As formation

evolution and genetic mechanism of subtle oil/gas reservoirs are very complicated

various methods

such as discovery process model inversion

theoretical forward computation of hydrocarbon accumulation threshold and comprehensive prediction method

should be comprehensively used

so as to increase the reliability of potential evaluation and provide scientific basis for high level decision-makers. These methods are used to predict the potentials of subtle reservoirs in Jiyang depression. The prediction results show that there are still more than 2.024 billion tons reserves to be discovered in subtle reservoirs in the depression

which account for over 75% of the remaining provable reserves. The undiscovered possible reserves in subtle reservoirs in Dongying

Zhanhua

Chezhen and Huimin sags are 783 million tons

353 million tons

378 million tons and 352 million tons respectively. Laterally

subtle oil/gas reservoirs are mainly distributed in the reservoiring systems having relatively high abundance of reserves and relatively low proved reserves. Vertically

although the 4

th

member of Shahejie Formation and the targets above it have highly been explored

they are still the key horizons for discovering new reserves in subtle reservoirs. Lithologic lenticular reservoir

unconformity-screened reservoir and buried hill reservoir are the main types of subtle reservoirs to be explored in the future.