Extensive aerated mud experiments were performed in a unique field-scale elevated pressure and elevated temperature flow loop (6″ × 3.5″ annular test section, 73 ft length, horizontal configuration without drillpipe rotation). A view port was installed to observe flow patterns in the test section. Two nuclear densitometers were used to measure steady state mean void fraction. During test runs, the liquid and gas phase flow rates were in the range of 50-250 gal/min and 50-150 scf/min, respectively. For all the test runs, measurements of pressure drop and average liquid holdup over the entire annular section were carried out.

The two-phase flow patterns were identified by visual observations through the view port. Stratified and slug flow were the two flow patterns observed over the range of the chosen test matrix. The presence of slug flow does not justify many existing simulation practices, which assume a homogeneous gas-liquid flow.

A mechanistic model has been developed for aerated mud hydraulics based on conservation equations and existing two-phase pipe flow correlations. An extensive sensitivity analysis is presented to quantify the influence of mud properties and flow parameters on the bottom-hole pressure. Comparisons between the predictions of the model and experimental measurements show a satisfactory agreement. The present model is particularly suitable for the design of underbalanced coiled tubing applications.

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