With increasing measured depths and horizontal displacements in extended-reach (ERD) wells, good hole cleaning and cuttings removal remains a major challenge. Poor hole cleaning may result in lost circulation, hinder the casing or liner to be run into its selected position, excessive over pull on trips, high rotary torque, excessive equivalent circulation density, formation break down, slow rate of penetration, excessive bit wearing and pipe sticking. There are methods and models have been introduced to find the minimum flow rate required to remove the cuttings from the well. Larsen's model that can be used to find this flow rate from 55 to 90 degrees of hole inclination. Another one is Moore's correlation that is used to find the slip velocity of the cuttings in vertical wells.

This paper represents a new approach to achieve both optimized hole cleaning and flow rate, as a result of precise manipulations and redesigning of drilling mud rheological parameters, which have been elaborately explained in this paper. Calculations performed by computerized iterations via simulation software, which is developed based on theoretical concepts. Furthermore, Comparisons between calculated data and measured field data have been made. This method is valuable for prediction and calculation of the optimum flow rate for cuttings removal for all range of inclination, namely from 0 to 90 degrees and for providing guidance in further evaluations of this problem as well.

Data form a horizontal well YS5 which is drilled in Yort-e-Sha field in Iran is used to demonstrate the application of this method. As the significant outcomes, When the results of optimization applied, good hole cleaning condition achieved and negative effects of excessive flow rate such as drilling mud loss and drag were minimized.

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