US2658036A - Composition for preventing deposition and corrosion in oil well equipment - Google Patents

Description

l atenied Nov. 3, 1953 UNITED STATES TENT OFFICE TION' AND CORROSION. IN

EQUIPMENT H1 WELL Clark D. Core, Seguin, and Edward N. Jones,

Pettus,

'1ex.;v said Core assignor to Texas Acidizers, Incorporated, Seguin, Tex., a. corporation or Texas Nollrawing- Application July 19, 1950,. Serial.No. 174,788"

This invention relates to compositions for use in increasing the efiiciency and productivity of oil, gas or water producing wells.

The primary object of this invention is tov provide compositions which are more efiective in simultaneously preventing corrosion and scale deposition on the metal surface of well equipment, such as casing, tubing, surface connections, flow lines, separators, heaters and tanks than the conventional products presently employed.

Most fluids that come out of earth formations contain many complex inorganic as well as. organic chemicals which include compounds of calcium, magnesium, potassium, sodium, iron, carbon, hydrogen, barium and sulphur. While, the compounds are trapped in the earth formation, they existv in the fluids in a. state of. equilibrium which can be disturbed by changes. of heat and pressure. When the well is produced, the fluids leave the relatively high temperature and pressure conditions found at the formation and ascend toward the. surface of the earth while the temperature and pressure decrease. librium. so upset causes the formation of new compounds, such as carbonic. acid. and acetic acid, which have a marked corrosive eifect on steel, and also causes the formation of compounds which precipitate ont. upon the steel as. a hard scale deposit. Calcium carbonate, calcium sulphate, magnesium sulphate and iron sulphidev are several. of the compounds which precipitate. out as scale. The deposition of. the scale compounds and the corrosive compounds remains on the metallic equipment until holes form therein, making immediate replacement necessary. This not only interrupts the productio in the well, but also requires costly replacements, particularly in the case of high pressure wells Where even one small hole can start a series of costly consequences. Therefore, there is a constant demand in this art for compositions which will simultaneously prevent corrosion and also prevent the depositions of hard scale on the well equipment. The present composition effectively performs this dual function in a manner not heretofore possible. with the; many compositions presently available onthe market.

One. of the important ingredients in thepresent. composition is. a water-soluble, alkali metal arsenite, such assodium or potassium arsenite.

As. stated hereinabove, it is not. only necessary to provide a corrosion inhibitor which will effectively cover the metallic well equipment, but also an ingredient which will remove existing scale Claims; (0]. 252-855)- The equiand prevent further scale deposition inasmuch as the destruction of well equipment is due to a combination of" both the corrosion of the equipment by the acids in the well fluids and the scale depositiononthe equipment. Accordingly, the present composition includes a Water-soluble, a1-

kali metal hexametaphosphate, such as sodiumorpotassium hexametaphosphate, which accomplishes this purpose by holding in solution inprcper chemical equilibrium the compounds that would otherwise precipitate to form the scale. The sodium hexametaphosphate forms soluble complex compounds-- with the scale-forming compounds already in solution; the complex compounds being carried harmlessly' out of the Well equipment in solution with the fluids being produced.

It is well known in this artthat crude oil or.

paraffin films form upon the surfaces ofthe;

metal equipment which act as insulation between the metal surface and the treating solutions, and that this is further aggravated by the presence of resistant emulsions. of the water-oil and oilwater type. Accordingly, an. effective composition for preventing. deposition of scalev and corrosion must alsoinclude an ingredient. whichwill effectively remove the crude oil. or parafiin film from the metal surfaces and. at the same time effectively break up the resistant emulsions. Experimentation has been conducted with a number of detergents or Wetting agent'sfor incorporationv with the arsenite and hexametaphosphate, but it. hasv been found. that only a few of these wetting agents are really effective for the dual purpose. of removing the crude oil or paraffin film and the breaking up of the resistant water-oil and. oil-Water emulsions. Certain of the Wellknown Aerosol compounds have been employed to. advantage. Aerosol OS, has been found to have the best. properties, while it has also been found that Aerosol MA, Aerosol AY and Aerosol 15 could also be employed in the composition. Aerosol OS is a water soluble wetting agent or detergent otherwise known. as. isopropyl naphthalene sodium sulfonate, Aerosol MA is dihexyl sodiumsulfosuccinate, Aerosol AY is diamyl sodium sulfosuccinate; and Aerosol IB is diisobutyl sodium sulfosuccinate;

It will thus be seenthat" the basic compositionherein provided forpreventing deposition of scalewater-oil emulsions- This composition may be a dry or solid composition or may be an aqueous solution depending upon the-manner of applicaproportions of the ingredients employed:

EXAMPLE I a Per cent by weight Sodium arsenite, 40% aqueous solution by weight "14.0-45.0

Sodium hexametaphosphate 4;0-45.0 Aerosol O I 0.4 Remainder-Water.

