Abstract:

The origin and evolution of the reservoir’s diagenetic heterogeneity of Chang6 Member in Jiyuan area is discussed on the basis of identifying the features of its petrology, physical properties and diagenesis, by observation of the cores, thin sections, casting sections and SEM data of 57 wells, as well as comprehensive analysis techniques such as conventional physical properties study, X-ray diffraction and fluid inclusion study. The reservoirs of Chang6 Member in Jiyuan area are mainly low porosity, ultra low permeability arkose. Heterogeneity in original porosity was formed by mechanical differentiation in initial sedimentation. Reservoirs with different original porosities experienced differentiation in later diagenetic evolution. And four stages lead to diagenetic heterogeneity: early compaction, early acidulous water injection, carbonate cementation obstruction, and finally organic acid and hydrocarbon injections.

Key words: Ordos basin, Yanchang Formation, diagenetic heterogeneity, chlorite coating, carbonate cement, deposition control diagenesis, reservoirs