CA1058854A - Composition and method of removing scale from oil wells - Google Patents
Composition and method of removing scale from oil wellsInfo
- Publication number
- CA1058854A CA1058854A CA213,387A CA213387A CA1058854A CA 1058854 A CA1058854 A CA 1058854A CA 213387 A CA213387 A CA 213387A CA 1058854 A CA1058854 A CA 1058854A
- Authority
- CA
- Canada
- Prior art keywords
- weight percent
- scale
- alkali metal
- ammonium
- amine
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
- C02F5/08—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K8/00—Compositions for drilling of boreholes or wells; Compositions for treating boreholes or wells, e.g. for completion or for remedial operations
- C09K8/52—Compositions for preventing, limiting or eliminating depositions, e.g. for cleaning
- C09K8/528—Compositions for preventing, limiting or eliminating depositions, e.g. for cleaning inorganic depositions, e.g. sulfates or carbonates
Abstract
Abstract An aqueous alkaline solution of a chelating compound and a borate salt is used to remove water-insoluble scale deposits from an oil well bore and associated equipment.
The solution contains an effective amount of a chelating compound selected from ammonium, amine and alkali metal salts of aminopolycarboxylic acids and a synergistic borate salt selected from the group con-sisting of ammonium, amine and alkali metal borates, tetraborates and metaborates having a greater pH
than 8.
The solution contains an effective amount of a chelating compound selected from ammonium, amine and alkali metal salts of aminopolycarboxylic acids and a synergistic borate salt selected from the group con-sisting of ammonium, amine and alkali metal borates, tetraborates and metaborates having a greater pH
than 8.
Description
lOS8854 This invention is directed to the removal of calcium sulfate and/or calcium carbonate scale deposits from oil and gas wells and associated subsurface and surface equipment.
More particularly, the invention is directed to a novel composition useful in the treatment of oil and gas wells to remove accumulated water-insoluble scale deposits from the surface of subterranean rock strata, well bore casing, tubing and associated equip-ment.
In oil and gas wells, objectionable calcium sulfate deposits in the form of gypsum accumulate in the pores and channels of the fluid-producing strata and in the well bore equipment such as the tubing, screens, chokes and pumps. These gypsum deposits may also occur in oil field surface equipment including flow lines, separators, and emulsion treaters. The deposits are crystalline masses which adhere tightly to the formations and equipment and, as the masses build up, fluid flow is hindered and finally stopped.
This scale also causes many problems in oil and gas well treating operations, particularly when it builds up in the well tubing. Such scale deposits inhibit the flow of fluids such as oil, water and/or treating fluids through the piping. If left unchecked, a complete blockage of the pipe will result.
Removal of calcium sulfate from wells is difficult, particularly when the scale is in a massive, dense, impermeable form. Removal of such scale is presently accomplished by several methods including scraping and chemical treatment.
More particularly, the invention is directed to a novel composition useful in the treatment of oil and gas wells to remove accumulated water-insoluble scale deposits from the surface of subterranean rock strata, well bore casing, tubing and associated equip-ment.
In oil and gas wells, objectionable calcium sulfate deposits in the form of gypsum accumulate in the pores and channels of the fluid-producing strata and in the well bore equipment such as the tubing, screens, chokes and pumps. These gypsum deposits may also occur in oil field surface equipment including flow lines, separators, and emulsion treaters. The deposits are crystalline masses which adhere tightly to the formations and equipment and, as the masses build up, fluid flow is hindered and finally stopped.
This scale also causes many problems in oil and gas well treating operations, particularly when it builds up in the well tubing. Such scale deposits inhibit the flow of fluids such as oil, water and/or treating fluids through the piping. If left unchecked, a complete blockage of the pipe will result.
Removal of calcium sulfate from wells is difficult, particularly when the scale is in a massive, dense, impermeable form. Removal of such scale is presently accomplished by several methods including scraping and chemical treatment.
-2- ~
One chemical method involves treatment of the scale with a scale converter which converts the scale to an acid-soluble material, followed by treatment with a mineral acid such as HCl. For example, insoluble sulfate scales are generally first reacted with a converter such as a carbonate to yield a water-insoluble--acid soluble carbonate scale which is then treated with a mineral acid.
