The Geochemistry Characteristics of hydrocarbon expulsion from source rocks in Dongying depression
Chen Zhonghong, et al,GEOCHIMICA,2005,34(1):79-87
(The University of Petroleum, Dongying, Shandong, China,257061)
Abstract: Using geochemistry information to study hydrocarbon-expulsion behavior is an important and effective measure. The abundance of the geochemistry information in Dongying depression has great significance in studying hydrocarbon-expulsion behavior. The geochemistry characteristics indicated thatthe hydrocarbon-expulsion in Dongying depression had stronger heterogeneity: the efficiency of hydrocarbon-expulsion in the edge of mud is much higher than the inner of the mud; the efficiency of hydrocarbon-expulsion in the edge of mud was much higher than in the inner of the mud, which was more obvious in the thick mud (thicker than 30m) , and there were stagnant-expulsion zone in the thicker mud commonly; in different compaction phase the efficiency of hydrocarbon-expulsion had discrepancy, the efficiency of hydrocarbon-expulsion in the rapid-compaction phase was higher than in the slow-compaction phase and the stabilized-compaction phase. There were two types of overpressured systems: the open and the closed relatively. The episodic hydrocarbon-expulsion was an important hydrocarbon-expulsion behavior in the open system, and its efficiency was higher comparatively (50% averagely, higher than 40% in normal pressure system); the closed system was overpressure compartment and its efficiency of hydrocarbon expulsion is lower (averagely 20%), and the characteristics of geochemistry demonstrated the stagnant-expulsion. The disequilibrium compaction was considered to be the primary reason for the overpressure formation in the middle part of the Member 3 of Shahejie Formation, hydrocarbon-generation was the key factor for the overpressure in the upper part of the Member 4 of Shahejie Formation, and the overpressure in the lower part of the Member 3 of Shahejie Formation was a result of the both factors.