US3865435A - Stimulation of recovery from underground deposits - Google Patents
Stimulation of recovery from underground deposits Download PDFInfo
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- US3865435A US3865435A US422233A US42223373A US3865435A US 3865435 A US3865435 A US 3865435A US 422233 A US422233 A US 422233A US 42223373 A US42223373 A US 42223373A US 3865435 A US3865435 A US 3865435A
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- 238000011084 recovery Methods 0.000 title description 9
- 230000000638 stimulation Effects 0.000 title description 7
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 claims abstract description 57
- 239000003381 stabilizer Substances 0.000 claims abstract description 21
- 230000015572 biosynthetic process Effects 0.000 claims description 44
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 42
- 239000010949 copper Substances 0.000 claims description 42
- 229910052802 copper Inorganic materials 0.000 claims description 41
- 238000000034 method Methods 0.000 claims description 31
- 238000002386 leaching Methods 0.000 claims description 13
- DVRDHUBQLOKMHZ-UHFFFAOYSA-N chalcopyrite Chemical compound [S-2].[S-2].[Fe+2].[Cu+2] DVRDHUBQLOKMHZ-UHFFFAOYSA-N 0.000 claims description 12
- 229910052951 chalcopyrite Inorganic materials 0.000 claims description 12
- 238000011065 in-situ storage Methods 0.000 claims description 8
- NIFIFKQPDTWWGU-UHFFFAOYSA-N pyrite Chemical compound [Fe+2].[S-][S-] NIFIFKQPDTWWGU-UHFFFAOYSA-N 0.000 claims description 5
- 229910052683 pyrite Inorganic materials 0.000 claims description 5
- 239000011028 pyrite Substances 0.000 claims description 5
- YDONNITUKPKTIG-UHFFFAOYSA-N [Nitrilotris(methylene)]trisphosphonic acid Chemical group OP(O)(=O)CN(CP(O)(O)=O)CP(O)(O)=O YDONNITUKPKTIG-UHFFFAOYSA-N 0.000 claims description 4
- 150000002903 organophosphorus compounds Chemical group 0.000 claims description 4
- 239000002244 precipitate Substances 0.000 claims description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- 239000003795 chemical substances by application Substances 0.000 claims description 3
- 238000011068 loading method Methods 0.000 claims description 3
- 150000003839 salts Chemical class 0.000 claims description 3
- 150000001875 compounds Chemical class 0.000 claims description 2
- 230000006872 improvement Effects 0.000 claims description 2
- 230000035699 permeability Effects 0.000 abstract description 11
- 230000004936 stimulating effect Effects 0.000 abstract description 3
- 238000005755 formation reaction Methods 0.000 description 36
- 239000000243 solution Substances 0.000 description 28
- 230000008569 process Effects 0.000 description 14
- 238000002347 injection Methods 0.000 description 11
- 239000007924 injection Substances 0.000 description 11
- 238000005065 mining Methods 0.000 description 11
- 239000002360 explosive Substances 0.000 description 9
- 229910052500 inorganic mineral Inorganic materials 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 8
- 239000011707 mineral Substances 0.000 description 8
- RUTXIHLAWFEWGM-UHFFFAOYSA-H iron(3+) sulfate Chemical compound [Fe+3].[Fe+3].[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O.[O-]S([O-])(=O)=O RUTXIHLAWFEWGM-UHFFFAOYSA-H 0.000 description 6
- 229910000360 iron(III) sulfate Inorganic materials 0.000 description 6
- 239000011435 rock Substances 0.000 description 5
- 229910001779 copper mineral Inorganic materials 0.000 description 4
- 238000000354 decomposition reaction Methods 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 3
- 239000012530 fluid Substances 0.000 description 3
- 239000011800 void material Substances 0.000 description 3
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 description 2
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- 241000184339 Nemophila maculata Species 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 230000015556 catabolic process Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000005474 detonation Methods 0.000 description 2
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 2
- 238000009533 lab test Methods 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 238000012935 Averaging Methods 0.000 description 1
- QPLDLSVMHZLSFG-UHFFFAOYSA-N Copper oxide Chemical class [Cu]=O QPLDLSVMHZLSFG-UHFFFAOYSA-N 0.000 description 1
- 229940120146 EDTMP Drugs 0.000 description 1
- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 229910052770 Uranium Inorganic materials 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 230000003197 catalytic effect Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- ARUVKPQLZAKDPS-UHFFFAOYSA-L copper(II) sulfate Chemical compound [Cu+2].[O-][S+2]([O-])([O-])[O-] ARUVKPQLZAKDPS-UHFFFAOYSA-L 0.000 description 1
- 229910000366 copper(II) sulfate Inorganic materials 0.000 description 1
- OMZSGWSJDCOLKM-UHFFFAOYSA-N copper(II) sulfide Chemical compound [S-2].[Cu+2] OMZSGWSJDCOLKM-UHFFFAOYSA-N 0.000 description 1
- 229940090960 diethylenetriamine pentamethylene phosphonic acid Drugs 0.000 description 1
- DUYCTCQXNHFCSJ-UHFFFAOYSA-N dtpmp Chemical compound OP(=O)(O)CN(CP(O)(O)=O)CCN(CP(O)(=O)O)CCN(CP(O)(O)=O)CP(O)(O)=O DUYCTCQXNHFCSJ-UHFFFAOYSA-N 0.000 description 1
- NFDRPXJGHKJRLJ-UHFFFAOYSA-N edtmp Chemical compound OP(O)(=O)CN(CP(O)(O)=O)CCN(CP(O)(O)=O)CP(O)(O)=O NFDRPXJGHKJRLJ-UHFFFAOYSA-N 0.000 description 1
