Abstract: Forchheimer's Equation,a classical equation put forward by Forchheimer in 1901,has been used for offset the deficiency of Darcy's law at high flow rate by way of adding a non-Darcy term into Darcy's law.This term is a product among the non-Darcy coefficient, the fluid density and the square of flow velocity. To estimate the non-Darcy coefficient as accurately aspossible is one of the most important aspect for determination of non-Darcy effects. This paper establishes a new fully implicit 3-D gas reservoir mathematic model with multiple types of reservoirs and scopes of permeability based on study of a great numberof literatures and analysis of mathematic descriptions of various non-Darcy effects.In this model, the non-Darcy effect of gas athigh flow rate can be more effectively concerned about. In addition, using OrthoMin method to solve the algebraic equation seriesis quick in speed and reliable in stability.

Key words: percolation, non-Darcy flow, mathematic model, Darcy's law