Hydrophilic ether carboxylic acids as lubricant for salt based drilling systems

1. A clear brine-based drilling fluid consisting of:

(a) at least 10 wt % of an inorganic and/or organic, water soluble salt, based on the total weight of the clear brine-based drilling fluid;

(b) water; and

(c) an ether monocarboxylic acid of the general formula (I), an amide, a salt or an ester thereof as a lubricant

R—O(CH 2 CH 2 O) x (CH 2 CHR 1 O) y CH 2 —COOZ  (I)

wherein R is a saturated or unsaturated, branched or unbranched alkyl or alkenyl radical having from 6 to 22 carbon atoms;

x is an integer number of at least 5;

y is an integer number between 0 and 3;

R 1 is an alkyl radical having from 1 to 4 carbon atoms; and Z is a hydrogen atom or a monovalent or polyvalent cation;

wherein the clear brine-based drilling fluid can be tested for turbidity and does not comprise a water-insoluble lubricant, wherein said water-insoluble lubricant is any one or a combination of the following compounds:

a) carboxylic acid esters of formula (II)

R′—COO—R″  (II)

wherein R′ represents a saturated or unsaturated, linear or branched alkyl radical having 5 to 23 carbon atoms and R″ is an alkyl radical having 1 to 22 carbon atoms, wherein R″ may be saturated or unsaturated, linear or branched;

b) fatty acids of the general formula (III)

R′″—COOX  (III)

wherein R′″ is a saturated, unsaturated, branched or unbranched alkyl or alkenyl radical having from 5 to 23 carbon atoms and X is a hydrogen atom or a mono- or polyvalent cation; c) full or partial esters of glycerol with fatty acids of the above formula (III); and d) a paraffin

wherein the clear brine-based drilling fluid has a turbidity does not exceed the sum of 100 formazin nephelometric units (FNU) plus the turbidity of a composition solely comprising components (a) and (b), wherein the turbidity was determined at 20° C. using the ISO 7027:1999 turbidity method to measure the attenuation of a radiant flux.

2. The clear brine-based drilling fluid according to claim 1 , wherein R is a radical according to general formula (II) or (III):

CH 3 (CH 2 ) a CH═CH(CH 2 ) b CH 2 —  (II)

CH 3 (CH 2 ) a CH═CH(CH 2 ) a CH 2 —  (III)

wherein a and b are each individually selected from an integer of between 4 and 9.

3. The clear brine-based drilling fluid according to claim 1 , wherein the clear brine-based fluid does not comprise any precipitated material.

4. The clear brine-based drilling fluid according to claim 1 , wherein the clear brine-based drilling fluid is a lubricant composition and does not comprise any water-insoluble lubricant.

5. The clear brine-based drilling fluid according to claim 1 , wherein y=0.

6. The clear brine-based drilling fluid according to claim 1 , wherein x is at least 9.

7. The clear brine-based drilling fluid according to claim 1 , wherein y=0 and x=9.

8. The clear brine-based drilling fluid according to claim 1 , wherein the clear brine-based drilling fluid is not an emulsion.

9. The clear brine-based drilling fluid according to claim 1 , wherein R is a saturated or unsaturated C12-C22 alkyl.

10. The clear brine-based drilling fluid according to claim 1 , wherein R is a radical according to general formula (II) or (III):

CH 3 (CH 2 ) a CH═CH(CH 2 ) b CH 2 —  (II)

CH 3 (CH 2 ) a CH═CH(CH 2 ) a CH 2 —  (III)

wherein a and b are each individually selected from an integer of between 6 and 7.

11. The clear brine-based drilling fluid according to claim 2 , wherein the clear brine-based fluid does not comprise any precipitated material.

12. The clear brine-based drilling fluid according to claim 2 , wherein the clear brine-based drilling fluid does not comprise any water-insoluble lubricant.