CA2182091C - Method for removing alkaline earth metal scale - Google Patents
Method for removing alkaline earth metal scale Download PDFInfo
- Publication number
- CA2182091C CA2182091C CA002182091A CA2182091A CA2182091C CA 2182091 C CA2182091 C CA 2182091C CA 002182091 A CA002182091 A CA 002182091A CA 2182091 A CA2182091 A CA 2182091A CA 2182091 C CA2182091 C CA 2182091C
- Authority
- CA
- Canada
- Prior art keywords
- scale
- solvent
- production tubing
- mill head
- acid
- 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 - Lifetime
Links
- 238000000034 method Methods 0.000 title claims abstract description 27
- 229910052784 alkaline earth metal Inorganic materials 0.000 title description 5
- 150000001342 alkaline earth metals Chemical class 0.000 title description 4
- 239000002904 solvent Substances 0.000 claims abstract description 36
- 238000004519 manufacturing process Methods 0.000 claims abstract description 28
- 238000003801 milling Methods 0.000 claims abstract description 12
- 230000005484 gravity Effects 0.000 claims abstract description 6
- TZCXTZWJZNENPQ-UHFFFAOYSA-L barium sulfate Inorganic materials [Ba+2].[O-]S([O-])(=O)=O TZCXTZWJZNENPQ-UHFFFAOYSA-L 0.000 claims description 20
- 239000002253 acid Substances 0.000 claims description 11
- 239000002738 chelating agent Substances 0.000 claims description 8
- -1 monocarboxylic acid anion Chemical class 0.000 claims description 8
- ZLMJMSJWJFRBEC-UHFFFAOYSA-N Potassium Chemical compound [K] ZLMJMSJWJFRBEC-UHFFFAOYSA-N 0.000 claims description 6
- 239000002245 particle Substances 0.000 claims description 6
- 229910052700 potassium Inorganic materials 0.000 claims description 6
- 239000011591 potassium Substances 0.000 claims description 6
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Natural products CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 5
- KCXVZYZYPLLWCC-UHFFFAOYSA-N EDTA Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(O)=O)CC(O)=O KCXVZYZYPLLWCC-UHFFFAOYSA-N 0.000 claims description 5
- QPCDCPDFJACHGM-UHFFFAOYSA-N N,N-bis{2-[bis(carboxymethyl)amino]ethyl}glycine Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(=O)O)CCN(CC(O)=O)CC(O)=O QPCDCPDFJACHGM-UHFFFAOYSA-N 0.000 claims description 5
- DSAJWYNOEDNPEQ-UHFFFAOYSA-N barium atom Chemical compound [Ba] DSAJWYNOEDNPEQ-UHFFFAOYSA-N 0.000 claims description 5
- 150000003839 salts Chemical class 0.000 claims description 5
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 claims description 4
- YGSDEFSMJLZEOE-UHFFFAOYSA-N salicylic acid Chemical compound OC(=O)C1=CC=CC=C1O YGSDEFSMJLZEOE-UHFFFAOYSA-N 0.000 claims description 4
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 claims description 4
- 239000007864 aqueous solution Substances 0.000 claims description 3
- UBXAKNTVXQMEAG-UHFFFAOYSA-L strontium sulfate Inorganic materials [Sr+2].[O-]S([O-])(=O)=O UBXAKNTVXQMEAG-UHFFFAOYSA-L 0.000 claims description 3
- HCWPIIXVSYCSAN-IGMARMGPSA-N Radium-226 Chemical compound [226Ra] HCWPIIXVSYCSAN-IGMARMGPSA-N 0.000 claims description 2
- 239000000203 mixture Substances 0.000 claims description 2
- 150000002762 monocarboxylic acid derivatives Chemical class 0.000 claims description 2
- FJKROLUGYXJWQN-UHFFFAOYSA-N papa-hydroxy-benzoic acid Natural products OC(=O)C1=CC=C(O)C=C1 FJKROLUGYXJWQN-UHFFFAOYSA-N 0.000 claims description 2
- 239000012857 radioactive material Substances 0.000 claims description 2
- HCWPIIXVSYCSAN-NJFSPNSNSA-N radium-228 Chemical compound [228Ra] HCWPIIXVSYCSAN-NJFSPNSNSA-N 0.000 claims description 2
- 229960004889 salicylic acid Drugs 0.000 claims description 2
- DHCDFWKWKRSZHF-UHFFFAOYSA-L thiosulfate(2-) Chemical group [O-]S([S-])(=O)=O DHCDFWKWKRSZHF-UHFFFAOYSA-L 0.000 claims description 2
- 150000001242 acetic acid derivatives Chemical class 0.000 claims 1
- 230000000630 rising effect Effects 0.000 claims 1
- 229910021653 sulphate ion Inorganic materials 0.000 abstract description 4
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 abstract description 3
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 description 9
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 6
- 239000003054 catalyst Substances 0.000 description 6
- 239000013522 chelant Substances 0.000 description 6
- 150000001768 cations Chemical class 0.000 description 4
- 229960003330 pentetic acid Drugs 0.000 description 4
- 239000000047 product Substances 0.000 description 4
