To meet production targets and report fewer operational issues, many companies are looking to improve cluster efficiency during hydraulic fracturing operations by having more productive perforating clusters that contribute to well production. One key factor that has been emphasized in this regard is proppant transport. It is worth mentioning that the behavior of proppant transport could be decomposed into three main stages: in the horizontal pipe, through the perforations, and inside the fracture system.
This research work focused on the placement of the proppant through the perforations in hydraulic fracturing operations. To this end, an experimental setup was constructed to quantify how the proppant distributes and the key proppant & fluid parameters that affect the ability of the slickwater to transport and suspend the proppant, specifically the size and concentration of the proppant.
Proppant concentration and size are critical properties that control the transport and placement of proppant through the perforations. To begin with, the settling velocity of proppant was a major concern in this work, where various published analytical equations and empirical correlations were used to calculate the optimal injection rate. Then, a series of tests were performed considering different sizes and concentrations of proppant and fresh water as the carried fluid, it was observed that increasing the proppant concentrations and using larger proppant size led to poor proppant distribution.
A novel experimental setup was presented in this study with the aim of studying the placement of proppant through the perforations. The setup is a valuable resource for understanding and visually observing proppant transport behavior.
Achieving the desired conductivity within hydraulic fractures is a major concern for successful stimulation treatment. In fact, the fracture conductivity is directly related to the effectiveness of proppant placement within the fractures. However, research has demonstrated that the fluid and proppant do not move as a homogeneous mixture due to the difference between the proppant and fluid densities (Daneshy, 1978). This could be considered as the major cause of the non-uniform or biased proppant distribution where some fractures receive more proppant, namely the runaway fractures, or the bottom side of the fractures are generally receiving more proppant (bottom-biased distribution). Additionally, the uneven proppant distribution could be justified by the existence of dominant clusters generally in the toe or the heel of the lateral section of the well. This has been proven using the production logs (Miller et al., 2011) as well as recent pre- and post-fracture diagnostic techniques including perforation erosion measurement (optical and ultrasonic) (Roberts et al., 2020), fiberoptic (DAS&DTS) and proppant tracer, where the presence of unpropped or poorly conductive fractures were observed as shown in the Figure 1.