Nowadays the use of air and gas as a circulating medium for drilling oil and gas wells is becoming an attractive practice because of its great advantage over conventional mud drilling. However, the occurrence of some troubles due to poor carrying capacity of cuttings in air/mist drilling is not uncommon. Meanwhile, the determination of air/gas injection rate desired to undertake air and gas drilling is also closely related to the actual moving regularity of cuttings in annulus. It is obvious that researches on migration rate and carrying capacity of cuttings within borehole are essential to air/mist drilling. Although there are some theoretical models for prediction of cutting migration velocity and therefore the carrying capacity of cuttings, experimental studies are also essentially important because of the complexity of actual liquid, gas and solid multiphase flow in wellbore and the uncertainty of theoretical models. In this paper, some experimental studies were performed to investigate the moving regularity and carrying capacity of cuttings in wellbore. Some comparisons between the testing results and theoretical models are also presented in the paper. It is seen that such a study is valid and effective in prediction of the migration velocity and analysis of the motion regularity of cuttings in borehole. Therefore, the required practical air injection rate to keep the necessary carrying capacity in air/mist drilling can be determined definitely.

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