Construction of fracturing fluid with excellent proppant transport capacity using low molecular weight hydrophobic association polymer and surfactant

Abstract

Slick water fracturing fluid is widely used for fracturing unconventional reservoirs such as shale and tight gas, and it has aided in developing unconventional oil and gas reservoirs. However, the problem of slick water in terms of its weak proppant transport capacity has not been effectively solved. Conventional methods of increasing the proppant transport capacity of a fracturing fluid by increasing viscosity and pumping rate have resulted in serious reservoir damage and increased costs, showing more and more limitations. To address this issue, a low molecular weight polymer/surfactant (LMPS) fracturing fluid system was developed. LMPS increased the fluid elasticity through the interaction between the hydrophobic groups on the polymer and the surfactant while maintaining low viscosity, thus obtaining excellent proppant transport capacity. The low molecular weight polymer is a type of hydrophobic association water-soluble polymer (HAWSP) prepared by photoinitiation. Its viscosity-average molecular weight was determined to be 1.24 × 106 g/mol, much more than that of a typical drag reducer of traditional slick water (about 1 × 107 g/mol). The low molecular weight of HAWSP is conducive to preparation, dissolution, pumping, and reducing the damage of polymer to the reservoir. When 300 mg/L of sodium dodecyl benzene sulfonate (SDBS) surfactant was added to a 0.2 wt% HAWSP solution, it formed a robust self-assembled network that significantly enhanced the elasticity and raised the storage modulus G' from 0.11 to 5.95 Pa. The 20/40 mesh ceramsite proppant remained suspended in the LMPS solution (36 mPa·s) for 30 min, whereas ceramsite completely settled within 30 s in an ordinary linear polymer solution with similar viscosity. Simultaneously, despite having a lower molecular weight, the drag reduction rate test shows that the drag reduction performance of the LMPS fracturing fluid was similar to the tested conventional commercial linear polymer. The self-assembled network of HAWSP/surfactant can increase the viscoelasticity of the fracturing fluid, which is expected to overcome the weakness of insufficient proppant transport capacity of slick water, thus improving development efficiency of unconventional gas reservoirs.