Abstract:

The geological settings of Eastern Sag and Western Sag in Liaohe Depression are similar, but the volcanic reservoirs in Eastern Sag are much more abundant than that in Western Sag. According to the present research, migration of the subsidence center and depocenter from West Sag to East Sag results in the diversities of tectonic evolution between Western Sag and Eastern Sag, and finally leads to different reservoir accumulation conditions which are the key factors influencing oil accumulation in volcanics of Western Sag and Eastern Sag. Firstly, the oil and gas transporting system in Eastern Sag is better than that in Western Sag. Fault activities were different in the two sags. The fault systems in the Western Sag were active only in the early stage, while the fault systems in the Eastern Sag were active until the end of the Paleogene. Thus, the fault activity period could not match the accumulation period in Western Sag. Secondly, since the late Es4 stage, tectonic activities in Eastern Sag have become more intense than in Western Sag, and a lot of intrusive trachyte have developed in Eastern Sag. This kind of lithology is easily reformed and then fissures generates, forming better reservoirs in Eastern Sag. Thirdly，different with Western Sag, in Eastern Sag volcanic rocks in Es3 stage are chiefly concordant intrusion along fault, distributed as dikes, sills and laccolites, contacting directly with the source rocks which are convenient for oil migration.

Key words: volcanic rock reservoir, hydrocarbon accumulation, main controlling factor, tectonic activity difference, Liaohe Depression