Toward Sustainable Freshwater Conservation: Seawater-Based High Temperature Fracturing Fluids

Hydraulic fracturing uses water. A sustainable approach is to utilize seawater - abundantly available -for hydraulic fracturing applications. Although seawater-based fracturing fluids are available in the industry, there is a limitation on their usage with seawater rich in sulfate. Under downhole conditions, when the pumped seawater mixes with formation water containing high salinity and hardness, scale can form and potentially cause formation damage. Scale inhibitors become ineffective at such high temperatures and salinities. Due to its high scaling tendency, seawater should be pretreated - to remove specific ions that contribute most significantly to scaling. Typically, at high temperatures, the fracturing fluids used are based on metal crosslinkers that have a high shear degradation tendency. As the fracturing fluid is pumped downhole, the fluid experiences different shears, such as high shears due to tubulars, and low shear in the fracture. If the crosslinker shear degrades, the fracturing fluid will lose its ability to transport proppant effectively inside the fracture, which will result in near wellbore screen out. Therefore, it is of paramount importance to develop fracturing fluids that can be utilized with seawater, as well as demonstrate effective proppant carrying capability. This article highlights the development of a new zirconium (Zr) crosslinked, polysaccharide-based fracturing fluid system that was formulated using nanofiltered seawater for temperatures of 300 °F and above. The fluid is formulated using a stabilizer package that imparts temperature as well as shear stability to the fracturing fluid by controlling the Zr crosslinker reaction kinetics. The rheological characterization comprising of shear resilience and shear recovery capabilities of the new fracturing fluid are demonstrated through various shear history profiling experiments. The fluid maintained a viscosity of more than 300 cP at constant temperatures of 300 °F and above for 2 hours under various shear profiles, including multiple shear as well as constant shear. A proppant suspension test showed excellent proppant suspension capability of the fluid at elevated temperatures. Additionally, regain permeability results obtained using delayed breaker chemistries showcased excellent cleanup potential of the new fracturing fluid. Scaling tests performed with the nanofiltered seawater-based fluid demonstrated complete mitigation of scaling tendency at 300 °F, with an extremely low-scale inhibitor dosage. The nanofiltered seawater-based fracturing fluid comprised of the stabilizer package imparts several key advantages, including providing a seawater-based fluid with a near zero scaling tendency, as well as with high shear and temperature stability. © 2022 Aramco Services Company. All rights reserved.