US3456721A - Downhole-burner apparatus - Google Patents

Description

.Fufiy 22, 1969 R. v. SMITH 3,456,721

DOWNHOLE-BURNER APPARATUS Filed Dec. 19, 1967 INVENTOR. R. V. SMITH A TTORNEVS 3,456,721 DOWNHOLE-BURNER APPARATUS Robert V. Smith, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Dec. 19, 1967, Ser. No. 691,873 Int. Cl. E2lb 43/24 US. Cl. 166-59 1 Claim ABSTRACT OF THE DISCLOSURE A downhole-burner apparatus comprises a tubular combustion chamber positioned in a well bore, preferably at the lower extremity thereof, having a fuel burner at the upper end thereof, the lower end of the combustion chamber being open to the well bore, said burner having closed and open ends, the open end being in communication with the combustion chamber, fuel and oxidizing gas injection and mixing means in communication with the closed end of the burner; i.e., the upper end, fuel ignition means in said burner for igniting the mixture of fuel and oxidizing gas injected therein, a water jacket surrounding the combustion chamber having water inlet means in communication with water conduit communicating with the surface outlet of the bore hole, a plurality of water injection orifices in a side wall of the combustion chamber communicating between the interior of the combustion chamber and the water jacket, whereby water is injected into the combustion chamber in contact with the flame emanating from the burner.

Background of the invention Petroleum is generally found in sandstones or porous limestone situated between impervious layers of shale or the like. Initially, the oil is usually found to be associated with lighter hydrocarbons such as methane and ethane, which may exist as free gases in contact with the oil or dissolved in the oil. When such oil-bearing sands are reached by drilling, the expansive force of the gas, either free or dissolved under pressure existing at the depth of the oil reservoir, moves oil and gas toward the region of low pressure around the well bottom. With conditions at the casinghead uncontrolled, the rapid flow of oil and gas from the well creates a gusher and flush production results.

After the initial pressure existing has diminished with the escape of most of the gas associated with the oil from the well, the motive power bringing oil to the surface is largely dissipated. At this stage, the well is put to pumping with resultant increased production of oil from the well together with additional amounts of gas. In time the flow of oil produced by pumping diminishes to the point where pumping is no longer economical. The remaining oil has little pressure exerted upon it by the small amount of residual gases or vapors remaining in the reservoir and the heavier hydrocarbons present assume a more viscous, semi-solid state which tends to choke the pores of the sand preventing drainage of the oil to the well bottom.

In an attempt to increase productivity of such wells, the method of repressuring has been adopted. This operation involves forcing back into selected central wells either natural gas taken from other wells or air. The gas injected into the selected well under pressure passes through the porous oil-containing sands and is vented from adjacent wells. By this procedure, the gas mechanically forces some of the heavier oil into the well bottoms, and entrains any hydrocarbons existing in vapor form in the reservoir. Upon continued operation, this method also becomes unprofitable and it must be abandoned even though the reservoir is only partially depleted with respect to the oil initially present.

nite States Patent "ice 3,456,721 Patented July 22, 1969 Further attempt to increase production from such wells involves final resort to the so-called flooding procedure. In this procedure water under pressure is injected into selected wells and the entire oil reservoir is scoured with water bringing to the surface from adjacent venting wells a further portion of the residual oil. After practicing this method the oil field can no longer be utilized for further production.

It is well-known, that oil fileds which have been subjected to the foregoing successive treatments still contain in the sands about half of the oil known to be initially present.

It has been recognized heretofore, that the application of heat to the oil-containing sands tends to increase production of oil from oil reservoirs. For example, it has been proposed to inject heated gaseous products of combustion into partially depleted oil reservoirs in an attempt to drive out the residual oil by reducing the viscosity and thereby facilitating flow. In some instances, combustion of the oil itself has been proposed as the source of heat.

All of these procedures require that formation be exposed to temperature gradients of extreme degrees in order to effect the transmission of sufiicient amounts of heat into the formation to obtain the desired results of increasing formation pressure and reducing viscosity of residual hydrocarbons. These processes require the maintenance of temperatures within the well bore or along a flame front propagating through an oil-bearing formation which are by design considerably in excess of temperatures at which at least a substantial part of the residual hydrocarbon is reduced to carbonaceous deposits. Such operations result in the reduction in porosity and permeability in the vicinity of the well bore, and for that matter, throughout the formation where flame fronts are allowed to propagate throughout the oil bearing strata. At the same time the extremely high temperatures promote the dissipation of heat in all directions from the heat source which results in the loss of substantial amounts of heat by dissipation to adjoining formation.

Merriam et al., US. Patent 2,584,606 disclosed a process for exposing an oil-bearing formation in the immediate vicinity of a well bore to an unattenuated burner flame and the generation of steam within the formation by injecting water into the formation in the vicinity heated by the burner flame.

I have discovered a secondary recovery method and downhole steam generation device by which the vapor pressure in an oil-bearing formation can be increased and the viscosity of residual hydrocarbon retained therein reduced without exposing the formation to temperature sufiicient to convert the residual hydrocarbons to more viscous species, e.g., carbonaceous materials.

