Some oil-producing basins in eastern China, such as Songliao basin, Bohai Gulf basin, and Nanyang basin are extensively explored regions. In these basins, reserves in structural traps account for 34% of the total proved plus prospective, and 21% of the total estimated; in subtle traps, 7.6% of

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the proved plus prospective and 38.4% of the estimated.

The eastern China oil-bearing basins belong to the intracratonic basins of Mesozoic-Cenozoic age and can be separated into two basic types based on genetic and developing characteristics: depression (Songliao basin) and faulted depression (Bohai Gulf basin).

As a symmetrical, gentle syncline, the depressional basin occurred mainly in the Early Cretaceous, forming a unified vast deep-water lake and oil-generating center. Giant deltaic sandstone bodies wedged into the source rocks, constituting a sequence of oil and gas reservoirs. The faulted depressional basin occurred mainly in the Paleogene. The basin is composed of a series of uplifts and wedge-shaped faulted depressions with certain trends. The latter is an independent oil-bearing unit, in which very thick source rocks were deposited. The occurrence and distribution of oil and gas pools are controlled by structural framework and lithofacies zones in the faulted depression.

Geologic conditions were excellent for forming various types of subtle oil and gas pools. With the high potential of oil and gas reserves in eastern China, exploration for them will become increasingly important.

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