Drilling fluid comprising a lubricant
The present invention provides a drilling fluid comprising a compound c) which comprises a dimer and/or trimer fatty acid residue and an alkyleneoxy chain comprising a first ethyleneoxy section, a second ethyleneoxy section and a propyleneoxy section located between said first and second ethyleneoxy sections, wherein the propyleneoxy section comprises from 1 to 20 propyleneoxy groups. Use of such a drilling fluid to lubricate a drill bit, and a method of drilling a well bore comprising circulating such a drilling fluid, are also provided.
1. A drilling fluid comprising:
a) an aqueous brine phase;
b) a particulate solid phase;
c) a compound comprising a dimer and/or trimer fatty residue and an alkyleneoxy chain comprising a first ethyleneoxy section, a second ethyleneoxy section, and a propyleneoxy section located between the first ethyleneoxy section and the second ethyleneoxy section, wherein the propyleneoxy section comprises from 1 to 20 propyleneoxy groups; and
d) optionally, one or more additives selected from rheology modifiers, fluid loss control agents, shale inhibitors, gas hydrate inhibitors and dispersants;
wherein the drilling fluid is suitable for lubricating a drill bit during drilling in a geological formation, and
wherein the compound c) is a compound of the formula (I):
R 1 [(EO) p (PO) q (EO) r ] n R 2 (I)
wherein:
R 1 is a residue of at least one of: a dimer fatty diacid, a trimer fatty triacid, a dimer fatty diol and/or a trimer fatty triol;
R 2 is H or (CO) x R 3 where x is 0 or 1 and R 3 is a C 1 to C 6 aliphatic hydrocarbyl group;
EO is an ethyleneoxy group;
PO is a propyleneoxy group;
P is from 1 to 20;
q is from 1 to 20;
r is from 1 to 20;
n is from 1 to 3;
a weight ratio of R 1 to total ethyleneoxy and propyleneoxy groups in compound c) is 0.2:1 to 0.6:1; and
wherein the ratio of (p+r) to q is from 0.5 to 8:1.
2. The drilling fluid according to claim 1 wherein the particulate solid phase comprises barium.
3. The drilling fluid according to claim 1 comprising the particulate solid phase in an amount of from 1 to 75 wt %, by weight of the drilling fluid.
4. The drilling fluid according to claim 1 wherein the drilling fluid has a density of at least 1.1 g/cm 3 .
5. The drilling fluid according to claim 1 wherein the aqueous brine phase comprises at least one of:
i) dissolved calcium at a concentration of at least 0.1 molar,
ii) dissolved formate at a concentration of at least 0.5 molar;
iii) dissolved silicate at a concentration of at least 0.4 molar; or
iv) brine salts at a concentration of at least 90% by weight of the concentration at saturation.
6. The drilling fluid according to claim 1 wherein the aqueous brine phase comprises dissolved calcium as Ca 2+ ions at a concentration of at least 0.5 molar.
7. The drilling fluid according to claim 1 wherein the aqueous brine phase comprises dissolved alkali metal formate.
8. The drilling fluid according to claim 1 wherein the aqueous brine phase comprises dissolved alkali metal silicate.
9. The drilling fluid according to claim 1 wherein the aqueous brine phase comprises at least one brine salt at a concentration of at least 95% by weight of the concentration at saturation.
10. The drilling fluid according to claim 1 further comprising an oil phase.
11. The drilling fluid according to claim 1 wherein p is from 3 to 15.
12. The drilling fluid according to claim 1 wherein q is from 3 to 15.
13. The drilling fluid according to claim 1 wherein r is from 3 to 15.
14. The drilling fluid according to claim 1 wherein R 2 is H.
15. The drilling fluid according to claim 1 wherein n is from 1.2 to 3.
16. The drilling fluid according claim 1 wherein the compound c) acts as a drilling lubricant.
17. A method of drilling a well bore comprising the steps of circulating a drilling fluid through a drill string extending through the well bore and around a drill bit, wherein the drilling fluid is the drilling fluid according to claim 1 .
18. A method comprising lubricating a drill bit with a drilling fluid comprising:
a) an aqueous brine phase;
b) a particulate solid phase;
c) a compound comprising a dimer and/or trimer fatty residue and an alkyleneoxy chain comprising a first ethyleneoxy section, a second ethyleneoxy section, and a propyleneoxy section located between the first ethyleneoxy section and the second ethyleneoxy section, wherein the propyleneoxy section comprises from 1 to 20 propyleneoxy groups; and
d) optionally, one or more additives selected from rheology modifiers, fluid loss control agents, shale inhibitors, gas hydrate inhibitors and dispersants;
wherein the drilling fluid is suitable for lubricating a drill bit during drilling in a geological formation, and
wherein the compound c) is a compound of the formula (I):
R I [(EO) p (PO) q (EO) r ] n R 2 (I)
wherein:
R 1 is a residue of at least one of: a dimer fatty diacid, a trimer fatty triacid, a dimer fatty diol and/or a trimer fatty triol;
R 2 is H or (CO) x R 3 where x is 0 or 1 and R 3 is a C 1 to C 6 aliphatic hydrocarbyl group;
EO is an ethyleneoxy group;
PO is a propyleneoxy group;
p is from 1 to 20;
q is from 1 to 20;
r is from 1 to 20;
n is from 1 to 3;
a weight ratio of R 1 to total ethyleneoxy and propyleneoxy groups in compound c) is 0.2:1 to 0.6:1; and
wherein the ratio of (p+r) to q is from 0.5 to 8:1.