It is therefore one object of this invention to provide method and apparatus for increasing reservoir vapor pressure and to reduce the viscosity of reservoir fluids. It is another object of this invention to provide a method and apparatus for increasing reservoir heat content without exposing reservoir fluids to temperatures in excess of those at which reservoir fluids decompose or are reduced to more viscous materials. It is another object of this invention to provide method and apparatus for increasing the heat content of subterranean formations while reducing heat loss by transmission to formations adjoining the subject strata or to formations bordering the well bore. It is another object of this invention to provide a highly efficient downhole steam generator.

Summary of the invention In accordance with one embodiment of this invention a suitable fuel such as a hydrocarbon fuel gas or oil is combusted in the presence of an oxygen-containing gas in the approximate vicinity of a formation to which it is desired to add substantial amounts of heat, and the flame produced by such combustion is quenched by spraying water or low quality steam directly into the flame in a confined combustion zone whereby the water or low quality steam is converted to high pressure, high quality steam which passes into the formation.

In accordance with another embodiment of this invention steam is produced in a downhole steam generator comprising a fuel burner in a combustion zone by injecting water or low quality steam into the combustion zone to quench the flame and generate high quality, high pressure steam which is forced into the adjoining formation to increase the temperature thereof.

In accordance with another embodiment of this invention a downhole steam generator comprises a tubular combustion chamber positioned in a well bore having a fuel burner at the upper end of the chamber, the lower end of the chamber being open to the well bore, the chamber and burner being surrounded by a water jacket having a plurality of water inlet means; i.e., orifices, in the side wall of the chamber communicating between the interior of the combustion chamber and the water jacket for injecting water into the combustion chamber in direct contact with the flame from the burner whereby high pressure, high quality steam is produced and the flame is quenched prior to contacting with the adjacent formation.

One of the most significant advantages of this process and apparatus is that elevation of formation temperatures is accomplished by the injection of a homogeneous-steam phase containing quenched combustion products into the well bore and adjoining formation with the result that hot spots, localized overheating, and excessive temperature gradients which result in the decomposition of residual hydrocarbons and consequent formation plugging are avoided.

The method of the invention is preferably practiced by utilizing an existing oil well communicating with the oil reservoir as the input well, and employing one or more existing adjacent wells as the venting wells. If necessary, however, new venting wells may be drilled closer to the selected input wells. The combustion-supporting gas may be air, oxygen, or mixtures thereof, or any permanent gas containing sufficient oxygen to effect good combustion. The combustible gas may be any heating gas such as producer gas, water gas or natural gas. The input well is capped or closed in at the casinghead so that any desired pressures may be developed. The ignition products; i.e., the flame emanating from the burner, are quenched in a confined generation zone by the injection of Water or low quality steam directly into the flame. As a result of this procedure, the flame is quenched prior to contact with the adjoining formation and a homogeneous steam phase containing quench combustion products is continuously produced. The heat added to the formation adjoining the point of injection elevates tempera ture thereof and, depending on the volatility of constituouts of the reservoir fluid, volatilizes a portion of those reservoir fluids, e.g., hydrocarbons and reduces the viscosity of the remaining heavier constituents, whereby those constituents flow more easily through the formation under the influence of pressure developed in the injection well.

As the vaporized portions of the oil move into cooler regions of the oil-containing sands, they are partially condensed and release the latent heat of condensation at that point, which together with the sensible heat in the gaseous products of combustion serves to increase the temperature in the regions of the formations more remote from the input well. Thus, the entire reservoir is progressively heated and the hydrocarbon in vaporous and/ or fluid state is forced into the venting well bottom where it is removed by ordinary pumping means. Vaporization of a portion of the oil, and, in addition, formation of steam from the connate water adds to the total volume of gases facilitating removal of the oil from the reservoir.

Although it may be desirable, in some instances, to provide for an excess of oxygen in the burner flame which permeates the formation and may under certain conditions promote the oxidation of reservoir hydrocarbon, it is presently preferred that the ratio of oxygen to fuel in the burner be sufficient only to provide an economic degree of combustion of the burner fuel without introducing a substantial amount of free oxygen into the formation. This preference derives from the observation that oxidation of reservoir hydrocarbons generally results in 'an increase in the viscosity of certain hydrocarbon constituents by virtue of localized overheating due to rapid oxidation. This oxidation, itself, is not undesirable from the standpoint of the viscosity of the reaction products. On the contrary, these oxidation products; i.e., carbon monoxide and carbon dioxide, generally contribute to the total volume of the vapor, e.g., steam phase, and reduction of the viscosity of the remaining hydrocarbons. However, such oxidation if allowed to continue to a substantial' degree results in the consumption of hydrocarbons which might otherwise be recovered in the recovery well.

