paraffin alkane is single peak, with nC22 prominent peak. Pr/Ph ratio （isoprenoid） is 0.75, with the Pr and Ph prominent predominance comprised with nC17 and nC18, respectively. The aromatic hydrocarbons present a shape of camel shoulder suggesting complicate domponents, and the phenanthrene is the prominent peak. Based on the methyl phenanthrene index （MPI1） ,Ro for the crude oil is about 0.83%. The carbon number for the tricyclene is distributed from C19 to C30 ,with C23 prominent peak. C30 is the prominent peak in hopanoid and T-wax alkane is the medium intensity content. The C29 steroid is predominant in the sterane series,with the ＂V＂ shape distribution of C29〉C27〉C28. The values of maturity parameter C29 20S/（20S＋20R） and C29ββ/（ββ＋αα） are 0.39 and 0.31 respectively,which not reach the isomerization equilibrium. On the basis of regional geology,source rock characteristics of T1 f1 ,geochemical characteristics of petroleum and oil source correlation,we consider that the crude petroleum is a product of Cambrian source rock at the oil generation peak and the occurrence of crude petroleum in the limestone cave and seam is a result of tectonic destroys after the early oil accumulation.