CA1168427A

CA1168427A - Method of producing a homogeneous viscous well servicing fluid within a borehole and well servicing fluid compositions

Info

Publication number: CA1168427A
Application number: CA000380906A
Authority: CA
Inventors: Roy F. House; Lonnie D. Hoover
Original assignee: NL Industries Inc
Current assignee: NL Industries Inc
Priority date: 1980-08-08
Filing date: 1981-06-30
Publication date: 1984-06-05
Also published as: JPS5753584A; DE3129543A1; FR2488325A1; GB2085048A; AU7246481A; GB2085048B; NL8103523A; FR2488325B1; AU547470B2; IT1137819B; IT8123407A0; NO812494L; MX158191A

Abstract

Abstract of the Disclosure A method of producing a thickened aqueous medium within a borehole comprising adding to the aqueous medium a first hydrophilic polymer which increases the viscosity of the medium at ambient temperature and a second hydro-philic polymer which will not appreciably increase the viscosity at ambient temperature but which increases the viscosity at elevated temperature, mixing the aqueous medium and polymers to increase the viscosity, pumping the partially viscosified medium to the desired location in the borehole and aging the partially viscosified medium sufficient to allow both of the polymers to completely hydrate.

Description

f~ 7' Background of the Invention ' The present invention relates to methods of increasing the viscosity and decreasing the fluid loss of aqueous brines and to aqueous well servicing flulds pr~-pared thereby.
Thickened aqueous mediums, particularly those con~aining soluble salts, are commonly used as well servicing fluids such as drilling fluids, workover fluids, completion fluids, packer fluids, well treating fluids, subterranean formation treating fluids, spacer fluids, hole abandonment flùids, and other aqueous fluids in which an increase in viscosity is desired. It is known to use hydrophilic polymeric materials such as hydroxyethyl cel-lulose (HEC) and xanthan gums as thickening asents for aqueous mediums used in such well servicing fluids. How-ever, such polymers are not readily hydrated, solvated or dispersed in certain aqueous systems without elevated temperatures and/or mixing under high shear for extended periods of time. For example, hydroY.yethyl cellulose polymers are pooly hydrated, solvated or dispersed at ambient temperature in aqueous solutions containing one or more multivalent cation water soluble salts, such as heavy brines having a density greater than about 11.7 ppg which are used in well servicing fluids. Other polymers such as xanthan gum require elevated temperatures in even lower density solutions. In many cases, as for example, in workover operations, the equipment available for preparing the well servicing fluids does not readily lend itself to high temperature mixing. In well servicing operations where a solids-free well servicing 1uid is desired, such as certain completion operations, the fluid cannot be circulated in the hot borehole to increase the temperature of the fluid. Thus, it is common practice to "spot" the fluid in the borehole at the desired location where the completion operation is to take place. The temp2rature in '~.

~ zt7 the borehole is suficient to allow the polymer to hydrate when the fluid contains one or more hydrophilic polymers.
However, it has been found that on many occasions the polymer has formed a glob or mass of hydrated polymer containing a high polymer content. This glob of hydrated polymer not only prevents the polyrner from increasing the viscosity of all of the brine and/or decreasing the fluid loss of all of the brine, it can plug the perforations in the well and it forms plugs in the well when the fluid is lG circulated out of the well.

_4_ ~6~7 Summary of the_Inventi~n It is, therefore, an object of this invention to pro-vide a new method of producing within a borehole a homo-geneous aqueous medium containing one or more hydrophilic polymers which will not hydrate in the aquoeus medium at ambient temperatures.
A further object of this invention is to provide an improved aqueous, polymer containing well servicing fluid which will produce a homogeneous dispersion of hydrated polymer when statically aged within a borehole.
Another object of this invention is to provide a method of utilizing hydrophilic polymers in well servicing fluids.
These and other objects of the present invention will become apparent to one skilled in the art from the descrip-tion given herein.
In one embodiment of the invention, there is provided a method of producing within a borehole a viscous homogeneous aqueous solution which comprises adding to a solution con-taining a soluble salt of at least one multivalent cation and having a density of 10.75 ppg or greater (1) a hydro-philic polymer which will increase the viscosity of the solution at ambient temperature and a hydrophilic polymer which will not appreciably increase the viscosity of the solution at ambient temperature but which will hydrate in said solution at an elevated temperature to increase the viscosity of the solution, mixing the polymer containing solution to increase the viscosity of the solution, pumping the solution to the desired location in the borehole, and aging the solution to allow both polymers to completely hydrate in the solution due to the elevated borehole temperature.
In another embodiment of the invention, there is provided a well servicing fluid which is characterized as having a much higher viscosity when aged at an elevated temperature than it had before being aged which comprises an aqueous solution, a hydrophilic polymer which will not .~