- 150000001450 anions Chemical class 0.000 description 3
- 229910052788 barium Inorganic materials 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 239000012530 fluid Substances 0.000 description 3
- 235000011118 potassium hydroxide Nutrition 0.000 description 3
- 239000002244 precipitate Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- AEMRFAOFKBGASW-UHFFFAOYSA-N Glycolic acid Chemical compound OCC(O)=O AEMRFAOFKBGASW-UHFFFAOYSA-N 0.000 description 2
- 239000003125 aqueous solvent Substances 0.000 description 2
- HJMZMZRCABDKKV-UHFFFAOYSA-N carbonocyanidic acid Chemical compound OC(=O)C#N HJMZMZRCABDKKV-UHFFFAOYSA-N 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 238000005553 drilling Methods 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- CWERGRDVMFNCDR-UHFFFAOYSA-N thioglycolic acid Chemical compound OC(=O)CS CWERGRDVMFNCDR-UHFFFAOYSA-N 0.000 description 2
- 241000894006 Bacteria Species 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-M Bicarbonate Chemical compound OC([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-M 0.000 description 1
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 description 1
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 150000007513 acids Chemical class 0.000 description 1
- 230000001464 adherent effect Effects 0.000 description 1
- 229910052792 caesium Inorganic materials 0.000 description 1
- TVFDJXOCXUVLDH-UHFFFAOYSA-N caesium atom Chemical compound [Cs] TVFDJXOCXUVLDH-UHFFFAOYSA-N 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 239000001175 calcium sulphate Substances 0.000 description 1
- 235000011132 calcium sulphate Nutrition 0.000 description 1
- 239000007795 chemical reaction product Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000011284 combination treatment Methods 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- IRXRGVFLQOSHOH-UHFFFAOYSA-L dipotassium;oxalate Chemical compound [K+].[K+].[O-]C(=O)C([O-])=O IRXRGVFLQOSHOH-UHFFFAOYSA-L 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000009977 dual effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 229960004275 glycolic acid Drugs 0.000 description 1
- 239000008235 industrial water Substances 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000003891 oxalate salts Chemical class 0.000 description 1
- 235000006408 oxalic acid Nutrition 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- XAEFZNCEHLXOMS-UHFFFAOYSA-M potassium benzoate Chemical compound [K+].[O-]C(=O)C1=CC=CC=C1 XAEFZNCEHLXOMS-UHFFFAOYSA-M 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 229960001860 salicylate Drugs 0.000 description 1
- YGSDEFSMJLZEOE-UHFFFAOYSA-M salicylate Chemical compound OC1=CC=CC=C1C([O-])=O YGSDEFSMJLZEOE-UHFFFAOYSA-M 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 229910052712 strontium Inorganic materials 0.000 description 1
- 150000004764 thiosulfuric acid derivatives Chemical class 0.000 description 1
- 239000003643 water by type Substances 0.000 description 1
Classifications
-
- 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
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B37/00—Methods or apparatus for cleaning boreholes or wells
- E21B37/02—Scrapers specially adapted therefor
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B37/00—Methods or apparatus for cleaning boreholes or wells
- E21B37/06—Methods or apparatus for cleaning boreholes or wells using chemical means for preventing or limiting, e.g. eliminating, the deposition of paraffins or like substances
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Mining & Mineral Resources (AREA)
- Geology (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Environmental & Geological Engineering (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Geochemistry & Mineralogy (AREA)
- Organic Chemistry (AREA)
- Materials Engineering (AREA)
- Inorganic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- General Chemical & Material Sciences (AREA)
- Disintegrating Or Milling (AREA)
- Detergent Compositions (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
Abstract
The present invention relates to a method of removing alkaline earth sulphate scale (22) from the interior surface of downhole production tubing (16) comprising contacting the scale (22) with a solvent having a specific gravity of at least 1.2 while simultaneously milling the scale (22) with a rotating mill head (20) connected to a downhole motor.
