In this study, a 1-D unsteady-state, two-phase, mechanistic model of cuttings transport with foam in vertical wells has been developed. The model is solved numerically to predict the optimum foam flow rate and rheological properties to maximize the cuttings transport efficiency in vertical wells. Comparisons of model predictions with field test data have shown that model predictions are in close agreement with the field test results.; The numerical solution allows analyzing the effects of borehole geometry, drilling rate, foam rheological properties, gas and liquid flowing rates and reservoir fluid influx on the cuttings transport efficiency when drilling vertical wells. The results of a sensitivity analysis study are presented.; The vertical well flow model has been incorporated into a computer program and used for optimization of drilling hydraulic parameters (i.e. critical foam flow rate, back pressure, foam quality, and so on) for effective cuttings transport with foam in vertical wells. A series of simplified hole cleaning charts have been developed which enable the optimum hole cleaning parameters to be determined at the rig site.; A 1-D unsteady-state, two-phase, mechanistic model of cuttings transport with foam in horizontal wells has also been developed. The model is solved numerically to predict cuttings bed height as a function of the drilling rate, the gas and the liquid injection rates, the rate of gas and liquid influx from the reservoir and the borehole geometry. A new critical deposition velocity correlation for foam-cuttings flow is introduced. Comparisons of model predictions with experimental test data available from the literature have shown that model predictions agree reasonably well with the experimental results. The results of a sensitivity analyses study are presented.; The model has been incorporated into a computer program and used for finding a closed form critical foam velocity (CFV) correlation. Effects of key drilling parameters (i.e. drilling rate, annular geometry, foam quality, bottomhole pressure and temperature) on the critical foam velocity have also been investigated. Numerical examples are presented to illustrate how the CFV correlation can be used to determine the required gas and liquid flow rates at downhole conditions. The new CFV correlation can be used to predict the minimum foam flow rate required to remove stationary cuttings beds on the low-side of highly deviated and horizontal wells, or to prevent the formation of such beds.
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