US2506853A - Oil well furnace - Google Patents

Description

INVENTORS.

HTTOENEV 2 Sheets-Sheet 1 May 9, 1950 c. H. o. BERG ETAI- oIL WELL FURNACE Filed May 30, 1945 J7 /NSl/g/NG DZUG Gaafm Hare/cm wsu/.nwe

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HZ/VEV Patented May 9, 1950 UNITED STATES PATENT QFFICE 8 Claims.

This invention relates to an apparatus for improving the flow of oil in oil producing zones by the application of heat thereto. The Ainvention further relates to a type of apparatus which makes possible increased oil recovery from oil producing zones which increase is oi particular importance after the yields obtainable by conventional methods become commercially impractical.

It is generally recognized that approximately 'fi two-thirds of the oil inthe average oil reservoir remains after the production is exhausted by ordinary recovery methods. The economic producing limits are in most cases related to the ,de-

crease in `differential pressure between the reservoir sands and the well bore which occurs as gas and oil are Withdrawn from theproducing zone, the oil flow diminishing as this differential pressure becomes too small to overcomethe permeability of the reservoir rock. The permeability of reservoir rock is a measure of the resistanceu offered by it to movementY of fluids through its pore spaces. This factor of permeability, K, which is the rate of flow of uid of given viscosity through a cross section of one unit volume of a porous media in a given time interval is expressed according to Darcys law of fluid flow-through porous media in the following equation:

in which K is the permeability, u the viscosity of the fluid, Q the volume of fluid passing through the porous media in a given time, L the thickness of the formation, A the cross sectional area of the porous medium and A11' the differential pressure causing flow.

Therefore for any given producing zone, the permeability, available pressure,1 `thickness `and cross section ofthe lparticular zone being constant, it is possible to equate the quantity of flow and the viscosity of the oil, thusly:

where C is a constant of proportionality. Thus it is possible to increase ,the` oil-.flow at any given pressure dilerential by reducing the viscosity of the oil in the producing horizon. Also `when the flow of oil in a Well declines to a point Where it is commercially impractical to continue production by ordinary methodsit is possible :to employ means to reduce the viscosity of the ,oil sufficiently to materiaily increase the lflovv and thus recover substantially more oil than .otherwise possible.

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This reductionpof viscosity of the oil in the producing zone may be accomplished by the appliation of heat and to this end our invention is directed.

A number of methods have been reported for the application of heat to oil in an oil bearing formation, such as, applying heat by circulating hot oil, gas or Water from the surface ydown through the tubing and into the oil bearing formation. The I'disadvantage in the above mengtioned methods is that most ,of the heat applied by circulating from the surface is lost by interchange with risingV materials or to the earth above the producing zone. Direct red heaters inside the Well bore in the vicinly of the production formation are impractical because temperatures become-high enough` to carbonize the oil and to damage casings, liners, etc.

Electricalheaters ator near the formation have been used inthe past with limited success, because such heaters have only a small eiiective area and thereioreonly small amounts of heat can be released Without using such high temperatures -that local carbonization will occur. Also with electrical heaters expensive conductors must be employed or alternatively the tubing and cas,- ing must `act asl conductors with` resulting corro? sion hazards due to the high voltages required.

The `present invention is directed to an appa; ratus for increasing the rate of oil production at anystage in the life of a Well before production by conventional methods becomes uneconomical, Further the invention relates to an apparatus for recovering a substantial amount cf the remaining oil imprisoned in the oil'sands after the yield from the usual methods has ceased to be profitable.

More specifically the invention relates to an apparatus for applyingV heat to the producing horizon of an oil Well to reduce the viscosityof the oil contained in the formation.

More particularly the invention comprehends an improved apparatus for stripping the oil from the oil sands Which essentially consists lof a re-` fractory lined combustion furnace located at or near ther productive formation selected for treating and communicating with the earth surface by means of tubing, introducing a mixture Aof vair and iue'l intovthe tubing land Idown into the cornbustion furnace, .in proportions to `provide ap proximately complete .combustion of the gas and complete consumption of the oxygen in the air. When the combustible mixture reaches the combustion furnace. it Ais then ignited by means of anignter positioned in the combustion furnace as it issues thereinto from the tubing so as to continuously produce heated lproducts of combustion which are then mixed with controlled quantities of cooling gas to obtain a temperature in the mixed products of combustion and cooling gas that is high enough to transfer desired quantities of heat to the oil and formation and at the same time that is insufficiently high to carbonize the oil or damage the equipment in the well such as casing, tubing, etc. The cooling gas is carried to the lpoint of mixing through suitable annulus between tubings which is described hereinafter.