Description
"METHOD FOR REMOVING ALKALINE EARTH METAL SCALE"
This invention relates to a method for removing alkaline earth metal scale, particularly strontium and barium sulphate scale, from the interior surface of downhole production tubing using a high specific gravity scale-removing solvent in conjunction with milling the scale with a rotating mill head connected to a downhole motor.
Many waters contain alkaline earth metal cations, such as barium, strontium, calcium, magnesium and anions, such as sulphate, bicarbonate, carbonate, phosphate and fluoride. When combinations of these anions and cations are present in concentrations which exceed the solubility product of the various species which may be formed, precipitates form until the respective solubility products are no longer exceeded. For example, when the concentrations of the barium and sulphate ions exceed the solubility product of barium sulphate, a solid phase of barium sulphate will form as a precipitate. Solubility products are exceeded for various reasons, such as evaporation of the water phase, change the pH, pressure or temperature and the introduction of additional ions which can form insoluble compounds with the ions already present in the solution.
As these reaction products precipitate on the surfaces of the water-carrying or water-containing system, they form adherent deposits or scale. Scale may prevent effective heat transfer, interfere with fluid flow, facilitate corrosive processes, or harbour bacteria. Scale is an expense problem in any industrial-water system, in production systems for oil and gas, in pulp and paper mill systems, and in other systems, causing delays and shutdowns for cleaning and removal.
In US-A-4980077, US-A-4990718, US-A-5049297 and US-A-5084105, there is disclosed a method for removing barium sulphate and other sulphate scales by a solvent comprising a combination of a chelating agent comprising a catalyst or synergist comprising polyaminopolycarboxylic acid such as EDTA
or DTPA together with anions of (1) a monocarboxylic acid such WO 95/33581 ~ ~ ~ ~ !- J ~ + PCT/US95/00525 as acetic acid, hydroxyacetic acid, mercaptoacetic acid or salicylic acid; (2) oxalates=; (3) thiosulphates or (4) ~s~ale is removed under alkaline nitriloacetic acid. The, .,: , ~t~,~
conditions, preferably at'pH values of about 8.0 to about 14.0, with best results being achieved at about pH 12. When the solvent becomes saturated with scale metal cations, the spent solvent is disposed of by re-injection into the subsurface formation or regenerated.
. It is common practice when using scale dissolvers to pump a slug or volume of solvent into the well and leave it to stand static for a long period of time. This is not effective from an economic stand point because the well must be shut in for long periods of time, resulting in loss of production. Soaking is also not an efficient method from a reaction rate standpoint.
Also, circulating scale solvent into the well bore is too costly, due to the large volume of solvent needed to fill the tubing and allow circulation.
An article by A.D.F. Brown, S.J. Merrett, and J.S. Putman, entitled "Coil-Tubing Milling/Underreaming of Barium Sulphate Scale and Scale Control in the Forties Field",published by the Society of Petroleum Engineers in 1991 discloses milling barium sulphate scale from the interior walls of downhole production tubing using coiled tubing with a downhole motor which rotates an underreamer and/or bit.
This invention provides an effective method for removing alkaline earth metal scales from the interior surface of downhole production tubing by circulating a scale-removing solvent into the production tubing while simultaneously milling the scale walls with a rotating working drill or mill head connected to a downhole motor.
According to the present invention there is provided a method for removing alkaline earth scale from the interior surface of production tubing comprising:
(a) lowering a mill head connected to a downhole motor into the production tubing to a point adjacent the scale;
(b) injecting a solvent having a specific gravity of at least 1.2 into the soaked scale in the vicinity of the mill head while simultaneously milling the scale by rotating the mill head, and (c) recovering the solvent containing dissolved scale and scale particles from the production tubing.
Preferably, the solvent is an aqueous solution having a pH
of about 8 to about 14 and comprising a chelating agent comprising a polyamino-polycarboxylic acid present in a concentration of from 0.1 M to 1.OM or salt of such an acid, and a synergist in a concentration of from 0.1 to 1.0 M to dissolve the scale.
