Abstract:

Bohai Bay Basin is a Tertiary oil and gas-bearing fault basin of the 2nd subsiding belt of Neocathaysian in eastern China.Its basic outline is a reversed S-shape.Two groups of major faults,striking in NE and NW,have divided the basin into fault blocks in different size.These fault blocks,their unequilibrium shearing movements in space,control the formation of source sags(depressions)and the development of structural traces in different order.The repetition of these structural traces in different order have formed shear structure patterns in different type and size,among which the most common ones are ξ-type structure,λ-type structure,check-form structure,broom-like structure,etc.Those shear structure patterns are the main types of secondary structural belts which control the oil and gas accumulation within the basin.The major structural belts of ξ-type faults and broom-like faults are especially favorable to accumulation of oil and gas,and very often they turned into oil and gas-enriched belts.On the one hand the structural belts normally occurred together within the source sags or at the side of the source sags,with sufficient oil source,on the other hand they themselves not only have varied type of good traps but also have good reservoirs.So,some of the major fields within the basin are mainly located in these faulted strutural belts.The generation of the shear structure patterns mentioined above results from the mechanism of regional right lateral shear stress of NS trend.To recognize the above-mentioned features of various shear structures,their development law and their control of oil and gas occurrence will be of great value for guiding exploration and development of oil and gas in this basin or similar basins.