The Geochemical Characteristics Of Typical Heavy Oils Of The Tahe Oilfield In Tarim Basin

As the dwindling of conventional oil and gas resources that can be mined, theheavy oil with a huge amount of potential exploration and development has becomean important reserve resource, will have an important impact on future energysupply.The source, formation mechanism, distribution characteristics of heavy oil andmining technology of viscosity reduction has been relatively mature in Liaohe,Shengli and other continental viscous oil in our country. But the related research ofextensive development of west China Marine heavy oil is still relatively weak.Therefore, it is necessary to carry out the research on typical Marine geochemicalcharacteristics and origin of heavy oil.The ordovician carbonate reservoir in the oilfield is the biggest Marinecarbonate reservoir in China for now. Multiphase hydrocarbon injection and the latercomplex stage of reservoir formation result in some controversy over theunderstanding of the evolution and the distribution rule, which severely restricts thefurther exploration and development in the area and resource evaluation.This paper, taking Tahe oilfield and adjacent area of heavy oil as an example,through geochemical research, discusses the characteristics, sources and formationmechanism of thick oil. It is of important theoretical and practical significanceproviding the accurate assessment of Marine heavy oil resource potential based onscientific data. It mainly obtains the following understandings:(1) Although crude oil in Tahe oilfield suffers some degree of biodegradation, butthe peak corresponding normal alkanes is complete, and the distributioncharacteristics are similar, which illustrates the characteristics of multiphaseaccumulation.(2) It can be seen from the correlation diagram of Tahe crude oil samples ofPr/nC17–Ph/nC18that most of the study samples are in weak oxidation-reduction environment; Tahe crude oil samples rules that the relative content of steranedistributions are very consistent, which might represent the accumulation of thecrude oil with similar environment.(3) Tahe crude oil samples showed low luorine distribution characteristics, inaddition to Tahe12and10area, the rest of the block three luorine seriesdistribution difference is bigger, probably with the sedimentary environment changeand the period of accumulation.(4) Tahe crude oil total carbon and carbon isotope values’ corresponding normalalkanes was generally lower, which is quite different from the TZ62well and TD2well Cambrian crude oil, shows that the hydrocarbon source rocks of middle-upperrdovician is one of the important hydrocarbon source rocks.(5) In this study we identified the complete series of25-norbenzohopane (C31-C34)in the severely biodegraded oils from the Ordovician reservoirs in Tahe Oilfield andfound that the ratios of25-norbenzohopane to corresponding benzohopane are wellcorrelated with other parameters reflecting biodegradation extent. In addition thenew ratio parameter is much bigger than others and therefore it is necessary tofurther evaluate this new parameter in the future studies to obtain more detailedinformation on biodegradation extent.