Hole cleaning is one of the major considerations at both design and application stages for a drilling operation. This concept is more emphasized as the wellbore inclination is high, and the size of the wellbore flow area is lower. Especially at horizontal or high inclinations, if the fluid velocity is lower than a critical value, a stationary bed develops, which may cause various problems such as high drag, higher probability of pipe stuck, higher hydraulic requirements, etc, if not removed properly. Therefore, it becomes important and essential to identify the critical velocity. This study aims to estimate the critical fluid flow velocity for preventing the development of a stationary bed using empirical correlations that can be used easily at the field. Also, a rough estimation of bed thickness is also introduced if the flow velocity is lower than the critical velocity. For this purpose, extensive cuttings transport experiments with water have been conducted at Middle East Technical University, Petroleum and Natural Gas Engineering Department, Cuttings Transport Flow Loop for various inclinations, flow rates and rate of penetrations. The inner pipe is subjected to a sagging, therefore, more realistic annulus representation is achieved. Observations showed that, a stationary bed can be developed even the inclination of the wellbore is down to 50 degrees. Results showed that, the critical velocity could be estimated using the proposed correlations with a reasonable accuracy when compared with the experimental results. Also, for flow velocities less than the critical values, the thickness of the stationary bed can be detected within an error range of ± 10%.

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