塔里木盆地库车坳陷大宛齐—大北地区原油轻烃特征及地球化学意义

Geochemical application of light hydrocarbons in Kuqa Depression of Tarim Basin:Case study of Dawanqi-Dabei areas

大宛齐—大北地区是塔里木盆地库车坳陷的重要油气勘探区,区域内原油以轻质油为主,其轻烃地球化学特征研究薄弱。采用气相色谱对大宛齐—大北地区的原油轻烃化合物进行分析和地球化学特征研究。研究区原油中C_4—C_7化合物组成特征和甲基环己烷指数均表明其为腐殖型母质来源的陆相油;Mango轻烃参数K1基本符合轻烃稳态催化动力学成因模式,其成因具有较好的一致性;庚烷值和异庚烷值显示其成熟度较高,根据原油形成温度与成熟度相互关系推测其母源成熟度R_O值约为0.8%~0.93%;轻烃的芳香度指数及链烷烃指数相关性和C_7轻烃蚀变参数相关性分析认为,原油轻烃不仅遭受了生物降解蚀变,还经历了蒸发分馏和水洗作用。研究结果对确定原油母源、成熟度及次生蚀变具有重要意义。

Located in the Kuqa Depression of Tarim Basin, the Dawanqi and Dabei areas are important oil and gas exploration areas.Light oil takes the predominant composition of the hydrocarbons while the fur- ther exploration was impeded by the weakness research of the geochemical characteristics. Gas chromato- graphic method was taken to analyze the composition and geochemical features of the light oils in Dawanqi and Dabei areas.The C4-Cr composition and methylcyclohexane index of light hydrocarbons suggest the oils were derived from terrigenous humic source. K1 of Mango parameter is largely in line with the transition metal catalysis genesis model showing a preferably coherences of similar origins.Heptane value and isohep- tane values show the oils bears with relatively high maturity,which is well conformed to the maturity （Ro =0.8^-0.93Y00） calculated based on the relevance to oil generation temperatures.The results based on the aromaticity/ paraffin indexes and alteration parameters of Cr suggest that several types of alterations inclu- ding biodegradation,evaporation fractionation and water washing have affected the light hydrocarbons.The study on the characteristic analysis of light hydrocarbon will be of great importance to identify the original source, maturity and alterations.