Abstract:

With the advance of exploration and development of seismic data quality，we discovered a tectonic style called “cabbage” structure in Qibei and Shaxi tectonic zone of Qikou Sag. Applying the geometric characteristics，stratigraphic distribution，fault type and the migration of flower’s centre，we have made clear of the formation mechanism and hydrocarbon enrichment of “cabbage” structure in the two zones. The results show that the “cabbage” structure in Qibei tectonic zone formed in the period of neotectonic movement. Shaxi tectonic zone controlled by extension has experienced three stages，including extrusion uplift，thermal subsidence and neotectonic movement. The difference of tectonic evolution leads to the difference of hydrocarbon accumulation. Qibei tectonic zone has the characteristics of late-stage accumulation. Mid-shallow strata is favorable section. Meanwhile Shaxi tectonic zone has two periods of reservoir-forming，the middeep strata is favorable section as the influence of thick shale in Dongying Formation.

Key words: “cabbage&rdquo, structure, tectonic evolution, formation mechanism, accumulation difference, Qikou Sag