A second conventional method employs strongly caustic solutions of chelating or sequestering agents, such as ethylene~
diamine tetraacetic acid or nitrilotriacetic acid. The use of the sequestering agent is conventionally a one-step operation.
The sequestering agents act very slowly and require very high pH conditions to dissolve the scale and relatively long well shut-downs are necessary for the treating operation.
In a variation on these methods, a sulfate scale con-verting solution is used which contains a water soluble con-verting agent such as a bicarbonate for converting the scale to a more readily-ionizable form, and a chelating agent for dissolving and complexing the converted scale. Scale removal in this instance appears to be facilitated by the concurrent converting and complexing reactions and the action is somewhat improved over the action of the chelating agent alone. Ad-ditionally, at least under low pressure conditions, carbon dioxide evolution occurs, causing agitation and apparently giving a mechanical assist to the scale removal. As with the use of sequestering agents alone, this method requires opera-tion under controlled pH conditions. Additionally, where the scale converter employed is a carbonate or bicarbonate, in-creased corrosion of the iron surfaces of the casing and as-"`` 10588S4 sociated well-bore equipment may occur by way of the well-known carbonate corrosion phenomenon.
A scale removing composition for effecting a rapid removal of scale deposits formed in an oil well bore and associated equip-ment which does not require potentially hazardo~s and corrosive, strongly caustic solutions, which can be employed with less pre-:~ cise control of pH and which avoids the use of potentially cor-rosive carbonates or bicarbonates is clearly needed.
This invention may be briefly described as a composition and method useful in the removal of water-insoluble scale deposits from the surface of an oil well bore and associated well bore equipment. More particularly, the.instant composition comprises an aqueous solution of a polyaminocarboxylic acid and a borate salt which is highly effective in removing calcium sulfate de-posits such as gypsum and anhydrite from the surface of oil well tubing, casing and rock strata, as well as a method for the re-moval of scale deposits from oil wells.
The scale-removing composition of this invention generally comprises a water solution containing an effective amount of a polyaminocarboxylic acid chelating agent, a borate salt, and optionally, surfactants and freezing point depressants, which is adjusted in alkalinity to a pH above a value of 8 by addition of a suitable caustic.
In one particular aspect the present invention provides a composition useful in the removal of water-insoluble scale de-posits from an oil well b.ore and the surfaces of associated well bore equipment comprising an a~ueous solution, having a pH greater than 8, containing from about 5 to about 12 weight percent of a chelating compound selected from ammonium, amine and alkali metal salts of aminopolycarboxylic acids and from about 1 to about 5 weight percent of a borate salt selected from the group consisting of.ammonium, amine and alkali metal borates, tetra-~P
mjp/~ 4-``` 105~854 borates and metaborates.
In another aspect the present invention provides a method for removing water-insoluble scale from the surfaces contained within an oil well bore comprising contacting the sur~aces with an aqueous solution, having a pEI greater than 8, compris-ing from about 5 to about 12 weight percent of a chelating agent selected ~rom the alkali metal, amine and ammonium salts of amino polycarboxylic acids, and from about 1 to about 5 weight percent of a borate salt selected from the amine, ammon-ium and alkali metal borates, tetraborates and metaborates.
Examples of suitable polyaminocarboxylic acid chelating agents are widely known, and include alkylene diamine tetra-acetic acids such as ethylenediamine tetraacetic acid (EDTA), and aminotriacetic acids such as nitrilotriacetic acid (NTA), as well as the corresponding ammonium and alkali metal salts.
Aqueous solutions of these compounds -mjp/~ a~
alone have long been employed for scale removal.
sorate salts useful in the practice of this invention include the alkali metal tetraborate and metaborate salts.
Preferably, sodium tetraborate or the hydrated analog Na2g407. lO
H20 (borax) is employed by virtue of ready availability, however, sodium metaborate and the analogous ammonium, lithium and potassium salts are also useful in the practice of this invention.
