Study on cuttings starting velocity in air drilling horizontal and highly deviated wells

Air injection rate as the key parameter of drilling air is directly related to the success of drilling procedure. In the previous studies, most of air injection rate models were built based on the vertical wells, which are not appropriate for horizontal and highly-deviated well and limit the wide application of air drilling to some extent. Based on the movement analysis of cuttings, this paper assumed that after the cuttings deposit to the low side of borehole, Air is injected to carry the cuttings out of the wellbore. Then, the starting velocity model in different hole angles is established through the stress analysis of cuttings motion, which can be used to calculate the minimum air injection rate. The numerical simulation results show that starting velocity of cuttings reaches the maximum in the hole angle 60-70 degrees. The larger diameter cuttings require a high starting velocity, which is difficulty to be transported. This means some appropriate methods should be applied for air drilling procedure, like using secondary crush tools. The subsidence degree is one important factor to the calculation model, and it is necessary to study cutting subsidence degree in next step. © Xiaofeng et al.