THE CONTROLLING FACTORS OF UNEVEN VERTICAL ENRICHMENT OF HYDROCARBON IN THE CENTRAL SUB-SAG OF FULIN SAG OF ZHANHUA DEPRESSION

In the area near the Kenli fault in the Central Sub-sag of the Fulin Sag, there occurs uneven hydrocarbon vertical distribution. Hydrocarbon accumulations have been found in the deep layer of Es₃ and the shallow layers of Ed and Ng_x, while the traps in the middle layers Es₂ and Es₁ are mostly empty. Based on oil-source correlation, source rock hydrocarbon-generating evolution analysis, fault activity analysis and other kinds of methods, we studied the characteristics of hydrocarbon accumulation and controlling factors. Results show that the hydrocarbon in the reservoirs of Es₃ is from the Es_3x source rocks of the Central Sub-sag in the Fulin Sag while the hydrocarbon in Ed and Ng_x reservoirs comes from Es_3x source rocks in the Gunan sag. The hydrocarbon from the Fulin Sag is limited, and the migration conditions are restricted since the hydrocarbon-expulsion period of the source rock did not match the active period of the Kenli fault. Therefore, the hydrocarbon can only migrate for a short distance and accumulate in the reservoirs of Es₃. However, the hydrocarbon from source rocks of the Gunan Sag was sufficient, and the Kenli fault was active during the hydrocarbon-expulsion period of the source rock, so the hydrocarbon is able to migrate through the fault for a long distance and accumulate in the Ed and Ngx in the Central Sub-sag of Fulin Sag.