Method of obtaining mineral oil using a silica fluid

1. A method of obtaining mineral oil, comprising the steps of:

a) providing a fluid comprising surface-modified silica particles;

b) introducing this fluid into a mineral oil deposit via a first well in contact with this mineral oil deposit;

c) recycling a mixture comprising the fluid and mineral oil via the first well or a further well; and

d) 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, wherein 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 bonded to a carbon atom of the hydrocarbon radical, the surface modification being selected from the group consisting of Si—(CH 2 ) n —Y m —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, —CH 3 , —C 2 H 5 , —OH, —OCH 3 , —OC 2 H 5 , —C(═O)OCH 3 , —C(═O)OC 2 H 5 , —O—C(═O)CH 3 , —O—C(═O)CH 3 , —O—C(═O)CH═CH 2 , —O—C(═O)CH═CH(CH 3 ), —C(═O)CH 3 , —CH(O)CH 2 and hydrolysates of —CH(O)CH2; and,

if m=0, the aforementioned R radicals without —H, —CH 3 , —C 2 H 5 ;

Y=—(OCH 2 CH 2 ) 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 Al 2 O 3 /SiO 2 of 0.1:99.9-5:95;

c2) an average particle diameter d 50 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.

2. The method of claim 1 , wherein the surface modification comprises an aluminium atom which is bonded via an oxygen atom to a silicon atom of the particle surface.

3. The method of claim 1 , wherein the mixed silicon-aluminium oxide is a fumed mixed silicon-aluminium oxide having a BET surface area of 140-200 m 2 /g and an aluminium oxide content of 0.3%-1.3% by weight.

4. The method of claim 1 , wherein (Al 2 O 3 /SiO 2 ) surface /(Al 2 O 3 /SiO 2 ) ttl is 0.1-10.

5. The method of claim 1 , wherein the surface modification further comprises Al.

6. The method of claim 5 , wherein the proportion of Al in the surface modification is ≤0.15 mg Al/m 2 of BET surface area.

7. The method of claim 1 , wherein the surface modification is selected from the group consisting of: Si(CH 2 ) 3 —(OCH 2 CH 2 ) 6-9 —OCH 3 , Si(CH 2 ) 3 —(OCH 2 CH 2 ) 9-12 —OCH 3 , Si(CH 2 ) 3 —(OCH 2 CH 2 ) 21-24 —OCH 3 , Si(CH 2 ) 3 —(OCH 2 CH 2 ) 8-12 OH and Si—(CH 2 ) 3 —CH(O)CH 2 .

8. The method of claim 2 , wherein the mixed silicon-aluminium oxide is a fumed mixed silicon-aluminium oxide having a BET surface area of 140-200 m 2 /g and an aluminium oxide content of 0.3%-1.3% by weight.

9. The method of claim 8 , wherein (Al 2 O 3 /SiO 2 ) surface /(Al 2 O 3 /SiO 2 ) ttl is 0.1-10.

10. The method of claim 9 , wherein the surface modification further comprises Al.

11. The method of claim 10 , wherein (Al 2 O 3 /SiO 2 ) surface /(Al 2 O 3 /SiO 2 ) ttl is 0.1-10.

12. The method of claim 1 , wherein the surface modification further comprises Al.

13. The method of claim 3 , wherein the silane is mixed with at least one metal compound selected from the group consisting of the metal alkoxides and metal acetylacetonates of aluminium, titanium and zirconium, and also sodium aluminate wherein the molar metal/Si ratio of the surface modification is 1:2-1:20 before it is added to the predispersion.

14. The method of claim 1 , wherein the fluid is introduced into a mineral oil deposit having a temperature of 10-200° C.

15. A method of obtaining mineral oil, comprising the steps of:

a) providing a dispersion comprising more than 5 wt.-% of surface-modified silica particles by:

a1) dispersing a mixed aluminium-silicon oxide powder having a ratio of the proportions by weight of Al 2 O 3 /SiO 2 of 0.1:99.9-5:95 and Si atoms and Al atoms each bearing hydroxyl groups on the surface of the particles in an aqueous solution to an average particle diameter d 50 40-200 nm and subsequently;

a2) adding the agent for surface modification;

a3) causing the mixture to react to obtain the dispersion comprising of surface-modified silica;

a4) optionally removing the hydrolysis product; and

a5) optionally adjusting the pH;

wherein the agent for surface modification is added in such an amount as to obtain a carbon content of 3-25% by weight, taking account of the hydroxyl groups, alkoxy groups or chloride groups detached in the hydrolysis, and

wherein the agent for surface modification is a silane selected from the group consisting of:

X 4-a [Si—(CH 2 ) n —Y—R] a with a=1, 2 or 3; preferably a=1; n=1, 2 or 3;

X=OH, OCH 3 , OC 2 H 5 , Cl; Y=—(OCH 2 —CH 2 ) o− , o=5-15,

R=—H, —CH 3 ,—C 2 H 5 , —OH, —OCH 3 , —OC 2 H 5 , —C(═O)OCH 3 , —C(═O)OC 2 H 5 , —O—C(═O)CH 3 , —O—C(═O)CH 3 , —CH(O)CH 2 or a hydrolysate of —CH(O)CH 2 ;

b) diluting the dispersion to obtain a fluid having a content of 0.01%-5% by weight of the surface modified mixed aluminium-silicon oxide particles, and having a pH of the aqueous phase of 7≤pH≤8.5 or adjusting the pH to this range;

c) introducing this fluid into a mineral oil deposit via a first well in contact with this mineral oil deposit;

d) recycling a mixture comprising the fluid and mineral oil via the first well or a further well; and

e) separating the mineral oil from the mixture.

16. The method of claim 15 , wherein the fluid is introduced into a mineral oil deposit having a temperature of 10-200° C.