Mechanism research and field practice of elastic sand-carrying capacity in novel-functionality slickwater

Abstract

Slickwater fracturing fluid is commonly used for unconventional oil and gas reservoirs, but its proppant-carrying capacity is limited. Enhancing this capacity without increasing viscosity significantly is a key challenge. The study constructs a device to quantify fluid viscoelastic sand carrying, using pure viscous glycerol as a benchmark fluid. The research explores the impact of fluid elasticity (G’=0.001 ∼ 10,000 Pa) on sand settling (some types of processed sand can be used as proppants), leading to a revised sand-carrying settling formula. Experimental results demonstrate that the laboratory-synthesized viscoelastic slickwater (VSW), despite exhibiting power-law behavior, possesses superior elasticity and at least 90 % lower settling rate of single-particle sand than glycols of matched viscosity, establishing a non-linear relationship between sand concentration and settling time. By considering the equivalent viscosity of elastic effects through coupling, the applicability of the single-particle Stokes settling formula is extended to describe the settling behavior of sand in viscoelastic fluid. Dynamic sand-carrying experiments within fractures reveal that sand concentration, shear rate, viscosity, and elasticity collectively influence sand settling. Highly elastic fluids show superior dynamic sand-carrying effects, with the concentration of friction reducer affecting sand-carrying capacity. The modified single-particle settling rate V_V improves the calculation of dynamic sand-carrying settling. Concentric-cylinder experiment highlights that elastic sand-carrying is more sensitive to shear rate response, and highly elastic fluids can establish dominance in elastic sand-carrying at lower shear rates. Combined with the concentric-cylinder sand-carrying experiment, elastic sand-carrying is more sensitive to shear rate response, and highly elastic fluids can establish dominance in elastic sand-carrying at lower shear rates (with elasticity/viscoelasticity ratio exceeding 90 %). VSW slickwater forms a network structure, displaying good elasticity and sand-carrying capacity. The combination of the two sand-carrying devices, along with the revised settling formula and the sand-carrying settling threshold diagram, is effectively applicable to VSW fluids. This combination accurately predicts the settling behavior of multi-particle sand in highly elastic fluids within wellbores and fractures, providing critical guidance for future fracturing applications.