In most instances, the solution should contain at least about 5 weight percent of the chelating compound to be effective, together with greater than about 1 weight percent of the borate salt. While increased concentration tends to promote the rate of dissolving and scale removing, the solubility of these compounds is limited, and aqueous solutions will normally contain no more than about 12 weight percent of the chelating compound and about 4 to 5 weight percent of the borate salt in dissolved form at room temperature. The preferred concentration range of each component is from about 5 weight percent to about 12 weight percent of the chelating compound and from about l weight percent to about 5 weight percent of the borate salt. Although even lower concentrations may be somewhat effective, the rate of scale dissolving and removal becomes considerably slower and therefore impractical for most purposes.
The composition of this invention is most effective in removing scale deposits when alkaline. More particularly, when the pH of the composition is above a value of about 8, and more preferably in a range of values of from about 9 to 11, the rate of scale removal is rapid and the resulting com-position is not so caustic as to present a high degree of potential danger in handling. Adjustment of the pH may be ~058854 readily accomplished by the addition of caustic. While any of the common caustics such as alkali metal oxides or ammonium or alkali metal hydroxides may be employed for this purpose, soda lye or sodium hydroxide is conveniently available and may be added either in the solid form or as a concentrated aqueous solution. The precise amount employed to produce the desired pH will of course depend upon the type and amounts of the chelating agent and borate salts.
The effectiveness of the compositions of this in-vention in dissolving and removing scale deposits is demonstrated by the test data in the Table I below. These data report the results of a series of comparative tests run with a variety of compositions and employing gypsum board samples as the test specimen. The weight of the gypsum dissolved is taken as a measure of relative effectiveness of the particular composition.
The test data in Table I were obtained by the following procedure: Squares of 1/2" gypsum board measuring approximately 1/4" x 1/4" were weighed into a 100 ml beaker, to a total sample weight of six grams. A
50 ml. portion of the "scale remover" formulation was then added to the beaker, and the beaker containing the test mixture was placed in an air oven at 100 F for 24 hours. A sheet of aluminum foil was loosely placed over the beaker to retard evaporation. The beaker was then removed from the oven and the remaining gypsum board sample was collected by filtration, washed, and then dried at 150 F. for a period of 2 to 3 hours.
The cooled sample was then reweighed to determine the weight loss. The weight loss for a series of six such tests is reported in Table I, expressed in the form lbs. of gypsum board dissolved per gallon of "scale remover" employed.
iOS8~354 The formulation for each "scale remover" is also given in Table I, where the amounts indicated are expressed in weight percent of the total formulation.
Table I. Testing of Aqueous sOrate - EDTA
Mixtures with Gypsum Board Samples TEST RUN NO.
Composition 1 2 3 4 5 6 7 EDTA (1) 10.7 1~.712.8 10.710.7 10.7 10.7 NaOH(2) 6.4 6.4 6.4 3.9 6.4 6.4 6.4 Na2B407 10H20 (3) 2.12.12.1 2.1 2.1 ---- ----H2O (4) 80.8 80.378.7 83.380.3(6)82.9 82.9 Surfactant (5) ---- 0.5 ---- ---- 0.5 ---- ----pH 12.8 11.7 9.4 7.511.6 12.8 10.7 Test Results Gypsum Board Dissolved, (lbs/gal) 0.57 0.550.55 0.100.65 0.48 0.24 ... ..
Notes: (1) EDTA = Ethylenediamine tetraacetic acid (2) NaOH = Reagent ~rade pellets
One chemical method involves treatment of the scale with a scale converter which converts the scale to an acid-soluble material, followed by treatment with a mineral acid such as HCl. For example, insoluble sulfate scales are generally first reacted with a converter such as a carbonate to yield a water-insoluble--acid soluble carbonate scale which is then treated with a mineral acid.
A second conventional method employs strongly caustic solutions of chelating or sequestering agents, such as ethylene~
diamine tetraacetic acid or nitrilotriacetic acid. The use of the sequestering agent is conventionally a one-step operation.
The sequestering agents act very slowly and require very high pH conditions to dissolve the scale and relatively long well shut-downs are necessary for the treating operation.