appreciably increase the viscosity of the solution at . ambient temperature but which will hydrate in and viscosify the solution at an elevated temperature~ and a hydrophil.ic - polymer which will hydratc in and viscosify the solution at an ambient temperature in an amount sufficient to suspend the other polymer which is not hydrated at ambient temperature.

Descrlption of the Preferred E~bodiment_ The well servicing fluid of this invention requires an aqueous solution, a first hydrophilic polymer (hereinafter designated FEIP) which does not appreciab~y hydrate in and thus viscosify the solution at ambient temperature but which will hydrate in and viscosify the - solution at an elevated temperature and a second hydro-philic polymer (hereinafter designated SHP) which will hydrate in and viscosify the solution at ambient tem-peratures. Thus, the SHP imparts initial viscosity to the solution to keep the FHP suspended such that the FHP Will not hydrate as a lump of particles which has separated from the solution when statically aged at an elevated tem-perature.
~he aqueous solution utilized may be any solution which exhibits the desired characteristics of a well servicing ~luid such as density, a minimal effect on the formation, etc. ? for which a FHP and a SHP can be found.
In one embodiment of the invention, the aqueous solution contains a salt selected from the group consisting of calcium chloride, calcium bromide, ~inc bromide, and mixtures thereof, and has a density in the range from about 10.75 ppg (pound per gallon of fluid) to about 19.2 ppg.
Representative, non-limiting, solutions are given in Table I. Solutions in the density range from about 10.75 to about 15.1 ppg contain a salt selected from the group consisting of calcium chloride, calcium bromide, and mixtures thereof. Solutions in the density range from about 15.1 to about 19.2 ppg contain zinc bromide and a salt selected from the group consisting of calcium chloride, calcium bromide, and mitures thereof. Solutions in the density range from about 14.2 to about 15.1 ppg can be formulated to contain zinc bromide and either calcium chloride, calcium bromide, or mixtures thereof. In all of these solutions the FHP may be XC Polymer.

qZ7 TABLE I
. .

Density % % % ~, _ppg. CaCl~ CaBr~ Zn~2 ~ _ 10.75 29.2 0 0 70.8 11.6 37.~ 0 0 62.4 14.2 0 53 4 47 15.0 16.3 43.2 0 40.~5 15.5 4.4 32.9 24.0 38.7 16.0 0 38.7 24.6 36.7 17.5 0 29.1 41.3 29.6 19.2 ~! 20 '~7 23 XC Polymer is the heteropolysaccharide produced by Xanthomonas campestris bacteria from a suitable carbo-hydrate containing nutrient solution. This is a well known xanthan gum polymer which has found many uses as S a viscosifier in aqueous mediums. See for example, U.S.
Patent No. 3,988,246. XC polymer hydrates in and increases the viscosity of heavy brines as represented in Table I
only slightly or not at all at ambient temperatures. At a temperature'above abou~ 130F, XC polymer hydrates in these solutions. I~ the solution is agitated at the elevated temperatures, the XC polymer hydrates to produce a homogeneous, visceous solution. However, upon static aging, the XC polymer hydrates as a mass of particles producing a "glob" and a low viscosity solution.
In solutions having a density greater than about 14.5 ppg the FHP may be hydroxyethyl cellulose (HEC). Thus, in solutions containing a salt selected from the group con-sisting essentially of calcium chloride, calcium bromide, and mixtures thereof, having a density in the range from about 14.5 to about 15.1 ppg, HEC will not hydrate at ambient temperatures but readily hydrates at elevated temperatures above about 130F. Hydroxyethyl cellulose also is a suitable FHP in solutions containing zinc bromide and a salt selected from the group consisting of calcium chloride, calcium bromide, and mixtures thereof, having a density in the range from about 14.3 ppg to about 19.2 ppg.
Hydroxyethyl cellulose is a well known viscosifier for aqueous mediums. See for example, U.S. Patent No.
3,852,201. The HEC polymers are solid, particulate materials which are water soluble or water dispersible and which upon solution or dispersion in an aqueous medium increase the viscosity of the system. HEC polymers are generally high yield, water soluble, non-ionic materials ~,` 1"

