This paper presents the results from series of experiments performed to study the effect of coiled tubing (CT) curvature on friction pressure loss of nitrogen gelled foam fluids. A_1/2 in., 10 ft of straight tubing and four sets of coiled tubing with curvature ratio (r/R) values of 0.01, 0.019, 0.031, and 0.075 are used in the experiment. A set of tests are performed using 20 and 30 lb/Mgal xanthan gum as base fluid and 0 to 80% quality nitrogen xanthan foams. Friction pressure data are gathered by monitoring the pressure drop across a 10-ft straight section and a given CT simultaneously. All data are gathered at ambient conditions and at a system pressure of 1000 psi. It is found that the friction pressure losses of nitrogen gelled foams in CT are significantly higher than the straight tubing even at low Reynolds number. The extent of CT curvature determines the magnitude increase in friction pressure loss. Empirical correlations for the prediction of friction pressure loss of gelled foams in both the straight and coiled tubing are developed for laminar, transition and turbulent flow regime. These are based on the dimensionless quantities of Fanning friction factor and generalized Dean number.
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