The chelating agent and the synergist to dissolve the scale may be as disclosed in US-A-4980077. Suitable chelating agents comprise polyaminopolycarboxylic acid such as EDTA or DTPA which is intended to form a stable complex with the cation of the alkaline earth scale forming material. The chelant may be added to the solvent in the acid form or, alternatively, as a salt of the acid, preferably the potassium salt. The concentration of the chelant in the aqueous solvent should normally be in the range of 0.1 M to 1.0 M. The concentration of the catalyst or synergist in aqueous solvent will also be in the range of 0.1 M to 1.0 M. In any event the alkaline conditions used in the scale removal process will convert the free acid to the salt.
The scale generally comprises of barium, strontium or calcium sulphate and mixtures thereof; it may also comprise naturally occurring radioactive material (NORM), mainly radium 226 and radium 228.
The preferred synergist is the oxalate anion as described in US-A-4980077. The oxalate is preferably used in an amount of about, 0.1 to 1.0 M, preferably about 0.5 M, with a pH of 8.0 to 14.0, preferably 11 to 13, and most preferably 12. The desired pH value may be obtained by the addition of a base, preferably a potassium base such as caustic potash, potassium hydroxide. An alternative synergist or catalyst is a monocarboxylic acid anion, preferably salicylate, as described in US-A-5084105. The thiosulphate or nitriloacetic acid synergists are described in US-A-5049297. The amounts of the WO 95/33581 2182-0 91 PCT/US95,00525 chelant used with the monoqarbdxylic acid and other synergists are comparable to the hioVin~ts used with the oxalate synergists and comparable solution pH volume are also used, i.e. chelant and synergist concentration from 0.1 to 1.0 M, usually about 0.5 M, solution pH from 8 to 14, usually 11 to 13 and for best results, about 12.
The preferred solvents comprise about 0.1 to about 1.0 M
of ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA), or salts of these acids, as a chelant. In addition, the preferred oxalate catalyst is added to the aqueous solution in about 0.1 to about 1.0, preferably about up to 0.5 M. The pH of the solvent is then adjusted by the addition of a base to the desired value, preferably to about pH 12. We have found that it is important to avoid the use of sodium cations when operating at high pH
values, about pH 8, and instead, to use potassium or, alternatively, cesium as the cation of the scale-removing agent.
Potassium is preferred for economy as well as availability.
Thus, the normal course of making up the solvent will be to dissolve the chelant and the oxalic acid (or potassium oxalate) in the water to the desired concentration, after which a potassium base, usually potassium hydroxide is added to bring the pH to the desired value of about 12.
The mode of operation of the synergist or catalyst is not presently understood. While not desiring to be bound to a particular theory concerning the actual mechanism of its activity in converting or dissolving the scale, it is believed that adsorption of the synergist or catalyst on the barium sulphate surface may modify the surface crystal structure in such a way that the barium in the modified crystal is easily removed by the chelating agent.
The pH of the solvent is preferably maintained at pH
values of about 8.0 to about 14.0, more preferably at about 11 to 13, and most preferably about 12. The solvent is preferably brought to the specified pH by the addition of a potassium base.
The scale may be contacted with the solvent at a temperature from 25 C to 100 C.
WO 95/33581 2 182' ~ 91;
This invention relates to a method for removing alkaline earth metal scale, particularly strontium and barium sulphate scale, from the interior surface of downhole production tubing using a high specific gravity scale-removing solvent in conjunction with milling the scale with a rotating mill head connected to a downhole motor.
Many waters contain alkaline earth metal cations, such as barium, strontium, calcium, magnesium and anions, such as sulphate, bicarbonate, carbonate, phosphate and fluoride. When combinations of these anions and cations are present in concentrations which exceed the solubility product of the various species which may be formed, precipitates form until the respective solubility products are no longer exceeded. For example, when the concentrations of the barium and sulphate ions exceed the solubility product of barium sulphate, a solid phase of barium sulphate will form as a precipitate. Solubility products are exceeded for various reasons, such as evaporation of the water phase, change the pH, pressure or temperature and the introduction of additional ions which can form insoluble compounds with the ions already present in the solution.
As these reaction products precipitate on the surfaces of the water-carrying or water-containing system, they form adherent deposits or scale. Scale may prevent effective heat transfer, interfere with fluid flow, facilitate corrosive processes, or harbour bacteria. Scale is an expense problem in any industrial-water system, in production systems for oil and gas, in pulp and paper mill systems, and in other systems, causing delays and shutdowns for cleaning and removal.