g produced by treating ceLlulose with sodium hydroxide followed by reaction with ethylene oxide. Each anhydro-glucose unit in the cellulose molecule has three ~eactive hydroxy groups. The Degree of Substitution (D.S.) designates the average number of hydroxy positions on the anhydroglucose unit that has been reacted with ethylene oxide. The maximum D.S. is 3. The molar substitution (M.S.) is defined as the average number of ethylene oxide molecules that have reacted with each anhydroglucose unit. Once a hydroxyethyl group is attached to each unit, it can further react with additional ethylene oxide. Good water solubility is obtained at a D.S. value in the range from about 0.75 to about 1.75 and a M.S. value in the range from about 1.75 to about 3Ø
In solutions having a density less than about 14.5 ppg containing a salt seleeted from the group consisting of caleium chloride, caleium bromide, and mixtures thereof, the SHP ean be hydroxyethyl eellulose. HEC will readily hydrate in and viseosify such solutions at ambient temperatures.
Solutions having a density in the range from about 14.5 to about 15.1 ppg eontaining a salt selected fromn the group consisting essentially of calcium ehloride, ealeium bromide, and mixtures thereof, and solutions having a density in the range from about 14.5 to about 19.2 ppg eontaining zine bromide and a salt selected from the group eonsisting of ealeium chloride, ealcium bromide, and mixtures thereof are very difficult to viscosify at ambient temperatures. However, it has been shown in U.S.
Patent 4,330,414 and Canadian Application Serial No.
374,309, filed Mareh 31, 1981, that HEC ean be aetivated such that it will readily hydrate in and viscosify such brines at ambient temperatures. Thus, for these solutions, HEC is an effective SHP provided that it has been activated.

a~ s Exemplary SHP compositions useful in the present inven-tion, as indicated in U.S. Patent 4,330,414, comprise: hydroxy~
ethyl cellulose, a solvating agent comprising a wàter miscible, polar organic liquid which when uniformly mixed with the HEC in a weight ratio of HEC to solvating agent of 1:2 produces a mixture with no free liquid solvating agent present after remaining quiescent for one week at ambient temperature in a sealed container, and a diluting agent comprising an organic liquid which is not a solvat-ing agent. Preferred solvating agents are ethyleneglycol, glycerol, the propane glycols, the butane glycols, and mixtures thereof. The preferred diluting agents are isopropanol and the lower alkyl ethylene glycol ethers such as ethylene glycol n-propyl ether, ethylene glycol n-butyl ether, ethylene glycol isobutyl ether, and the like.
Preferably this SHP composition contains from about 15%to about 25% HEC, from about 15% to about 50% solvating agent, and from about 25% to about 70% di]uting agent.
Other exemplary SHP compositions which are useful in the present invention, as indicated in copending Canadian applic-ation Serial No. 374,309 filed March 31l 1981~ comprise: HEC
an aqueous liquid, and a water soluble organic liquid which wnen uniformly mixed with the HEC in a weight ratio of HEC
to organic liquid of 1:2 produces a mixture with no free liquid present after remaining quiescent for one week at ambient temperature in a sealed container. Representative organic liquid are isopropanol and the lower alkyl ether of ethylene glycol such as 2-ethoxyethanol, 2-propoxy-ethanol, 2-butoxyethanol and the like. The aqueous may be water or an acidic solution, but is preferably a basic solution having a dissolved hydroxide content less than about 3N. Preferably this SHP composition contains from about 15% to about 25% HEC, from about 15~ to about 30%
aqueous liquid, and from about 45% to about 70% of the water soluble organic liquid.

b "

