| Summary: | A comprehensive analysis is done to investigate the exploration maturity and exploration potential in the petroleum-rich sags in the Bohai Bay Basin, indicating that the re-exploration program is of great significance. The advances in geological theories, key engineering technologies and exploration methods involved in the re-exploration program are described. Taking the Raoyang sag as an example, the study documents how the program was conducted and discusses its promising future of application. Petroleum-rich sags, with an oil resource abundance of greater than 20×104 t/km2 and a total oil resource of over 3×108 t, are the main domains for petroleum exploration and production in the Bohai Bay Basin. With a discovery maturity of more than 50%, these petroleum-rich sags have entered the high maturity exploration stage and discovery of new oil and gas reserves has become more and more difficult. However, the undiscovered oil resources in these sags are abundant and amount to 105×108 t, so that they are still the main exploration domains in the Bohai Bay Basin. With the petroleum-rich sags in the Jizhong depression of the Bohai Bay Basin as an example of the re-exploration program, the study presents a detailed documentation of oil accumulation in subsags, reservoir-forming in the subtle buried hills, and oil migration and accumulation in the weakly deformed structural slopes. It deals with the advances in the merged 3-D seismic prospecting over an entire sag, facies-based reservoir prediction, stimulation techniques for complex reservoirs and fast efficient drilling techniques. Furthermore, it proposes the re-exploration program, which comprises a new round of overall exploration philosophy, new evaluation and planning. It discusses the important roles played by the re-exploration program in sustaining the reserve additions in the highly explored petroleum-rich sags. Key words: Bohai Bay Basin, petroleum-rich sag, re-exploration program, theoretical cognition, technical approach, exploration practice
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