Abstract: The Chang-6 reservoir in the Jiyuan area, the Ordos Basin, is a typical ultra-low permeability reservoir, for which the fluid identification is a challenging task due to its strong heterogeneity and less oil-water differentiation. In this paper, based on the coincidence of three porosity curves, i.e. compensated neutron log (CNL), compensated density log (CDL) and acoustic time (AC), the porosity curve indexes are constructed to reflect the lithologic purity. By combining the deep inductive resistivity (DIR) log reflecting the fluid properties and the AC log describing the reservoir properties, the fluid identification indexes are constructed to determine the oil-bearing potential of the reservoir. Then, oil-water layer and water layer are further identified in accordance with the relationship between water productivity and water saturation. Eventually, the oil/water identification chart is prepared by integrating the fluid identification indexes and the water productivity. The logging data of 58 wells in the study area were interpreted and compared with the well testing data. The results show that the proposed method can achieve an accuracy of 91.4% in fluid identification, suggesting an enhanced accuracy of fluid identification in reservoirs.

Key words: Ordos Basin, Jiyuan area, low-permeability reservoir, reservoir evaluation, fluid identification, log response characteristic