关键词: 钻井液, 卡森流变模式, 流变参数, 拟合方差, 非线性最小二乘估计算法

Abstract: A new method for the non-linear least square estimation was proposed on the basis of the characteristics of Casson rheological formula.It is unnecessary to artificially give an initial iteration value.The iteration process of this method can converge steadily to a unique minimum point in the domain of parameter and can not fall into the trap of the minimum point.This method requires a little storage and can converge rapidly.This is a globally optimized algorithm and can derive a rheological parameter estimation,showing superior statistic features including near unbiasedness of fitting residual error and almost least variance.The calculation cases,using a large amount of practical drilling fluid dada,indicate that the new method has smaller fitting variance,more similar mean value and more superior statistical feature of fitting residual error than the linear regression.This method can be used to determine the rheological parameter in Casson model of drilling fluid,optimize rheological model,adjust and evaluate the performance of drilling fluid.

Key words: drilling fluid, Casson rheological model, rheological parameter, fitting residual error, non-linear least square estimation method