Petrophysical property limits of effective tight oil reservoirs in the lower part of the first member of Cretaceous Tengger Formation, A'nan Sag, Erlian Basin, North China

The lower part of the first member of Cretaceous Tengger Formation (K₁t^1x) is a main target for tight oil exploration in the A'nan Sag. Two favorable tight reservoir types including tuffites and sandstones have been found. The porosity and permeability of tight reservoirs change greatly. The heterogeneity of oil-bearing strata is strong, which is controlled obviously by porosity and permeability. Based on physical property measurements, well testing, mercury injection data and so on, we determined the petrophysical property cutoffs of effective tight oil re-servoirs in K₁t^1x using an oil-bearing occurrence method, experimental statistics, distribution function, well testing and minimum effective pore throat. The cutoff of effective reservoir porosity of tuffites is 4.0%, and that of permeability is 0.008×10^-3 μm². The cutoff of effective reservoir porosity of sandstones is 5.0%, and that of permeability is 0.05×10^-3 μm². The determination of cutoffs of an effective reservoir provides a scientific basis for "sweet spot" reservoir prediction, resource potential evaluation and exploration target selection of tight oil.