- 230000002708 enhancing effect Effects 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 239000010931 gold Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 229910001608 iron mineral Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 239000011733 molybdenum Substances 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000000644 propagated effect Effects 0.000 description 1
- 230000001902 propagating effect Effects 0.000 description 1
- 239000004405 propyl p-hydroxybenzoate Substances 0.000 description 1
- 238000005086 pumping Methods 0.000 description 1
- 230000008929 regeneration Effects 0.000 description 1
- 238000011069 regeneration method Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 150000004760 silicates Chemical class 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- -1 temperature Substances 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- DNYWZCXLKNTFFI-UHFFFAOYSA-N uranium Chemical compound [U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U][U] DNYWZCXLKNTFFI-UHFFFAOYSA-N 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
- C09K8/60—Compositions for stimulating production by acting on the underground formation
- C09K8/62—Compositions for forming crevices or fractures
- C09K8/72—Eroding chemicals, e.g. acids
- C09K8/74—Eroding chemicals, e.g. acids combined with additives added for specific purposes
-
- 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
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/28—Dissolving minerals other than hydrocarbons, e.g. by an alkaline or acid leaching agent
Definitions
- This invention relates to the treatment of underground deposit-bearing formations. More particularly, it relates to an improved method for fracturing such underground formations to enhance or stimulate the recovery of the desired deposits therefrom.
- explosives implanted in crevices, cracks, or fissures are common in mining and quarrying operations. Such explosives have included both solid and liquid-type explosives.
- the detonation of an explosive device or materials in a well-bore to achieve explosive fracturing of the surrounding formation suffers from the same disadvatange noted above with respect to hydrofracturing operations, namely the difficulty of propagating the fracture at increasing distances from the injection well-bore.
- Explosive fracturing by the detonation of an explosive device in a well-bore also requires a subsequent clean up operation before recovery of operations can be begun at that wellsite, increasing both the time and expense involved in such a treating action. Explosive fracturing also presents numerous safety problems; it has been experienced in the past that several people have been killed in conjunction with the utilization of explosives for carrying out the desired end result; i.e., fracturing-underground formations.
- the objects of the present invention are accomplished by a process in which prior to any hydrometallurgical operation being conducted on the underground deposits, there is injected into the formation, via the wellbore, an aqueous hydrogen peroxide solution containing a stabilizing agent therefor. It has unexpectedly been found that the utilization of a stabilized aqueous hydrogen peroxide solution functions in such a manner, hereinafter described, to uniformly open up fractures and stimulate the underground formation.
- the stabilized aqueous hydrogen peroxide solution penetrates even the smallest fractures, for example, 1/32 of an inch or less, in all directions from the well-bore due to the solutions flow characteristics.
- the stabilized hydrogen peroxide solution comes into contact with metal values in the formation such as iron and copper values, the metal values react with the stabilizing agent in the hydrogen peroxide solution and there results a precipitation of the stabilizing agent from the solution.
- the stabilizing agent After the stabilizing agent has precipitated from the hydrogen peroxide solution, the hydrogen peroxide then undergoes rapid decomposition to form a gaseous medium which has a pressure greater than the formation breakdown pressure. Consequently, additional fractures are created in addition to the enlargement of the present fractures.
- the hydrogen peroxide solution which contains a stabilizing agent therefor is an aqueous solution containing from about 30 percent to about 98 percent by weight, based on the total weight of the solution, hydrogen peroxide. Lower concentrations of hydrogen peroxide can be utilized; however, it has been found that it is more desirable and effective to utilize a hydrogen peroxide solution containing at least 30 percent by weight hydrogen peroxide therein.
- the hydrogen peroxide solution also is desirably at a pH of less than 6.0 and preferably at a pH of about 4.0 or lower.
- the pH of the hydrogen peroxide solution When it is required to adjust the pH of the hydrogen peroxide solution, this may be accomplished by the addition thereto of an acid such as sulfuric acid, nitric acid, phosphoric acid, and acetic acid in any amount required to obtain the desired end pH value.
- an acid such as sulfuric acid, nitric acid, phosphoric acid, and acetic acid in any amount required to obtain the desired end pH value.
- the temperature of the overall hydrogen peroxide solution is initially at ambient temperature; however, temperatures of about 20 to about C can be used where one so desires.
