Multistage hydraulic fracturing has become the key technology for completing horizontal and many vertical wells. In horizontal wells, the perf-and-plug method is the most commonly used staging method; in each stage, multiple perforation clusters are used to create separate transverse fractures at each cluster. How these clusters are placed can significantly affect a well's short- and long-term production performance. The simultaneous creation of multiple fractures is a cost effective and time saving method for stimulating both vertical and horizontal wells. Multistage fracturing is an effective method from the perspective of production, but the challenge of achieving even proppant distribution to each cluster is an intricate task for the industry.
Numerical simulations predict uneven proppant distribution for the fluid streams entering different perforation clusters. Field data indicates that, in many cases, some of the clusters do not contribute to production. This led to hypothesizing that actual proppant and fluid distribution along the stimulated clusters might be different from the assumed uniform distribution. However, in limited entry fracture design concept, the proppant distribution among the different perforations is assumed to be the same as the fluid distribution. Until recently, this assumption remained unchallenged.
This paper presents an extensive study and investigation of proppant transport in different perforation clusters within a single stage by using computational fluid dynamics (CFD) techniques. The effects of varied fluid and proppant specific gravity, viscosities, proppant sizes, and slurry flow rates were analyzed while keeping outside-casing parameters constant. Validation of empirical proppant transport CFD simulation results are compared to experimental test data. This is helpful to better understand fluid and proppant behaviors in multicluster fracturing processes to help achieve maximum efficiency.
The results of the study indicate that proppant transport can be accurately modeled when the effects of single particle settling, density driven flow, particle velocity profiles, and slurry rheology are all considered. The investigation shows CFD is an effective tool for optimizing proppant distribution among perforation clusters and enhancing production.