With the porosity range of 4% to 6% and the permeability range of 0.01?10

-3

μm

2

-0.30?10

-3

μm

2

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

μm

2

providing basis for determining effective thickness and estimate reserves.