In a variation on these methods, a sulfate scale con-verting solution is used which contains a water soluble con-verting agent such as a bicarbonate for converting the scale to a more readily-ionizable form, and a chelating agent for dissolving and complexing the converted scale. Scale removal in this instance appears to be facilitated by the concurrent converting and complexing reactions and the action is somewhat improved over the action of the chelating agent alone. Ad-ditionally, at least under low pressure conditions, carbon dioxide evolution occurs, causing agitation and apparently giving a mechanical assist to the scale removal. As with the use of sequestering agents alone, this method requires opera-tion under controlled pH conditions. Additionally, where the scale converter employed is a carbonate or bicarbonate, in-creased corrosion of the iron surfaces of the casing and as-"`` 10588S4 sociated well-bore equipment may occur by way of the well-known carbonate corrosion phenomenon.
A scale removing composition for effecting a rapid removal of scale deposits formed in an oil well bore and associated equip-ment which does not require potentially hazardo~s and corrosive, strongly caustic solutions, which can be employed with less pre-:~ cise control of pH and which avoids the use of potentially cor-rosive carbonates or bicarbonates is clearly needed.
This invention may be briefly described as a composition and method useful in the removal of water-insoluble scale deposits from the surface of an oil well bore and associated well bore equipment. More particularly, the.instant composition comprises an aqueous solution of a polyaminocarboxylic acid and a borate salt which is highly effective in removing calcium sulfate de-posits such as gypsum and anhydrite from the surface of oil well tubing, casing and rock strata, as well as a method for the re-moval of scale deposits from oil wells.
The scale-removing composition of this invention generally comprises a water solution containing an effective amount of a polyaminocarboxylic acid chelating agent, a borate salt, and optionally, surfactants and freezing point depressants, which is adjusted in alkalinity to a pH above a value of 8 by addition of a suitable caustic.
In one particular aspect the present invention provides a composition useful in the removal of water-insoluble scale de-posits from an oil well b.ore and the surfaces of associated well bore equipment comprising an a~ueous solution, having a pH greater than 8, containing from about 5 to about 12 weight percent of a chelating compound selected from ammonium, amine and alkali metal salts of aminopolycarboxylic acids and from about 1 to about 5 weight percent of a borate salt selected from the group consisting of.ammonium, amine and alkali metal borates, tetra-~P
mjp/~ 4-``` 105~854 borates and metaborates.
In another aspect the present invention provides a method for removing water-insoluble scale from the surfaces contained within an oil well bore comprising contacting the sur~aces with an aqueous solution, having a pEI greater than 8, compris-ing from about 5 to about 12 weight percent of a chelating agent selected ~rom the alkali metal, amine and ammonium salts of amino polycarboxylic acids, and from about 1 to about 5 weight percent of a borate salt selected from the amine, ammon-ium and alkali metal borates, tetraborates and metaborates.
Examples of suitable polyaminocarboxylic acid chelating agents are widely known, and include alkylene diamine tetra-acetic acids such as ethylenediamine tetraacetic acid (EDTA), and aminotriacetic acids such as nitrilotriacetic acid (NTA), as well as the corresponding ammonium and alkali metal salts.
Aqueous solutions of these compounds -mjp/~ a~
alone have long been employed for scale removal.
sorate salts useful in the practice of this invention include the alkali metal tetraborate and metaborate salts.
Preferably, sodium tetraborate or the hydrated analog Na2g407. lO
H20 (borax) is employed by virtue of ready availability, however, sodium metaborate and the analogous ammonium, lithium and potassium salts are also useful in the practice of this invention.
In most instances, the solution should contain at least about 5 weight percent of the chelating compound to be effective, together with greater than about 1 weight percent of the borate salt. While increased concentration tends to promote the rate of dissolving and scale removing, the solubility of these compounds is limited, and aqueous solutions will normally contain no more than about 12 weight percent of the chelating compound and about 4 to 5 weight percent of the borate salt in dissolved form at room temperature. The preferred concentration range of each component is from about 5 weight percent to about 12 weight percent of the chelating compound and from about l weight percent to about 5 weight percent of the borate salt. Although even lower concentrations may be somewhat effective, the rate of scale dissolving and removal becomes considerably slower and therefore impractical for most purposes.
