Effect of Coiled Tubing Curvature on Friction Pressure Loss of Newtonian and Non-Newtonian Fluids - Experimental and Simulation Study

Abstract

Coiled tubing is widely used in the petroleum industry to pump fluids in the well bore at high rates. The friction pressure losses occurring in the tubing at these high rates are an issue of immense concern to the industry. Most of this friction loss can be attributed to the section of the tubing reeled on the spool during the treatment. The dimension of the reel used in the treatment governs the degree of curvature of the tubing and in turn the corresponding pressure drop. These pressure losses apart from increasing the cost of the treatment due to increased energy requirements also reduce the life of the tubular used. Experimental and simulation study has been undertaken to determine friction pressure loss in 1 1/2 and 2 3/8-in. coiled tubings using water and 35 lb/Mgal guar as test fluids. Computational Fluid Dynamics software FLUENT has been used to generate simulations that have been validated with limited experimentation using a field-scale test setup. Previous experiments used limited flow rates and few curvature ratios due to high field-scale experimentation costs. But using CFD simulations friction pressure loss data have been gathered for a range of curvature ratios and flow rates that are comparable to the ones used in the field. Results obtained have been used to determine the effect of curvature ratio on friction pressure losses while pumping Newtonian and non-Newtonian fluids in 1 1/2-in. and 2 3/8-in. tubing. Introduction Coiled Tubing (CT) units are being used in a multitude of applications in the industrial arena. This technology due to its versatility has found a range of applications in the petroleum industry including drilling, cementing, cleaning sand from a well bore, acidizing, scale removal and formation fracturing to name a few. Most of these applications involve pumping fluids through these coiled tubing units at very high rates. The frictional pressure losses occurring across the tubing length impose economic concerns and limit the flow rates that can be achieved while using this technique. Since fluid transport through coiled tubing has gained popularity in numerous engineering applications, including the petroleum industry, an accurate calculation of the frictional pressure loss in such tubing is of extreme importance. Accurate estimation of frictional pressure loss plays a crucial role in determining the horsepower requirements for pumping fluids through coiled tubing. Furthermore, friction pressure loss calculations are very important in the design of any hydraulic fracturing treatments using coiled tubing and estimating bottomhole treating pressure, and maximum wellhead pressure. The coiled part of the tubing during a fracturing operation exhibits significantly higher losses as compared to the straight section. Higher frictional losses in coiled geometries are generally caused by increased secondary flow effects that dominate the flow pattern in turbulent flow regime. Even small increase in friction pressure gradients can become critical due to the large lengths of tubing involved in fracturing operation. Some critical factors in the accurate determination of magnitude of friction losses occurring across the tubing lengths are fluid type, tubing length, tubing diameter and tubing curvature. Various experimental approaches have investigated the effect of tubing size1,4. The effect of using different fluid has also been studied for common fracturing fluids10. But these studies have been limited to the straight conduit. On the other hand, the flow behavior of commonly used fluids in coiled tubing, which takes into account the effects of curvature, has scarcely been reported in the literature.

An Experimental Study of Flow Behavior of Coiled Tubing Drilling System

“…Figure 4 shows the pressure losses gradient contrast of coiled and straight tube, where the value of CR for CT is 0.0242. A significant increase in pressure losses in CT is observed as compared to that of straight tube in Figure 4, and the experimental results of coiled tube are about 11-17% higher than that of straight tube, which is very close to the results of Jain et al [7]. We can also find out that the calculation results derived by Sas-Jaworsky (S-J) correlation are slightly larger than the experiment results.…”

“…Although the flow rate is not large, the partial pressure drop of BHA is very large. Referring to the pump delivery capacity of actual CTDS by curve fitting the similar scale of partial pressure can be calculated according to (7). If tool sets mentioned in this paper are adopted, the partial pressure drop of BHA not including screw motor and bit is 5-6 MPa.…”

“…Willingham and Shah [6] studied the law of frictional pressure losses of four kinds of polymer with different concentration and a kind of drilling mud and arrived at frictional pressure losses correlations which are applicable to the above fluid by fitting the experimental data according to the least squares method. Jain et al [7] studied the impact of bending curvature of CT with water and non-Newtonian fluids on pressure losses, and by comparing results of straight and coiled tube, they found that curvature effects are more 2 Advances in Mechanical Engineering significant for flow of non-Newtonian fluids as compared to Newtonian fluids. From Zhou and Shah [8,9], there has been an excellent agreement between the new friction factor correlation and the experimental data obtained from experiments of typical drilling and completion fluids in the full-scale coiled tubing flow loop.…”

Reel-to-Injector Fluid-Flow Analysis Using CFD Software

“…7,8 This method enabled cross-comparisons of parameters between different applications. For example, the same size tubing and the same flow rate were used.…”

Fluid-Flow Phenomenon in CT Using CFD

“…The results are similar to the results in previous work. 6,7 As the tubing is in an arc shape, fluid (including non-Newtonian fluid) concentrates the maximum velocity toward the outer side of the arc. The difference in this study is that results are analyzed from slurry entering an arc from a straight tube.…”