US3235006A - Method of supplying heat to an underground formation - Google Patents

Description

Feb. 15, 1966 K. L. HUJSAK 3,235,006

METHOD OF SUPPLYING' HEAT TO AN UNDERGROUND FORMATION Filed 001;. 11, 1963 KAROL L. HUJSAK INVENTOR.

ATTORNEY.

United States Patent Office 3,235,006 Patented Feb. 15, 1966 3,235,006 METHOD OF SUPPLYING HEAT TO AN UNDERGROUND FORMATION Karol L. Hujsak, Tulsa, Okla., assignor to Pan American Corporation, Tulsa, Okla., a corporation of Delaware Filed Oct. 11, 1963, Ser. No. 315,451 1 Claim. (Cl. 16639) The present invention relates to a method for supplying heat to an underground carbonaceous formation penetrated by a well. More particularly, it is concerned with a means by which the necessary heat is generated by decomposition of a material substantially opposite such formation.

Many methods have been employed in the prior art for applying heat to hydrocarbon-containing formations such as, for example, by electrical means, by injecting heat transfer agents such as steam, hot oil, etc., into the well, and by burning natural gas in the well bore. One of the principal difficulties has been that in the course of heating the formation to ignition temperature, the casing or screen as well as any other equipment in the vicinity of the heated zone is damaged by the excessive temperatures generated. In fact, the temperatures produced have been so high that the burner itself was considered an expendable item. The electric heaters employed for ignition and for paraflin deposition control have been subjected to a number of practical problems, including shorting out; in some instances, such equipment has been lost in the hole and is extremely difiicult to recover. In addition, these and other methods formerly used to deliver 'heat to underground formations required expensive equipment and detailed operating experience to accomplish the results desired.

Accordingly, it is an object of my invention to provide a cheap, efficient method for heating an underground formation. It is a further object of my invention to provide a method for the stimulation of oil-bearing formations by supplying heat to such formations through the use of a material which can be decomposed with liberation of large amounts. of heat at the desired portion of the formation. It is still another object of my invention to provide a means for igniting or heating an oil-bearing formation by which relatively little additional equipment is used and whereby no harmful residual materials are left in the well once the heating step has been carried out.

Briefly, my invention contemplates heating an oil-bearing formation, for example, with a composition that can be made to decompose with the liberation of large amounts of heat under existing Well bore conditions, hereinafter referred to as decomposable material." Such substance which, for example, may be hydrogen peroxide, on decomposition, generally by catalytic means, generates sufiicient heat to melt any waxy deposits on the well wall and to lower the viscosity of the oil in the vicinity of the well bore whereby a noticeable increase in production is realized. If it is desired to carry out an underground combustion operation, the formation can be ignited by the use of a somewhat larger quantity of the decomposable material.

In using high-strength hydrogen peroxide, e.g., 75 percent strength, or higher, or equivalent materials, care should be taken that it does not react with oxidizable substances on the way down the tubing. Accordingly, if a high-strength, decomposable material is to be used, clean tubing substantially free of oil, wax, or other organic matter, should be employed. Otherwise, on contact with such compounds, the decomposable material reacts spontaneously. On the other hand, a diluted formof such material too weak to react with said compounds, likewise, will be too weak to react with the oil in the formation. The use of a catalyst active to decompose the hydrogen peroxide, or equivalent materials, avoids this difficulty and still provides the advantages of placing heat simply and cheaply in large amounts over a relatively small area in a well bore. With the use of a catalyst, enough heat is generated by decomposition to initiate reaction between the hydrocarbon in the formation and the decomposable material. In general, I prefer to use hydrogen peroxide solutions of about 50 percent strength because such solutions do not react spontaneously with oil or wax, except at temperatures produced by decomposition of the peroxide.

In the event only a heat stimulation treatment is desired, the catalyst, if employed, is removed from the tubing string, the well placed on pump, and the resulting oil of lowered viscosity produced. Depending, of course, on the thickness of the formation and the amount of hydrogen peroxide, or other decomposable material used, increased production can be obtained from such treatment over a period of from several weeks to several months. Because of the simplicity of the procedure involved, additional treatments can be made at frequent intervals at a minimum cost. Where hydrogen peroxide is employed, the quantity used may vary rather widely. However, in general at least one barrel of a 35 to 90 percent solution should be employed to gain any beneficial result. If a thick, i.e., to 200 ft., formation is involved, several barrels, i.e., 10 to 20 barrels, of such solution should be used.

My invention can be further described in detail by reference to the accompanying drawing, in which a well 2 having casing 4, running partially the length thereof, penetrates a heavy oilor tar-bearing sand 6. A tubing string 8, secured to wellhead 10, extends somewhat below the upper level of sand 6 into open hole suction 7. The lower joint of tubing in string 8 has secured to the end thereof a wire basket 12, containing finely divided silver turnings or silver gauze 14. Leading into tubing string 8 and above wellhead 10 is valved line 16, equipped with pump 18. At the top of tubing string 8 is valved flow line 20, through which products are brought from the well once it has been placed on pump or permitted to flow after stimulation treatment.

In operation, a standard commercial strength hydrogen peroxide solution is pumped into tubing string 8 via line 16 by means of pump 18. The hydrogen peroxide flows down tubing 8 and contacts silver gauze 14 retained in basket 12, causing the hydrogen peroxide to decompose, giving up heat to the oil or tar sand 6. Hydrogen peroxide not only liberates heat on decomposition, but also releases free oxygen which, under the conditions of use, reacts with hydrocarbons to produce additional heat. For example, a single barrel of 50 percent hydrogen peroxide is capable of generating 700,000 B.t.u. which ordinarily is capable of supplying sufiicient heat to raise a 7-foot linear section of tar sand to ignition temperature. This is an extremely economical method of releasing such quantities of heat, since the barrel of 50 percent hydrogen peroxide costs somewhat less than $100.00. The principal advantage of decomposable material such as hydrogen peroxide is that a heat stimulation treatment can be performed much more cheaply than by any other method based on equal heat injected, and leaves no harmful residue in the well.