The composition of this invention is most effective in removing scale deposits when alkaline. More particularly, when the pH of the composition is above a value of about 8, and more preferably in a range of values of from about 9 to 11, the rate of scale removal is rapid and the resulting com-position is not so caustic as to present a high degree of potential danger in handling. Adjustment of the pH may be ~058854 readily accomplished by the addition of caustic. While any of the common caustics such as alkali metal oxides or ammonium or alkali metal hydroxides may be employed for this purpose, soda lye or sodium hydroxide is conveniently available and may be added either in the solid form or as a concentrated aqueous solution. The precise amount employed to produce the desired pH will of course depend upon the type and amounts of the chelating agent and borate salts.
The effectiveness of the compositions of this in-vention in dissolving and removing scale deposits is demonstrated by the test data in the Table I below. These data report the results of a series of comparative tests run with a variety of compositions and employing gypsum board samples as the test specimen. The weight of the gypsum dissolved is taken as a measure of relative effectiveness of the particular composition.
The test data in Table I were obtained by the following procedure: Squares of 1/2" gypsum board measuring approximately 1/4" x 1/4" were weighed into a 100 ml beaker, to a total sample weight of six grams. A
50 ml. portion of the "scale remover" formulation was then added to the beaker, and the beaker containing the test mixture was placed in an air oven at 100 F for 24 hours. A sheet of aluminum foil was loosely placed over the beaker to retard evaporation. The beaker was then removed from the oven and the remaining gypsum board sample was collected by filtration, washed, and then dried at 150 F. for a period of 2 to 3 hours.
The cooled sample was then reweighed to determine the weight loss. The weight loss for a series of six such tests is reported in Table I, expressed in the form lbs. of gypsum board dissolved per gallon of "scale remover" employed.
iOS8~354 The formulation for each "scale remover" is also given in Table I, where the amounts indicated are expressed in weight percent of the total formulation.
Table I. Testing of Aqueous sOrate - EDTA
Mixtures with Gypsum Board Samples TEST RUN NO.
Composition 1 2 3 4 5 6 7 EDTA (1) 10.7 1~.712.8 10.710.7 10.7 10.7 NaOH(2) 6.4 6.4 6.4 3.9 6.4 6.4 6.4 Na2B407 10H20 (3) 2.12.12.1 2.1 2.1 ---- ----H2O (4) 80.8 80.378.7 83.380.3(6)82.9 82.9 Surfactant (5) ---- 0.5 ---- ---- 0.5 ---- ----pH 12.8 11.7 9.4 7.511.6 12.8 10.7 Test Results Gypsum Board Dissolved, (lbs/gal) 0.57 0.550.55 0.100.65 0.48 0.24 ... ..
Notes: (1) EDTA = Ethylenediamine tetraacetic acid (2) NaOH = Reagent ~rade pellets
(3) Na2B4O7. 10H20 = Reagent grade borax
(4) H20 = deionized water
(5) Proprietary alkanolamine surfactant
(6) Tap Water The test was repeated five times with the formulation shown for Test Run No. 1. The results were reproduced within 5.0%. Similarly, five runs employing the formulation of Test Run No. 6 gave results reproduced within 3.4%.
A practical test of the instant scale solvent compositions was carried out by measuring the dissolution of actual scale samples collected from oil wells, using the procedure followed for gypsum board tests. The results of these tests are reported in Table II, and it will be apparent from a comparison of these data with the data ~d 7 1(~58854 reported in Table I that an adequate correlation of tests on gypsum board with tests on field samples is realized.
Table II. Testing of Aqueous Borate - EDTA
Mixtures with Actual Scale Samples TEST RUN NO.
Compositions 8 9 10 EDTA (1) 10.710.7 10.6 NaOH (2) (3) 6.4 4.8 4.1 Na2B4O7 10H20 2.1 3.2 5.3 H2O 80.380.7 79 5 Surfactant ( ) 0.5 0.5 0.5 pH 10.5 8.5 8.3 Test Results Scale Dissolved lbs./gal. 0.520.48 0.48 Notes: (1) Technical Grade Ethylenediamine tetraacetic acid (2) Technical Grade (3) Technical Grade (4) Tap Water (5) Proprietary alkanolamine surfactant .