In US-A-4980077, US-A-4990718, US-A-5049297 and US-A-5084105, there is disclosed a method for removing barium sulphate and other sulphate scales by a solvent comprising a combination of a chelating agent comprising a catalyst or synergist comprising polyaminopolycarboxylic acid such as EDTA
or DTPA together with anions of (1) a monocarboxylic acid such WO 95/33581 ~ ~ ~ ~ !- J ~ + PCT/US95/00525 as acetic acid, hydroxyacetic acid, mercaptoacetic acid or salicylic acid; (2) oxalates=; (3) thiosulphates or (4) ~s~ale is removed under alkaline nitriloacetic acid. The, .,: , ~t~,~
conditions, preferably at'pH values of about 8.0 to about 14.0, with best results being achieved at about pH 12. When the solvent becomes saturated with scale metal cations, the spent solvent is disposed of by re-injection into the subsurface formation or regenerated.
. It is common practice when using scale dissolvers to pump a slug or volume of solvent into the well and leave it to stand static for a long period of time. This is not effective from an economic stand point because the well must be shut in for long periods of time, resulting in loss of production. Soaking is also not an efficient method from a reaction rate standpoint.
Also, circulating scale solvent into the well bore is too costly, due to the large volume of solvent needed to fill the tubing and allow circulation.
An article by A.D.F. Brown, S.J. Merrett, and J.S. Putman, entitled "Coil-Tubing Milling/Underreaming of Barium Sulphate Scale and Scale Control in the Forties Field",published by the Society of Petroleum Engineers in 1991 discloses milling barium sulphate scale from the interior walls of downhole production tubing using coiled tubing with a downhole motor which rotates an underreamer and/or bit.
This invention provides an effective method for removing alkaline earth metal scales from the interior surface of downhole production tubing by circulating a scale-removing solvent into the production tubing while simultaneously milling the scale walls with a rotating working drill or mill head connected to a downhole motor.
According to the present invention there is provided a method for removing alkaline earth scale from the interior surface of production tubing comprising:
(a) lowering a mill head connected to a downhole motor into the production tubing to a point adjacent the scale;
(b) injecting a solvent having a specific gravity of at least 1.2 into the soaked scale in the vicinity of the mill head while simultaneously milling the scale by rotating the mill head, and (c) recovering the solvent containing dissolved scale and scale particles from the production tubing.
Preferably, the solvent is an aqueous solution having a pH
of about 8 to about 14 and comprising a chelating agent comprising a polyamino-polycarboxylic acid present in a concentration of from 0.1 M to 1.OM or salt of such an acid, and a synergist in a concentration of from 0.1 to 1.0 M to dissolve the scale.
The chelating agent and the synergist to dissolve the scale may be as disclosed in US-A-4980077. Suitable chelating agents comprise polyaminopolycarboxylic acid such as EDTA or DTPA which is intended to form a stable complex with the cation of the alkaline earth scale forming material. The chelant may be added to the solvent in the acid form or, alternatively, as a salt of the acid, preferably the potassium salt. The concentration of the chelant in the aqueous solvent should normally be in the range of 0.1 M to 1.0 M. The concentration of the catalyst or synergist in aqueous solvent will also be in the range of 0.1 M to 1.0 M. In any event the alkaline conditions used in the scale removal process will convert the free acid to the salt.
The scale generally comprises of barium, strontium or calcium sulphate and mixtures thereof; it may also comprise naturally occurring radioactive material (NORM), mainly radium 226 and radium 228.
The preferred synergist is the oxalate anion as described in US-A-4980077. The oxalate is preferably used in an amount of about, 0.1 to 1.0 M, preferably about 0.5 M, with a pH of 8.0 to 14.0, preferably 11 to 13, and most preferably 12. The desired pH value may be obtained by the addition of a base, preferably a potassium base such as caustic potash, potassium hydroxide. An alternative synergist or catalyst is a monocarboxylic acid anion, preferably salicylate, as described in US-A-5084105. The thiosulphate or nitriloacetic acid synergists are described in US-A-5049297. The amounts of the WO 95/33581 2182-0 91 PCT/US95,00525 chelant used with the monoqarbdxylic acid and other synergists are comparable to the hioVin~ts used with the oxalate synergists and comparable solution pH volume are also used, i.e. chelant and synergist concentration from 0.1 to 1.0 M, usually about 0.5 M, solution pH from 8 to 14, usually 11 to 13 and for best results, about 12.
