Openhole, multi-stage fracturing systems are commonly used today in many applications, including unconventional shale gas reservoirs. As many as forty stages have been successfully completed in a single horizontal well and the industry is aiming even higher. One problem that has a major impact on job success is the ability to accurately calculate maximum pump rates for a given surface pump pressure. When frac fluid is pumped through a downhole multi-stage fracturing system, each time a new stage is completed, the flow splits at different sleeves in the completion string.
To determine minimum surface pump pressure and maximum pump flow rate, predicting split flow rate and the resulting pressure loss at each stage is essential. Traditionally, laboratory tests and field experience are used to predict these values. However, these types of predictions are not possible for hydraulic fracturing jobs that use a multiple sliding sleeve system, as is commonly employed. To simulate the hydraulic fracturing process, the Computational Fluid Dynamics (CFD) approach has been used, as it is a proven methodology. However, extensive CFD analysis requires computational overhead and significant software and hardware costs.
This paper presents a methodology which combines CFD and theoretical approaches to calculate split flow rate and pressure loss for non-Newtonian frac fluids in a multiple sliding sleeve system. These methods are incorporated into the multiple sliding sleeve design process and hydraulic fracturing plan optimization. The method can also be extended as a general solution for calculating pressure loss due to split flow.