The Development and Performance of a Gemini Viscoelastic Surfactant with Tricationic Groups Applied in Unconventional Oil and Gas Reservoir Stimulation

Abstract To improve water solubility and salt tolerance of viscoelstic surfactants ( VESs ), modifying the spacer of Gemini VES was adopted and a novel Gemini VES nominated TC ‐ 2OH , with tri‐cationic groups and double hydroxyls on the spacer, was developed. The basic surface activity properties of TC ‐ 2OH and the molecular aggregate behavior stimulated by NaCl or NaSal were measured and analyzed to investigate the mechanism of viscoelastic fluid forming by TC ‐ 2OH solution, and it proved that TC ‐ 2OH is more sensitive to NaSal, compared with NaCl, due to the embedded structure of salicylate. The molecular structure of TC ‐ 2OH imparts excellent solubility to itself, and with the assistance of ethanol, the dissolution time in water can be shortened to within 45 seconds. In addition, oscillation experiments, heat and shear resistant experiments, and drag reduction tests were conducted to study the advantage of NaSal for stimulating the formation of the slickwater compared with NaCl. The slickwater stimulated by NaSal indeed exhibit superior drag reduction and proppant carrying capacity. To effectively disassemble the wormlike micelles for gel breaking, ethylene glycol butyl ether performs better than the hydrocarbons because of its high polarity and water solubility. The gel breaking fluids of slickwater caused extremely low damage to the tight sandstone cores. The successful development of TC ‐ 2OH enables instant preparation of slickwater and variable‐viscosity for fracturing in unconventional reservoirs, which also realizes convenient switching between the slickwater with different viscosity.