The apparatus of my invention may be readily understood by reference to the attached diagrammatic vertical section drawings illustrating two modifications of the invention. In the modification of Figure l, the heating furnace is positioned at the lower end of the smallest tubing. In the modification of Figure 2, the heating furnace is positioned in the annulus between the two tubings.

Referring to Figure 1, E represents a conventional oil well casing with perforated liner F suspended therefrom into which has been placed one modification of the apparatus employed according to our invention for heating the oil contained in the producing zone. This apparatus consists of an outer pipe D of somewhat smaller diameter than the casing creating an annular space between the two and an inner pipe A of smaller diameter than pipe D, the two pipes being joined to each other by flange I0 and these in turn to the casing by flange I I.

According to this diagram air and fuel gas are introduced into pipe A by inlets I2 and I3 respectively, in such proportions as to provide upon ignition approximately complete combustion of the gas and complete consumption of the oxygen. In this regard, it is desira-ble as will hereinafter be observed, to employ a slight excess of fuel gas to insure complete utilization of the oxygen. This combustible mixture of gas and air is forced downwardly through pipe A into a combustion furnace B lined with'a refractory and located at or near the productive formation. The combustion furnace is essentially a conical shaped chamber, and thus having a relatively smaller cross-sectional area at the top and a relatively larger cross-sectional area at the base, so designed with respect to the rate of flow of air and gas that the velocities in the upper or small diameter portion of the furnace will exceed the rate of flame propagation, and at some point in the lower or larger diameter portion of the furnace velocities will be less than that of flame propagation. Thus after ignition, a flame will burn steadily at some point as for example zone I4 within the conical furnace. -As an added precaution against name propagation upwardly in tube A, a constriction in the flow line can be incorporated at C or a conventional flame arrestor may be employed. There are many modincations which may be used to effect the transfer of the air and gas to the furnace or combustion zone. For example, it is possible to replace the single tube A with two concentric tubes, and' in this manner force the fuel gas through the smaller of these tubes and the air through the annulus between the two or vice versa. The gas and air are thereafter mixed at some point just above the combustion chamber where the smaller inner tube terminates.

One of innumerable possible methods of igniting the air-gas mixture in the furnace is shown.

In this illustration an electrical resistance wire heating coil I8 is placed in the furnace in such a manner as to initiate the combustion of the gas mixture and at the same time to be above the actual flame Zone so as to eliminate overheating of the Wire. In this example tube A comprises half the conductor and the insulating Wire the other half. The current is furnished by means of generator I5 or other suitable means and flows through wire I6 which passes into tube A through the insulating plug I'I and is connected with one end of heating coil I8 by means of the connector or brush I9. 'I'he other end of heating coil I 8 is attached to tube A in such a manner as shown in the diagram and returns thereby to the source of power.

Another method of inducing combustion is to electrically insulate tube A from tube D with suitable non-conducting spacers and an electrically insulating gasket between surface flanges and incorporating in tube A a non-conducting section of tubing just above the furnace. One end of the heating coil would be connected by a Sort length of wire to tubing A above the section of nonconductive tubing and the other end would be connected to the outside conducting steel shell of the furnace which would make contact to D at stop 20 or through a spring guide. In this manner tube A would comprise half the electric circuit and tube D the other half. Also a spark plug or similar igniting device could be substituted for the heating coil and in any case the ignition coil or plug is located in the furnace above the point of combustion as pointed out above so that it will not be injured by the high temperatures of the frame.

In order to avoid the application of destructively high temperatures a cooling gas preferably recycled flue gas from the process is introduced by means of inlet 22 and into the annulus between tubes A and D in such quantities as to cool the outside of the furnace B and such that when mixed with the products of combustion below the furnace in tubing D the mixed gases have any desired temperature which is below that which would damage the various elements of the system or cause appreciably carbonization of the oil. Herein lies one of the important elements of our invention, namely the ability resulting from the wide flexibility of our apparatus to control the temperature induced in the producing zone within comparatively narrow limits.

The installation of this apparatus is relatively simple. Tubing D with a suitable stop such as stop 20 inserted at any desired point above its lower end is run into the well in a conventional manner. Following this, tubing A with furnace B attached to the lower end thereof is run inside tubing D until the furnace makes contact with the stop. If the wire go-devil type conductor 23 in Fig. 1, is employed it is run in so as to reside in the constricted part of tube A as shown and the apparatus is then connected with sources of high pressure fuel gas, air, cooling gas and electric power and is ready for operation.

