Abstract: A common feature for the flow curves of drilling fluids is that, there is one bending section with one similar straight line section which related an angle to γ axis.According to this feature, a new rheological model: τ=τ_ｓ+η_pγ(1+β/γ)^1/2 was proposed by the author.In which, there are three individual parameters: gel strength τ_ｓ, plastic viscosity η_p and shear thinnig coefficient β. When comparing the new equation with others by using the experimental results, it is found that equation exhibits minimum residual standard deviation having the highes predication accuracy.This new equation can describe the rheology of not only the plastic fluid but also many other fluids.When τ_ｓ=0, it describes the pseudo plastic fluid; when β=0, the Bingham's fluid, and while τ_ｓ=0 and β=0, the Newtonian fluid.Besides, the new equation has an outstanding feature that when the share rate increased to a value high enough, the new equation becomes the same as the Bingham's. This proved again that the Bingham's equation can only be applied to the intermediate and high shear rate ranges.

Key words: drilling fluid, rheology, rheological model, mathematical model

摘要： 钻井液流变曲线的一般特点,是有一弯曲段及一与γ轴成一定角度的近似直线段.据此特点,文中提出了一个新的流变模型：τ=τ_ｓ+η_pγ(1+β/γ)^1/2.新的流变方程中有三个独立参数：静切应力τ_ｓ,塑性粘度ηp及剪切稀释系数β.试验比较了几个现有的方程,结果表明,新方程的剩余标准差最小,预报精度最高.新方程不但描述了塑性流体的流变性,还可描述多种其他流体的流变性.当τ_ｓ=0时,描述假塑性流体;当β=0时,描述宾汉流体;当τ_ｓ=0,β=0时,描述牛顿流体.新方程还有一显着的特点,即当γ足够大时,新方程变得与滨汉方程相同.证明了宾汉方程只适用于中、高剪切区的实践经验.

关键词: 钻井液, 流变性, 流变模型, 数学模型