It is apparent from the data of Test Runs 1-3, when compared with run 4, that an alkaline pH is necessary for effective reaction and dissolution of the gypsum board, and from Test Runs 4, 9 and 10 data that effective results are obtained above a pH of about 8. It will also be noted, when compared with Examples 6 and 7, that very high pH levels near 13 are required for solutions containing EDTA alone, but more moderate pH levels are quite effective when borax is present in the mixture. This composition is therefore particularly advantageous for field application in that a highly corrosive, strongly caustic solution is no longer necessary, thereby reducing the potential hazard to personnel, ~58854 and in addition minimizing the possibility of caustic etching and weakening of metal pipe, tanks, pumps and associated equipment.
As was said previously, the instant chelating compound--borate compositions are also desirable over the prior art mixtures containing carbonates or bicarbonates because of the reduced potential for carbonate corrosion of iron surfaces. It will also be apparent that mixing of the instant scale remover compositions to any pH value above about 8 results in an effective scale removing mixture, whereas common experience has shown that with mixtures of chelating compounds and carbonates or bicarbonates, best ~ ^
results are obtained in a narrow range near a pH of 7.5.
This provides an additional advantage in that for application in oil fields, a precise weighing of materials and measurement of pH is quite difficult to attain.
The compositions of this invention are most useful for removing calcium sulfate scale from the bore of an oil well. The following illustrative embodiment is provided to demonstrate a typical procedure to be followed and results that could be expected in such an application. 1 Scale Removal Procedure for_Oil Well Use 450 gallons of tap water are placed in a mix tank, together with 2 gallons of alkanolamide sur-factant. The mixture is then agitated while 500 lbs of technical ethylenediamine tetraacetic acid are added, followed by 100 lbs of technical borax. When the solids are dissolved, 300 lbs of technical grade flake caustic soda are added slowly with continuous mixing. After all solids are dissolved, the pH is found to be approximately 10.8. A
_g_ pre-flush of kerosene is normally employed first to clear the well fluids from the area. The treating mixture is pumped into the production tubing of the oil well to substantially fill the tubing and the casing therein below. The well is closed in and the treating solution, optionally capped by pumping in a small slug of kerosene, is allowed to stand for a period of 24 hours. The treating solution is then swabbed from the well, and the well is placed back into production.
An oil well in the San Andreas Formation near Brownfield, Texas was treated with 500 gallons of scale remover composition substantially according to the procedure above. Well production was increased by approximately 50%
as a result of this scale removing treatment.
The use of well-treating compositions in oil fields often requires the addition of surfactants such as alkanolamides, ethoxylated phenols and the like and fluid-friction reducing compounds such as polyacrylonitrile, polyethylene oxide and the like to meet practical handling requirements, for example, the reduction of interfacial tension, the emulsification of crude oil components present in the well fluid and the increase of the pumpability of the fluid. Ad-ditionally, where the well treatments are carried out under extreme weather conditions, it may be necessary to substitute a freezing point depressant such as ethylene glycol for a portion of the water. Such additions and substitutions may be made without markedly affecting the properties of the novel composition of the instant invention and so are contemplated as being within its scope.
_
A practical test of the instant scale solvent compositions was carried out by measuring the dissolution of actual scale samples collected from oil wells, using the procedure followed for gypsum board tests. The results of these tests are reported in Table II, and it will be apparent from a comparison of these data with the data ~d 7 1(~58854 reported in Table I that an adequate correlation of tests on gypsum board with tests on field samples is realized.
Table II. Testing of Aqueous Borate - EDTA
Mixtures with Actual Scale Samples TEST RUN NO.
Compositions 8 9 10 EDTA (1) 10.710.7 10.6 NaOH (2) (3) 6.4 4.8 4.1 Na2B4O7 10H20 2.1 3.2 5.3 H2O 80.380.7 79 5 Surfactant ( ) 0.5 0.5 0.5 pH 10.5 8.5 8.3 Test Results Scale Dissolved lbs./gal. 0.520.48 0.48 Notes: (1) Technical Grade Ethylenediamine tetraacetic acid (2) Technical Grade (3) Technical Grade (4) Tap Water (5) Proprietary alkanolamine surfactant .
