Criterion of starting pressure gradient existence of non-Darcy flowing in low permeability porous media

It is very important to research non-darcy flowing and predict starting pressure gradient for developing low permeability reservoirs.The paper analyzes and matches a lot of the results of experiments of the single oil and water phase flow curves of low permeability cores.Research results show that(1)The new matching equation can response the law of non-Darcy flowing of low permeability media very well;(2) the reasonableness of the matching equation and the physical meaning of coefficients in the equation is proven by boundary layer theory.;(3) A criterion of starting pressure gradient existence is put forward,that is,the maximum value of critical average throat radius,and the prediction of starting pressure gradient existence that is made using the criterion is the same as the results of the core experiments.