The concentration of SHP in the well servicing fluids oE this invention need only be sufficient to produce a viscosity which will keep the F~]P suspended and dispersed while the well servicing fluid is statically aged at an 5 elevated temperature in a borehole. Preferably the con-centration will be sufficient to impart an API apparent ~riscosity of at least 100 centipoise to the fluid. The ma~imum concentration would be limited only by the maximum viscosity of the fluid which can be pumped downhole with the ln existing equipment at the wellsite.
The concentration of FHP in the well servicing fluid is dependent upo~ the viscosity desired ater the fluid has been statically aged at the elevated temperature.
The more FHP in the fluid the greater will be the viscosity lS after hot aging. Preferably the concentration of FHP will be in the range from about 0.5 ppb (pounds per ~2-gal.
barrel of fluid) to about 10 ppb, most preferably 1 ppb to about 5 ppb.
It is another feature of this invention that ~ery viscous homogeneous solutions can be obtained do~nhole at the desired location and prevailing temperature in a bore-hole where prior art solutions would be too viscous to prepare and pump at the surface.
The method of the present invention may be practiced by preparing the well servicing fluid comprising the a~ueous liquid, FHP and SHP, mixing the fluid to allow the SHP to hydrate in and viscosify the fluid suficiently to suspend the FHP, pumping the fluid to the desired location in a borehole, and aging the fluid at the pre-vailing temperature in the borehole.
The use of the term "homogeneous" throughout this specification and the claims is understood to be in reference to the entire volume of well servicing fluid since the FHP hydrates in the fluid in the limited area in which it is suspended and thus the viscous well servicing fluid after agin~ downhole could be considered to be a viscous suspension of hydrated polymer and, on a micro-scopic scale, appear not to be homogeneous.
A simple test to determine if a hydrophilic polymer will function as a FHP or a SHP in a particular aqueous medium is as follows:
1. mix the aqueous medium and the hydrophilic po]ymer together at room temperature for one hour; and

2. agitate the polymer containing aqueous medium overnight at a ternperature in the range from about 130F to about 250F, pre-ferably at the expected do~nhole tem-perature.
If the polymer readily viscosifies the aqueous medium at room temperature, then it can be used as a SYP.
I~ the polymer does not appreciably increase the viscosity at room temperature and does increase the viscosity at the elevated temperature, then it can be used as a FHP. If the polymer does not increase the viscosity at the elevated temperature, then it cannot be used in the well servicing fluids and method of this invention.
Other hydrophilic polymers ~7hich are useful in this invention may be selected from the ~roup consisting o other cellulose derivatives, water-dispersible starch derivatives, other polysaccharide gums, synthetic acrylic polyrners and copolymers, and the like. Exemplary cellulose derivatives are the carboxyalkyl cellulose ethers, such as carboxymethly cellulose and carboxyethyl cellulose;
hydroxyalkyl cellulose ethers such as hydroxypropyl cel-lulose; and mixed cellulose ethers such as: carboxyalkyl hydroxyalkyl cellulose, i.e. carboxymethyl hydroxyethyl cellulose; alkyl hydroxyalkyl cellulose, i.e. methyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose;
alkyl carboxyalkyl cellulose, i.e. ethyl carboxymethyl -~.6~7 cellulose. See U.S. Patent No. 4,110,230. Exemplary starch derivatives are the carboxyalkyl starch ethers such as carboxymethyl starch and carboxyethyl starch; hydroxy-alkyl starch ethers, such as hydroxyethyl starch and hydroxypropyl starch; and mixed ethers such as: carboxy-alkyl hydroxyalkyl starch i.e., carboxymethyl hydroxyethyl starch; alkyl hydroxyalkyl starch, i.e. methyl hydroxy-ethyl starch; alkyl carboxyalkyl starch, i.e., ethyl-carboxymethyl starch. Exemplary polysaccharide gums include: other biopolymers such as other Xanthomonas (xanthan) gums; galactomannan gums, such as guar gum, locust bean gum, tara gum; glucomannan gums; and deriva-tives thereof, paricu]arly the hydroxyalkyl derivatives.
See U.S. Patent Nos. 4,021,355 and 4,105,461.
In particular, guar gum can be used as a SHP in solutions having a density up to about 14.2 ppg containing calcium chloride, calcium bromide, or mixtures thereof.
To more fully illustrate the present invention, the following non-limiting examples are presented. All phys-ical property measurements were made in accordance with API testing procedures set forth in STANDARD PROCEDURE
FOR TESTING DRILLING FLUID, API RP 133, seventh edition, April, 1978.
Example I
~n aqueous solution having a density of 15.0 ppg.
containing 16.3~ calcium chloride, 43.2% calcium bromide, and 40.5% water was mixed with the polymers indicated in Table II for 5 minutes on a Multimixer at ambient temper-ature (74F). After obtaining the API rheological values the ~luids were rolled at ambient temperature for 55 minutes and the API rheology evaluated. The fluids were then statically aged at 165F for 18 hours, cooled to room temperature, and evaluated. The data obtained are given in Table II.

