In the ever growing directional and horizontal drilling, hole cleaning is a common and costly problem. It can become particularly critical in the case of extended reach drilling, where larger and longer wellbores are drilled. During the past two decades, especially in the recent years, many laboratory studies as well as field observations have been directed to address the cuttings transport problem. This has resulted in better understanding of the subject, and some remedies to overcome the problems. Several correlations/models have also been developed which give the field engineer a tool to better specify hydraulic requirements to clean the hole. However, due to the complexity of the subject, a comprehensive and proven model, not existing at this time, requires much more laboratory research and field studies. This will be the major topic addressed in this article.

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