Sedimentary Features and Reservoir Characteristics of Chang 6 Strata of Fanchuan District, Zhidan Oilfield

According to casting thin section identification, SEM, XRD, mercury-injection test, core analysis and logging data, the sedimentary features and reservoir characteristics of Chang 6 oil-bearing layer are comprehensively studied. It is shown that the sedimentary facies of Chang 6 layer in Fanchuan district of Zhidan oilfield is a set of continental lake delta sedimentary system, with the subfacies of delta front and prodelta. The reservoir is mainly composed of fine, silt-fine and medium-fine grained feldspar sandstone. There are strong diagenesises in the study area which include compaction, pressolution, cementation and dissolution. Though the first three diagenesises tend to lower the physical properties of reservoir, dissolution can improve the property to some extent instead. The reservoir space are mainly intergranular pores and feldspar dissolution pores. Based on its fine porosity and low permeability, the reservoir belongs to medium porosity and low-permeability reservoir. According to reservoir property parameters mentioned above, four types of reservoirs can be classified. The typeⅠis the best reservoir in the study area, which is mainly distributed in Chang 6¹ and Chang 6² reservoir. The typeⅡis a better one and distributed in Chang 6¹ reservoir. The sample of type Ⅲ is also mainly distributed in Chang 6¹ but has a poor property. With several samples distributing in Chang 6² and Chang 6³ reservoir subgroups, the last type Ⅳ is too poor to be a reservoir.