It is apparent from the data of Test Runs 1-3, when compared with run 4, that an alkaline pH is necessary for effective reaction and dissolution of the gypsum board, and from Test Runs 4, 9 and 10 data that effective results are obtained above a pH of about 8. It will also be noted, when compared with Examples 6 and 7, that very high pH levels near 13 are required for solutions containing EDTA alone, but more moderate pH levels are quite effective when borax is present in the mixture. This composition is therefore particularly advantageous for field application in that a highly corrosive, strongly caustic solution is no longer necessary, thereby reducing the potential hazard to personnel, ~58854 and in addition minimizing the possibility of caustic etching and weakening of metal pipe, tanks, pumps and associated equipment.
As was said previously, the instant chelating compound--borate compositions are also desirable over the prior art mixtures containing carbonates or bicarbonates because of the reduced potential for carbonate corrosion of iron surfaces. It will also be apparent that mixing of the instant scale remover compositions to any pH value above about 8 results in an effective scale removing mixture, whereas common experience has shown that with mixtures of chelating compounds and carbonates or bicarbonates, best ~ ^
results are obtained in a narrow range near a pH of 7.5.
This provides an additional advantage in that for application in oil fields, a precise weighing of materials and measurement of pH is quite difficult to attain.
The compositions of this invention are most useful for removing calcium sulfate scale from the bore of an oil well. The following illustrative embodiment is provided to demonstrate a typical procedure to be followed and results that could be expected in such an application. 1 Scale Removal Procedure for_Oil Well Use 450 gallons of tap water are placed in a mix tank, together with 2 gallons of alkanolamide sur-factant. The mixture is then agitated while 500 lbs of technical ethylenediamine tetraacetic acid are added, followed by 100 lbs of technical borax. When the solids are dissolved, 300 lbs of technical grade flake caustic soda are added slowly with continuous mixing. After all solids are dissolved, the pH is found to be approximately 10.8. A
_g_ pre-flush of kerosene is normally employed first to clear the well fluids from the area. The treating mixture is pumped into the production tubing of the oil well to substantially fill the tubing and the casing therein below. The well is closed in and the treating solution, optionally capped by pumping in a small slug of kerosene, is allowed to stand for a period of 24 hours. The treating solution is then swabbed from the well, and the well is placed back into production.
An oil well in the San Andreas Formation near Brownfield, Texas was treated with 500 gallons of scale remover composition substantially according to the procedure above. Well production was increased by approximately 50%
as a result of this scale removing treatment.
The use of well-treating compositions in oil fields often requires the addition of surfactants such as alkanolamides, ethoxylated phenols and the like and fluid-friction reducing compounds such as polyacrylonitrile, polyethylene oxide and the like to meet practical handling requirements, for example, the reduction of interfacial tension, the emulsification of crude oil components present in the well fluid and the increase of the pumpability of the fluid. Ad-ditionally, where the well treatments are carried out under extreme weather conditions, it may be necessary to substitute a freezing point depressant such as ethylene glycol for a portion of the water. Such additions and substitutions may be made without markedly affecting the properties of the novel composition of the instant invention and so are contemplated as being within its scope.
_
Claims (4)
PROPERTY OF PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A composition useful in the removal of water-insoluble scale deposits from an oil well bore and the surfaces of associ-ated well bore equipment comprising an aqueous solution, having a pH greater than 8, containing from about 5 to about 12 weight percent of a chelating compound selected from ammonium, amine and alkali metal salts of aminopolycarboxylic acids and from about 1 to about 5 weight percent of a borate salt selected from the group consisting of ammonium, amine and alkali metal borates, tetraborates and metaborates.
2. The composition of claim 1 wherein the chelating agent is a sodium salt of ethylenediamine tetraacetic acid and the borate salt is borax.
