关键词: 非牛顿流体, 波动压力, 偏心, 环形空间, 数值模拟

Abstract: Drilling fluid properties and annular geometry have great impact on surge pressure.This paper presents the governing equations of steady surge pressure of non-Newtonian fluid in an eccentric annulus under bi-polar coordinates.A numerical model for this elliptic,non-linear,non-homogeneous partial differential equations with variable coefficients worked out by box-integration and finite-difference methods.Take the Power-law fluid as an example,the paper calculates the surge pressure gradient and velocity distribution in eccentric annuli produced by-running pipe in the wellbore.Numerical results show that with the increase of eccentricity,surge pressure decreases.The velocity distribution differs greatly in the wider and the narrower section of the annulus.The surge pressure as the inner pipe fully lies in the lower side of the wellbore is only half of that as the inner pipe is coaxial with the wellbore.Moreover,the paper also compares the numerical solution with that of approximation method and empirical method.

Key words: non-Newtonian fluid, eccentric, surge pressure, annulus numerical model