Modeling of Proppant Transport and Placement in Hydraulic Fractures

Abstract

ABSTRACT Proppants are injected to keep the fractures open during hydraulic fracturing. It is of great importance to identify where the injected proppants go. However, proppant placement in the fractures has remained a challenging question given that proppant placement is a complicated phenomenon coupling several physics such as fracture nucleation and growth, fluid flow inside fracture, fluid leak-off, and proppant settling and jamming. An integrated numerical model will be required to understand the physics of proppant transport in hydraulic fractures and guide field operations. In this study, the pore pressure cohesive elements were enhanced with concentration Degree of Freedom (DOF) to simulate proppant transport in hydraulic fractures. The numerical model was validated against slot tests and the simulated proppant distribution is in good agreement with the laboratory measurements. This paper focuses on the proppant properties and investigates how the proppant settling affects the propped fracture area. This paper also investigates how the presence of bedding layers affects the proppant transport and placement. The results indicate that the bedding layers can significantly affect the fracture geometry and lead to highly non-uniform patterns of proppant distribution. The advanced numerical model can predict the proppant transport in fractured reservoirs and ensure a safe and efficient well completion. INTRODUCTION Hydraulic fracturing is a technique to inject a high-pressure fluid into the subsurface volume to create fractures in tight formations (Adachi et al., 2007; Detournay, 2016; Wu & Olson, 2015). Once fractures are created, solid particles, called proppant, are injected to keep the fractures open by withstanding high closure stress near the fractures (Liang et al., 2016). Therefore, proppant transport in the stimulated fractures is critical to maintain fractures open and provide conductive pathways for fluid flow in otherwise ultra-low permeability rock (Barboza et al., 2021; Tong & Mohanty, 2016). However, since proppants were first used in hydraulic fracturing, the question of proppant placement in the fractures has remained mostly unanswered (Bokane et al., 2013; Zhang et al., 2017). The final distribution of proppant in the fractures is conditioned jointly by the injection strategies, properties of proppant and fracturing fluid, complexity of the fractures, etc. (Blyton et al., 2018; Chang et al., 2018; Hu et al., 2018; Li et al., 2021; Liu & Sharma, 2005; Shrivastava & Sharma, 2018; Singh et al., 2021; Tong et al., 2019). The proppant size is in general between 8 and 140 mesh (i.e. 105 μm to 2.38 mm) (Liang et al., 2016). The proppant types include the silica sand used in the first fracking job (Barati & Liang, 2014) and other materials such as precured resin-coated sand, curable resin-coated sand, intermediate-strength ceramic proppant, lightweight ceramic proppant and high-strength proppant (Belyadi et al., 2019; Zoveidavianpoor & Gharibi, 2015). The common fracturing fluids to carry proppants include slickwater, gel and crosslinked fluid, whose viscosities change greatly from 1 cp to over 1000 cp (Al-Muntasheri, 2014). It is estimated that over 80% of the fracturing fluids used in fracking treatment in the United States is slickwater (Ely et al., 2014).