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-l4-The data indicates tha the SHP composition readily viscosified this solution producing a very viscous fluid at ambient temperature. The FHP did not viscosify this solution at ambient temperature and, because of a large glob of hydrated polymer formed on hot static aging, developed poor viscosity after heating. The fluid con-taining both the FHP and the SHP composition, illustrative of this invention, exhibited a low viscosity at ambient temperature and a very high viscosity after static aging.
The FHP used in this example was Natrosol~ 250 HHR
hydroxyethyl cellulose, a product of Hercules, Inc. The SHP used in this example was a composition containing 20%
Natrosol 250 HHR hydroxyethyl cellulose, 25% glycerol, 54.6% isopropanol, and 0.4% CAB-O-SI ~ M5. The concen-tration given in Table II is on a 100% active HEC basis.

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'7 Example 2 An aqueous solution haviny a density of 16.0 ppg containing 38.7~ calcium bromide, 24.6~ zinc bromide, and 36.7% water was mixed with 3 ppb o N~,TROSOL 250 Hll~
hydroxyethyl cellulose as in Example 1. Upon hot static aging a large mass of hydrated HEC was present on the surface of the solution. Mixing this solu.ion with 1 ppb of NAT~OSOL 250 HHR and 2 ppb (100% active HEC basis) of the SHP composition utilized in Example 1 provided a well servicing fluid which upon hot static aging produced a homogeneous viscous fluid.
Example 3 An aqueous solution having a density of 11.6 ppg containing 37.6% calcium chloride and 62.4% water was mixed with the polymers indicated in Table III for 15 minutes on a Multimixer and rolled at ambient temperature for 45 minutes. After obtaining the API rheological values, the fluids ~ere statically aged for 16 hours at 150F, cooled to room temperature, and evaluated. The data are given in Table III.
The data indicate that the HEC readily vis-cosified this solution at ambient temperature and was an efficient SHP. The XC polymer did not viscosify this solution at ambient tempera`_ure and upon hot static aging hydrated as a mass of polymer on the bottom of the con-tainer. The well servicing fluid containing HEC and XC
polymer exhibited an initial viscosity due to the hydration of the HEC and a very high viscosity after hot static aging due to co~bined hydration of the ~IEC and XC polymers.

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~il6~ L2.7 The invention may be embodied in other specific forms without departing from the sE)irit or essential char--acteristics thereof. The present embodiments are there-fore to be considered in all resp2cts as illustrative and not restrictive the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes~hich come within the meaning and range of equivalence of the claims are therefore intended to be embraced thereln.

Claims

Claims:

1. A method of producing, within a borehole, a viscous homogeneous aqueous solution containing one or more hydro-philic polymers which will not hydrate in the aqueous solution at ambient temperature comprising:
a) adding a first hydrophilic polymer to an aqueous solution containing a soluble salt of at least one multi-valent cation and having a density of 10.75 ppg or greater, said first hydrophilic polymer being of a type which will not appreciably hydrate in and increase the viscosity of said aqueous solution at ambient temperature but will hydrate in said aqueous solution at an elevated temperature to increase the viscosity of said aqueous solution;
b) adding to said aqueous solution a second hydrophilic polymer which will hydrate in said aqueous solution at ambient temperature, said second hydrophilic polymer being added in an amount sufficient to increase the viscosity of said aqueous solution sufficiently to keep said first hydrophilic polymer suspended;
c) mixing the polymer containing aqueous solution to allow the polymer in step b) to increase the viscosity of said aqueous solution at ambient temperatures;
d) introducing said polymer containing aqueous solu-tion to a desired location in a borehole; and e) aging said polymer containing aqueous solution in said borehole whereby said polymers completely hydrate due to the borehole temperature to produce said viscous homogeneous solution.

