METHOD OF OBTAINING MINERAL OIL USING A SILICA FLUID

Method of obtaining mineral oil, comprising the steps of: providing a fluid comprising surface-modified silica particles, introducing this fluid into a mineral oil deposit via a first well in contact with this mineral oil deposit, recycling a mixture comprising the fluid and mineral oil via the first well or a further well and separating the mineral oil from the mixture, wherein the fluid comprises surface-modified nanostructured silica particles in an aqueous phase, A) the surface modified silica particles a) being mixed aluminium-silicon oxide, where the mixed oxide component is also part of the particle surface, and b) the surface modification comprises a hydrocarbon radical which is interrupted by one or more heteroatoms and comprises a silicon atom is bonded to a carbon atom of the hydrocarbon radical, the surface modification being selected from the group consisting of Si-(CH2)n-Ym-R, where Si is the Si atom which is bonded via a C atom to a hydrocarbon radical, and n = 1, 2 or 3 and m= 0 or 1 R is a radical which does not impart hydrophobic properties, and if m = 1, is -H, -CH3,-C2H5, -OH, -OCH3, -OC2H5, -C(=O)OCH3, -C(=O)OC2H5, -O-C(=O)CH3, -O-C(=O)CH3,-O-C(=O)CH=CH2, -O-C(=O)CH=CH(CH3), -C(=O)CH3, - CH(O)CH2 and hydrolysates of -CH(O)CH2, and, if m = 0, the aforementioned R radicals without -H, -CH3,-C2H5, Y = -(OCH2CH2)o-, o = 5-15 or a mixture of the aforementioned R and Y radicals. c) having c1 ) a ratio of the proportions by weight of Al2O3/SiO2 of 0.1 :99.9-5:95 c2) an average particle diameter d50 of 40 - 200 nm and c3) a carbon content of 3% - 25% by weight and B) the fluid having d) a content of 0.01 % - 5% by weight of the surface modified silica particles, and e) a pH of the aqueous phase being 7 ≤ pH ≤ 8.5.