The preferred solvents comprise about 0.1 to about 1.0 M
of ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA), or salts of these acids, as a chelant. In addition, the preferred oxalate catalyst is added to the aqueous solution in about 0.1 to about 1.0, preferably about up to 0.5 M. The pH of the solvent is then adjusted by the addition of a base to the desired value, preferably to about pH 12. We have found that it is important to avoid the use of sodium cations when operating at high pH
values, about pH 8, and instead, to use potassium or, alternatively, cesium as the cation of the scale-removing agent.
Potassium is preferred for economy as well as availability.
Thus, the normal course of making up the solvent will be to dissolve the chelant and the oxalic acid (or potassium oxalate) in the water to the desired concentration, after which a potassium base, usually potassium hydroxide is added to bring the pH to the desired value of about 12.
The mode of operation of the synergist or catalyst is not presently understood. While not desiring to be bound to a particular theory concerning the actual mechanism of its activity in converting or dissolving the scale, it is believed that adsorption of the synergist or catalyst on the barium sulphate surface may modify the surface crystal structure in such a way that the barium in the modified crystal is easily removed by the chelating agent.
The pH of the solvent is preferably maintained at pH
values of about 8.0 to about 14.0, more preferably at about 11 to 13, and most preferably about 12. The solvent is preferably brought to the specified pH by the addition of a potassium base.
The scale may be contacted with the solvent at a temperature from 25 C to 100 C.
WO 95/33581 2 182' ~ 91;
In a preferred embodiment the downhole motor is connected to coiled tubing extended downhole inside the production tubing and the solvent is injected into the interior surface of the production tubing containing scale via the coiled tubing and mill head.
It is preferred that, prior to step (b), the solvent is injected into the scale in the vicinity of the millhead and allowed to soak into the scale.
. Reference is now made to the accompanying drawing, which is a schematic illustration of a method in accordance with this invention in which scale deposits are removed from the interior surface of downhole production tubing by contacting the scale with a solvent while simultaneously milling the scale walls with a rotating working drill or mill head connected to a downhole motor.
In the drawing a permeable subterranean formation 10 is penetrated by the borehole of a well 12. The well contains a perforated casing 14. A production tubing 16 extends inside casing 14 to a point near the bottom of the oil formation 10.
Coiled tubing 18 is pushed down inside the production tubing 16 onto which is attached a working drill or mill head 20 connected to a downhole motor (not shown). The drill or mill head 20 is rotated by the electric downhole motor attached to the coiled tubing 18.
During production operations, barium sulphate scale 22 forms on the interior surface of the production tubing 16. Once the scale 22 forms sufficiently to reduce production of the well the well is shut in and coiled tubing 18 with the working drill or mill head 20 is lowered into the production tubing 16 to a point adjacent the scale. Suitable coil tubing is disclosed in an article by Martyn Beardsell, Mark Corrigan and Ken Newman, entitled "The Coiled Tubing Revolution", published by Reservoir Engineering.
A scale-removing solvent having a specific gravity of at least 1.2 is injected into the interior surface walls of the production tubing 16 containing the scale 22 from the bottom of mill head 20 via the coiled tubing while simultaneously milling WO 95/33581 218 21) e71 PCT/U895,00525 the barium sulphate scale by the'-rotating mill head 20. The scale 22 is dissolved %n~b' the solvent and the solvent containing dissolved scale flows upward via the tubing annulus 24 and is carried to the top of the well for recovery. The solvent plays a dual role in the well: f irst, as a cooling ti fluid for the mechanical drill, and secondly as an efficient solvent for the milled scale cuttings released into the fluid.
Some other advantages of the combination treatment includes: softening very hard scale before drilling, increased bit life, prevention of scale sloughing into the well and possible tool sticking, increased scale dissolution and removal of solids by circulation. The high specific gravity of the solvent also enhances the removal, by circulation, of heavy scale particles that are released by milling/drilling.
Softening the scale before milling is also advantageous in order to prevent damage to downhole equipment, such as plugs and equipment, by milling over shots.
It is preferred that, prior to step (b), the solvent is injected into the scale in the vicinity of the millhead and allowed to soak into the scale.
