NO812339L - SALT WATER SUSPENSIONS AND WATER-REDUCING ADDITIVES FOR SUCH. - Google Patents

Description

When drilling and completing oil, gas and water wells, cement slurries or suspensions are often used for cementing the casing in the borehole itself, sealing zones that the borehole passes through, etc. In most cases, the cement slurry is pumped into the wellbore itself, after which it is allowed it all hardens as soon as it is in place in the borehole, or in contact with the desired zones in the formations.

A number of additives have been developed to improve the properties of cement suspensions, i.a. additives to reduce

sere the water loss from the suspensions while these are being transported to the place of use or after they have been placed.i Too large

water loss from the cement suspensions can i.a. prevent satisfactory hydration of the cement. If it e.g. If there is too much water loss while the suspension is being transported through the borehole, this can result in such severe dehydration that the cement becomes attached to it. the bore wall itself, which does

that the cement cannot be properly placed. Although the water loss reducing additives developed so far are effective in cement suspensions prepared with fresh water or with water

containing low concentrations of salt, such additives are essentially ineffective in cement suspensions that contain high concentrations of salts, and especially those cement suspensions that are saturated with salts. Thus, e.g. a number of cellulose derivatives have been used to control

clay fluid loss from cement suspensions containing little or no salt. However, such cellulose derivatives are essentially ineffective in reducing water loss from saltwater cement suspensions. Furthermore, it can be mentioned that other water loss-reducing additives that have been used in cement suspensions. prepared with fresh water, such as polyacrylamides, polyethylene imides mixed with phanthalene sulfonic acid, and poly-2-acrylamide-3-propylene sulfonic acid salts, are not effective in reducing water loss from saltwater cement suspensions.

The present invention provides water loss-reducing additives for salt water cement suspensions which are effective in preventing water loss from suspensions within a wide temperature range. In addition, the invention provides .. the use of additives and salt water cement suspensions which contain such additives. The term "salt water" as used here is understood seawater, brine and other aqueous solutions of salts which may include ammonium, alkali metal and alkaline earth metal halides and nitrates with salt concentrations up to the saturation point. Salts other than those mentioned above can be tolerated in cement suspensions according to the present invention to a certain extent, although they can react with or change the suspension's properties, for example; bicarbonates, phosphates and sulphates. The term 11 salt water cement suspension" is understood here as a cement suspension consisting of water, cement, one or more salts and other components or additives that give the suspension the desired properties peculiar monkeys. The amount of salt or the concentration of the salts in the cement suspension is here expressed in % by weight in relation to the water in the cement suspension. The quantities of water loss-reducing additives used in cement suspensions according to the present invention. etc., is expressed in % by weight in relation to the dry weight of semen

ten in the suspension.

The water loss reducing additives for salt water cement suspensions according to the present invention" consist of very low molecular weight carboxymethyl hydroxyethyl cellulose polymers. More particularly, carboxymethyl hydroxyethyl cellulose polymers can be used, which have a carboxymethyl substitution degree (D.S.) varying from 0.1 to 0.7, and a molar ratio .i between ethylene oxide and anhydroglucose units (M.S.) varying from 0.6 to 2.8.

The aforementioned carboxymethylhydroxyethyl cellulose polymers are derived from the type of cellulose indicated by a series of anhydroglucose units as follows: i

The part of the above structural formula which is within the parentheses consists of two anhydroglucose units, each of which has 3 reactive hydroxide groups. n is a number that gives the desired polymer length. When said polymer is treated with sodium hydroxide and reacted with chloroacetic acid and ethylene oxide under controlled conditions, carboxymethylhydroxyethyl cellulose is produced in the following way:

The Viste sodium salt of carboxymethylhydroxyethyl cellulose has one of the side hydroxyl groups substituted with carboxymethyl, and consequently the degree of carboxymethyl substitution (D.S.) is 0.5 per anhydroglucose unit. As mentioned above, the preferred degree of carboxymethyl substitution is for carboxymethylhydroxyethyl cellulose according to the present invention, in the range from 0.1 to 0.7. At a carboxymethyl D.S. of less than approx. 0.1, then the carboxymethyl hydroxyethyl cellulose has limited solubility in water, and at a carboxymethyl D.S. of more than about 0.7, the carboxymethyl hydroxyethyl cellulose will have too strong an anionic nature and will precipitate when it is added to the semeht suspension.

