THE GEOCHEMICAL CHARACTERISTICS OF HEAVY OIL AND ITS RECOVERY IN LIAOHE BASIN, CHINA

Heavy oils of the Lower Tertiary in the Liaohe Basin exhibit major differences in their biomarker composition although they have similar physical properties and bulk compositions. Our studies suggest that the formation of heavy oils is governed by two geochemical factors, namely biodegradation and maturation. The genetic classification of heavy oils has been made on the basis of GC and GC-MS analysis features. Biodegradation is a main pathway for forming heavy oils; when subjected to moderate biodegradation, light oils are converted to heavy oils. Low maturity heavy oils are only associated with those carbonates or evaporites which deposited under a highly reducing conditions. These oils are derived from kerogen degradation at the early stage of thermal evolution. Genetic research of heavy oils gives useful information for aiding oil recovery. Low maturity heavy oils accumulate in highly permeable zones of the trap. In this case, steam drive recovery is most effective. On the other hand, biodegraded oils are found in low permeable zones, whence recovery is difficult or impossible. This result has been verified by the actual situation of recovery in Liaohe Oil Field.