GB2085048A

GB2085048A - Method of Producing a Homogeneous Viscous Well Servicing Fluid Within a Borehole and Well Servicing Fluid Compositions

Info

Publication number: GB2085048A
Application number: GB8121994A
Authority: GB
Original assignee: NL Industries Inc
Current assignee: NL Industries Inc
Priority date: 1980-08-08
Filing date: 1981-07-16
Publication date: 1982-04-21
Also published as: IT1137819B; MX158191A; NO812494L; FR2488325A1; AU7246481A; FR2488325B1; DE3129543A1; IT8123407A0; JPS5753584A; CA1168427A; GB2085048B; AU547470B2; NL8103523A

Abstract

A thickened aqueous medium can be produced within a borehole comprising adding to the aqueous medium a first hydrophilic polymer which will not appreciably increase the viscosity at ambient temperature but which increases the viscosity at elevated temperature, and a second hydrophilic polymer which increases the viscosity of the medium at ambient 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

SPECIFICATION Method of Producing a Homogeneous Viscous Well Servicing Fluid within a Borehole and Well Servicing Fluid Compositions The present invention relates to methods of increasing the viscosity and decreasing the fluid loss of aqueous brines and to aqueous well servicing fluids prepared thereby.

Thickened aqueous mediums, particularly those containing soluble salts, are commonly used as well serivicing fluids such as drilling fluids, workoverfluids, completion fluids, packer fluids, well treating fluids, subterranean formation treating fluids, spacer fluids, hole abandonment fluids, and other aqueous fluids in which an increase in viscosity is desired. It is known to use hydrophilic polymeric materials such as hydroxyethyl cellulose (HEC) and xanthan gums as thickening agents for aqueous mediums used in such well servicing fluids. However, 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, hydroxyethyl cellulose polymers are poorly 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 1.402 g/mi. 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 fluid 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 temperature in the borehole is sufficient 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 polymer 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 circulated out of the well.

It is, therefore, an object of this invention to provide a new method of producing within a borehole a homogeneous aqueous medium containing one or more hydrophilic polymers which will not hydrate in the aqueous 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 description 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 the solution (1) a hydrophilic 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 hydrophilic polymer which will hydrate 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.

The well servicing fluid of this invention requires an aqueous solution, a first hydrophilic polymer (hereinafter designated FHP) which does not appreciably 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 hydrophilic polymer (hereinafter designated SHP) which will hydrate in and viscosify the solution at ambient temperatures. 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 temperature.

The aqueous solution utilized may be any solution which exhibits the desired characteristics of a well servicing fluid 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, zinc bromide, and mixtures thereof, and has a density in the range from about 1.29 to 2.30 grams per millilitre (g/ml.). Representative, non-limiting, solutions are given in Table 1. Solutions in the density range from 1.29 to 1.81 g/ml. contain a salt selected from the group consisting of calcium chloride, calcium bromide, and mixtures thereof. Solutions in the density range from 1.81 to 2.30 g/ml. contain zinc bromide and a salt selected from the group consisting of calcium chloride, calcium bromide, and mixtures thereof. Solutions in the density range from 1.70 to 1.81 g/ml. 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.

Table 1 Density % % % % g/ml. Ca Cl2 CaBr2 ZnBr2 H20 1.29 29.2 0 0 70.8 1.34 37.6 0 0 62.4 1.70 0 53 4 47 1.80 16.3 43.2 0 40.5 1.86 4.4 32.9 24.0 38.7 1.92 0 38.7 24.6 36.7 2.10 0 29.1 41.3 29.6 2.30 0 20 57 23 XC Polymer is the heteropolysaccharide produced by Xanthomonas campestris bacteria from a suitable carbohydrate containing nutrient solution. This is a well known xanthan gum polymer which has found many uses as 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 presented in Table I only slightly or not at all at ambient temperatures. At a temperature above 550 C, XC polymer hydrates in these solutions.If the solution is agitated at the elevated temperatures, the XC polymer hydrates to produce a homogeneous, viscous 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 1.34 g/ml. the FHP may be hydroxyethyl cellulose (HEC). Thus, in solutions containing a salt selected from the group consisting essentially of calcium chloride, calcium bromide, and mixtures thereof, having a density in the range from 1.34 to 1.81 g/ml., HEC will not hydrate at ambient temperatures but readily hydrates at elevated temperatures above about 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 1.71 to 2.30 g/ml.

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 produced by treating cellulose with sodium hydroxide followed by reaction with ethylene oxide. Each anhydroglucose unit in the cellulose molecule has three reactive hydroxy groups. The Degree of Substitution (D.S.) designates the average number of hydroxy positions on the anhydroglucose unit that have 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 3.0.

In solutions having a density less than 1.74 g/ml. containing a salt selected from the group consisting of calcium chloride, calcium bromide, and mixtures thereof, the SHP can be hydroxyethyl cellulose. HEC will readily hydrate in and viscosify such solutions at ambient temperatures.