The above structural formula also shows that the ratio of moles of ethylene oxide to anhydroglucose units (M.S.) is 1 mole for 2 units, or 0.5. The preferred ethylene oxide, M.S. for carboxymethylhydroxyethyl cellulose used according to the present invention is in the range from 0.6 to 2.8. Carboxymethyl hydroxyethyl cellulose with an ethylene oxide M.S.. outside specified ranges, does not give satisfactory water loss reducing properties to a salt water cement suspension.

The molecular amount of the carboxymethylhydroxyethyl cellulose polymers, i.e. the molecular weight of the polymers, must be very low in order to give low viscosity to the salt water cement suspension to which the polymers are added. More particularly, it can be used that the carboxymethylhydroxyethyl cellulose epQ.lymers that can be used in the present invention have a very low molecular weight, so that a 1% by weight aqueous solution of the carboxymethylhydroxyethyl cellulose at 25.5°C has a Viscosity varying from 10 to 225 cp measured using a

FIND viscometer at 300 rpm using No. 1 standard weight and standard sleeve. At higher molecular weights

than that which. is mentioned above, then the viscosity of the saltwater cement suspension produced when the carboxymethylhydroxyethyl cellulose is added will be too high, whereby the resulting suspension cannot be pumped in or otherwise treated. The FANN viscometer mentioned above is a FANN Model No. 35 viscometer manufactured by FANN Instrument Co. in Houston, Texas.

Although the carboxymethylhydroxyethyl cellulose polymers described above effectively reduce water loss from saltwater cement suspensions, the effectiveness of the polymer itself will decrease when the concentration of salts in the suspension is above 18% by weight. However, when a hydroxycarboxylic acid is added together with the carboxymethylhydroxyethyl cellulose polymers, the resulting additive will be very effective in reducing water loss from salt water cement suspensions with very high salt concentrations. With saltwater cement suspensions with salt concentrations above 18% by weight and up to saturation, you can use an additive consisting of the above-mentioned carboxymethylhydroxyethyl cellulose polymers, and a hydroxycarboxylic acid that is used in amounts of up to 50% by weight of the carboxymethylhydroxyethylcellulose in the additive. Particularly suitable hydroxycarboxylic acids which can be used are gluconic acid, tartaric acid, lactic acid, citric acid, maleic acid and mixtures of such acids.

Of these, gluconic acid, tartaric acid and citric acid are preferred, with citric acid being the most preferred acid.

A preferred water loss reducing additive for saltwater cement suspensions with salt concentrations below 18% by weight consists of carboxymethylhydroxyethyl cellulose with

a carboxymethyl D.S. varying from approx. 0.1 to approx. 0.7,

an ethylene oxide M.S. in the area from approx. 0.6 to 2.8, and such a molecular weight that a 1% aqueous solution of carboxymethylhydroxyethyl cellulose at 25.5°C has a viscosity varying from approx. 10 to approx. 225 cp measured on a FANN viscometer at 300 rpm using No. 1 spring. The most preferred additive of this type consists of carboxymethyl hydroxyethyl cellulose with a carboxymethyl D.S. of approx. 0.4, an ethylene oxide M.S. of approx. 2.0 and a molecular weight that gives a viscosity of a 1% by weight aqueous solution in the range from approx. 10 to approx. 200 cp.

A preferred water loss reducing additive for saltwater cement suspensions, which have salt concentrations varying from approx. 18% by weight of the water to saturation, consists of carboxymethyl hydroxyethyl cellulose, with a ^carboxymethyl D.S. varying from approx. 0.1 to approx. 0.7 r an ethylene oxide M.S. in the range from approx. 0.6 to approx. 2.8, and a molecular weight such that a 1% by weight aqueous solution of said carboxymethyl-hydroxyethyl cellulose at 25.5°C has a viscosity varying from 10 to 225 cp measured on a FANN viscometer at 300 rpm using No. 1 feather, and a hydroxycarboxy- . acid selected from the group consisting of gluconic acid, tartaric acid, lactic acid, citric acid, maleic acid and mixtures of such acids, and which is present in additives in an amount by weight of approx. 50% by weight of the carboxymethylhydroxyethyl cellulose in the additive.