. Reference is now made to the accompanying drawing, which is a schematic illustration of a method in accordance with this invention in which scale deposits are removed from the interior surface of downhole production tubing by contacting the scale with a solvent while simultaneously milling the scale walls with a rotating working drill or mill head connected to a downhole motor.
In the drawing a permeable subterranean formation 10 is penetrated by the borehole of a well 12. The well contains a perforated casing 14. A production tubing 16 extends inside casing 14 to a point near the bottom of the oil formation 10.
Coiled tubing 18 is pushed down inside the production tubing 16 onto which is attached a working drill or mill head 20 connected to a downhole motor (not shown). The drill or mill head 20 is rotated by the electric downhole motor attached to the coiled tubing 18.
During production operations, barium sulphate scale 22 forms on the interior surface of the production tubing 16. Once the scale 22 forms sufficiently to reduce production of the well the well is shut in and coiled tubing 18 with the working drill or mill head 20 is lowered into the production tubing 16 to a point adjacent the scale. Suitable coil tubing is disclosed in an article by Martyn Beardsell, Mark Corrigan and Ken Newman, entitled "The Coiled Tubing Revolution", published by Reservoir Engineering.
A scale-removing solvent having a specific gravity of at least 1.2 is injected into the interior surface walls of the production tubing 16 containing the scale 22 from the bottom of mill head 20 via the coiled tubing while simultaneously milling WO 95/33581 218 21) e71 PCT/U895,00525 the barium sulphate scale by the'-rotating mill head 20. The scale 22 is dissolved %n~b' the solvent and the solvent containing dissolved scale flows upward via the tubing annulus 24 and is carried to the top of the well for recovery. The solvent plays a dual role in the well: f irst, as a cooling ti fluid for the mechanical drill, and secondly as an efficient solvent for the milled scale cuttings released into the fluid.
Some other advantages of the combination treatment includes: softening very hard scale before drilling, increased bit life, prevention of scale sloughing into the well and possible tool sticking, increased scale dissolution and removal of solids by circulation. The high specific gravity of the solvent also enhances the removal, by circulation, of heavy scale particles that are released by milling/drilling.
Softening the scale before milling is also advantageous in order to prevent damage to downhole equipment, such as plugs and equipment, by milling over shots.
Claims (15)
1. A method of removing alkaline earth scale from the interior surface of production tubing in a well, said method comprising:
(a) lowering a mill head connected to a downhole motor into the production tubing to a point adjacent the scale and milling the scale by rotating the mill head to produce scale particles;
(b) injecting a solvent comprising an aqueous solution having a specific gravity of at least 1.2, a pH of about 8 to about 14 and comprising a chelating agent comp[rising a polyaminopolycarboxylic acid or salt of such an acid present in a concentration of from 0.1M to 1.0M, and a synergist in a concentration of from 0.1 to 1.0M into the scale in the vicinity of the rotating mill head to dissolve the scale from the production tubing, dissolve scale particles produced by the mill head, remove undissolved scale particles to the top of the well; and (c) recovering the solvent containing dissolved scale and undissolved scale particles from the production tubing.
(a) lowering a mill head connected to a downhole motor into the production tubing to a point adjacent the scale and milling the scale by rotating the mill head to produce scale particles;
(b) injecting a solvent comprising an aqueous solution having a specific gravity of at least 1.2, a pH of about 8 to about 14 and comprising a chelating agent comp[rising a polyaminopolycarboxylic acid or salt of such an acid present in a concentration of from 0.1M to 1.0M, and a synergist in a concentration of from 0.1 to 1.0M into the scale in the vicinity of the rotating mill head to dissolve the scale from the production tubing, dissolve scale particles produced by the mill head, remove undissolved scale particles to the top of the well; and (c) recovering the solvent containing dissolved scale and undissolved scale particles from the production tubing.
2. A method according to claim 1 wherein the chelating agent comprises DTPA.
3. A method according to claim 1 wherein the chelating agent comprises EDTA.
4. A method according to any one of claims 1, 2 or 3, wherein the scale comprises one of barium, strontium or calcium sulfate and mixtures thereof.
5. A method according to claim 4, wherein scale comprises a naturally occurring radioactive material (NORM) defined as comprising radium 226 and radium 228.