To increase the area over which heat can be transferred throughout the formation, the latter may be fractured in a known manner prior to the introduction of hydrogen peroxide, thereby permitting hot fluids to penetrate substantial distances into the rock or sand, allowing heat to diffuse over an increased volume of the formation near the well.

Once this heat treatment has been completed, the catalyst in basket 12 is removed by pulling tubing string 8, withdrawing the basket, and reinserting the tubing. Alternatively, pulling of the tubing can be avoided by lowering basket 12 on a wire line (not shown) to a level near the lower end of tubing string 8. After all the hydrogen peroxide has been pumped into the system, has ket 12 can be withdrawn and further operation of the well is resumed.

The catalyst used forms no part of my invention. Any catalyst known to be capable of decomposing hydrogen peroxide and equivalent materials may be used, such as a porous inert material, typically pumice, impregnated with permanganate salts, and/ or oxides of various heavy metals such as, for example, vanadium pentoxide. Also, materials other than hydrogen peroxide, such as peracetic acid, alkyl hydroperoxides, such as methyl, ethyl, isopropyl, l-cyclohexenyl and l-tetralyl hydroperoxides, as well as other peroxides which decompose spontaneously either on contact with such catalyst or under conditions existing at the bottom of the well or opposite the face of the formation to be heated, are contemplated as lying within the scope of my invention. Typical catalysts which may be used in addition to silver to decompose hydrogen peroxide are metals of the platinum group, manganese, copper, vanadium chromium, and cobalt. Also, activated charcoal serves as a good catalyst for this purpose. The alkyl hydroperoxides, particularly those of lower molecular weight, are readily decomposed by certain metallic ions, such as ferrous ions. Strong bases, likewise, serve to decompose such peroxides catalytically.

It will be apparent to those skilled in this field that many variations may be made in the foregoing procedure without departing from the scope of my invention. For example, although I generally prefer to use materials such as hydrogen peroxide in strengths of from about 40 to about 60 percent, stronger solutions thereof may be employed by first adding a slug of the high-strength hydrogen peroxide to the well tubing and allowing it to react with the oil, wax, or other organic matter present. The process may be repeated until all interfering oxidizable material has been burned off. Thereafter, high or substantially full strength hydrogen peroxide, or equivalent material, may be used to heat the formation, as previously described. In cases of this sort, of course, no catalyst is required. Alternatively, an aqueous solution of a catalyst, such as calcium permanganate, can be pumped down the tubing and into the formation ahead of the peroxide. On contact of the latter with the permanganate, for example, in the case of hydrogen peroxide, the latter decomposes into water and oxygen with the liberation of considerable heat. The heat thus generated, together with the free oxygen present, creates an ideal condition for combustion of hydrocarbons. Once such condition is produced, the combustion can then be carried out to the extent desired by the introduction of air, depending on whether the formation is to be subjected merely to a heat treatment or whether it is desired to produce hydrocarbons therefrom via ordinary combustion methods. If desired, the catalyst material may be used in' dry form by impregnating pumice, or similar materials, with a suitable solution to form a supported catalyst in the usual manner. In this case, the supported catalyst can be used in much the same way as silver, referred to in the description of the accompanying drawrng.

Still another alternative coming within the scope of my invention involves the use of other materials, i.e., readily oxidizable compounds, which react in the presence or absence of catalyst, such as alcohol, aldehydes, linseed oil, etc. These compounds can be introduced into the formation ahead of the peroxide and heat liberated within the formation by the subsequent oxidation of such compounds'with a following charge of a suitable decomposable peroxide. While the reaction between the peroxide and such readily oxidizable compounds is not the same as that involved where the peroxide is catalytically decomposed,'for the purpose of the present description and claim they are to be regarded as equivalents. Also, where the term peroxide is used in the claim, it is intended to means both hydrogen peroxide and organic peroxide compounds of the type enumerated herein.

While the present description has been confined generally to treatment of oiland tar-bearing formations, in accordance with my invention, it should be clearly understood that the principles thereof can be extended, without the exercise of the invention, to the treatment of shale, coal, and similar deposits.

1 claim:

The method of supplying heat to an oil-bearing formation penetrated by a well containing production tubing having organic deposits on the interior thereof which comprises the steps of introducing into said tubing a batch of liquid hydrogen peroxide solution of at least percent strength in an amount corresponding approximately to that required to convert said deposits to a substantially unoxidizable form, and thereafter adding through the resulting cleaned tubing a separate quantity of said hydrogen peroxide solution in bulk form which on contact with the oil on and near the face of said formation will decompose and generate approximately 100,000 B.t.u. per linear foot of said formation penetrated by said well.

References Cited by the Examiner UNITED STATES PATENTS 2,657,753 11/1953 Carpenter 166-43 X 2,680,486 6/1954 Carpenter 166-43 X 2,680,487 6/1954 Carpenter 166-43 X 2,863,510 12/1958 Tadema et al. 166-38 2,871,941 2/1959 Allen et al. 166-38 2,871,942 2/1959 Garrison et al. 166-38 3,127,935 4/1964 Poettmann et al. 166-11 CHARLES OCONNELL, Primary Examiner.

BENJAMIN HERSH, Examiner.

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