The aim of this paper is to review the major points of contention concerning secondary petroleum migration,to discuss the nature and primary controls of the positions of petroleum migration pathways in sedimentary basins,and to illustrate the importance of preferential petroleum migration pathways for the formation of large oil/gas fi elds away from generative kitchens. There is competition between the driving force(buoyancy) and the restraining force(capillary pressure controlled largely by permeability contrast) in controlling the positions of petroleum migration pathways in heterogeneous carrier beds. At a large scale,there is a critical angle of dip of the carrier beds which determines the relative importance of structural morphology or permeability contrasts in controlling the positions of petroleum migration pathways in heterogeneous carrier beds. Maximum-driving-force-controlled migration pathways occur in carrier beds with an angle of dip greater than the critical dip and the positions of petroleum migration pathways are controlled mainly by the morphology of the sealing surfaces. Minimum-restraining-force-determined migration pathways occur in carrier beds with an angle of dip smaller than the critical angle where permeability contrasts would exert a more important influence on the positions of petroleum migration pathways. Preferential petroleum migration pathways(PPMP) ,defi ned as very restricted portions of carrier-beds that focus or concentrate petroleum from a large area of the generative kitchen,determine the distribution of oil and gas in sedimentary basins. The focusing of petroleum originating from a large area of the generative kitchens into restricted channels seems to be essential not only for long-range petroleum migration in hydrostatic conditions,but also for the formation of large oil or gas fi elds. Regions may miss out on petroleum migration because of its three-dimensional behavior,and two-dimensional migration modeling may be misleading in predicting petroleum occurrences in certain
The Liaohe (辽河) depression is an important part of the Bohai (渤海) Bay Basin, and the Bohai Bay Basin located in the center of lithospheric destruction and thinning in the eastern North China Craton. The North China lithospheric thinning activities have been verified from evidences of structural geology, petrology, geochemistry and geophysics, but there are still some controversies on their timing, mechanism and controlling factors. The sedimentary basin is a thin-bedded geologic unit with a limited distribution in the upper lithosphere, and its formation and evolution represent the shal-low response of the deep geodynamic process. Therefore, its thermal evolution is closely related to the deep dynamic conditions. In this article, the Mesozoic-Cenozoic thermal history of the Liaohe depression is reconstructed using the vitrinite reflectance and apatite fission track data. Meanwhile "thermal" lithospheric thicknesses in the Mesozoic and Cenozoic are calculated using the geothermic method on the basis of the above thermal history results. The results show that the Liaohe depression has undergone the Cretaceous and Paleogene heat flow peaks, 81 and 83 mW/m2, respectively, corresponding to two strong rift movements. Accordingly, the depression has experienced two different levels of thinning processes in the Cretaceous and the Paleogene since the Mesozoic, and the "thermal" lithospheric thicknesses were 60 and 50 km, respectively. This may reveal that the depression has experienced two large-scale destructions. The work may provide valuable geo-thermal evidence for initial revealing the time, process and stage of the lithospheric thinning in the Liaohe depression.