The most preferred additive of this type consists of carboxymethyl hydroxyethyl cellulose with a carboxymethyl D.S. of approx. 0.4, an ethylene oxide M.S. of approx. 2.0 and a molecular weight such that a 1% by weight aqueous solution at 25.5°C has a viscosity of approx. 10 to approx. 200 cp measured on a FANN viscometer at 300 rpm using No. 1 spring,

and citric acid in an amount of approx. 50% by weight of carboxymethylhydroxyethyl cellulose in the additive.

A preferred salt water cement suspension with low water loss when in contact with permeable underground formations, according to the present invention, consists of salt water, cement and a water loss reducing additive, composed of carboxymethyl hydroxyethyl cellulose with a carboxymethyl D.S. from 0.1 to approx. 0.7, an ethylene oxide M.S. varying from 0.6 to approx. 2.8, and such a molecular weight that a 1% by weight aqueous solution at 25.5°C has a viscosity varying from

about 10 to about 225 cp, measured on a FANN viscometer at 300 rpm, using No. 1 spring.

Another preferred salt water cement suspension with low water loss when in contact with permeable underground formations consists of salt water, cement, and a water loss reducing additive composed of carboxymethyl hydroxyethyl cellulose with a carboxymethyl D.S. varying from:0.1 to 0.7,

an ethylene oxide M.S. varying from 0.6 to 2.8, and such a molecular weight that a 1% by weight aqueous solution at 25.5°C

has a viscosity varying from approx. 10 to approx. 225 cp, measured on a FANN viscometer at 300 rpm using No. 1 spring, and where said additive is present in the suspension in an amount varying from about 0.2 to about 2.0% by weight in relation to., the dry cement in the suspension, as well as a hydroxycarboxylic acid selected from the group consisting of gluconic acid, tartaric acid, lactic acid, citric acid, maleic acid and mixtures of such acids,

and where said acid or acids are present in amounts varying from 0.1 to 1.0% by weight in relation to the dry cement weight in the suspension.

The most preferred saltwater cement suspension

with low water loss consists of salt water, cement, and a water loss reducing additive consisting of carboxymethyl hydroxyethyl cellulose with a carboxymethyl D.S. of 0.4, an ethylene oxide M.S. of approx. 2.0, and such a molecular weight that a 1% by weight aqueous solution at 25.5°C has a viscosity of from 10

to approx. 200 cp, measured on a FANN viscometer at 300 rpm when using a No. 1 spring, and where the carboxymethyl hydroxyethyl cellulose is used in amounts of^from 0.25 to 1.0% by weight

in relation to the dry cement weight in the suspension, as well as citric acid which is used in amounts from 0.1 to 0.9% by weight in relation to the weight of dry cement in the suspension.

When water loss reducing additives according to the present invention are used to reduce water loss from a saltwater cement suspension used to cement wells,

then the additive is mixed with the salt water cement suspension before its use. The water loss-reducing additive is preferably dry-mixed with other dry components which are then added to the water used to prepare the cement suspension. If the mixed water does not already contain salts, then these can preferably also be dry-mixed together with the other dry components and the mixture prepared by adding to water. As soon as the suspension is properly mixed, it is introduced into the wellbore and/or the subterranean formation penetrated by the borehole, after which it is allowed to harden into a hard, permeable mass. The water loss-reducing additives and cement suspensions containing such additives are effective in preventing water loss at temperatures within a wide temperature range, i.e. from approx. 37 to approx. 182°C.

It should be understood that salt water cement suspensions according to the present invention may also contain a number of other components and additives to produce certain desired results, such as solid fillers, e.g. sand, retarding curing agents, accelerators etc.

The following examples illustrate the invention.

EXAMPLE 1.

Cement suspensions or slurry were produced. nings using fresh water containing different concentrations of sodium chloride, cement and water loss reducing additives according to the present invention, consisting of low molecular weight carboxymethylhydroxyethyl cellulose polymers (D.S. of 0.4, M.S. of 2.0, and such a molecular weight that a 1% by weight aqueous solution at 25 .5°C had a viscosity from 10 to

200 cp, measured on a•FANN viscometer at 300 rpm using No. 1 spring) and tartaric acid. The suspension and additives were mixed in a Waring mixer for 35 seconds at high speed. Surface mixture viscosity of the suspensions was determined

at 37.7, 48.8, 65.5 and 87.7°C, using a Halliburton consistometer. as described in US patent no.