- the critical feature in the present invention relates to the utilization of a stabilizing agent with the hydrogen peroxide solution.
- a stabilizing agent is the safety feature in conjunction with the use of the hydrogen peroxide solution per se.
- the stabilizing agent thus provides a safe period of time during which hydrogen peroxide is pumped through the well-bore into the fractures surrounding the well-bore. Thus the possibility of a blow-back" through the well-bore is substantially reduced.
- the stabilizing agent is any material which is slowly precipitated out of solution by metal values in the formation.
- the material is an organophosphorus compound such as amino trimethylene phosphonic acid, ethylene diamine tetramethylene phosphonic acid, diethylene triamine pentamethylene phosphonic acid and the like and water soluble salts thereof. It is to be understood that other organophosphorus compounds can be used as long as they function in the required manner.
- the processes of the present invention are particularly effective in conjunction with the in-situ mining of underground formations which contain copper metal values in the form of chalcopyrite and pyrite ores. It has been found that the uniform stimulation of a low permeability deposit is an important factor for an economically viable in-situ mining operation. In the particular case relating to the underground (or solution) mining of chalcopyrite and pyrite ores, this uniform stimulation permits the leaching solvent to contact more of the copper minerals, thus increasing both the leach efficiency and copper loadings. Both of these parameters are critical for economically mining deep-lying low grade copper ores by in-situ mining techniques.
- the process comprises the steps wherein the aqueous hydrogen peroxide solution, containing the stabilizing agent therein, is pumped down a well and allowed to flow into the deposit.
- the hydrogen peroxide flows or diffuses into small fractures (or pores) where it comes into contact with copper and iron minerals, together with other minerals present in the formation.
- the stabilizing agent contained in said solution is precipitated out leaving the hydrogen peroxide in an unstabilized condition.
- the hydrogen peroxide then decomposes because of the catalytic action of the chalcopyrite and pyrite thereon, the rate of decomposition being a function of the minerals contacted, the solid exposed surface area in contact with the hydrogen peroxide, temperature, additives present in the hydrogen peroxide, strength of hydrogen peroxide solution and the like.
- a large gas pressure is built up and when this pressure exceeds the parting pressure of the formation, fracturing or stimulation occurs. It has been found that because of the rapid decomposition of the hydrogen peroxide, the fracturing or stimulation is conducted in a uniform, radial manner and at substantial distances from the well-bore due to the good penetration of the hydrogen peroxide into the smallest of fractures.
- the copper leaching solution is injected in order to subsequently recover the copper values.
- the copper leaching procedures can be carried out in any manner known to those skilled in the art of in-situ mining such as those procedures described in U.S. Pat. No. 3,574,599, U.S. Pat. No. 3,640,579, and U.S. Pat. No. 3,708,206, all of which publications are incorporated herein by reference.
- the hydrogen peroxide solution can be used at any time where one so desires.
- the solution is used as a pretreatment of the formation or deposit.
- said solution can be employed where deposits have already been subjected to hydrometallurgical operations.
- EXAMPLE I An ore body acres in area and averaging 1,000 feet in thickness lies at an average depth of 4,000 feet below the surface of the earth in Arizona. Samples of the ore show that it is composed primarily of granitic igneous rock and that it contains chalcopyrite as the principal copper mineral. The ore samples also show that it contains approximately 1.4 weight percent chalcopyrite and that the total copper content ofthe ore averages 0.5 percent. The volume of ore in the deposit is, therefore 10 acre-feet or 4.356 X 10 cubic feet. The specific gravity of the granitic ore is 2.6. Therefore, the total weight of the ore in the deposit is 3.54 X 10 tons, and the copper content of the ore body is 3.54 X 10 pounds.
- Approximately 50 wells are drilled into the ore body in an array such as to provide a five-spot pattern, and the wells are completed such that fluids may be either injected or produced from individual wells.
- the void volume within the randomly oriented fracture system is equivalent to 2 percent of the bulk ore volume, that the fracture spacing averages 6 inches, and that the permeability of the ore body to liquid averages less than about 2 millidarcys. This permeability is less than desired for economic recovery of copper.
- Petrographic examination of core samples taken from the ore body shows that about 2 percent of the rock surface area exposed by the fractures is covered by the chalcopyrite mineral and that the rock matrix bounded by the fracture system is substantially cubical in configuration.
- the surface-to-volume ratio of the ore blocks bounded by the fractures is approximately equal to that for cubically shaped blocks and the surface area to volume ratio for the ore blocks is equal to 6/L, where L is the length of the side of a cube. In this case L 0.5 feet, and the surface area to volume ratio is equal to 12 square feet/cubic foot.
- the total surface area of ore exposed by the fracture network is equal to 12 X 4.36 X or 5.227 X 10 square feet.
- the surface area of the chalcopyrite mineral exposed by the fracture system is equal to 2 percent of the total surface area, or 1.045 X 10 square feet.
