A New Method of Non linear Least Square Estimation of Rheological Parameter for Drilling Fluid

Abstract:

The estimation problem of rheological parameter for drilling fluid usually resorts to the linear regression method to get the solution.As a result, the statistic feature of measurement error becomes different,and the derived rheological parameter estimation tends to be no unbiasedness and with the least variance.A new method of non linear least square estimation is proposed according to the characteristics of three non linear rheological equations.There is no need to give an initial iteration value artificially.The iteration process can converge steadily to a unique minimum point without falling into the minimum point trap.Little storage space is in need but with a rapid convergence.A rheological parameter estimation derived on the basis of the algorithm presents superior statistic features of near unbiasedness of fitting residual error and with almost the least variance.Lots of practical drilling fluid cases validate that the new method is of smaller fitting variance with the similar mean,and a superior statistical feature of fitting residual error over that of linear regression.