By studying the tectonic background of QHD29-2 oil field and the geochemical characteristics of oil and gas and its source rocks,the dissimilarity of crude oil physical properties was discussed from the perspective of evaporative fractionation and biodegradation. Oil source comparison confirmed that the oils in Paleogene and Neogene had the same source. However, there were significant differences in light hydrocarbon composition, family composition and the chromatographic distribution of saturated hydrocarbons,indicating that they had expe-rienced a strong evaporative fractionation. Combined with the analyses of source rock thermal evolution,accumu-lation stage and fault activity history, it was believed that the intrusion of mantle-derived CO2gas had caused evaporative fractionation in the area. The evaporative fractionation and biodegradation jointly controlled crude oil physical properties in the reservoir. Evaporative fractionation and biodegradation were the main factors controlling the differences of crude oil physical properties in reservoirs,and the differences were mainly controlled by evapo-rative fractionation,whereas,the oil in shallow reservoirs was controlled by both evaporation and biodegradation. Extra-heavy,light,condensate and heavy oils distributed in sequence from deep to shallow reservoirs. The two mechanisms had an impact on the same reservoir simultaneously. The early reservoirs in deep formations were affected by evaporative fractionation. After the shallow reservoirs of the post-accumulation were biodegraded,they were continuously charged in the late stage of the pre-existing reservoir.%通过对秦皇岛29-2油田地质构造背景、油气及其烃源岩地化特征等方面研究,从蒸发分馏与生物降解共控的角度探讨了秦皇岛29-2油气藏原油物性差异性成因.研究结果表明:油源对比证实该古近系油藏与新近系油藏同源,但它们在轻烃组成、族组成和饱和烃色谱分布上存在显著差异,表明经历了强烈的蒸发分馏作用.结合该区烃源岩热演化、成藏期次和断裂活动史认为,幔源CO2气体侵入引起了该区蒸发分馏作用;蒸发分馏和生物降解作用联合控制着该油气藏的原油物性差异分布,深、浅层油藏整体受控于前者,浅层油藏同时受控于后者,从深到浅依次分布着特稠油、轻质油、凝析油和稠油;2种作用共存于同一油藏,既需要有已遭受蒸发分馏影响的先存深层油藏,也需要后成藏的浅层油藏遭到生物降解的同时,接受先存油藏的晚期持续充注.
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