- the 0.4 molar ferric sulfate solution in order to supply 0.4 molar ferric sulfate solution to the ore body at the optimum rate; i.e., at the rate sufficient to produce the maximum amount of copper and at the same time allow total reaction of the ferric iron, the 0.4 molar ferric sulfate solution must be injected initially at a rate equal to 69,700 barrels/day.
- the required average residence time for the solution within the ore body is fixed by the injection rate and the void volume of the ore body;
- the hydrogen peroxide solution containing the stabilizer is used to increase the permeability to the economical range.
- the wells are operated for a sufficient period of time to reach equilibrium and the copper produced averages about 187,000 pounds per day.
- Example I has been described as applicable to the copper sulfide ores, it should be understood that the process is also applicable to ores bearing native copper and also to ores of copper oxides and silicates where the copper is present in the cuprous valence state.
- the copper is present in its elemental or lower valence state, it is susceptible to oxidation by ferric iron to form solutions of cupric sulfate.
- the leach solution will be injected through a well, permitted to remain in contact with the ore body for a period of time, and then withdrawn through the same well.
- the pregnant leach solution is then passed to a copper recovery stage, a regeneration stage and ultimately reinjected.
- the improvement which comprises the step of prior to contacting said copper-containing formation with said leaching solution, the formation is contacted with an aqueous hydrogen peroxide solution containing a stabilizing agent therefor and whereby said agent reacts with the copper-containing formation to form a precipitate and the resultant substantially unstabilized hydrogen peroxide decomposes to form a gaseous medium which causes additional fracturing of the formation whereby greater leaching efficiency and copper loading is achieved with the subsequent copper leaching step.
- concentration of the hydrogen peroxide in solution is from about 30 percent to about 98 percent, by weight, based on the total weight of said solution and the pH of said solution is less than about 6.0.
- the stabilizing agent is an organophosphorus compound which precipitates out of said solution when said compound comes into contact with the copper-containing formation.
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Abstract
Uniform stimulating of a low permeability deposit by the use of a hydrogen peroxide solution containing a stabilizer therefor.
Description
United States Patent Sareen et al.
STIMULATION OF RECOVERY FROM UNDERGROUND DEPOSITS Inventors: 'Sarvajit S. Sareen, 24 Concord Ave., Cambridge, Mass. 02138; Lucien Girard, III, Prescott Rd., Boxboro, Mass. 01719; Robert A. Hard, Still River, Mass. 01467 Filed: Dec. 6, 1973 Appl. No.: 422,233
US. Cl 299/5, 166/307, 166/309, 252/8.55 R
Int. Cl. E216 41/06 Field of Search 166/307, 308, 309, 270, 166/271; 299/5, 4, 3; 252/855 R; 423/273 References Cited UNITED STATES PATENTS 8/1951 Scott 299/5 Primary Examiner-Ernest R. Purser Assistant Examiner-William F. Pate, 111
Attorney, Agent, or FirmLowe11 H. McCarter; John L. Sniado; James .1. Mullen [57] ABSTRACT Uniform stimulating of a low permeability deposit by the use of a hydrogen peroxide solution containing a stabilizer therefor.
5 Claims, N0 Drawings STIMULATION OF RECOVERY FROM UNDERGROUND DEPOSITS This invention relates to the treatment of underground deposit-bearing formations. More particularly, it relates to an improved method for fracturing such underground formations to enhance or stimulate the recovery of the desired deposits therefrom.
The prior art considered in conjunction withthe preparation of this specification are as follows:
U.S. Pat. No. 2,944,803; U.S. Pat. No. 285,342; U.S. Pat. No. 3,309,140; U.S. Pat. No. 3,387,888; U.S. Pat. No. 3,533,471; U.S. Pat. No. 3,561,532; U.S. Pat. No. 3,565,173, U.S. Pat. No. 3,574,599; U.S. Pat. No. 3,587,744; U.S. Pat. No. 3,593,788; US. Pat. No. 3,593,793; U.S. Pat. No. 3,640,579; U.S. Pat. No. 3,654,990; U.S. Pat. No. 3,708,206; and U.S. Pat. No. 3,713,698. All of these publications are to be considered as incorporated herein by reference.
It is well known in the art that the recovery of minerals and fluids from underground formations of relatively low permeability can be ehanced by fracturing the formation rock to create areas of high permeability. One commonly employed technique for fracturing such formations is hydro-fracturing. In this technique, a fracturing fluid is injected into the formation through a well-bore at a pressure above the formation breakdown pressure. The fracture initiates at the well-bore and hopefully propagates outward into the formation in a radial manner. While this technique is generally use ful, complete radial coverage of the formation and controlled propagation of the fracture at increasing distances from the well-bore are generally not achieved.
