US 2436198 A
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, Feb. 17, 1948. H. CARDWELL ETAL 2,436,198
CHEMICAL REMOVAL AN ACID-SOLUBLE METAL PART IN A DEEP WELL Filed Aug. 6, 1945 I I .I
IN ll 8 I l l I 2 1 I 5 7 x i INVENTORS Pay/H Carowe// By Louis H Ef/ers ATTORNEYS Patented Feb. 17, 1948 @HEMICAL REMOVAL OF AN ACID-SOLUBLE METAL PART IN A DEEP WELL Paul H. Cardwell and Louis H. Eilers, Tulsa,
Okla, assignors to The Dow Chemical Com.- pany, Midland, Mich, a corporation of Delaware Application, August 6., 1945,. Serial No. 609,254 1 Claims. (01. 252-855) 1 The invention relates to the chemical removal of an acid-soluble metalpart in a deep well. It more particularly concerns an improved method of completin wells, traversing a plurality of strata, in which a chemically soluble casing section located opposite a selected stratum is removed by chemical action to permit fluid flow between the well bore and the stratum.
In the usual well completion in which a chainlcally soluble section is included in the casing string opposite a productive zone, the soluble section is made of aluminum or an aluminum alloy, and its removal is effected by prolonged treatment with a quantity of hydrochloric acid.
A disadvantage of this method which limits its usefulness is that the action of the acid is quite slow, so that an inordinate amount of time is consumed in the operation and complete removal is somewhat uncertain. Y
A particular object of the invention is to provide an improved method of, and composition for, chemically dissolving an aluminum or aluminum alloy part, such as a casing section, in the bore of a well whereby complete rapid removal is achieved. Other objects and advanta es will become. apparent as thedescription of the invention proceeds.
According to the invention dissolution of parts or equipment made of aluminum or aluminum alloy in the well is achieved by subjecting the metal part to the corroding action'of a hydrochloric acid solution to which has been added a relatively small amount of .a phosphorus acid, such as phosphoric acid (H3PO4) and hypophos phorous acid (H(H2PO2)). To'prevent or reduce attack by the acid solution on adjacent ferrous metal parts, when such are present, an inhibitor of such action may be included in the acid solution.
The invention may be more readily understood from the following detailed description and accompanying drawing of a mode of carrying out the invention, such mode illustrating but one of various ways in which the principle of the invention may be used. In the said drawingthe single figure illustrates schematically in vertical section an oil well in which an acid-soluble section located in the casing string opposite a productive zone is being removed chemically.
Referring more particularly to the drawing, the well bore l is provided with a casing. string 2 containing an aluminum alloy (acid-soluble) section 3. Various aluminum-base alloys are suitable for the purpose as, for example, one containing about 1 per cent of silicon, about, 1 per cent of magnesium, and about 0.3 per cent of chromium, the balance being aluminum. If desired, unalloyed aluminum may be used. The aluminum or aluminum alloy section is placed in the casing string so that the sectionis op- 2 posite a productive zone 4, the annular space between the casing string and the well hole being filled with cement 5. Such well construction is conventional and forms no part of the invention.
In preparing the well for treatment so as to remove the soluble section 3 according to the inventiomthe portion of the well below the productive zone 4 is bridged as with a filler 6, and a packer 1' is set in the casing at the top of the zone thereby to isolate for treatment the portion of the well containing the soluble section. The packer is provided with a central passage for admitting the outer tube 8 extending from the top of the well to just below the packer. An inner tube 9' is strung through the outer tube and extends from the top of the well to near the bottom of the soluble section.
After arranging the apparatus as described. the chemical solvent of hydrochloric acid to which has been added a suitable phosphorus acid may be, introduced through tube 9 so as to fill the space ID in the cased portion of the well between the top of the bridge 8 and the bottom of the tube 8. ,As the chemical solvent becomes spent by dissolving the metal of the soluble section 3 of the casing, fresh solvent maybe introduced,
if necessary, thereby'displacing the spent solution from the well through tube 8 It is referable to continuously circulate the chemical solvent into the space I0 through tube 9 while the spent or partially spent solvent solution is displaced through tube 8. The amount of solvent to employ depends upon the concentration of HCl therein and the Weight of the aluminum section to be removed, and may be computed on the basis of the known stoichiometrical relationship between HCl and aluminum to form aluminum chloride (A1013). For example, approximately 1.7 gallons of 25 per cent hydrochloric acid solution is required per pound of aluminum section. Various concentrations of HCl may be used, such as 10 to 35 per cent, concentrations between about 15 and 20 per cent being preferred.
