Friction characteristics of proppant suspension and pack during slickwater hydraulic fracturing

Abstract

Proppant transport is a crucial part of the slickwater hydraulic fracturing process, during which numerous hard particles are injected into formations with fracturing fluid to avoid fracture closure and maintain conductivity for hydrocarbon transport. Consequently, the distribution of proppants in fractures determines the well-to-reservoir contact efficiency and long-term post-fracture performance. Proppant distribution is controlled primarily via the transportation of suspended granules and the stability of proppant packs within fractures, whereas suspended granule transport and proppant pack stability can be profoundly affected by the friction characteristics of suspended and packed proppants, respectively. However, inter-particle friction is underestimated in numerical simulations based on the continuum assumption, leading to unrealistic proppant distribution patterns. Moreover, few experimental studies have discussed the friction characteristics of proppant packs. In this study, frictional parameters—such as the apparent viscosity of suspensions, internal friction angle, and cohesion of proppant packs—were measured by means of specially designed experiments. The ranges of the internal friction angle and cohesion ranged from 25.56° to 31.81° and 0.264 kPa–3.839 kPa, respectively, when the viscosity of slickwater was less than 50 mPa s. The correlation between the friction factor, average particle size, and liquid viscosity was determined. Based on the experimental results, new insights into model improvement and more accurate numerical simulations for solid-liquid flow were obtained.