Investigation of Flow Behavior of Slickwater in Large Straight and Coiled Tubing

Abstract

Summary Low-damage fracturing fluids are normally used for better fracture-dimension confinement and lower residue. This leads not only to longer fracture lengths, but also to higher fracture conductivity. Slickwater fracturing technology, developed in the 1980s, is less expensive than gel treatments. Fluid and proppant volumes can be reduced, and treatment flow rates can be increased significantly. When compared to conventional gel treatments, slickwater fracturing can generate similar or better production responses. In frac treatments, slickwater is pumped through straight tubing (ST) and coiled tubing (CT). As a result of secondary flow, frictional pressure losses in CT are higher than in ST. Determining these losses is of the utmost importance for successful treatments. Customarily, laboratory-generated flow data are used to develop correlations to predict frictional pressure loss of fluids flowing in ST and CT. These correlations are then, without verification, applied to field applications, which employ much larger conduit sizes. The present study is aimed to experimentally investigate the hydraulic properties of a commonly used drag reducer—Nalco ASP-820—in larger tubing sizes. This is a modified partially hydrolyzed polyacrylamide (PHPA). Previously, we reported flow data gathered employing ½-in. ST and CT (varying curvature ratio) and the correlations developed to predict frictional pressure losses of fluids in ST and CT. In this investigation, the large-scale flow data acquired from 200-ft ST and 1,000-, 2,000-, and 3,000-ft,1½-in. CT, and 1,000-ft 2⅜- and 2⅞-in. CT, are compared with the predictions from the correlations developed from ½-in.-pipe data. The effects of shear intensity, shear duration, and pipe roughness on flow properties of the ASP-820 fluid are also investigated. Results show significantly lower drag reduction in CT than in ST because of secondary flow caused by the CT curvature. Polymer degradation because of shear (shear intensity and duration) and/or tubing roughness can reduce drag reduction significantly. The results are discussed in light of a recently developed "drag-reduction envelope" to evaluate the drag reduction characteristics of slickwater fluid in ST and CT.