6. A method according to any one of claims 1 to 5, wherein the synergist comprises a monocarboxylic acid anion.
7. A method according to claim 6, wherein the monocarboxylic acid is salicylic acid or a substituted acetic acid.
8. A method according to any one of claims 1 to 5, wherein the synergist comprises oxalate anion.
9. A method according to any one of claims 1 to 5, wherein the synergist is selected from thiosulfate and nitriloacetate anions.
10. A method according to any one of claim 1 to 9, wherein the pH of the solvent is about 12.
11. A method according to any one of claims 1 to 10, wherein the solvent is brought to the pH of about 8 to about 14 by the addition of a potassium base.
12. A method according to claim 1 in which the scale is contacted with the solvent at a temperature from 25°C to 100°C.
13. The method according to any one of claims 1 to 12, wherein the downhole motor is connected to coiled tubing extended downhole inside the production tubing and the solvent is injected into the interior surface of the production tubing containing scale via the coiled tubing and mill head.
14. The method according to any one of claims 1 to 13, wherein prior to step (b) the solvent is injected into the scale in the vicinity of the millhead and allowed to soak into the scale.
15. The method of claim 1, wherein solvent is injected into the production tubing and allowed to soak into the scale prior to lowering the mill head into the production tubing.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US08/254,334 US5415696A (en) | 1993-07-26 | 1994-06-06 | Method for removing alkaline sulfate scale in downhole tubulars |
US08/254,334 | 1994-06-06 | ||
PCT/US1995/000525 WO1995033581A1 (en) | 1994-06-06 | 1995-01-13 | Method for removing alkaline earth metal scale |
Publications (2)
Publication Number | Publication Date |
---|---|
CA2182091A1 CA2182091A1 (en) | 1995-12-14 |
CA2182091C true CA2182091C (en) | 2007-05-15 |
Family
ID=26789460
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
CA002182091A Expired - Lifetime CA2182091C (en) | 1994-06-06 | 1995-01-13 | Method for removing alkaline earth metal scale |
Country Status (2)
Country | Link |
---|---|
CA (1) | CA2182091C (en) |
NO (1) | NO311904B1 (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN113020127B (en) * | 2021-02-07 | 2022-12-30 | 广东艾普升智能装备有限公司 | Machine tool gap rust removal protection device |
-
1995
- 1995-01-13 CA CA002182091A patent/CA2182091C/en not_active Expired - Lifetime
-
1996
- 1996-09-19 NO NO19963937A patent/NO311904B1/en not_active IP Right Cessation
Also Published As
Publication number | Publication date |
---|---|
NO311904B1 (en) | 2002-02-11 |
CA2182091A1 (en) | 1995-12-14 |
NO963937D0 (en) | 1996-09-19 |
NO963937L (en) | 1996-09-19 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US5183112A (en) | Method for scale removal in a wellbore | |
US7470330B2 (en) | Method for dissolving oilfield scale | |
US5685918A (en) | Composition for removing scale | |
US20070213233A1 (en) | Diverting compositions, fluid loss control pills, and breakers thereof | |
CA2624791C (en) | A process for consolidating a formation | |
US5084105A (en) | Sulfate scale dissolution | |
CA3016099A1 (en) | Composition useful in sulfate scale removal | |
EP0663510A2 (en) | Sulfate scale dissolution | |
US4485874A (en) | Method for scale removal and scale inhibition in a well penetrating a subterranean formation | |
US11655411B2 (en) | Thermochemical composition for well cleanup | |
EP0764061B1 (en) | Method for removing alkaline earth metal scale | |
US4495996A (en) | Method for scale removal and scale inhibition in a well penetrating a subterranean formation | |
US5026481A (en) | Liquid membrane catalytic scale dissolution method | |
CA2182091C (en) | Method for removing alkaline earth metal scale | |
EP0772696B1 (en) | Method for removing alkaline sulfate scale | |
US5366016A (en) | Use of variable density carrier fluids to improve the efficiency of scale dissolution | |
US5068042A (en) | Dissolution of sulfate scales | |
WO1993024199A1 (en) | Method for removing alkaline sulfate scale | |
WO1995003140A1 (en) | Method for removing alkaline earth scale from the interior surface of production tubing | |
RU2232879C1 (en) | Method for processing of formation face zone | |
EP0447120B1 (en) | A liquid membrane catalytic scale dissolution method | |
CA1216516A (en) | Method for scale removal and scale inhibition in a well penetrating a subterranean formation |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
EEER | Examination request | ||
MKEX | Expiry |
Effective date: 20150113 |