Geochemical Characteristics Of Hydrocarbon Accumulation In Offshore Area, Liaohe Depression

Liaohe offshore area is the transition zone of Liaohe depression and the tectonic units of Liaodong Bay area. It has a similar petroleum geology characteristic and history of tectonic evolution with Liaohe depression. Exploration confirmed that the geological conditions is superior in Liaohe offshore area, and oil-generating strata, reservoir strata, cap rock is complete and with good configuration, formed several consociation. It has the conditions to form multi-formation and multi-type reservoirs. It is also the main follow-up areas of exploration for Liaohe Oilfield Company .In this treatise, based on the modern theories and analytical techniques of geochemistry/petroleum system, petroleum migration and accumulation of offshore areas in Liaohe are analyzed synthetically. According to analysis of the three sets of hydrocarbon source rocks in offshore areas, the results showed that the lacustrine shale of Es3 member is the main source rock,while the Es1+2 member is the subsidiary and the Ed formation is poor. The Ed formation plays a relatively small role in eastern and western depression.The physical property of oil is complex in the area. Both condensate and normal oil with low density and viscosity and heavy oil with high density and viscosity had been founded. The contributing factor of oil is a little different. The source rock is in a similar oil-generating background as there were subtle differences. This shows that the sedimentary environment is multivariant during the deposition.By method of geochemical fractionation parameters and geological log of petroleum, patterns, direction and intensity of hydrocarbon in offshore areas are analized systematically. We find that the main migration method is vertical migration, lateral migration is secondary. On this basis, combing research results of hydrocarbon migration intensity, advanced hydrocarbon migration direction of secondary structural zones were rasied. These areas near the dominant faults is the priority structure for the oil and gas gathering.The treatise rasied four different types of conduit systems on the basis of study of tectonic and sedimentary. The main conduit systems is discordogenic fault-led and fault ladder model, while the lower combination of hydrocarbon conduit systems is mainly fault-unconformity or unconformity model. The development of fault and the development of the sedimentary structure is the main hydrocarbon distribution control factors. The control factor of oil accumulation is different as a result of different conditions for oil accumulation. The oil sources conditions is sufficient, translocation system play a decisive role in oil accumulation process. Although the sand and non-integration also play a role in the process of oil accumulation, compare with the impact of faults, the effect is much smaller. Therefore, the scale of reservoir is much smaller when there is no deep fault. The development of fault and the development of the sedimentary structure is the main hydrocarbon distribution control factors.