Abstract: Oil-rich sags in fault basins in East China, have favorable conditions for hydrocarbon accumulation. Over 40 years of extensive exploration, these sags can be classified as matured areas with high degree of exploration. The subtler exploration targets become more and more difficult to be identified and discovered. However, since these sags still contain large quantities of remaining resources, they are still promising zones for revealing large-scale oil and gas reserves. Based on existing resources, a series of delicate and innovative exploration practices including detailed studies, fine description, intensive searching, meticulous operations, careful selection and innovative management have been developed to enhance geologic understanding, to verify exploration targets, to forecast the hydrocarbon potential, and to achieve high-efficiency management over relevant exploration operations in matured areas. In this paper, these exploration practices are presented with the Niudong ultra-deep and ultra-high temperature buried hill oil reservoir in the Baxian sag, the stratigraphic lithologic oil reservoir in weak structural belt of the Lixian slope in the Raoyang sag, the Daliuquan complex structural reservoir in the Langgu sag, and the reservoir in the Aer sag (a newly discovered sag in the Erlian Basin) as examples. It is concluded that these delicate and innovative exploration practices provide valuable guidances for further exploration and continuous reserve enhancement within matured areas in East China.

Key words: oil-rich sag, fine exploration, subtle buried hill, weak structural slope, complex structural area, innovative exploration management