- As the corrosion and scale deposition problems vary greatly in different areas,chemical analysis of the well fluidsshould be made to determine starch and mold the mixture, after which the tion. The examples which follow illustrate the water isexpelled by heat evaporation.

, Thus, it will be seen that novel compositions 'are'provided which, due to their power to re- -move as well as prevent the formation of scale depositions in well tubing, surface connections and flow lines, free and unobstructed flow of the well fluids is obtained throughout substantially the entireproductive life of the Well. Inasmuch as these compositions also contain surface-active materials which not only'remove crude oiland paraffin deposits on the metallic equipment, but

the variations which must-be made in the pro portions of the above ingredients, In the case of highlycorrosive wells in which very little scale develops, it would be necesary to increase the arsenite concentration and decrease the phosphate concentration correspondingly. On the other hand, if a well has extreme scale develop-.

ment and very little corrosion, the phosphate concentration should be increased and the arsenite concentration correspondingly decreased.

Inasmuch as aldehydes, such as formaldehyde, act as corrosion inhibitors in metallic oil well equipment, and particularly because of a reaction between formaldehyde and hydrogen sulphide in 1 the well fluid to produce a protective film, formaldehyde may be added to the above composition to replace some of the water and the preferred percentage by weight of the added formaldehyde The preferred composition and one which has proven highly efiective in widespread areas is given in the following example: 1

EXAMPLE II Per cent by weight Sodium arsenite, 40% by weight of an aqueous solution 45.0 Sodium hexametaphosphate 4.0 Aerosol OS 0.4

Remainder-Water.

It will be understood that the above compositions can be administered a number of different ways, but preferably will be injected into the annular space between the well tubing and the long string of casing.- The composition trickles down the metallic surfaces of the well equipment to the bottom of the tubing and is picked up in small quantities, but continuously,

by the well fluids ascending inside of the tubing. Instead of the aqueous solutions mentioned hereinabove, a solid mixture of the ingredients, either in stick or pellet form, may be administered in the oil well, and the following example gives the ingredients in their proper percentage by weight for the solid composition:

EXAMPLE III Per cent Sodium arsenite powder 24-71 Sodium hexametaphosphate powder 24-71 Aerosol OS powder 2 Starch 3 The starch is used as a binder and a small amount of water is used initially to dissolve the sodium sulfonate to act as a also act as demulsification agents for effectively breaking up the oil-water and water-oil emulsionsnormally found in wells, both the corrosion inhibiting arsenites and the scale preventing hexametaphosphates can at all times perform their desired functions efiectively.

, While preferred embodiments of the present I composition have been described hereinabove, it will. be understood that minor variations in the composition can be made by those skilled in'the I art without departing from the spirit of the invention or the scope of the appended claims.

Having described the invention, what is claimed as new is:

11A composition for removing and preventing scale deposition and preventing corrosion in oil well'equipment comprising 4-45% by weight of I a 40% aqueous solution of an alkali metal arsenite, 4-45% by weight of an alkali metal hexametaphosphate and a minor amount of surfaceactive demulsification agent, the balance being water. a

2.'The composition of claim 1 wherein said demulsification agent is selected from the class consisting of isopropyl naphthalene sodium sul-.

fonate, dihexyl 'sodium sulfosuccinate, diamyl sodium sulfosuccinate and diisobutyl sodium sulfosuccinate.

3. The composition of claim 1 wherein said arsenite is sodium arsenite and said hexametaphosphate is sodium hexametaphosphate.

4. A composition for removing and preventing scale deposition and preventing corrosion in oil References Cited in the file Of this patent UNITED STATES PATENTS Number Name Date 935,695 Schultze Oct. 5, 1909 1,877,504 Grebe et a1 Sept. 13, 1932 1,903,041 Hall et al. Mar. 28, 1933 2,204,580 De Groote June 18, 1940 2,262,737 De Groote Nov. 11, 1941 2,426,318 Menaul Aug. 26, 1947 2,429,594 Case Oct. 28, 1947 2,468,163 Blair et al. Apr. 26, 1949

Claims (1)

1. A COMPOSITION FOR REMOVING AND PREVENTING SCALE DEPOSITION AND PREVENTING CORROSION IN OIL WELL EQUIPMENT COMPRISING 4-45% BY WEIGHT OF A 40% AQUEOUS SOLUTION OF AN ALKALI METAL ARSENITE, 4-45% BY WEIGHT OF AN ALKALI METAL HEXAMETAPHOSPHATE AND A MINOR AMOUNT OF SURFACEACTIVE DEMULSIFICATION AGENT, THE BALANCE BEING WATER.