In spite of surfactant-based (SB) fluids wide use as friction reducer and/or fracturing fluid in the oil and gas industry, the flow data in large pipe sizes as well as coiled tubing are very scarce. Majority of the available flow data are gathered in small size straight tubing. The present study involves experimental investigation on the flow properties of aqueous surfactant-based (SB) fluids in small and large-scale coiled tubing. The unique viscoelastic properties of SB fluid affect their flow behavior in large pipe sizes. This phenomenon is called as "diameter effect" or "scale-up factor".

The properties of widely used Aromox APA-T, a highly-active surfactant used as a gelling agent in aqueous and brine base fluids, are thoroughly investigated. Rheological measurements are conducted using Bohlin rheometer for SB fluid concentration of 1.5, 2, 3, and 4 vol. %. Flow data are gathered using ½, 1½, 2⅜, and 2⅞-in. OD coiled tubing with various curvature ratios.

The results show that SB fluids exhibit non-Newtonian pseudo-plastic behavior. Elastic and viscous properties of SB fluids are very sensitive to surfactant concentration. Friction losses in coiled tubing are significantly higher than those in straight pipes due to secondary flow effect. Increasing curvature ratio yields higher friction pressure losses. Also, small-scale data correlations using only simple power law model fluid rheological parameters lead to erroneous results when scaled-up to a large pipe sizes.

New technique, based on the modified Deborah number, including fluid elasticity and pipe shear effect, has been developed to correlate data from the small laboratory-scale tubing and large field-scale pipes. Correlation to predict Fanning friction factor of SB fluids in coiled tubing as a function of Deborah number and fluid flow behavior index is presented. Correlation is validated by comparing predictions with the experimental data. It is shown that the new correlation accurately predicts friction factor of SB fluids and thus alleviates the scale-up issue.

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