3. A composition useful in the removal of water-insoluble scale deposits from an oil well bore and the surfaces of associ-ated well-bore equipment, comprising an aqueous solution, having a pH in the range 9 to 11.5, containing from about 5 weight per-cent to about 12 weight percent of a compound selected from a sodium salt of ethylenediamine tetraacetic acid and a sodium salt of nitrilotriacetic acid and from about 1 weight percent to about 5 weight percent of borate salt selected from sodium tetra-borate and borax,
4. A method for removing water-insoluble scale from the surfaces contained within an oil well bore comprising contacting the surfaces with an aqueous solution, having a pH greater than 8, comprising from about 5 to about 12 weight percent of a chelating agent selected from the alkali metal, amine and ammonium salts of amino polycarboxylic acids, and from about 1 to about 5 weight percent of a borate salt selected from the amine, ammonium and alkali metal borates, tetraborates and metaborates.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US41557373A | 1973-11-14 | 1973-11-14 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1058854A true CA1058854A (en) | 1979-07-24 |
Family
ID=23646259
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA213,387A Expired CA1058854A (en) | 1973-11-14 | 1974-11-08 | Composition and method of removing scale from oil wells |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1058854A (en) |
| GB (1) | GB1458607A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105600953A (en) * | 2015-12-22 | 2016-05-25 | 常州科威天使环保科技股份有限公司 | Non-phosphorus scale and corrosion inhibitor for recirculating cooling water system, as well as preparation method and application of non-phosphorus scale and corrosion inhibitor |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2158487B (en) * | 1984-05-11 | 1987-10-28 | Dow Chemical Co | Gelled acid composition for acidizing subterranean formations |
| US4708207A (en) * | 1985-11-21 | 1987-11-24 | Union Oil Company Of California | Scale removal treatment |
| GB201210034D0 (en) | 2012-06-07 | 2012-07-18 | Univ Leeds | A method of inhibiting scale in a geological formation |
-
1974
- 1974-11-08 CA CA213,387A patent/CA1058854A/en not_active Expired
- 1974-11-14 GB GB4934474A patent/GB1458607A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105600953A (en) * | 2015-12-22 | 2016-05-25 | 常州科威天使环保科技股份有限公司 | Non-phosphorus scale and corrosion inhibitor for recirculating cooling water system, as well as preparation method and application of non-phosphorus scale and corrosion inhibitor |
Also Published As
| Publication number | Publication date |
|---|---|
| GB1458607A (en) | 1976-12-15 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US3951827A (en) | Composition and method for removing insoluble scale deposits from surfaces | |
| US3953340A (en) | Dissolving siliceous materials with self-acidifying liquid | |
| US11149185B2 (en) | Multifunctional foaming composition with wettability modifying, corrosion inhibitory and mineral scale inhibitory/dispersants properties for high temperature and ultra high salinity | |
| Fink | Oil field chemicals | |
| US4261421A (en) | Method for selectively acidizing the less permeable zones of a high temperature subterranean formation | |
| US3828854A (en) | Dissolving siliceous materials with self-acidifying liquid | |
| US4039459A (en) | Composition and method for drilling a reservoir containing a high temperature aqueous liquid | |
| EP0130006A1 (en) | Method and composition for reducing the corrosivity of acids to ferrous metals | |
| EA012513B1 (en) | Solids-free high density brine solution for use in wellbore fluids | |
| MX2010010834A (en) | Organic corrosion inhibitor package for organic acids. | |
| US4359093A (en) | Method for enhanced oil recovery in reservoirs containing dissolved divalent metal cations | |
| US3762873A (en) | Corrosion inhibiting method using substituted succinimides | |
| JPH05208199A (en) | Method for controlling scale in device for usein stratum containing petruleum and in relation thereto | |
| WO2020205358A1 (en) | Methods of inhibiting scale with alkyl diphenyloxide sulfonates | |
| US3899293A (en) | Method for inhibiting the corrosion of iron and alloys thereof in an aqueous environment with sulfite compositions | |
| RU2581859C1 (en) | Composition for treatment of bottomhole formation zone | |
| US4203492A (en) | Method for acidizing siliceous materials contained in high temperature formations | |
| US4148360A (en) | Method for acidizing high temperature subterranean formations | |
| CA1058854A (en) | Composition and method of removing scale from oil wells | |
| US3756257A (en) | Acrylic composition for water treatment and process for making same | |
| US4096869A (en) | Formulation for the dissolution of gypsum | |
| NO161864B (en) | HIGH-DENSITY LIQUID FOR OPERATING A DRILL, AND USING THE FLUID. | |
| US3682831A (en) | Method of and composition for the prevention of scale | |
| CN109957383A (en) | A kind of preparation method for cleaning neutral spontaneous heating de-plugging scale remover for oil pipeline | |
| EP0869258A1 (en) | Method and composition for acidizing subterranean formations utilizing corrosion inhibitor intensifiers |