NL192620C - Aqueous well treatment fluid. - Google Patents

Description

1 192620

Aqueous well treatment fluid

The present invention relates to an aqueous well treatment fluid comprising, in solution, a cesium salt of a carboxylic acid. Such a well treatment fluid is known from EP-A-0.572.113.

It is well known that aqueous media, especially those containing oilfield brines, are commonly used as well treatment fluids such as drilling fluids, finishing fluids, packer fluids, well maintenance fluids, subterranean formation test fluids, spacer fluids and abandoned borehole fluids. In all these applications, such brines preferably have a relatively high density. To achieve this, various ingredients have been added to such liquids. Examples thereof include heavy brines such as zinc bromide or combinations thereof with, for example, hydrophilic polymeric materials such as hydroxyethyl cellulose. One of the problems that arise with such brines in use today is that they contain zinc atoms that are harmful to the environment. In addition, the polymeric hydroxyethyl celluloses are poorly hydrated, solvated or dispersed in aqueous systems containing water-soluble polyvalent metal salts.

Other well treatment fluids are also known. EP-A-0,137,872 describes, for example, drilling and finishing fluid compositions containing, inter alia, a clay stabilizing agent of the formula RC (0) 0M, wherein R is hydrogen or a methyl, ethyl or propyl group and M is potassium, rubidium, cesium or ammonium. This material is used to prevent the clay from swelling, which could cause water-sensitive clay-containing materials that make contact with the liquid compositions to slip.

In addition to these salts, an amount of density enhancer, such as barite, is added to the fluids of this document.

GB-A-2,251,876 relates to drilling fluids containing a polar organic compound and a water-soluble organic potassium or ammonium compound. These materials are added for the purpose of preventing clay swelling. In order to obtain the correct density, an aggravating agent is added here, such as barium sulfate.

EP-A-0 572 113 mentioned in the preamble describes a well treatment liquid containing a carboxylate salt of cesium and at least one other alkali metal, wherein the carboxylate anion is derived from a saturated C 1 -C 8 monocarboxylic acid.

The problem with these liquids is that to increase the density they include sparingly soluble substances, such as barite. Such substances and also substances such as potassium formate tend to clump.

It is an object of the present invention to provide a composition which provides the desired high density aqueous brine systems with much lower ecotoxicity.

The present invention now provides an aqueous well treatment fluid according to the preamble characterized in that the carboxylic acid has: a) at least one carboxil group and b) at least one other carboxil and / or hydroxil group.

Thus, the cesium carboxilate used in the well treatment fluids of the present invention may be derived from simple di- or polycarboxylic acids or from the corresponding 40 hydroxy carboxylic acids. In a preferred embodiment, the carboxylic acid is aliphatic and saturated and is selected from the group consisting of oxalic acid, malonic acid, succinic acid, adipic acid, lactic acid {also known as 2-hydroxypropionic acid), citric acid (also known as 2-hydroxy-1,2,3 -propane-tricarboxylic acid) and tartaric acid (also known as 2,3-dihydroxibutanedioic acid).

In a further preferred embodiment, the cesium salt is cesium oxolate, cesium lactate, 45 cesium citrate or cesium tartrate.

According to another preferred embodiment, the liquid comprises a cesium carboxilate in an amount such that the liquid has a density of 1.6-2.63 g / cm3. It is therefore a highly desirable density enhancing compound for well treatment fluids and the salts are environmentally safe and easy to use.

The amount of cesium carboxilates used in a well treatment fluid composition can be easily determined. The simplicity of the invention should allow these values to be easily determined by simple experiments. An important consequence of this invention is that it allows to use lower concentrations of the relatively expensive cesium carboxilates in the composition to achieve the desired densities in the well treatment fluids.

Optionally, the cesium carboxilates can be used in combination with other alkali metal salts. According to yet another preferred embodiments, the liquid further comprises the acetates and / or formates 1926202 of potassium, sodium and / or cesium. By varying the relative concentrations of the carboxylic acid salts in the liquid, it is possible to achieve the desired density of the brine or the final treatment liquid in which the brine is used. Thus, densities of 1.6 to 2.63 g / cm3, preferably 1.8 to 2.5 g / cm3, can be achieved using compositions of the present invention.

The well treatment fluids of the present invention can be prepared by mixing aqueous solutions of individual salts. Also, a mixture of the aqueous solutions of the respective bases of the alkali metals may first be prepared to which the desired carboxylic acid is added to obtain the respective carboxilates. The desired concentration of the respective salts in the aqueous solution thus formed can be adjusted by evaporating the water from the mixed solution.

The invention is further illustrated by the following examples:

Examples

A number of organic cesium salts were prepared from a 50% w / w cesium hydroxide solution by adding an organic acid. After reaction and at a final pH of 7-8, the mixture was heated and the by-product, water, was evaporated until a saturated solution of the cesium carboxilate was obtained. Samples were taken during the evaporation step, cooled to room temperature (about 25 ° C), and densities and concentrations were measured. Clear top layers were taken from the saturated solutions and used as the cesium carboxilate liquid. The salt concentration in this liquid was determined by gravimetric analysis and subtracting the water content of the sample. The water content was determined by Karl Fischer titration.

The results of the above-described examples with different salts are shown in the table below.

25 1. Cesium citrate

Conc. (wt.%) Cs salt Conc Cs (wt.%) Density (g / cm3) 51.8 35.1 1.65 30 68.7 46.6 2.00 78.8 53.4 2.28 89.2 60.5 2,631 * - a very viscous solution 35 2. Cesium lactate:

Conc (wt%) Cs salt Conc (wt%). Cs Density (g / cm3); 40 54.9 32.9 1.53 66.0 39.5 1.69 75.9 45.5 1.87 89.5 53.6 2,121 - a viscous solution.

t 45 3. In a subsequent experiment, cesium oxalate was used and it was shown that at a cesium salt concentration of 72.8 wt%, it had a cesium concentration of 54.7 wt% and a density of 2.17 g / cm3.

In view of the relative non-ecotoxicity of these materials, such cesium carboxilates are very valuable additives for producing heavy brines.

Claims (5)

An aqueous well treatment fluid comprising, in solution, a cesium salt of a carboxylic acid, characterized in that the carboxylic acid: a. At least one carboxil group and b. has at least one carboxil and / or hydroxyl group. Aqueous well treatment fluid according to claim 1, characterized in that the carboxylic acid is aliphatic and saturated and is selected from the group consisting of oxalic acid, malonic acid, succinic acid, adipic acid, lactic acid (also known as 2-hydroxypropionic acid), citric acid (also known as 2-hydroxy-1,2,3-propane-tricarboxylic acid) and tartaric acid (also known as 2,3-dihydroxibutanedioic acid). An aqueous well treatment fluid according to any one of the preceding claims, characterized in that the cesium salt is cesium oxalate, cesium lactate, cesium citrate or cesium tartrate. 3 192620 An aqueous well treatment fluid according to any one of the preceding claims, characterized in that the fluid comprises a cesium carboxilate in an amount such that the fluid has a density of 1.6-2.63 g / cm3. Aqueous well treatment fluid according to any one of the preceding claims, characterized in that the fluid further comprises the acetates and / or formates of potassium, sodium and / or cesium.