SYNERGETIC EFFECT OF AUXILIARY SURFACTANTS WITH RESPECT TO RHEOLOGICAL CHARACTERISTICS OF LIQUIDS FOR DRILLING, WELL COMPLETION/FORMATION OPENING AND FORMATION HYDRAULIC FRACTURING Russian patent published in 2019 - IPC C09K8/35 C09K8/00 C09K8/74 C09K8/68 E21B43/26 

FIELD: oil and gas industry.

SUBSTANCE: group of inventions relates to liquids based on viscoelastic surfactants and methods of use thereof in oil deposits. Viscoelastic liquid for use in the liquid composition for stimulation of the well contains at least one viscoelastic surfactant and at least one auxiliary surfactant, having synergetic action. Said viscoelastic surfactant is an amphoteric surfactant of general formula (I): (I), where R₁ is a saturated or unsaturated hydrocarbon group having from 17 to 29 carbon atoms, R₂ and R₃ each is independently selected from an alkyl or hydroxyalkyl group with a straight or branched chain, having from 1 to 6 carbon atoms, R₄ is selected from H, hydroxyl, alkyl or hydroxyalkyl groups having 1 to 4 carbon atoms; k is integer from 2 to 20 and n is integer from 0 to 20, m is integer from 1 to 20. Said auxiliary surfactant, having synergetic action has general structure (II) (II), where R₁ is a saturated or unsaturated hydrocarbon group having from 12 to 22 carbon atoms, R₂, R₃ and R₄ each is independently selected from an alkyl or hydroxyalkyl group with a unbranched or branched chain, having from 1 to 4 carbon atoms; and from hydroxyl group. Viscoelastic liquid has density of more than 1.2 kg/l.

EFFECT: improved viscosity in high-density brines at high temperatures of more than 300 °F.

21 cl, 11 dwg, 2 tbl, 11 ex