High Viscosity Friction Reducers - Potential for Fracture Damage and Impact of Brines on Proppant Transport Capability

Abstract

Abstract High viscosity friction reducer (HVFR) fracturing fluids are widely implemented for unconventional reservoir development. HVFR's are easy to apply and reduce chemical costs. The research objective of this paper is to measure polymer cleanup in both propped and unpropped fractures utilizing multiple methods. Additionally, the study will compare rheological measurements to proppant transport observations in brines using a large-scale slot flow device. API conductivity cells determined pack damage over a range of proppant sizes, HVFR's, and temperatures. An extended length conductivity (ELC) apparatus was utilized for comparison with the API cell. Cleanup in unpropped fractures employed a core holder using fractured core plugs. HVFR rheological property measurements include low and high steady shear measurements, and oscillatory measurements used to determine elastic properties. Mix waters include fresh water, salt solutions, and a simulated field brine. Proppant transport in fresh and simulated field brine is evaluated in a 1 × 8 foot slot flow device. Proppant deposition rates are recorded using video cameras. Propped fracture cleanup in the API cell and ELC apparatus is a function of proppant mesh size and HVFR type. As mesh size decreased, the potential for damage increased. Tests with 50/140 mesh proppants in the API cell in some cases showed significantly impaired regain conductivities as low as 65%. When compared to the ELC, API cell cleanups were in some cases significantly optimistic. Cleanup also varied greatly with HVFR product. Even with a low loading of HVFR of 1 gallon per thousand gallons of fluid (gpt) significant damage was sometimes noted. The tests of the unpropped fractures showed that very severe damage to unpropped fractures may occur. The presence of salts significantly and negatively affects HVFR rheological properties for most of the materials selected for this study. Viscosity at higher shear rates (10-511/sec) do not necessarily reflect HVFR performance at lower shear rates. In all tests, the rheological performance between different products exhibited a wide variation in properties, likely reflecting the potentially wide variation in chemical composition. Proppant transport testing validates the rheology measurements. The slot flow evaluations showed a significant loss of transport capability in brines. Commercial HVFR's are not equivalent and require laboratory performance evaluations. The study demonstrated that the potential for significant damage to the proppant pack and reservoir is present with HVFR fluid systems. Even low salt concentrations significantly influence the HVFR rheological performance. Mix water compatibility must be a primary concern when selecting HVFR's. The results of this study provide useful information to engineers for selecting HVFR's and describes a methodology for evaluating damage potential, and proppant transport.