US3250328A - Oil production method utilizing in situ chemical heating of hydrocarbons - Google Patents

Description

CHEMICALHEATING F HYDROCARBONS Philip J. Closrnrinn and Michael Prats, Houston, Tex.,

assignors to Shell Oil Company, New York, N. Y.,"a corporation of Delaware No Drawing. FiledNov. 19, 1963, Scr. N 324,843

fiowable nature under normal formation conditions.

This invention constitutes a desirable method for supply! ing heat to an underground oil-bearing formation for the purpose of increasing the oil recoverytherefrom.

The" primary production of petroleum hydrocarbon from oil-bearing formations is usually effected by drilling through or into the oil-bearing sand and providing access to the formation through the borehole so as to permit oil' to flow into the borehole from which it may be recovered by conventional methods and apparatus. If the formation contains oil of low medium viscosity at reservoir conditions, the 'well may -be' produced either by flowing or pumping in a mannerwell known to the art. If, on

' the other hand, the formation contains a highly'viscous oil at reservoir conditions, it may be necessary to heat the formation in the vicinity of the borehole, to reduce the viscosity of the oil so that the oil may flow into the borehole although asubstantial amount of oil still re-- mains in the producing formation underground. The residual oil left in the formation underground is very difficult to produce and considerable research has been carried out on secondary recovery methods.to recover this residual oil. Various methods have been devised such as heating, underground combustion, flooding with water or a miscible fluid, etc. These methods involve injection of water, gas, air, fuel, solvents, etc. or a combination of these into the formation through one or more input wells, while the hydrocarbon or components thereof are withdrawnthr ough one or more output or producing wells. The flooding of underground formations -f0r primary or secondary recovery of hydrocarbon materials,

such as oil, presents many problems, especially intight or relatively non-permeable formations. 'In the water flooding of an oil-bearing underground'format-ion, it is neces- -'sary to employ flood water free of clays, colloidal material, un dissolved salts, etc., which would tend to plug the face of the oil formation and perhaps 'withinthe oil formation itself when the water is injected thereinto. In addition, many producing formations being flooded contain a certain amount of swelling clay in the form of a bentonite or montmorillonite clay, which upor't swelling,

United States Patent 05 ice on. n-onUcrtoN Mentor), UTILIZING IN srru PatentedMay 10, 1966 2 A siblythousands of feet of pipe to the desired location in the well. 1 t It is thereforea primary object of the present invent on to provide a method for heating an underground hydrm carbon-bearing formation in a relatively inexpensive maner so as to increase the yield of oil from the formation.

Another object of the present invention is to provide a method of heating an underg ound hydrocarbon-beating formation by means of injecting a fluid thereinto which does not have to be heated at the surface before pumping it down the well.

'A further object of thepresent invention is to provide method for the primary or secondary recovery of oil from a formation by injecting a heat-creating chemical i.c., one. that reacts exothermic-ally in the formation with the hydrocarbon contained therein.

Still another object of the present invention is to provide a method whereby permeable flow channels may be formed extending outwardly from 'a well, or extending between at least two wells, in a manner such that ordinary or presently-known flood methods can be carried out between wells penetrating the formation after the permeable channels have been formed.

Anotherobiect of the present invention is to provide amethod for heating an underground oil-bearing formation Y without the necessity of employing heating equipment at the well site.

A still further object of tlse present invention is to provide a method of increasing the permeability of the obviates the hazard encountered in injecting a gaseous."

reactant at .a pressure sufficient to form fractures in the formation.

These and other objects ofthis invention will be understood from the following description.

The method according to-the present invention contem- I plates producing liquid or liquifiable hydrocarbons from a hydrocarbon-bearing subsurface formation which is penetrated by one well, by introd'ucinginto the well a quantity of solid-free liquid reactant which reacts exothcrmically with hydrocarbons, confining the liquid reactant reduces the permeability of the formation. The use of i solvents as a flood or the use of chemicals added to the water for flooding a formation is often prohibitive in cost. Additionally, many of the oils left in the'formation are very viscous and it is essential that they be heated in order to cause them to flow to a producing well. While under-- as steam, hot water, hot ,solyents, etc. in the formation,