In operation in a well with a relatively high formation pressure, the mixture of combustion and cooling gas flowing up the annulus between tubing D and the casing may be used to gas lift oil out of the well into a suitable trap where the gas and oil is separated. Part of the gas is then recycled as the cooling gas introduced in inlet 22. It should be pointed out that with very high production rates it may be necessary to cool the material between the well head and the trap` which may be accomplished in any desirable manner.

For wells with low formation pressures and productive indices, intermittent operation might be used. During the heating cycle no production would be obtained and the heat inputv would go into the formation thus raising the temperature for a considerable distance from the well'. After heating, the inner string D' may be pulled and a conventional pump installed. The heat stored in the formation atrelatively high temperature would decrease the viscosity of the oil and thereby increase the rate of ilow into the well, and through the pump and tubing.

Formation productivity could be greatly increased if temperatures adjacent to the wells were high enough to evaporate the interstitial' water in the productive sands.V In many formations the removal of vthis water would cause a very large increase in effective permeability by preventing the swelling of clay and evenin those sands not impaired by swelling clays the elimination of water would greatly increase the permeability of the sands to oil and decrease the permeability to water. In some cases it might even prevent 'the ii'ow of Water into the well. However, capillary forces would, in time re-wet the sand and the heating process would have to be repeated. After heating the formation to a ternperature sufficient to evaporate the water, it may be desirable to force into the sands a material such as quinoline that wouldcause the sands to be hydrophobic and preferentially wet by oil thus tending to prevent the capillary migration of y water back to the region of the well bore. It is possible that the dehydrating and heating efficiency could be increased greatly in some cases by shutting off the production ofgas (and oil) and forcing the hot mixed products of combustion and cooling gas back into the productive formations.

Figure 2, illustrating another apparatus for employing the heat'generated by the combustion of a mixture of gas and air within the producing f horizon to lower the viscosity of the oil contained in the formation, is particularly effective in minimizing heating of the casing and further illustrates another system of ignition in which the tubing and casing serve to carry the electric curi rent. In this system tubing D inserted inside the casing E carries a furnace assembly in its iower end and is electrically insulated from the casing by means of insulators 30 and 3| and spider spacers 5|. Tubing A is run inside tubing D and is packed olf from it, as illustrated, above the combustion chamber. This packing 33 is not attached to the furnace assembly and as a consequence may move in a vertical direction as tubing A expands or contracts.

In this illustration air and fuel gas are injected into the annulus between tubes A and D by means of inlets 34 and 35 respectively and are intermingled therein during their passage down through the well. bore flowing into the furnace assembly created in the annulus space between tube D and tube F attached thereto passing therefrom into the furnace contacting in the small diameter part of the furnace the resistance wire ignitors 36 and 31 and burning therein within the furnace at a location as for example at e8 below the location of the heating wire. This location of burning is controlled as above described by the conical design of the furnace, i. e., by reason of the furnace having a relatively smaller crosssectional-area at the top and a relatively l.larger cross-sectionall area at the base, and'occ'urs'at the place where the velociti7 ofthe gas is approximatelyv equal to the velocity offiame propagation. intervals through the circumference of the inner and outer walls of the furnace at a level lbelow thatv of flameV propagation through which, cooling gas which is introduced 'into the annulus space between the well case and'vtube D by means of inlet 44' passes into the furnace mixingl therein with the hot combustion gases prior to contact of these gases with any metal surface or oil.l In,

the remaining portion passing through the annular space between the tapered walls of the fur.- nace and tubing A as indicated by arrows adjacent to ducts 6 and 47. That portion of lthe cooling gas which does not pass through ducts e5 and 46 continues downwardly in the annular space betweenV the casing and tubing D andra part passes through the ducts 2S and 42 in the furnace wall and is admixedwithin the furnace with the hot combustion. gases, the remainder passing through the annular space existingbetween the outer tapered edge of the furnace and the casing.

The outside of the combustion chamber or furnace B is electrically insulated` from tubing D by a non-conducting collar 3| as illustrated 'and` is provided with spring guides t9 and 50'which.

serve the purpose not only of centering the furnace in the casing but of providing a path for the electric current from the casing through the outer wall of the furnace through the resistance wire ignitor to tubing D and further` toconstrict the ow of the cooling gas so that part of the gas will be forced through ducts. 39, 42', 45`and 46. In this regard the size of these ducts may be varied over comparatively wide limits depending upon the desired ratio of gas to be passed through ducts 45 and 45.

With the arrangement shown in Figure 2 ther they may be supported from the surface and anyl large differences in thermal expansion between them isitaken upby providing for relative motion at the packer 33. In this case thepacker is fixed to A packing oif against a cylindrical element of D with a tapered guide section above the packer i. e., the packer does not seat against the tapered guide.