The use of explosives implanted in crevices, cracks, or fissures is common in mining and quarrying operations. Such explosives have included both solid and liquid-type explosives. The detonation of an explosive device or materials in a well-bore to achieve explosive fracturing of the surrounding formation, however, suffers from the same disadvatange noted above with respect to hydrofracturing operations, namely the difficulty of propagating the fracture at increasing distances from the injection well-bore. Explosive fracturing by the detonation of an explosive device in a well-bore also requires a subsequent clean up operation before recovery of operations can be begun at that wellsite, increasing both the time and expense involved in such a treating action. Explosive fracturing also presents numerous safety problems; it has been experienced in the past that several people have been killed in conjunction with the utilization of explosives for carrying out the desired end result; i.e., fracturing-underground formations.
The aforementioned disadvantages inherent in the prior art processes are now overcome by practicing the processes of the present invention.
Accordingly, it is an object of the present invention to provide an improved method for stimulating the recovery of materials from underground deposits.
It is another object of the invention to provide an improved process for fracturing underground formations.
It is another object of the invention to provide for enhancing the radial propagation of the fracture into the formation around a well-bore.
It is a further object of the invention to provide a process for extending the distance from the well-bore to which the fracture may be propagated.
It is a further object of the invention to provide aprocess for fracturing a formation in which the necessity for subsequently cleaning up the injection well-bore may be obviated.
These and other objects of the present invention will be readily apparent in conjunction with the description of the present invention hereinafter set forth, including the appended claims.
The objects of the present invention are accomplished by a process in which prior to any hydrometallurgical operation being conducted on the underground deposits, there is injected into the formation, via the wellbore, an aqueous hydrogen peroxide solution containing a stabilizing agent therefor. It has unexpectedly been found that the utilization of a stabilized aqueous hydrogen peroxide solution functions in such a manner, hereinafter described, to uniformly open up fractures and stimulate the underground formation.
Specifically, it has been found that the stabilized aqueous hydrogen peroxide solution penetrates even the smallest fractures, for example, 1/32 of an inch or less, in all directions from the well-bore due to the solutions flow characteristics. Once the stabilized hydrogen peroxide solution comes into contact with metal values in the formation such as iron and copper values, the metal values react with the stabilizing agent in the hydrogen peroxide solution and there results a precipitation of the stabilizing agent from the solution. After the stabilizing agent has precipitated from the hydrogen peroxide solution, the hydrogen peroxide then undergoes rapid decomposition to form a gaseous medium which has a pressure greater than the formation breakdown pressure. Consequently, additional fractures are created in addition to the enlargement of the present fractures.
The hydrogen peroxide solution which contains a stabilizing agent therefor, is an aqueous solution containing from about 30 percent to about 98 percent by weight, based on the total weight of the solution, hydrogen peroxide. Lower concentrations of hydrogen peroxide can be utilized; however, it has been found that it is more desirable and effective to utilize a hydrogen peroxide solution containing at least 30 percent by weight hydrogen peroxide therein. The hydrogen peroxide solution also is desirably at a pH of less than 6.0 and preferably at a pH of about 4.0 or lower. When it is required to adjust the pH of the hydrogen peroxide solution, this may be accomplished by the addition thereto of an acid such as sulfuric acid, nitric acid, phosphoric acid, and acetic acid in any amount required to obtain the desired end pH value. The temperature of the overall hydrogen peroxide solution is initially at ambient temperature; however, temperatures of about 20 to about C can be used where one so desires.
The critical feature in the present invention relates to the utilization of a stabilizing agent with the hydrogen peroxide solution. Such use is predicated upon the fact that the stabilizing agent is the safety feature in conjunction with the use of the hydrogen peroxide solution per se. The stabilizing agent thus provides a safe period of time during which hydrogen peroxide is pumped through the well-bore into the fractures surrounding the well-bore. Thus the possibility of a blow-back" through the well-bore is substantially reduced. The stabilizing agent is any material which is slowly precipitated out of solution by metal values in the formation.
Preferably the material is an organophosphorus compound such as amino trimethylene phosphonic acid, ethylene diamine tetramethylene phosphonic acid, diethylene triamine pentamethylene phosphonic acid and the like and water soluble salts thereof. It is to be understood that other organophosphorus compounds can be used as long as they function in the required manner.
The preparation of a stabilized hydrogen peroxide solution may be undertaken by the procedure set forth in U.S. Pat. No. 3,383,174, which is incorporated herein by reference.
While the generic inventive concept described herein is applicable to increasing the permeability of any rock formation, the processes of the present invention are particularly effective in conjunction with the in-situ mining of underground formations which contain copper metal values in the form of chalcopyrite and pyrite ores. It has been found that the uniform stimulation of a low permeability deposit is an important factor for an economically viable in-situ mining operation. In the particular case relating to the underground (or solution) mining of chalcopyrite and pyrite ores, this uniform stimulation permits the leaching solvent to contact more of the copper minerals, thus increasing both the leach efficiency and copper loadings. Both of these parameters are critical for economically mining deep-lying low grade copper ores by in-situ mining techniques.
