A New Approach for Predicting Frictional Pressure Losses of Non-Newtonian Fluids in Coiled Tubing

Abstract

Abstract The importance of the pressure loss in the design of treatments for various field applications while using non-Newtonian fluids necessitates the estimation of the pressure loss in the reeled part of the coiled tubing unit. The present work discusses the analysis of frictional pressure loss of non-Newtonian fluids flowing through coiled tubing and includes the effects of fluid concentration and the influence of coiled tubing curvature and length. An experimental investigation of three polymeric solutions is conducted to predict the frictional pressure losses related to their flow behavior in coiled tubing. A total of 1500 ft of 1-in., 5000 ft of 1 1/2-in. and 3000 ft of 2 3/8-in. coiled tubing was used for this purpose. Also, straight sections of coiled tubing were employed for obtaining frictional losses in straight sections, which then are compared with those of reeled coiled tubing. Experimental results are also compared with the correlations presented earlier by Srinivasan for Newtonian fluids and McCann for non-Newtonian fluids. From the data analysis, it was found necessary to develop a new model which includes Dean number. The Dean number takes into account the curvature effect. This new model is proposed for the prediction of the friction factor in coiled tubing for fluids exhibiting power law pseudoplastic type behavior with flow behavior index less than unity. Introduction Coiled tubing is no longer just a circulatory tool but has now gained popularity in downhole tool transmission. Coiled tubing is used in many engineering applications especially in petroleum industry such as gas lift, acid washing, sand clean out, scale milling, underreaming, set of straddle packers, set of bridge plugs and cement retainers, logging, cementing, fishing, completions up to 3 1/2-in. and for underbalanced drilling. Coiled tubing is the best tool used to do various drilling operations in horizontal wells with considerable time saving compared to drill pipes. 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. Friction pressure loss calculations are very important in the design of any hydraulic fracturing treatments. They are not only useful in determining horsepower requirements, but also in estimating bottomhole treating pressure, and maximum wellhead pressure. The bottomhole treating pressure is given by BHTP=Pwh + Phy - ?Pfr (1) The majority of the applications mentioned above involve the flow and requires accurate calculation of frictional pressure loss in the pipes and coiled tubings. 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. Thus, it is useful to develop correlations that give an accurate prediction of the friction factor in the coiled tubing. An obvious benefit of the empirical correlations for non-Newtonian fluid flow in coiled tubing is that they provide tremendous cost savings in terms of time and experimentation, by directly estimating the frictional pressure loss in coiled tubing, thereby accurately determining the pumping requirements for flows through such tubing. Over-design of the treatment can cause costly waste since horsepower will be purchased which is above and beyond the standard backup horsepower required on location.