2,122,765.

The liquid loss characteristics of the suspensions were determined using API standard methods (API RP-10B) on a: 3 26 mesh sieve at 71.4 kg/cm 2 at 37.7, 48.8, 65.5 and 87.7°C.

The results of the tests are given in table 1.

It appears from table 1 that carboxymethylhydroxyethylcellulose-tartaric acid additives provide good surface mixing viscosities and liquid loss reduction in cement suspensions containing different amounts of salt.

EXAMPLE 2.■

The procedure from example 1 was repeated, with the water loss-reducing additives consisting of a low molecular weight carboxymethylhydroxyethyl cellulose polymer, as described, and various hydroxycarboxylic acids;

The results are shown in table 2. I

From the table it appears that good liquid loss reductions are achieved when additives according to the present invention are used at temperatures from 37.7 to 182.2°C. It also appears that additives that include hydroxycarboxylic acids are more effective in saltwater suspensions that contain salt concentrations above approx. 18% by weight than those containing only

CMHEC.

Claims (10)

Water loss reducing additive for use in salt-water cement slurries or suspensions, characterized by including carboxymethyl hydroxyethyl cellulose with a carboxymethyl D.S. in the range of 0.1 to 0.7, an ethylene oxide M.S. in the area from approx. 0.6; to approx. 2.8, and such a molecular weight that a 1% by weight aqueous solution at 25.5°C has a viscosity varying from approx. 10; to approx. 225 cp measured on a FANN viscometer at 300 rpm, using No. 1 spring. 2. Additive according to claim 1, characterized in that said carboxymethylhydroxyethyl cellulose has a carboxymethyl D.S. of approx. 0.4, an ethylene oxide M.S. of approx. 2.0, and such a molecular weight that said viscosity lies in the range from 10 to 200 cp. 3. Additive according to claim 1, characterized in that a hydroxycarboxylic acid is also added. 4. Saltwater cement suspension with low water loss in contact with permeable underground formations, characterized by consisting of: Salt water; cement; and a water loss reducing additive consisting of carboxymethyl hydroxyethyl cellulose with a carboxymethyl D.S. in the area from approx. 0.1 to approx. 0.7, an ethylene oxide M.S. in the area from approx. 0.6 to approx. 2.8, and such a molecular weight that a 1% by weight aqueous solution at 25.5°C has a viscosity in the range from approx. 10 to approx. 225 cp,' measured on a FANN viscometer at 300 rpm when using spring No. 1\ 5. Cement suspension according to claim 4, characterized in that said carboxymethylhydroxyethyl cellulose has a carboxymethyl D.S. of approx. 0.4, an ethylene oxide M.S. of approx. 2.0 and such a molecular weight that said viscosity lies in the range from approx. 10 to approx. 200 cp..•' 6. Cement suspension according to claim 4, charac- characterized by said carboxymethylhydroxyethyl cellulose being present in said cement suspension in amounts of from 0.2 to approx. 2.0% by weight in relation to the weight of dry cement in the suspension. 7. Cement suspension according to claim 4, characterized in that it also contains a hydroxycarboxylic acid. 8. Method for reducing water loss from a salt-water cement suspension that is used to cement a well, characterized by mixing a water-loss-reducing additive with said salt-water cement suspension before using the latter, and where said additive consists of carboxymethyl hydroxyethyl cellulose with a carboxymethyl D.S. in the area from approx. 0.1 to approx. 0.7, an ethylene oxide M.S. in the area from approx. 0.6 to approx. 2.8, and such a molecular weight that a 1% by weight aqueous solution at 25.5°C has a viscosity varying from approx. 10 to approx. 225 cp, measured on a FÅNN viscometer at 300 rpm using spring #1. 9. Method according to claim 8, characterized in that said carboxymethyl hydroxyethyl cellulose has a carboxymethyl D.S. of approx. 0.4, an ethylene oxide M.S. of approx. 2.0, and a molecular weight such that said viscosity lies in the range from approx. 10 to approx. 200 cp. 10. Method according to claim 8, characterized in that said additive also includes a hydroxycarboxylic acid...