In general, the process comprises the steps wherein the aqueous hydrogen peroxide solution, containing the stabilizing agent therein, is pumped down a well and allowed to flow into the deposit. The hydrogen peroxide flows or diffuses into small fractures (or pores) where it comes into contact with copper and iron minerals, together with other minerals present in the formation. Upon coming into contact with these minerals, the stabilizing agent contained in said solution is precipitated out leaving the hydrogen peroxide in an unstabilized condition. The hydrogen peroxide then decomposes because of the catalytic action of the chalcopyrite and pyrite thereon, the rate of decomposition being a function of the minerals contacted, the solid exposed surface area in contact with the hydrogen peroxide, temperature, additives present in the hydrogen peroxide, strength of hydrogen peroxide solution and the like. As a result of this decomposition, a large gas pressure is built up and when this pressure exceeds the parting pressure of the formation, fracturing or stimulation occurs. It has been found that because of the rapid decomposition of the hydrogen peroxide, the fracturing or stimulation is conducted in a uniform, radial manner and at substantial distances from the well-bore due to the good penetration of the hydrogen peroxide into the smallest of fractures.
Subsequent to the above described injection of the hydrogen peroxide solution, the copper leaching solution is injected in order to subsequently recover the copper values. The copper leaching procedures can be carried out in any manner known to those skilled in the art of in-situ mining such as those procedures described in U.S. Pat. No. 3,574,599, U.S. Pat. No. 3,640,579, and U.S. Pat. No. 3,708,206, all of which publications are incorporated herein by reference.
It is to be understood that the hydrogen peroxide solution can be used at any time where one so desires. Preferably the solution is used as a pretreatment of the formation or deposit. However, it is also within the scope of the invention that said solution can be employed where deposits have already been subjected to hydrometallurgical operations.
It is a preferred embodiment of the present invention to utilize the process for the solution mining of copper from subterranean formations in a particular pattern design of injection and production wells. It is preferred that the injection and production wells either be drilled in concentric patterns about each other with a single production well contained within the center of the pattern, for example a five-spot, or that the injection and production wells be drilled in offsetting line patterns so as to form a line drive mechanism within the copper formation. Generally, the distance between the injection and production wells will be from 20 to l,000 feet, with particular depth, thickness, permeability, porosity, water saturation of the formation, and economic value of the copper mineral contained therein being the engineering constraints upon which the design of the solution mining patterns are based. Therefore, through patterned well completion in the copper formation, the process may be used sequentially across the copper deposit through a series of line drive wells or concentric pattern wells so that the entire copper deposit may be leached.
EXAMPLE I An ore body acres in area and averaging 1,000 feet in thickness lies at an average depth of 4,000 feet below the surface of the earth in Arizona. Samples of the ore show that it is composed primarily of granitic igneous rock and that it contains chalcopyrite as the principal copper mineral. The ore samples also show that it contains approximately 1.4 weight percent chalcopyrite and that the total copper content ofthe ore averages 0.5 percent. The volume of ore in the deposit is, therefore 10 acre-feet or 4.356 X 10 cubic feet. The specific gravity of the granitic ore is 2.6. Therefore, the total weight of the ore in the deposit is 3.54 X 10 tons, and the copper content of the ore body is 3.54 X 10 pounds.
Approximately 50 wells are drilled into the ore body in an array such as to provide a five-spot pattern, and the wells are completed such that fluids may be either injected or produced from individual wells. By measurements on core samples and by injection and production tests on individual wells, it is determined that the void volume within the randomly oriented fracture system is equivalent to 2 percent of the bulk ore volume, that the fracture spacing averages 6 inches, and that the permeability of the ore body to liquid averages less than about 2 millidarcys. This permeability is less than desired for economic recovery of copper.
Petrographic examination of core samples taken from the ore body shows that about 2 percent of the rock surface area exposed by the fractures is covered by the chalcopyrite mineral and that the rock matrix bounded by the fracture system is substantially cubical in configuration.
Thus, the surface-to-volume ratio of the ore blocks bounded by the fractures is approximately equal to that for cubically shaped blocks and the surface area to volume ratio for the ore blocks is equal to 6/L, where L is the length of the side of a cube. In this case L 0.5 feet, and the surface area to volume ratio is equal to 12 square feet/cubic foot.
The total surface area of ore exposed by the fracture network is equal to 12 X 4.36 X or 5.227 X 10 square feet. The surface area of the chalcopyrite mineral exposed by the fracture system is equal to 2 percent of the total surface area, or 1.045 X 10 square feet.