2. The method of Claim 1 wherein said hydrophilic polymer in step (a) is hydroxyethyl cellulose.

3. The method of Claim 2 wherein said hydrophilic polymer in step (b) is Xanthan gum.

4. The method of Claim 3 wherein said aqueous solution contains a salt selected from the group consisting of calcium chloride, calcium bromide, and mixtures thereof, and has a density in the range from about 10.75 to about 15.1 ppg.

5. The method of Claim 3 wherein said aqueous solution contains a salt selected from the group consisting of calcium chloride, calcium bromide, zinc bromide, and mixtures thereof, and has a density in the range from about 10.75 to about 19.2 ppg.

6. The method of Claim 1 wherein said aqueous solution has a composition such that hydroxyethyl cellulose will not hydrate in said solution at ambient temperature.

7. The method of Claim 6 wherein said hydrophilic polymer in step (a) is hydroxyethyl cellulose which has been activ-ated to hydrate in said solution at ambient temperature.

8. The method of Claim 7 wherein said hydrophilic polymer in step (b) consists essentially of hydroxyethyl cellulose.

9. The method of Claim 8 wherein said aqueous solution contains a salt selected from the group consisting of calcium chloride, calcium bromide, and mixtures thereof.

10. The method of Claim 8 wherein said solution contains a salt selected from the group consisting of calcium chloride, calcium bromide, zinc bromide, and mixtures thereof.

11. The method of Claim 10 wherein said solution has a density in the range from about 14.3 to about 19.2 ppg.

12. The method of Claim 9 wherein said solution has a density in the range from about 14.5 to about 15.1 ppg.

13. A well servicing fluid characterized as having a much higher viscosity when aged at an elevated temperature prior to said aging which comprises:
a) an aqueous solution containing a soluble salt of at least one multivalent cation and having a density of 10.75 ppg or greater;
b) a first hydrophilic polymer which does not apprec-iably hydrate in and viscosify said aqueous solution at ambient temperature but which will hydrate in said aqueous solution at an elevated temperature to increase the viscosity thereof; and c) a second hydrophilic polymer which will hydrate in and increase the viscosity of said aqueous solution at ambient temperature, said second hydrophilic polymer being present in an amount sufficient to impart an initial vis-cosity to the aqueous solution to keep the first hydro-philic polymer suspended.

14. The well servicing fluid of Claim 13 wherein said hydrophilic polymer in (a) is hydroxyethyl cellulose.

15. The well servicing fluid of Claim 14 wherein said hydrophilic polymer in (b) is Xanthan gum polymer.

16. The well servicing fluid of Claim 15 wherein said aqueous solution contains a salt selected from the group consisting of calciuam chloride, calcium bromide, and mixtures thereof.

17. The well servicing fluid of Claim 15 wherein said aqueous solution contains a salt selected from the group consisting of calcium chloride, calcium bromide, and zinc bromide.

18. The well servicing fluid of Claim 17 wherein said aqueous solution has a density in the range from about 10.75 to about 19.2 ppg.

19. The well servicing fluid of Claim 16 wherein said aqueous solution has a density in the range from about 10.75 to about 15.1 ppg.

20. The well servicing fluid of claim 13 wherein said aqueous solution contains a salt selected from the group consisting of calcium chloride, calcium bromide, zinc bromide, and mixtures thereof, and wherein said solution has a density in the range from about 14.5 to about 19.2 ppg.

21. The well servicing fluid of Claim 20 wherein said hydrophilic polymer in (b) is hydroxyethyl cellulose.

22. The well servicing fluid of Claim 21 wherein said hydrophilic polymer in (c) is hydroxyethyl cellulose which has been activated such that it will hydrate in said solution at ambient temperature.