the heating of the flooding material at the surface is expensive and of course there is some heat loss in trans. milling the heated material from the surface down pos- Further, while forma in the well opposite a selected interval of the hydrocarboncontaining formation, applying a pressure to the liquid reactant sufficient to force it into the hydrocarbon-' containing formation, maintaining the liquid reactant in situ for a time sufiicient for the liquid reactant to react exothermically with a portion of the hydrocarbon of the formation and heat the hydrocarbon-containing formation adjacent the well and/or adjacent fractures formed in the format-ion, and subsequently producing oil from the heated formation. In some cases, the liquid reactant is forced into the formation at a pressure at which the formation is fractured While being supplied into the fraeture in a quantity sufficient so that the liquid reactant is forced into the walls forming the fractur This method of generating heat in an oil-bearing formation by means 'of a liquid reactant is especially suitable for selectively heating a limited region or selected location. within an oil reservoir formation. When using a liquid reactant as a heat-creating medium, the need for heating equipment at the well'site is avoided. A liquid reactant is superior to a gaseous reactant as the useof a gaseous reactant would necessitate the use of expensive high pressure compressing equipment at the wellhead.

The liquid reactant is allowed to remain in the formation for a time sufficient to heat the desired portionof the formation. The heating of the reservoir formation I I need only be sufiicient to move the petroleum within the selected region of the formation or to put the petroleum in a condition that it will move readily from the formation when the well is produced. The'deg'ree to which the oil mobilization is attained can readilybe determined by applying a pressure gradientacross the selected region,

formation of'fracturesdoes not create either a hazard or ,a significant disadvantage as would the case be if the reactant were a gas. Preferably, the injection wellis opened at a point opposite the oil-containing reservoir formation to' communicate with a vertically extensive interval of the reservoir formation to encourage uniform -penetration and/or vertical or horizontal fracturing. After injectinga selected .volume of liquid reactant, for

example 200 barrels, into a f'ormationhaving a thickness of feet, the well is shutin at the injection pressure. well is reduced so as to initiate backfiow of oil into the well; The backfiow results from the pressure drop be:

tween the injection pressure, or the formation fluid pressure, ahd the 'pr'essure'within the well. The wells can be swabbed or pumped to reduce the pressure in the well to substantially atmosphericv pressure, if dcsired.-

Thismethod of thermal soaking of a formation with a liquid reactant can take place in a single well which would be used both as an injection and a production well.

Fracturing of the formation may or may not take place during the thermal soaking process. Thermal soaking of a well permits producing a high viscosity oil from a reservoir that has a significant but low permeability. The

liquid reactant, is preferably a liquid oxidant which isinjected into the reservoir and maintained there for a time sufficient to oxidize reservoir oil and-heat the reservoir prior to 'producinga reservoir. in most reservoirs significant advantages can be obtained by injecting a fluid containing a higher concentration of oxidant than can be feasibly obtained from a free-oxygen-containing gas. Since it is undesirable to inject a gas into a reservoir at a pressure exceeding the overburden pressure, a liquid reactartt or a liquid phase oxidant in accordance with the present-invention is advantageous.

- The method of the present invention can also be em ployedin oil fields containing at least two wells which penetrate an oil-bearing formation of significant but low permeability wherein the liquidoxidant would be'injected through one well, into the formation and thence 'to the ;produc tiori well. An example of this modification of the present process is given. A well completed into a tar sand of significant but low permeability is freed of or ganic material by circulating a slug of hydrocarbon vsolvent followedby a slug of aqueous liquid containing a detergent. A slug of fresh water is then injected into the formation while fluids are withdrawn from an adjac'ent production well that is completed into the same reservoir at a distance of, for example, 50 feet. In a ,typical'situation about 400 barrels of 5% aqueous hyrogen peroxide would be injected into the well and into the oil-bearing 'tarsand. The hydrogen peroxide injection might required about 1 to 2 weeks and the peroxide is left in the formation about'l to 2 months. Fluids are then produced from the heated reservoir by means of secondary recovery methods suitable for an oil of about medium viscosity.

After such a soaking, the pressure within the tensive portion of the formation around the well.

In the preferred modification of the present invention, a pressure is applied. to the liquid reactant in the. well which is sulficient to form fractures in the formation extending outwardly from the well. then forced into the fractures and into the formation forming the walls of the fractures to heat a radially ex- When at least two wells are involved a pressure may be 'sub' sequently applied to the liquid reactant sufficient to extend the-fractures to a second well with the pressurebcing maintained-at a value sufficient to maintain the fractures open in the absence of propping agents/whereby the hydrocarbons in the formation forming the walls of the fractures are heated; i

