The use of friction reducers (FRs) has increased rapidly, not only in traditional slickwater treatments, but also as a replacement for linear and even crosslinked guar based fluids for proppant transport at higher loadings. However, the current understanding of proppant carrying capability of FRs is limited since most of the literature is focused on simple viscosity measurement at high shear rate. We report herein the study of full rheological characterization of FR based fracturing fluids.
The viscosity and elasticity of three FRs were measured across a wide range of concentrations under varying shear conditions using advanced rotational rheometer. Proppant carrying capability was assessed using the static proppant settling test as well as via slot flow testing designed to mimic the fracturing fluid traveling through a fracture. For comparison purpose, the traditional linear gel was also tested.
Unlike traditional fracturing fluids, there are different mechanisms that lead to enhanced proppant suspension for FR fluids. The authors correlated the results of viscosity measurements over a wide range of shear rates, elasticity measurements, static proppant settling tests, and dynamic proppant settling tests, and proposed mechanisms that are dependent on different conditions. The results provided insights on why certain FRs showed poor proppant transport capability despite having relatively high viscosity. The industry accepted testing standards appear unsuitable for evaluating FR proppant carrying capability. The selection of FRs should follow different testing protocols.
This paper is the first to provide a comprehensive study of FRs as linear or crosslinked guar system replacement for transporting proppant. An in-depth understanding of the key factors controlling proppant carrying capability of FRs is critical to improved fracturing fluid design and can provide guidance for future FR development.
The sand transport capacity in hydraulic fracturing operation is always of great importance. The productivity of a well after hydraulic fracturing depends mainly on propped fracture length and fracture conductivity, both of which are highly related to proppant transport. Crosslinked guar or derivative guar systems were widely used in conventional wells for proppant transport. There is a fair amount of literature discussing the mechanisms for those systems (Kesavan & Prudhomme, 1992; Brule & Gheissary, 1993; Acharya, 1988; Hu, Chung, & Maxey, 2015; Loveless, Holtsclaw, Saini, Harris, & Fleming, 2011).