摘要:
酒西坳陷大部分原油的生物标记物分布特征较单一,主要表现为三环萜烷、降新藿烷、C30重排藿烷和重排甾烷不发育,伽玛蜡烷相对比较发育,C29甾烷异构化参数较低,一般在0.45~0.5之间,尚未达异构化终点,反映其源岩成熟度并不高。此类原油主要源于青西凹陷下沟组沉积于较强还原环境的藻纹层泥质白云岩。此外,酒西坳陷还发现了部分在生物标记物特征上有别于该区“主体原油”的原油,其表现为三环萜烷、C29Ts、C30重排藿烷和重排甾烷、伽玛蜡烷相对比较发育,而且部分原油(如窿8井、窿4井和窿10井原油)成熟度较高,甾烷C2920S/(20S+20R)值高达0.56~0.58(已达异构化终点),属酒西坳陷成熟度最高的原油,特别是这些原油中绝大部分的C29ββ/(ββ+αα)值也高于“主体原油”,表明其经受了较长距离的运移。根据生物标记物所反映的沉积环境和生源前身物分析以及将其与酒东坳陷主要源于赤金堡组的原油的比较结果,认为在酒西坳陷中,这部分相对于“主体原油”而言的生标特征异常原油可能源于青西凹陷深部的赤金堡组,这一认识对酒泉盆地的深层油气勘探具有实际指导意义。
Abstract:
The main oils of Jiuxi Depression have single characteristics of biomarker, it shows that the tricyclic terpane, C29-norhopane, C30-rearranged hopane and diasterane's content of these oils are low, gammacerane's content is high relatively and the isomerization parameter of sterane is lower,it is from 0.45 to 0.5, So it didn′t close to the terminal point of isomerization and it's source rock′s maturity isn′t high. This type oil is mainly from the laminar algal shaly dolomite of Xiagou formation that deposited in the reduction environment of Qingxi Depression region. Besides, there have another type of oil which it′s biomarker characteristics are different from the main part. These oils have relatively higher content of tricyclic terpane, C29-norhopane, C30-rearranged hopane ,diasterane and gammacerane, and part of it (such as the oils from long8,long4 and long10 wells) have high maturity. The isomerization parameter of sterane of these oils may reach from 0.56 to 0.58(it has closed to the terminal point of isomerization); it is the highest maturity oil of Jiuxi Depression. Especially, the main oils of this type have higher amount of C29ββ/(ββ+αα), it means that this oils have long distance migration. According to the result of analysis of depositional environment and native source precursor and contrast it with the oils which mainly from the Chijinbu formation of Jiudong Depression, we hold that those oils which have unusual biomarker characteristics might be in relation to the Chijinbu formation from deep part of Qingxi Depression.This viewpoint will have practical significance to the exploration of deep oil and gas in Jiuquan basin.
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