Revamping Polymer Architecture for Optimized Fracturing Fluids in Fresh and Produced Water

Abstract

The presence of extensive tight oil reserves in regions with scarce or intermittent supply of ground or surface freshwater resources underscores the importance of water reduction, reuse, and recycling strategies to ensure the sustainability of hydraulic fracturing. Currently, the advantages of using synthetic high viscosity friction reducers (HVFRs) does not extend to fluids composed of high salinity produced water or wastewater because these products cannot transport proppant effectively under such conditions. The use of a new fully synthetic polymer architecture bearing interchain association is described which provides a significant increase in brine tolerance and fluid rheology, giving rise to effective proppant transport and friction reduction in water salinity exceeding 200,000 TDS. Two variations of the polymer architecture are described: a product that operates effectively in fluid below 100,000 TDS such as seawater (SW-HVFR) and a second high brine product that works in all fluids up to and above 200,000 TDS (HB-HVFR). Proppant transport was studied dynamically using a slot flow apparatus, which demonstrated performance with the new system that exceeded guar and greatly exceeded other conventional HVFRs at equivalent polymer loadings. Slot flow results indicated consistent transport performance throughout the salinity range investigated by proper selection of SW-HVFR and HB-HVFR. Although high shear viscosity of the new polymers was inferior to that of guar, advanced rheological studiesindicated that the superior performance was due to enhanced viscosity and unusually high elasticity of the derived fluids within the relevant shear rate range between 1 and 100 s−1. In addition, anomalous dependence of viscosity on temperature is described, featuring a viscosity maximum above ambient temperature. This unusual rheology behavior was attributed to the associative polymer architecture of the new system. The new HVFRs exhibit effective friction reduction within their intended salinity ranges as well as good tolerance toward biocides and clay control agents. Furthermore, the operational salinity range of SW-HVFR can be extended up to 200,000 TDS in the presence of certain production enhancement aids due to a synergistic effect on the polymer dissolution rate. Lastly, bottle testing indicated that the polymers are effectively broken by common oxidative breakers, enabling their flowback. These results demonstrate the flexibility of the new HVFR system to make total fluids utilizing any water source, enabling sustainable fracturing in a variety of situations.