Water-soluble polymers for high-temperature resistant hydraulic fracturing: A review

Water-soluble polymers, as thickeners, are the vital component of high temperature-resistant fracturing fluids. With the expansion of oil and gas exploration and development to deep unconventional reservoirs, better performances for polymer-based fracturing fluids are required. According to the types of polymers, polymer-based fracturing fluids can be divided into biopolymers, synthetic polymers and composite systems (including synergistic blends and nanocomposites). The relationships between structures and high-temperature resistance mechanisms of different polymers types were discussed in detail. The results showed that high molecular weight, extensive intermolecular association of guar gum chains through hydrogen bonds in aqueous solution and the use of high-temperature resistant additives (organic metal crosslinkers and gel stabilizers) make the biopolymers resistant to the high-temperature environment below 150 °C. The main chain structure connected by C–C covalent bonds with high bond energy, the auxiliary effects of functional side chain groups (hydrophilic groups, cross-linking groups, rigid groups and hydrophobic groups) and high-temperature resistant additives (organic metal crosslinkers and gel stabilizers) make the synthetic polymers temperature resistant up to 240 °C. Based on the noncovalent interactions between molecules (such as hydrophobic associations, hydrogen bonds, electrostatic attractions, etc.), the temperature tolerance range of the synergistic blending systems is 110–150 °C. Relying on nanomaterials as the core points to crosslink the polymer molecular chains to form a stable three-dimensional structure, the temperature resistance of nano composite fracturing fluids is about 120 °C. Therefore, high-temperature resistant crosslinkers with higher crosslinking efficiency, and synthetic polymers with better ultra-high temperature stability and lower cost from the perspective of molecular structure design for polymers need to be vigorously developed, aimed at catering to the trend of oil and gas resources development in the future.