MIGRATION-ACCUMULATION CHARACTERISICS OF NATURAL GAS IN THE DIAPIR STRUCTURE BELT OF YINGGEHAI BASIN
ZHANG Min qiang
The diapir structure belt is the highly overpressured zone and the overpressure origin of Yinggehai basin. It belongs to a typical vertical pressure\|transfer system. The hot fluids were very active in this zone. The gas migration and accumulation showed three very different features from other hydrocarbon\|bearing provinces. First, the abnormal temperatures and pressures produced high fluid trend, and the abnormal pressures provided a great force to gas migration. Second, hydrofracture generated a good vertical migration path for natural gas, and the fluid\|transporting system in the diapir structure belt is mainly the fractured surface. Third, the activity model of the hot fluid controlled gas migration. Hydrofracture caused the release of fluid, which lowered the porosity pressure. The fractured surface was resealed after the release of fluid. The formation pressure increased again with the thickening of the overburden rocks, which caused the release of fluid again. This process repeated and the shutter\|like activity of fluid formed. As a part of the hot fluid, the accumulation of the natural gas is shutter\|like, and the gas is under the positive dynamic balance of accumulation\|dissipation\|reaccumulation, in which the supply of gas is greater than its dissipation.