Abstract: Many factors,such as depositional environment,maturation of organic matters,hydrocarbon migration and secondary alteration,may cause difference of petroleum fingerprint,i.e.the vertical and lateral difference in reservior.However,diffusion and density overturn can adjust the difference and reach a new dynamic balance.But close fault and rocks with low permeability will destroy the balance.Therefore,some geochemical information can be used to describe reservior,such as correlation of small beds,division of faults and flow units,water/oil contact,paleowater flow.It will provide useful information for development of Xidaliya Oilfield.