Methods for determining the petrophysical property cutoffs of extra-low porosity and permeability sandstone reservoirs——an example from the Xishanyao Formation reservoirs in Yongjin oilfield

With the porosity range of 4% to 6% and the permeability range of 0.01×10-3 μm2-0.30×10-3 μm2,the Xishanyao Formation reservoirs in the Yongjin oilfield of the Junggar Basin are typical extra-low porosity and extra-low permeability reservoirs.According to the static and dynamic data and petrophysical experiments,we have determined the effective porosity and permeability cutoffs of these reservoirs through methods of empirical statistics,oil-bearing occurrence test,physical property test,nuclear magnetic resonance,minimal pore throat radius and displacement pressure.The results show that the lower limit of porosity is 6% and the lower limit of permeability is 0.08×10-3 μm2,providing basis for determining effective thickness and estimate reserves.