PALAEOGEOMORPHOLOGIC CONTROL ON GRAVITY FLOW DEPOSITS AND GAS RESERVOIR FORMATION:A CASE STUDY FROM THE MIOCENE IN YINGGEHAI BASIN

For the purpose to identify the next exploration target which has remained unclear so far in the central depression of the Yinggehai Basin, and based on the principles of reservoir formation and gas accumulation, this paper studies the palaeogeomorphologic patterns and their control over gravity flow deposition and gas reservoir formation. Results show that the increases in slope and water depth near the flexure slope break is the key condition for submarine fan to form, and the limited grooves and valleys determine the injection mouth and the direction of sediment movement, and the subsiding centers formed by the uneven subsidence controls the unloading area for submarine fan deposits. Gravity flow sediments are always deposited under the slope break in the LST, and, therefore, disconnected to the deltaic deposits near the slope break. It is easy to form a good reservoir-cap association with overlying shallow sea mud deposit formed in the TST-HST as covers. It is favorable for the formation of effective trap. Since the paleo-depocenter migrated from north to south, the northern Dongfang region is precocious and matured. However, the organic matter in the Ledong region is matured late but rapid. Based on the above research, this paper points out that the central depression of the Yinggehai Basin is a favorable area for next cycle of exploration.