A convenient way to introduce hypophosphorous acid into. the hydrochloric acid solution is to employ a solublev salt of hypophosphorous acid, such as sodium hyp p p (NaH2PQ2)- A suitable amount of the hydrated salt,
NaHzPOzHzq may be dissolved in the hydrochloric acid solution which then behaves in the same manner as when hypophosphorous. acid itself is used. Preferred proportions of sodium'hypophosphite or hypophosphorous acid to use are between about 0.1 and 2 per cent of the weight of the hydrochloric acid solution; those of phosphoric acid are between about 0.5 and 2 per cent.
In order to reduce or prevent attack by the acid on the ferrous metal parts of the well which 3 may be exposed to the acid solution, particularly the steel casing adjacent to the acid-soluble part to be removed, any of the well known corrosion inhibitors may be used, such as a soluble-' arsenic compound, e. g., the arsenate or arsenite of sodium, organic sulfur compounds, such as the mercaptans, organic nitrogen bases, etc., in' I generation of heat is an advantage as it speeds.
After the aluminum section has been removed, the packer I and tubing strings 8 and 9 are removed so as to permit drilling out the cement sheath II opposite the zone 4 and removal of the bridge 6, if desired,
- As illustrative of the increased rate of action of hydrochloric acid n aluminum alloy tubing brought about by the addition of a corrosion accelerator of a phosphorus acid, tests were made in which pieces of the tubing were subjected to the dissolving action of hydrochloric acid solution to which the aluminum corrosion accelerator was added. In conducting these tests 300 cc. lots of acid solution were placed in a calorimeter together with a piece of an aluminum alloycontaining 0.2 per cent copper, 1 per cent magnesium, 0.4 per cent silicon, 0.2 percent chromium, the balance being aluminum, and the rate of dissolving of the aluminum alloy determined by observing from time to time the temperature attained by the reacting materials. In these tests the higher the temperature attained by the materials in a given number of minutes after the reaction begins the faster the dissolving of the aluminum alloy occurs. Tables I and II present data so obtained.
TAsLa I Rate of reaction of hydrochloric acid solutions on aluminum alloy Rate of reaction of hydrochloric acid solutions on aluminum alloy Temperature F.) of Reacting Materials After Composition of Acid Solution i Min. Min. Min. Min. Min.
% HCI (Blank) 86 109 162 220 220 20% 0.5% HiPOi. 86 107 168 213 20% 0.5% NEHgPOz.-. v 86 150 216 218 216 The data in the tables show that by adding a phosphorus acid in relatively small amount to hydrochloricacid solution its rate of'attack'lon aluminum alloy is' increased; Thisis evident from the fact that the temperature of the reacting materials attains a higher value in less time when a phosphorus acid is present in the acid solution.
The term aluminum used herein and the appended claims is used to mean all grades of aluminum metal, and the term aluminum alloy means alloys of aluminum containing at least about per cent of aluminum.
1. A composition for dissolving a metal part formed of aluminum and its alloys which comprises hydrochloric acid containing from about 15 to 20 per cent of HCl and 0.1 to 2 per cent of hypophosphorous acid.
2. A composition for dissolving a metal part formed of aluminum and its alloys which comprises an aqueous solution of hydrochloric acid containing from about 15 to 20 per cent of HCl to which has been added 0.1 to 2 per cent of sodium hypophosphite.
3. The method of removing from a well ametal part formed of aluminum and its alloys which comprises subjecting the part to the dissolving action of an aqueous solution comprising hydrochloric acid containing from about 10 to 35per cent of HCl and 0.1 to 2 per cent of a phosphorus acid selected from the group consisting of phosphoric acid and hypophosphorous acid.
4. The method of removing from a well a metal part formed of aluminum and its alloys which comprises subjecting the part of the dissolving action of an aqueous solution comprising hydrochloric acid containing from about 10 to 35 per cent of HCl and 0.1 to 2 per cent of-a phosphorus acidselected from the group consisting of phosphoric acid and hypophosphorous acid and an inhibitor of the action of hydrochloric acid on ferrous metal.
5. The-method of removing from a well a metal partformed of aluminum and its alloys which comprises subjecting the part to the dissolving action of an aqueous solution comprising hydrochloric acid containing from about 15 to 20 per cent of HCl and 0.1 to 2 per cent of hypophosphorous acid. r 6. The method of removing from a well a metal part formed of aluminum and its alloys which comprises subjecting the part to the dissolving action of an aqueous solution comprising hydrochloric acid containing from about 15 to 20 per cent of HCl to which has been added 0.1 to 2 per cent of sodium hypophosphite..
'7. The method of removing from a well a metal part formed of aluminum and its alloys which comprises subjecting the part to the dissolving action of an aqueous solution comprising hydrochloric acid containing from about 15 to. 20 per cent of HCl and 0.5 to 2 per cent of phosphoric acid. PAUL H. CARDWELII LOUIS H. EILERS. 1
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS