STUDY ON THE DIAGENESIS OF CLASTIC OIL FORMATION ASSEMBLAGE

The first member of Dainan Formation(E₁d¹)in Gaoyou Depression, Northern Jiangsu can be devided into high, middle and low evolutionary zones in which the depth for the middle evolutionary zone is of 2800m-3300m. Its organic matter has evoluted to early and middle maturation stages. So that a large amount of low-mature oil was generated and subsequently migrated into sandstone belt with first secondary porosity created by the formation water released from clays. The depth of the high evolutionary zone is about 3300m-4000m where highly mature oil and condensate gas were generated at the later stage of maturation. Thereafter, the oil/gas migrated to the belt with second secondary porosity along the microfractures in claystones,and such a zone would be a favourable interval with a significant oil/gas potential.