Current unconventional reservoir development depends on an assumed network of induced fractures created by hydraulic fracturing operations that facilitate production. In many cases natural fractures are linked to the created fractures and also contribute to production. Only in some fraction of the created and natural fracture network will proppant have been placed during the fracturing operation. In order to model the production from these fracture systems, reservoir and completion engineers often make optimistic assumptions about propped fracture half-lengths based on inaccurate expectations regarding proppant transport and proppant pack behavior. This work addresses proppant transport behavior by presenting results from large-scale lab testing of proppant transport with a range of fluid rheologies utilizing a slot flow apparatus.
Proppant transport tests were performed at multiple rates and proppant concentrations utilizing a 4-foot by 16-foot fracture slot. The primary testing objective was to compare proppant transport in friction reducer (FR)-based fluids against previously published results and other work that has been performed in this apparatus. Additional tests using guar based fluids of a similar nominal viscosity will be used for comparison and to demonstrate the need for other rheological properties for planning and predicting completion results.
The results of this testing will provide a more realistic description of proppant transport. Through this enhanced understanding, reservoir and completion engineers will be able to make improved assumptions about propped fracture dimensions that will drive better decisions regarding fracture design, improving recovery, optimizing spacing, and field development while reducing the need for costly future interventions and refracturing treatments. After an introductory review of important conclusions from previously published work performed in this and other slots, the results of this testing will be used to evaluate the validity of these conclusions. Additionally, relationships and interactions between viscosity, rate, proppant concentration, and other fluid properties will be established and reviewed to facilitate the development of improved models for proppant transport in unconventional reservoirs.
Much of the earlier lab work performed in slots of this scale was performed when crosslinked fluids were the preferred fluids in almost all applications. Since that time, the industry has shifted to a preference for slickwater fluids and other systems of much lower viscosity in the hope that increased velocity would make up for the loss in viscosity. This work will highlight where this hope is unrealized and when other fluid properties make the drop in viscosity less important than expected.