| abstract |
The invention relates to a method for extracting petroleum from underground oil reservoirs, wherein an aqueous, salt-containing surfactant formulation comprising a surfactant mixture for lowering the interfacial tension between oil and water to < 0.1 mN/m is pressed into an oil reservoir through at least one injection well and crude oil is removed from the reservoir through at least one production well, wherein the oil reservoir has a temperature of ≥ 90°C and a formation water having a salinity of ≥ 30000 ppm of dissolved salts and wherein the surfactant mixture contains at least one ionic surfactant (A) of general formula (I): (R 1 ) k -N + (R 2 ) (3-k) R 3 (X - ) l and at least one anionic surfactant (B) of general formula (II): R 4 -O-(CH 2 C(R 5 )HO) m -(CH 2 C(CH 3 )HO) n -(CH 2 CH 2 O) o -(CH2) p -Y - M + , wherein, during injection, there is a molar ratio of ionic surfactant (A) to anionic surfactant (B) of 90 : 10 to 10 : 90 in the surfactant mixture and wherein R 1 to R 5 , k, l, m, n, o, p, X, Y and M have the meaning indicated in the claims and in the description. The invention further relates to a concentrate containing surfactant (A), surfactant (B), or the surfactant mixture. |