In the event that the fractures extending from the injection well did not extend all the way to the production well, the fracture into which the reactive liquid was i-njected can be subscquentlyswept free ofthe spent reactant and the oil of reduced viscosity by liquid displacement of th se 'fiuids into the formation or by allowing themto drain back to the injection well., Subsequently, the fracture could be retreated with a new quantity of liquid reactant to remove'more of the oil from the formation,

which step could be repeated, as needed. In the fnormalIy-porous' reservoir formations that are plugged with-viscous oils, a removal of the'oil contained in the walls of the fracture createst a permeable path through the-reservoir formation. As soon as such a permeable I path or layer has obtained a thickness of a few inches,

the reservoir formation can be readily heated and produced by conventional thermal drive procedures, such as Liquid reactant is steam or hotwater injections, which, because of the permeable path,are not dependent upon propped fractures or injection pressures that exceed the overburden pressure of the depth of the-reservoir. Thus, once the oil has been removed from the wallsurrounding a frao-' ture to form a permeable flow path along the fracture,

the pressure at which the liquid reactant was injected can be reduced below that needed to hold the fracture ,open.

A modification of the heating and fracturing process a described hereinabove would permit a fracture extending from the injection well, after being freed of organic anaterial, to have water injected into it at a pressure and a volume sufiicient to extend the fracture to, the production well. The water would then be displaced from the fracture by injecting enough hydrogen peroxide through the injection well and fracture to cause a layer of hydrogen peroxide to-be produced at the production well.

The rate of hydrogen peroxide injection ismaintained until the front of the concentrated solution of hydrogen peroxide reaches the production well, at which time injection is stopped and the peroxide reactant is allowed toremain in the formation for a one to two month period in order to heat the entire formation. I

A liquid phase reactant or oxidant may beemployed which reacts exothc'rmically with the oil of the formation. This for example hydrogen peroxide, nitrous oxide, sulfur trioxide, etc., and liquids containing these materials are suitable. If sulfur trioxide is to be used it is preferably in the form of oleum,.i.e. concentrated sulfuric acid having an excess of sulfurtrioxide present. Clear solutions rather than suspensions must be employed as suspensions of material are undesirable as the solid mate rial in the suspension filters out on the surface of the borehole wall and limits .or prevents further injection of fluid into the formation. Nitrogen oxides which are used in accordance with the present invention are used in a reservoir in which the overburden pressure is a value which the nitrogen oxide forms an aqueoussolution. Nitrogen'oxide may be used in the form of fuming l'lllllC acid. Thus the reactants that are contemplated for use in the presentproccss comprise single phaseliquid systems which are readily injected into the earth formations.

In respect to using oleum in fractures in the formation at which the nitrogen oxide being usedjis liquid, or at I t a in accordance with the present method, the fracture would be tmmediately heated by the heat of hydration and/or neutraliiation released as the oleu'mdisplaces an aqueous fracturing fluid andlonan'ywater in the pores of the formation. When a layer of oleunt extends from an injecuon well tothe vicinity of a production well, the

injection of the oleum is preferably stopped to prevent its flowout of the formation and the oleum is allowed to complete its reaction with the hydrocarbons in'the wall ofthe-fractures. After allowing this reaction with its. concurrent heating to occur, the spent oleum maybe displaced or contacted with caustic, thus causing further heating withinthe formation due to neutralization of the unreacted sulfuric acid.- This action would also enhance the emulsification of the oil in the injected liquids due to the surfactant properties of thesalt s of the sulfonated aromatic compounds formed by the reaction of some of the' sulfur tri'oxide with a p'ortion'of the hydrocarbons in the formation, This method of heatingisparticularly advantageous in that the heat is generated in situ all along the walls of the fractures that may penetrate deeply into, the formation. It provides a means for relatively quickly heating a substantial volume of 'an oil-bearing reservoir. As indicatedhereinabove, a liquid phase reactive fluid comprises a particularly advantageous means of chemically heating portions of an underground reservoir formaform fractures in said hydrocarbon-containing formation, 1 subsequently maintaining said liquid reactant in said fractures for a time sufficient for the liquid reactant to react exothemically with a portion of said hydrocarbon of said formation and heat the hydrocarboncontaining formation adjacent the well, and subsequently prociuc hydrocarbon-containing, formation adjacent the fractures to form permeable flow channels in said formation along said fractures 2. The method of 1 wherein the hydrocarbons are 'i 4 produced back into the wellby discontinuing the applica" tion of pressure to the liquid reactant and opening the well in a manner permitting flow'of hydrocarbon into the well. 1

3. Die method of ciaim 1 carried out inone well positioned in the vicinity of a second or production well wherein the hydrocarbons are-produced into said second well by maintaining a pressure on the liquid reactant forced into said formation.

tion because it is dangerous to injecta gas at pressures exceeding the overburden pressure of the reservoir formation. The use of liquid is advantageous because the pressure applied to them is immediately reduced (by the effects within the formation) whenever fracturing occurs.

