| As unconventional oil and gas resources in the oil industry, heavy and extra heavy oil has being played more and more important position and role. Sufficiently useing the theory of petroleum geology and geochemistry, in this dissertation I have systematically analysised the characteristics of heavy oil samples in the North Slope of the Biyang Depression. Based on the identification of these characteristics, can we carry out heavy oil-oil and oil-source correlation. The results might provide a scientific basis for oil and gas exploration and development both in the region and similar areas.In this article, the North Slope of Biyang Depression has been divides into two zones to study, including Yanglou-Wangji-Xinzhuang zone and Gucheng-Jinglou zone. We have researched the regionally geochemical characteristics of heavy oil samples which collected from two regions. The consequence, originated from respectively geochemical characteristics of heavy oil samples, illuminated that there are two main types of heavy oil the North Slope.One type was the mixed heavy oil that was basically created by the original changes, which mixed with both biodegradable and other secondary changes. This kind of heavy oil mainly distributed in Yanglou zone. The other type was densified secondary factors, particularly biological degradation. This biological degraded type appeared in the Xinzhuang zone, Gucheng zone and Jinglou zone. According to the biodegraded degree, combined with the geochemical characteristics, the heavy oil samples were classified for four groups:slightly biodegraded heavy oil (1～3 grade), moderately biodegraded heavy oil (4～5 grade), severely biodegraded heavy oil (6～7 grade), extremely biodegraded heavy oil (8 grade).Slightly biodegraded heavy oil (1～3 grade). N-alkanes in such heavy oil was subject to certain biodegradation, but the chain n-alkanes and isoprenoid hydrocarbons can be recognized. Steranes and terpane constituted the main peak of gas chromatogram. The content of (3-carotane was also high. This type of heavy oil mainly distributed in Biyang Yanglou zone of the northern slope (Bi 276 well, Yang 21218 well, Yang J3624 well and Yang 3515 well).Moderately biodegraded heavy oil (4～5 grade). N-alkanes in such heavy oil have been essentially degraded. The gas chromatogram roughly showed the chain of isoprenoids. But the series of steranes and terpane were remainly intact. They basically composed the main peak of gas chromatogram.β-carotane was visibly high.25-norhopane did not be detected. This type of heavy oil mainly distributed in Yanglou zone (Yang 50714 well), Xinzhuang zone (Xinqian 25 well and Xin 5005 well), Gucheng zone (Gu 412 well) and Jinglou zone (Lou 3917 well).Severely biodegraded heavy oil (6～7 grade). N-alkanes in such heavy oil almost disappeared.25-norhopane was detected markedly. The series of steranes and terpane began to be affected. Some of steranes and methyl steranes were not able to be detected. This type of heavy oil mainly distributed in Xinzhuang zone (E Xin 8 well and Xin 6164 well) and Jinglou zong (Jing 1131 well, Jing2111 wells and Jing J1520 well).Extremely biodegraded heavy oil (8 grade). In these heavy oilsβ-carotane structured the main peak of the saturated hydrocarbon chromatograms. N-alkanes could not be identified. Even steranes, methyl-steranes and 25- norhopane were not detected. The content of C3o-hopane were significantly reduced. This type of heavy oil mainly distributed in Yanglou zone (Yang 1900 well), Gucheng zone (Gu 574 well, Gu 580 well) and Jinglou (Lou 3913 well).Due to the influtency of varying degrees of biodegradation, the characters might not reflect the originally geochemical information that contained in heavy oil from the northern slope in Biyang Depression. (Some biomarkers in crude oil were destroyed by biodegradation). We have researched ratio of C29-hopane and C3o-hopane in 259 samples of normal crude oil and source rocks, which were collected from other domestic depressions. Basis on the results, we proposed the new gammacerane index [C30-gammacerane/(2xC29-hopane)] to replace the former gammacerane index (C30-gammacerane/C30-hopane). Using the new gammacerane index, we efficiently identified the oil-source correlation between the biodegraded heavy oil and normal crude oil. At the same time, we have designed a related diagram, which consisted of (2x C24 tetracyclic terpane)/C26-long-chain tricyclic terpane ratio as X axis and C30-Gammacerane/(2x C29-hopane) ratio as Y axis.The related plates accurately distinguished the heavy oil created from different layers in different regions. Through the oil-source correlation studies, it draw the following conclusions:the heavy oil of Yanglouzone derived from the immature to low-mature source rocks of lower Eh3 section in near area or mixed with some of mature crude oil from deep- depression district. The heavy oil of upper Eh3 section in Wangji and Xinzhuang zone derived from source rocks of upper Eh3 section in deep- depression district, and Xinzhuang migrated from Wangji zone. The heavy oil of Eh2 section in Wangji and Xinzhuang zone derived from this area's source rocks of upper Eh3 section, and it may mixed with some of Eh2 low-mature crude oil from deep-depression district. The heavy oil of lower Eh3 section in Gucheng and Jinglou zone derived from the source rocks of lower Eh3 section in deep-depression district, but it could not exclude the contribution of source rocks from lower Eh3 section in near area. The maturity of upper Eh3 heavy oil decreased from south to north in Gucheng zone.It was the mixed oil that shew the characters of source rocks from the upper and lower Eh3.But the proportion was different in different area. The amount of lower Eh3, mixed into Gucheng zone, increased from the south to north. Heavy oil wells on the floor, mainly for the nuclear three-three on the origin of nuclear mature oil, but also a certain amount of crude oil mixed with the nuclear three. The heavy oil of upper Eh3 section in Jinglou zone generally derived from this area's mature source rocks of upper Eh3 section, and it also mixed with some crude oil from lower Eh3 source rocks.
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