Abstract: When a deep-seated hydrocarbon accumulation had formed in a structurally active area,the hydrocarbons will migrate vertically up through a fault or a fracture,the major part of which was apt to lose to the surface,but the minor part was cut off by the caprocks to form into various shallower secondary oil/gas pools with their specific oil-gas laws.The study highlights pool-forming mechanisms related to chimney effects such as the basis of hydrocarbon source,conduits and power,the impedance type of cutoff process,the compactness of rocks etc;and mainly approaches to the geological conditions for the oil/gas fields of secondary enrichment.