In contrast, a gas, which is a relatively extensively compressible fluid, would immediately expand into the greater- 'volu me made available by the fracture and would continue to exert a relatively high -pressure in a manner liable to cause .a' blowout through the surface. Blowouts,

especially around a well casing, have been eliperien'ced when using a gas asan injectioniluid in a formation.

As compared to gases, liquid reactants have theadditional advantages of requiring materially less equipment and energy to provide a given high injection pressure and also have thefl capability of containing a much greater mass of reactants per unit volume. I

The method of the present invention is not concerned with heating a formation to ignition temperature of'the oil to carry out secondary'recovery of oil by underground combustion methods.v This high degree of heating is not pertinent to thepresent process. All that needed is a temperature rise sufiicient to move a localized portion of the oil adjacent the well or the fractures extending therefrom. The amount of heating obtained by the present method does not cause cracking or distillation of oil in the reservoir. It need only render the oil susceptible to fluid displacement and/or entrainment by the reactant liquid and/or other fluids that are subsequently pumped through or displaced within the selected portion of the reservoir formations. I

We claim as our invention: l. A method of producing liquid or liquifiable hydro carbons from a hy drocarbonvcontaining subsurface formasaid methodcom'prising:

introducing into a well-a quantity of a solids-free liquid.

reactant which reacts exothermically with hydrocarbons-,

' confining said liquid reactant in said well opposite a- .selec ted interval of said hydrocarbonecontaining formation,

applying a pressure to said liquid reactant sutficient to tion, said'formation being penetrated by at least one well,

4. The'method of claim 1 including the step of applying a pressure to said iiquid reactant sufficient to extend" said fractures to a second well, and maintaining said pressure at a yalue snficient to maintain said fractures open in the absence of propping agents whereby the hydrocarbons in the formation forming the wallsof the fractures are heated. 1

5. The method of claim 4 including the step of producing heated hydrocarbons from the fractures 6. :l'h'e method of claim 5 including the step of increasing the permeability of the hydrocarbon-containing formation adjacent the fractures throughout the length thereof by injecting additional liquid reactant until a chemically-heated permeable tlow channel is formed through said formation adjacent the fractures, and subsequently reducing the injection pressure below that necessary to maintain the fractures open while being sutiicient to force fluid through the permeable flow channels formed in the formation. p I. The method of claim 6 including the step of sub sequently producing the hydrocarbon-containing formation by injecting a hon-reactant fiuid in one well under orrnzn REFERENCES- 7 Uren, Petroleum Production Engineering, Oil Field Exploitation, 2nd Edition, McGraw Hill Book Co-., Inc., N.Y. (l939),pages376-379 relied on.

CHARLES E. O'CONSELL, Primary Examiner.

BENJAMIN 111211511, Examiner. 4 S. I NOVOSAD, Assistant Examiner.

g hydrocarbons from the heated pressure so that it drives hydrocarbons to said second

Claims (1)

1. A METHOD OF PRODUCING LIQUID OR LIQUIFIABLE HYDROCARBONS FROM A HYDROCARBON-CONTAINING SUBSURFACE FORMATION, FORMATION BEING PENETRATED BY AT LEAST ONE WELL, SAID METHOD COMPRISING: INTRODUCING INTO A WELL A QUANTITY OF A SOLIDS-FREE LIQID REACTANT WHICH REACTS EXOTHERMICALLY WITH HYDROCARBONS, CONFINING SAID LIQUID REACTANT IN SAID WELL OPPOSITE A SELECTED INTERVAL OF SAID HYDROCARBON-CONTAINING FORMATION, APPLYING A PRESSURE TO SAID LIQUID REACTANT SUFFICIENT TO FORM FRACTURES IN SAID HYDROCARBON-CONTAINING FORMATION, SUBSEQUENTLY MAINTAINING SAID LIQUID REACTANT IN SAID FRACTURES FOR A TIME SUFFICIENT FOR THE LIQUID REACTANT TO REACT EXOTHERMICALLY WITH A PORTION OF SAID HYDROCARBON OF SAID FORMATION AND HEAT THE HYDROCARBONCONTAINING FORMATION ADJACENT THE WELL, AND SUBSEQUENTLY PRODUCING HYDROCARBONS FROM THE HEATED HYDROCARBON-CONTAINING FORMATION ADJACENT THE FRACTURES TO FORM PERMEABLE FLOW CHANNELS IN SAID FORMATION ALONG SAID FRACTURES.