Solutions having a density in the range from 1.74 to 1.81 g/ml. containing a salt selected from the group consisting essentially of calcium chloride, calcium bromide, and mixtures thereof, and solutions having a density in the range from 1.74 to 2.30 g/mi. containing zinc bromide and a salt selected from the group consisting of calcium chloride, calcium bromide, and mixtures thereof are very difficult to viscosify at ambient temperatures. However, it has been shown in copending British patent applications No. 8101828 and 8109880, that HEC can be activated 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.

Exemplary SHP compositions useful in the present invention, as indicated in copending British Patent Application No. 8101 828 comprise: hydroxyethyl cellulose, a solvating agent comprising a water miscible, polar organic liquid which when uniformaly 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 solvating agent Preferred solvating agents are ethylene glycol, 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 1 5% to about 50% solvating agent, and from about 25% to about 70% diluting agent. Other exemplary SHP compositions which are useful in the present invention, as indicated in copending British Patent Application No. 8109880 comprise: HEC an aqueous liquid, and a water soluble organic liquid which when uniformaly mixed with the HEC in a weight ratio of HEC to organic liquid of 1:2 produces a mixture with 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-propoxyethanol, 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 1 5% to about 25% HEC, from about 1 5% to about 30% aqueous liquid, and from about 45% to about 70% of the water soluble organic liquid.

The concentration of SHP in the well servicing fluids of this invention need only be sufficient to produce a viscosity which will keep the FHP suspended and dispersed while the well servicing fluid is statically aged at an elevated temperature in a borehole. Preferably the concentration will be sufficient to impart an API apparent viscosity of at least 100 centipoise to the fluid. The maximum concentration would be limited only by the maximum viscosity of the fluid which can be pumped downhole with the existing equipment at the wellsite.

The concentration of FHP in the well servicing fluid is dependent upon the viscosity desired after the fluid has been statically aged at the elevated temperature. The more FHP in the fluid the greater will be the viscosity after hot aging. Preferably the concentration of FHP will be in the range from 1.4 to 28.5 g/litre, most preferably 2.85 to 14.25 g/litre.

It is another feature of this invention that very viscous homogeneous solutions can be obtained downhole at the desired location and prevailing temperature in a borehole 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 aqueous liquid, FHP and SHP, mixing the fluid to allow the SHP to hydrate in and viscosify the fluid sufficiently to suspend the FHP, pumping the fluid to the desired location in a borehole, and aging the fluid at the prevailing 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 aging downhole could be considered to be a viscous suspension of the hydrated polymer, and, on a microscopic 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 polymer together at room temperature for one hour; and 2. agitate the polymer containing aqueous medium overnight at a temperature in the range from 55 to 1250 C, preferably at the expected downhole temperature.

If the polymer readily viscosifies the aqueous medium at room temperature, then it can be used as a SHP. If 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 which are useful im this invention may be selected from the group consisting of other cellulose derivatives, water-dispersible starch derivatives, other polysaccharide guns, synthetic acrylic polymers and copolymers, and the like. Exemplary cellulose derivatives are the carboxyalkyl cellulose ethers, such as carboxymethyl cellulose and carboxyethyl cellulose; hydroxyalkyl cellulose ethers such as hydroxypropyl cellulose; 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 cellulose. See. U.S. Patent No.4,110,230.

Exemplary starch derivatives are the carboxyalkyl starch ethers such as carboxymethyl starch and carboxyethyl starch; hydroxyalkyl starch ethers, such as hydroxyethyl starch and hydroxypropyl starch; and mixed ethers such as: carboxyalkyl hydroxyalkyl starch i.e., carboxymethyl hydroxyethyl starch; alkyl hydroxyalkyl starch, i.e. methyl hydroxethyi starch; alkyl carboxyalkyl starch, i.e., ethylcarboxymethyl 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 derivatives thereof, particularly 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 1.70 g/ml.

containing calcium chloride, calcium bromide, or mixtures thereof.

To more fully illustrate the present invention, the following non-limiting examples are presented.

All physical 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, 1 978.

Example I An aqueous solution having a desnity of 1.80 g/ml. 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 temperature (230C). After obtaining the API rheological values the fluids were rolled at ambient temperature for 55 minutes and the API rheology evaluated. The fluids were then statically aged at 740C for 1 8 hours, cooled to room temperature, and evaluated. The data obtained are given in Table II.

The data indicate that 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 containing 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-SIL M5. The concentration given in Table II is on a 100% active HEC basis.

Table II API Rheology After 5 Minutes After 1 Hour at After 18 Hours Total on Multimixer Room Temperature at 74 OC gil. gIl. gil.