Laboratory tests with the ore samples showed that ferric sulfate solutions will dissolve copper from the chalcopyrite of the ore body at a rate equal to 0.002 pound of copper per square foot of chalcopyrite surface area per day. The initial maximum rate of copper production attainable from the ore body by in-situ leaching with ferric sulfate would be 0.002 X 1.045 X 10 209,000 pounds of copper per day. The laboratory tests also showed that by allowing a 0.4 molar solution of ferric sulfate to react completely with the chalcopyrite and other minerals in the ore, a pregnant leach solution containing 3.0 pounds of copper per barrel (42 gallons) could be obtained. Therefore, in order to supply 0.4 molar ferric sulfate solution to the ore body at the optimum rate; i.e., at the rate sufficient to produce the maximum amount of copper and at the same time allow total reaction of the ferric iron, the 0.4 molar ferric sulfate solution must be injected initially at a rate equal to 69,700 barrels/day. The required average residence time for the solution within the ore body is fixed by the injection rate and the void volume of the ore body;
Average Residence time void volume/injection rate (0.02) (436x10 cubic feet/(69,700 bbL/day) (5.615 cu. ft./bbl.) 22.3 days The injection and withdrawal rates of the wells are thus regulated to permit the ferric sulfate solution to remain in the ore body for approximately 22 days.
When the initial deposit permeability is substantially below the l-5 millidarcy economical range, the hydrogen peroxide solution containing the stabilizer, therefore, is used to increase the permeability to the economical range.
Utilizing the above set of conditions, the wells are operated for a sufficient period of time to reach equilibrium and the copper produced averages about 187,000 pounds per day.
These wells are then shut down and treated with a 75 percent by weight aqueous hydrogen peroxide solution (pH 4.0) containing amino trimethylene phosphonic acid as the stabilizing agent therefor. Specifically each well is treated for approximately 4 hours at a pumping rate of 20 gallons of solution per minute. After this 4 hour period, the wells remain inoperative for 2 hours and then the leaching treatment is initiated under the same conditions specified heretofore. After equilibrium has been established, it is determined that copper is now being produced at an average rate of 235,000 pounds per day. Thus the use of the hydrogen peroxide solution has resulted in additional production directly as a result of the new fractures formed and enlargement of old fractures.
While Example I has been described as applicable to the copper sulfide ores, it should be understood that the process is also applicable to ores bearing native copper and also to ores of copper oxides and silicates where the copper is present in the cuprous valence state. When the copper is present in its elemental or lower valence state, it is susceptible to oxidation by ferric iron to form solutions of cupric sulfate.
It should also be understood that while it is preferred to conduct the process in an ore body between an input and withdrawal well, a single well process is also included within the scope of the invention. In a single well process, the leach solution will be injected through a well, permitted to remain in contact with the ore body for a period of time, and then withdrawn through the same well. The pregnant leach solution is then passed to a copper recovery stage, a regeneration stage and ultimately reinjected.
While the processes have been described as particularly effective in the in-situ mining of copper-bearing deposits, it is also within the scope of the present invention to treat other types of mineral-bearing deposits which contain, for example, silver, gold, molybdenum, uranium and the like. Furthermore, deposits containing oil may also be effectively treated.
The present invention has been described herein with reference to particular embodiments thereof. It will be appreciated by those skilled in the art, however, that various changes and modifications can be made therein without departing from the scope of the invention as presented.
What is claimed is:
1. In a hydrometallurgical operation for the in-situ underground mining of a low grade copper-containing formation by the use of a copper leaching solution for extracting copper values from said formation, the improvement which comprises the step of prior to contacting said copper-containing formation with said leaching solution, the formation is contacted with an aqueous hydrogen peroxide solution containing a stabilizing agent therefor and whereby said agent reacts with the copper-containing formation to form a precipitate and the resultant substantially unstabilized hydrogen peroxide decomposes to form a gaseous medium which causes additional fracturing of the formation whereby greater leaching efficiency and copper loading is achieved with the subsequent copper leaching step.
2. The method as set forth in claim 1 wherein the concentration of the hydrogen peroxide in solution is from about 30 percent to about 98 percent, by weight, based on the total weight of said solution and the pH of said solution is less than about 6.0.
3. The method as set forth in claim 2 wherein the stabilizing agent is an organophosphorus compound which precipitates out of said solution when said compound comes into contact with the copper-containing formation.
4. The method as set forth in claim 3 wherein the copper-containing formation contains chalcopyrite and pyrite.
5. The method as set forth in claim 4 wherein the stabilizing agent is amino trimethylene phosphonic acid or a water soluble salt thereof.
Claims (5)
1. IN A HYDROMETALLUGICAL OPERATION FOR THE IN-SITU UNDERGROUND MINING OF A LOW GRADE COPPER-CONTAINING FORMATION BY THE USE OF A COPPER LEACHING SOLUTION FOR EXTRACTING COPPER VALUES FROM SAID FORMATION, THE IMPROVEMENT WHICH COMPRISES THE STEP OF PRIOR TO CONTACTING SAID COPPER-CONTAINING FORMATION WITH SAID LEACHING SOLUTION, THE FORMATION IS CONTACTED WITH AN AQUEOUS HYDROGEN PEROXIDE SOLUTION CONTAINING A STABILIZING AGENT THEREFOR AND WHEREBY SAID AGENT REACTS WITH THE COPPER-CONTAINING FORMATION TO FORM A PRECIPITATE AND THE RESULTANT SUBSTANTIALLY UNSTABILIZED HYDROGEN PEROXIDE DECOMPOSES TO FORM A GASEOUS MEDIUM WHICH CAUSES ADDITIONAL FRACTURING OF THE FORMATION WHEREBY GREATER LEACHING EFFICIENCY AND COPPER LOADING IS ACHIEVED WITH THE SUBSEQUENT COPPER LEACHING STEP.
