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Origin And Exploration Of Hydrocarbons In Baiyinchagan Depression

Posted on:2004-10-06Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y M TanFull Text:PDF
GTID:1100360092496256Subject:Institute of Geochemistry
Abstract/Summary:PDF Full Text Request
Origin and Exploration of hydrocarbons in Baiyinchagan DepressionTan Yuming (Geochemistry) Directed by Fu Jiamo, Sheng Guoying and Pan ChangchunBaiyinchagan Depression is located at the western end of Erlian Basin. The main strata in this depression are of Cretaceous. According to the organic carbon content, kerogen type and maturity, three source rocks have been identified: Duhongmu I, Tenggeer Formation and Aershan II. The source rock of Duhongmu Formation I is characterized by high organic carbon content and low maturity. The most prominent molecular geochemical features include: (1) the Ph/nC18 ratio is very high (>2) while the Pr/Ph ratio is relatively low (<0.4); (2) both the ratios of C2920S/(20R+20S) and pp/( + ) steranes are relatively low (<0.25); (3) the ratios of C21/(C21+IC29) steranes and C21/(C21+C30) terpanes are also relatively lower than are those in the other two source rocks. Both the source rocks of Tenggeer Formation and Aershan Formation II are characterized by relatively low organic carbon content and high maturity. The main molecular features of both source rocks are: (1) the Ph/nC18 ratio is relatively low (<1) while the Pr/Ph ratio is relatively high (>0.6); (2) both the ratios of C2920S/(20R+20S) and /( + ) steranes are relatively high (>0.40); (3) the ratios of C21/(C21+ C29) steranes and C21terpane/(C21terpane+C30hopane) are also significantly higher than those are in the other two source rocks.Oils are greatly various in viscosities within Daerqi Oilfield, in which the ordinary oil, viscous oil and extremely viscous oil are distributed. Based on the physical features, group compositions, molecule's geochemistry and biodegradation effects, these oils are classified into five types. Oil Type 1, non-biodegraded oil, is characterized by low viscosity, low density, high content of saturated fraction, low content of resin and asphaltene and high ratio of isomerization of steranes. This oil is derived from the deep buried, mature source rocks of Tenggeer Formation and Aershan Formation II. Oil Type 2, also non-biodegraded, is characterized by extremely high viscosity, relatively high density, low content of saturated fraction, high content of resin and asphaltene and low ratios of isomerization of steranes. This type of oil is derived from the shallowly buried, immature or lowly mature source rock of Duhongmu Formation I. The type 1 and 2 oils are two basic types in Daerqi Oilfield. The oil of type 3 is of a mixture by typel and 2, and dominated by the former. This oil is characterized by relatively low isomerization ratios of steranes, but slightly higher density and viscosity than those of type 1. The oil of type 4 is of a biodegraded one from type 1 and characterized by relatively high density and viscosity. The oil of type 5 is the biodegraded one from the oil of type 3, and characterized by a density and viscosity similar to type 4. However, the isomerization ratio is lower in the type 5 than that inthe type 4.The occurrence and intensity of biodegradation on oils in Daerqi Oilfield is not only determined by burial depth and exposure to meteoric water, but also related to the group composition and physical feature of the oil. Although the oil of type 2 is shallowly buried it is not affected by biodegradation while the neighboring, or inter-bedded oils of type 1 and type 3 are strongly biodegraded.According to the oil occurrence and evaluation on traps in various structural zones, in combining with practice of oil exploration in recent years, two targets for further intense exploration, three targets for further evaluation and three targets for primary exploration have been chosen.
Keywords/Search Tags:Daerqi Oilfield, Oil mixing, Origin of viscous oil, Biodegradation
PDF Full Text Request
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