SHP FHP HEC 600 > 300 3 600 > 300 3 600 > 300 3 11.4 0 11.4 224 125 5 300 300 135 300 300 205 5.7 5.7 11.4 124 70 1.5 300 198 21 300 300 215 0 11.4 11.4 58 29 0 61 31 0 116* 68 2 *Obtained on the liquid decanted away from the large lump of HEC Example 2 An aqueous solution having a density of 1.92 g/ml. containing 37.6% calcium chloride and 62.4% zinc bromide, and 36.7% water was mixed with 8.6 gIl. of NATROSOL 250 HHR 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 solution with 2.58 gIl. of NATROSOL 250 HHR and 5.7 g/i. (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 1.34 g/ml. containing 36.6% calcium chloride and 62.4% water was mixed with the polymers indicated in Table Ill for 1 5 minutes on a Multimixer and rolled at ambient temperature for 45 minutes. After obtaining the API rheological values, the fluids were statically aged for 1 6 hours at 650C cooled to room temperature, and evaluated. The data are given in Table Ill.

The data indicate that the HEC readily viscosified this solution at ambient temperature and was an efficient SHP. The XC polymer did not viscosify this solution at ambient temperature and upon hot static aging hydrated as a mass of polymer on the bottom of the container. The well servicing fluid containing HEC and XC polymer exhibited an initial viscosity due to the hydration of the XEC and a very high viscosity after hot static aging due to combined hydration of the HEC and XC polymers.

Table Ill API Rheology SHP FHP After One Hour at After 16 Hours Room ----- Room Temperature at 65 OC gil gll NATROSOL 250 HHR XC Polymer 600 > 300 3 600 > 300 3 5.7 0 196 146 24 229 173 25 0 8.6 16 8 0 30 16 5.7 8.6 196 144 23 300 300 53

Claims

1. A well servicing fluid having a much higher viscosity when aged at an elevated temperature than it had before being aged, which comprises: (a) an aqueous solution; (b) a first hydrophilic polymer which will not increase the viscosity appreciably at ambient temperature but which will hydrate in said solution at an elevated temperature to increase the viscosity thereof; and (c) a second hydrophilic polymer in an amount sufficient to increase the viscosity of said solution at ambient temperature.

2. A well servicing fluid as claimed in claim 1 wherein the first hydrophilic polymer is XC polymer (as hereinbefore defined).

3. A well servicing fluid as claimed in claim 1 or 2 wherein the second hydrophilic polymer is hydroxyethyl cellulose.

4. A well servicing fluid as claimed in any preceding claim wherein the aqueous solution contains calcium chloride and/or calcium bromide, and has a density from 1.29 to 1.81 g/ml.

5. A well servicing fluid as claimed in any of claims 1 to 3 wherein the aqueous solution contains calcium chloride, calcium bromide, and/or zinc bromide, and has a density from 1.29 to 2.30 g/ml.

6. A well servicing fluid as claimed in claim 1 or 2 wherein the second hydrophilic polymer is hydroxyethyl cellulose which has been activated such that it will hydrate in said solution at ambient temperature.

7. A well servicing fluid as claimed in claim 6 wherein the aqueous solution contains calcium chloride, calcium bromide and/or zinc bromide, and has a density from 1.74 to 2.30 g/ml.

8. A well servicing fluid as claimed in claim 1 and substantially as hereinbefore described with reference to any of the Examples.

9. A method as claimed in Claim 8 and substantially as hereinbefore described.

9. A method of producing within a borehole a fluid as claimed in any preceding claim which comprises: (a) mixing the aqueous solution with the first and second hydrophilic polymers to allow the second hydrophilic polymer to increase the viscosity of the solution; (b) pumping the resulting solution to the desired location in a borehole; and (c) aging the solution, whereby said polymers completely hydrate, due to the borehole temperature, to produce a viscous homogeneous solution.

10. A method as claimed in claim 9 and substantially as hereinbefore described.

New Claims or Amendments to Claims filed on

10.11.81.

Superseded Claims 1 8 5.

New or Amended Claims:

1. A well servicing fluid having a much higher viscosity when aged at an elevated temperature than it had before being aged, which comprises: (a) an aqueous solution containing one or more of calcium chloride, calcium bromide, and zinc bromide, and having a density from 1.29 to 2.30 g/ml; (b) a first hydrophilic polymer which will not increase the viscosity appreciably at ambient temperature but which will hydrate in said solution at an elevated temperature to increase the viscosity thereof; and (c) a second hydrophilic polymer in an amount sufficient to increase the viscosity of said solution at ambient temperature.

5. A well servicing fluid as claimed in Claim 1 or 2 wherein the second hydrophilic polymer is hydroxyethyl cellulose which has been activated such that it will hydrate in said solution at ambient temperature.

6. A well servicing fluid as claimed in Claim 5 wherein the aqueous solution contains calcium chloride, calcium bromide and/or zinc bromide, and has a density from 1.74 to 2.30 gimp.

7. A well servicing fluid as claimed in Claim 1 and substantially as hereinbefore described with reference to any of the Examples.

8. A method of producing within a borehole a fluid as claimed in any preceding Claim which comprises: (a) mixing the aqueous solution with the first and second hydrophilic polymer to allow the second hydrophilic polymer to increase the viscosity of the solution; (b) pumping the resulting soluting to the desired location in a borehole; and (c) aging the solution, whereby said polymers completely hydrate, due to the borehole temperature, to produce a viscous homogeneous solution.