2. The method as set forth in claim 1 wherein the concentration of the hydrogen peroxide in solution is from about 30 percent to about 98 percent, by weight, based on the total weight of said solution and the pH of said solution is less than about 6.0.
3. The method as set forth in claim 2 wherein the stabilizing agent is an organophosphorus compound which precipitates out of said solution when said compound comes into contact with the copper-containing formation.
4. The method as set forth in claim 3 wherein the copper-containing formation contains chalcopyrite and pyrite.
5. The method as set forth in claim 4 wherein the stabilizing agent is amino trimethylene phosphonic acid or a water soluble salt thereof.
Priority Applications (2)
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US422233A US3865435A (en) | 1973-12-06 | 1973-12-06 | Stimulation of recovery from underground deposits |
US517677A US3896879A (en) | 1973-12-06 | 1974-10-24 | Stimulation of recovery from underground deposits |
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US422233A US3865435A (en) | 1973-12-06 | 1973-12-06 | Stimulation of recovery from underground deposits |
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US3865435A true US3865435A (en) | 1975-02-11 |
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US422233A Expired - Lifetime US3865435A (en) | 1973-12-06 | 1973-12-06 | Stimulation of recovery from underground deposits |
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Cited By (6)
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US4223948A (en) * | 1977-12-27 | 1980-09-23 | Atlantic Richfield Company | Process for the reduction of competitive oxidant consuming reactions in the solution mining of a mineral |
US4302429A (en) * | 1976-11-08 | 1981-11-24 | E. I. Du Pont De Nemours And Company | Process for solution mining of uranium ores |
US4317487A (en) * | 1978-08-17 | 1982-03-02 | Molecular Energy Research Company, Inc. | Method of recovering oil and other hydrocarbon values from subterranean formations |
US4320923A (en) * | 1976-11-08 | 1982-03-23 | E. I. Du Pont De Nemours And Company | Method for solution mining of uranium ores |
US5063997A (en) * | 1989-01-04 | 1991-11-12 | Nowsco Well Service Ltd. | Method of preventing precipitation of iron compounds during acid treatment of wells |
US6308778B1 (en) | 1999-02-25 | 2001-10-30 | Bj Services Company | Compositions and methods of catalyzing the rate of iron reduction during acid treatment of wells |
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US2563623A (en) * | 1951-08-07 | scott | ||
US2900026A (en) * | 1955-07-21 | 1959-08-18 | Shell Dev | Process for freeing stuck drilling tools |
US3387888A (en) * | 1966-11-16 | 1968-06-11 | Continental Oil Co | Fracturing method in solution mining |
US3574402A (en) * | 1969-03-18 | 1971-04-13 | Continental Oil Co | Fracture initiation by dissolving a soluble formation |
US3640579A (en) * | 1970-04-28 | 1972-02-08 | Arthur E Lewis | In situ pressure leaching method |
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US2563623A (en) * | 1951-08-07 | scott | ||
US2900026A (en) * | 1955-07-21 | 1959-08-18 | Shell Dev | Process for freeing stuck drilling tools |
US3387888A (en) * | 1966-11-16 | 1968-06-11 | Continental Oil Co | Fracturing method in solution mining |
US3574402A (en) * | 1969-03-18 | 1971-04-13 | Continental Oil Co | Fracture initiation by dissolving a soluble formation |
US3640579A (en) * | 1970-04-28 | 1972-02-08 | Arthur E Lewis | In situ pressure leaching method |
Cited By (6)
Publication number | Priority date | Publication date | Assignee | Title |
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US4302429A (en) * | 1976-11-08 | 1981-11-24 | E. I. Du Pont De Nemours And Company | Process for solution mining of uranium ores |
US4320923A (en) * | 1976-11-08 | 1982-03-23 | E. I. Du Pont De Nemours And Company | Method for solution mining of uranium ores |
US4223948A (en) * | 1977-12-27 | 1980-09-23 | Atlantic Richfield Company | Process for the reduction of competitive oxidant consuming reactions in the solution mining of a mineral |
US4317487A (en) * | 1978-08-17 | 1982-03-02 | Molecular Energy Research Company, Inc. | Method of recovering oil and other hydrocarbon values from subterranean formations |
US5063997A (en) * | 1989-01-04 | 1991-11-12 | Nowsco Well Service Ltd. | Method of preventing precipitation of iron compounds during acid treatment of wells |
US6308778B1 (en) | 1999-02-25 | 2001-10-30 | Bj Services Company | Compositions and methods of catalyzing the rate of iron reduction during acid treatment of wells |
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