The ratio of oxygen to fuel in the burner feed will, of course, depend upon the characteristics of the fuel. For example, ratios of oxygen to fuel within the range of from 290 to about 340 standard cubic feet per gallon generally result in the substantially complete combustion of fuel when No. 6 grade fuel oils are employed. Oxygen to fuel ratios of from 2 to about 6.2 cubic feet per cubic foot at standard conditions are those preferred for these purposes where light hydrocarbon gas fuels such as those containing hydrocarbons having from 1 to 4 carbon atoms are employed. In this latter instance, i.e., where light hydrocarbon gas fumes are employed as burner feed, they are conveniently obtained from the recovery wells by separating the necessary amount of these light hydrocarbons from the hydrocarbon recovered in those wells and recycling the lighter hydrocarbons as fuel to the downhole steam generators of this invention. It is also necessary, of course, to assure that the back pressure on the fuel supply, oxygen supply and water or steam supply to the steam generator be sufiiciently in excess of the pressures developed in the immediate vicinity of the generator. These pressures can vary over a wide range and can be determined to some extent by the original pressure of the reservoir. Pressures usually encountered in such operations are generally within the range from about 200 to about 2,000 p.s.i.g. Similarly, temperatures encountered within the immediate vicinity of the steam generator are preferably maintained below about 500 F. Preferred temperatures are generally within the range of from 300 to about 400 F. In order to accomplish this result, the rate of steam or water injection into the burner flame prior to its contact with the adjoining strata must be sufficient to quench the flame and exhaust gases; the amount of steam or water injection required to accomplish this purpose will, of course, depend upon the rate of heat generation by the burner which in turn is determined by the size of the injection well and the rate at which it is desired to inject steam into the formation. Steam injection rates are preferably within the range of from 675 to about 3750 standard cubic feet per hour per square foot of wall surface of the injection zone; i.e. steam injection rates are usually within the range of from 25 to pounds per hour per square foot of wall surface in the injection zone at the conditions of temperature and pressure above-referred to. To accomplish these purposes, the burner should generate heat at a rate of about 29,000 to about 162,000 B.t.u.s per hour per square foot of bore hole surface in the injection zone, which in turn requires the injection of from 31 to about pounds per hour of water into the quench zone; i.e., steam generator, per hour per square foot. Obviously, where low quality steam is injected into the steam generator, the pound rate injection rate of steam will necessarily be higher in order to accomplish the same degree of quenching of the burner flame.

The concept of this invention will be better understood by reference to the drawing which presents a schematic illustration of the steam generator of this invention.

Referring now to the drawing, the steam generator provides an isolated quench zone defined by water jacket 4 having an interior refractory lined boundary 6 provided with water or steam injection ports; i.e., orifices, 7. Burner 5 positioned in the closed end of the steam generation zone and containing the flame 11 is fueled by suitable fuel as above-described which enters the burner by way of conduit 2. Oxygen-containing gas such as pure oxygen, air etc., is mixed with the fuel prior to injection into burner 5 in a suitable mixing zone 12 into which it is injected by way of conduit 3. Water or steam is passed to jacket 4 by way of conduit 1 from which it is sprayed into steam generation zone 10 via orifices 7.

Suitable provision is also made for auto or remote control ignition of the fuel-air mixture in burner 5 so that the burner can be ignited when situated in the bore hole. Such ignition devices as resistive or spark igniters illustrated graphically by numeral 8 are generally well known in the art. Igniter 8 in this example can be controlled from the surfaces; i.e., at the well head by virtue of suitable electrical connections 9. Said connections 9 can also be used for thermocouples located near igniter 8 which with suitable means control fuel and air supply to burner 5.

As the flame 11 emanates from the downhole open end of burner 5 into the steam generation zone 10 it is inwardly contacted and quenched with water or steam sprayed from jacket 4 via orifices 7. The length of the generation zone; i.e., the distance between the open end of burner 5 and the exit of the generation zone 10* from which quenched exhaust gases and steam enter the bore hole is sufficient to allow the complete mixing of water or lower quality stea'rn injected via ports 7 and the combustion products in the flame to provide the complete quenching thereof. This mixture of quenched exhaust gases and generated steam then exits the downhole open end of generation chamber 10 and is forced into the formation under the influence of pressures generated in the generation zone.

I claim:

1. A downhole-burner apparatus comprising a tubular interiorally refractory lined combustion chamber positioned in a well bore, said chamber having a fuel burner at the upper end thereof, the lower end of said chamber being opened to said well bore, said burner having one closed end and one open end, said open end being in communication with said combustion chamber, fuel and oxidizing gas injection and mixing means in communication with said closed end of said burner, fuel ignition means in said burner for igniting the mixture of fuel and oxidizing gas therein, a water jacket surrounding said combustion chamber having water inlet means in communication with a water conduit, a plurality of water injection orifices in the side wall of said chamber communicating with the interior of said combustion chamber and said water jacket for injecting water into said combustion chamber in contact with the flame resulting from the ignition of said fuel and oxidizing gas.

References Cited UNITED STATES PATENTS 2,584,606 2/1952 Merriam et al. 16659 X 2,712,35l 7/1955 Roth et a1. 175l4 X 2,725,929 12/ 1955 Massier.

3,093,197 6/1963 Freeman et al l14 DAVID H. BROWN, Primary Examiner

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