Experimental study of flow friction behavior in coiled tubing

Abstract

Coiled tubing (CT) technology has been widely applied in well cleanouts, drilling plug, and shale oil and gas fracturing. Fluid flow in CT produce a more significant flow friction pressure loss because of the long length and small tubing diameter coiled on the reel. Accurately prediction of flow friction pressure is a key problem of coiled tubing operation. In this paper, the flow friction behaviors in straight tubing (ST) and CT with different sizes and lengths were investigated experimentally. We analyzed experimental results and compared the test data with prediction results of published correlations. And the effects of tubing size and curvature ratio on friction factors were studied. Research findings show that the friction factor is significantly higher in CT than the corresponding ST friction factor, the maximum difference between them can be up to 30%. Furthermore, curvature ratio a remarkable effect on the friction pressure of CT. The friction factor increases as the curvature ratio increases from 0.012, 0.019, 0.031 to 0.076. For turbulent flow, a new empirical formula of friction factor in CT with roughness was proposed and validated with experimental data. The research results can support CT hydraulics design, which is the foundation and guarantee for the success of CT operation.

Keywords

• Coiled tubing (CT)
• Friction factor
• Rough pipe
• Hydraulics design