Geochemical characteristics and reservoir controlling factors of Ordovician ultra-deep crude oil in No.1 and No.5 fault zones in Shunbei area,Tarim Basin
The Ordovician reservoir in the Shunbei area has great potential for oil and gas exploration.It is one of the most important research areas for ultra-deep oil and gas exploration.Shunbei No.1 and No.5 fault zones are located in the middle of Shunbei Oilfield.It is very important to clarify the source,thermal maturity,oil cracking degree and reservoir-controlling factors of crude oil in this area to reveal the hydrocarbon accumulation model and guide the later oil and gas exploration.In this paper,19 crude oil samples from No.l and No.5 strike-slip faults in Shunbei Oilfield were selected for saturated hydrocarbon,aromatic hydrocarbon,adamantane and carbon isotope analysis to reveal their geochemical characteristics.The results show that the crude oil samples of No.l and No.5 fault zones have been subjected to different degrees of thermal stress transformation,and the traditional biomarker parameters are distorted and cannot be used to indicate the oil source.The similar light hydrocarbon carbon isotope distribution characteristics indicate that the crude oil in the study area belongs to the same group.The n-alkane carbon isotope values of the crude oil range from-37％o to-30％o,which is comparable to the Cambrian source rocks.It is considered that the crude oil in this area is produced from the Lower Cambrian Yuertus Formation.The maturity of crude oil in the No.5 fault zone gradually increases from north to south.The average value of crude oil equivalent vitrinite reflectance converted by aromatic hydrocarbon parameters is between 0.80％and 1.43％,indicating that the crude oil is in the mature-high mature stage.The maturity of crude oil on the north and south sides of the No.l fault zone is not much different,which is equivalent to the maturity of crude oil in the middle of the No.5 fault zone.The overall maturity is between 1.06％and 1.20％,and the crude oil is in the mature stage.The order of crude oil cracking degree in the study area is the southern section of No.5 fault zone,the northern section of No.5 fault zone and No.1 fault zone.Comprehensive analysis shows that the development characteristics of strike-slip fault zone and the difference of reservoir temperature jointly control the changes of oil and gas physical properties and geochemical parameters of No.1 and No.5 fault zones in Shunbei area.This study can provide guidance for ultra-deep oil and gas exploration in Shunbei area.
Tarim BasinShunbei areastrike-slip fault zonegeochemical characteristicsfactors of controlling reservoir
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