塔里木盆地顺托果勒地区奥陶系原油中乙基桥键金刚烷系列的检出及意义

Detection of ethanodiamondoids in the Ordovician crude oil from Shuntuoguole area in Tarim Basin and its significance

乙基桥键金刚烷是金刚烷的变形化合物,其在油气地球化学中的应用薄弱。使用气相色谱-质谱(GC-MS)、气相色谱-质谱/质谱(GC-MS/MS)分析方法,在塔里木盆地顺托果勒地区奥陶系原油中检测出完整的乙基桥键金刚烷系列,包括C—C乙基桥键单金刚烷系列和C—C乙基桥键双金刚烷系列。通过分析典型化合物的质谱特征并与文献对比,确认了上述化合物的存在。使用D-单金刚烷作为定量内标,顺托果勒地区奥陶系原油中乙基桥键金刚烷系列化合物的浓度为93.66~8 542.70μg/g。原油中甲基-乙基桥键单金刚烷(META)指数与甲基单金刚烷指数、甲基菲比值之间存在良好的正相关性,表明甲基-乙基桥键单金刚烷指数可以作为确定原油成熟度的指标。6-META+1-META+2-META浓度与4-甲基双金刚烷+3-甲基双金刚烷浓度之间具有很好的正相关关系,且二者的浓度在同一数量级上,表明6-META+1-META+2-META浓度可以作为确定深层油气藏遭受次生改造作用的良好指标。顺托果勒地区奥陶系的现今地温具有从NW向SE方向逐渐增高的趋势,其中,顺托工区和顺南工区经历的最高古地温高于顺北工区,这也导致顺托工区和顺南工区奥陶系的原油遭受强烈裂解,部分原油叠加了硫酸盐热化学还原(TSR)作用。由顺北工区向顺托工区再至顺南工区,奥陶系的油气藏相态由轻质油、挥发油至凝析油气再至干气变化,6-META+1-META+2-META浓度由NW向SE方向逐渐增加,这为深层油气藏的热裂解作用及TSR作用提供了地球化学证据。

As a variant compound of diamondoid, ethanodiamondoid is less applied in petroleum geochemistry. Using GC-MS and GC-MS/MS methods, complete ethanodiamondoid series, such as C—Cethanoadamantanes and C—Cethanodiamantanes, were detected in Ordovician crude oil from Shuntuoguole area, Tarim Basin. The existence of above compounds was confirmed by analyzing the mass spectrum characteristics of typical compounds and comparing them with literature. Taking D-adamantane as the quantitative internal standard, the concentrations of ethanodiamondoids in Ordovician crude oil from Shuntuoguole area is ranged from 93.66 μg/g to 8 542.70 μg/g. The results show that there is a good positive correlation between methylethanoadamantane(META)index and methyladamantane index and methylphenanthrene ratios in crude oil, suggesting that META index can be used as an index for determining the maturity of crude oil. Meanwhile, there is a good positive correlation between the concentrations of 6-META+1-META+2-META and those of 4-methyldiadamantane and 3-methyldiadamantane, and their concentrations are in the same order of magnitude, indicating that the concentrations of 6-META+1-META+2-META can be used as good indexes for determining whether deep oil and gas reservoirs are affected by secondary alteration. In Shuntuoguole area, the present formation temperature of Ordovician tends to increase from northwest to southeast. Specifically, the maximum paleo-temperature of Ordovician in Shuntuo area and Shunnan area is higher than that in Shunbei area, as a result of which the Ordovician crude oil in Shuntuo area and Shunnan area suffers from strong oil cracking, and some crude oils are also affected by thermochemical sulfate reduction(TSR). From Shunbei area to Shuntuo area and then to Shunnan area, the phase of the Ordovician oil and gas reservoirs changes from light oil, volatile oil, condensate to dry gas, and the concentrations of 6-META+1-META+2-META tend to increase from northwest to southeast, providing a geochemical evidence for thermal cracking and TSR of deep oil and gas reservoirs.