For a pumping well the system may besubstantially the same as shown by Figure 2.

Ducts 39, 40, lIH andv 42 are provided at In this case the pump may be located in tubing A below the combination chamber, as for example, at some point X and tubing A may be provided with ports above the pump at Y to permit the flow of gases up the annulus between tubing A and the pump rods. The rods may be tubular, oil production thereby flowing through them.

Other methods of pumping might also be used. For example, the combustion gas could be sent down a small tube at high pressure and supply power to an engine that would operate the pump. In this case the exhaust gas from the engine would pass into a combustion chamber below the pump where it would be burned to supply heat.

The system described herein has great advantage over apparatus for applying heat by circulating hot oil, gas or water from the surface in that the heat is generated at or near the producing zone where it is most eiective whereas most of the heat applied by circulating from the surface is lost by interchange with rising materials or to the earth above the producing zone.

It has several important advantages over electrical heaters at or near the formation. Some such heaters have limited area and therefore only small amounts of heat can be released without using such high heater temperatures that local carbonization will occur. Also with electrical heaters expensive conductors must be em ployed or the tubing and casing must act as conductors with resulting corrosion hazards. With the apparatus herein described the ignition system would require the consumption of a very small amount of electrical energy at relatively low voltage and corrosion and conductor problems are relatively unimportant. very large amounts of heat can be released under controlled conditions of temperature such as to avoid damage and at the same time provide adequate temperature differentials to transfer very large amounts of heat to the productive formation by substantially direct contact between sand surfaces and hot gases.

It is to be realized that the foregoing description of Various modifications of the apparatus of our invention are only illustrative thereof inasmuch as there are many modifications which may be employed without departing from the spirit or scope of the invention, the essence of which is the accomplishment of the reduction of the o viscosity of the oil contained in the oil bearing formation of a well bore by means of heat supplied by the ignition within the well bore of a predetermined mixture of fuel gas and air and the dilution of the resulting hot combustion gases with a quantity of cooling gas suicient to induce within the producing horizon any desired temperature below that of combustion.

Having fully described the principles of our invention and illustrations thereof and with the above defined scope in mind we claim:

1. An apparatus for heating the oil contained in an oil bearing formation which comprises two concentric tubes located within the Well bore extending from the surface to the producing horizon, the inner tube terminating in a refractory lined cone type furnace, the outer tube projecting some distance below said inner tube, means for introducing into said inner tube a mixture of a combustible gas and an oxygen containing gas under sufficient pressure to force said mixture into the furnace at the lower end of said inner tube, an ignition means within said furnace to ignite the combustible gas mixture therein, means for introducingla cooling gas in the annular space between the inner tube and the outer tube under Furthermore,

suicient pressure to force said cooling gas downwardly in said annular space to commingle with the hot combustion gases issuing from the opening at the bottom of said furnace, and means for withdrawing the gas mixture traveling upwardly through the annular space between the outer tube and the well bore after contacting the oil bearing formation.

2. An apparatus for heating the oil contained in an oil bearing formation which comprises two concentric tubes to be inserted in a well bore, the outer of which tubes carries at its lower end a refractory lined furnace consisting of a circular member projecting from said tube towards the wall of said well bore and a circular member projecting from said tube towards said inner tube to furnish thereby a furnace the shape of a conic section rotated through 360, means for introducing'into the annular space between said inner tube and said outer tube a combustible mixture of fuel gas and an oxygen containing gas, means for causing said mixture to flow through the opening at the top of said furnace, means within said furnace to ignite said combustible mixture, the taper in the sides of said furnace being sufficient to cause flame propagation at a point above the base of said furnace, means for introducing cooling gas into the annular space between said outer tubing `and said well bore, means for commingling said cooling gas with the products of combustion within said furnace at a point between the point of name propagation and the base of said furnace, and means for withdrawing the gaseous mixture traveling upwardly through the inner tube after contacting the oil bearing strata.

3. An apparatus according to claim 2 in which said means to ignite said combustible mixture consists of a resistance wire in the vicinity of the combustion zone.

4. An apparatus according to claim 2 in which said means to ignite said combustible mixture consists of a spark plug located in the well bore in the vicinity of the combustion Zone.

5. An apparatus for heating the oil contained in an oil bearing formation which comprises two concentric tubes insertable in a well bore, the outer of said tubes supporting at its lower end a refractory lined furnace comprising a circular member projecting from said tube towards the wall of said well bore and a circular member projecting from said tube toward said inner tube to furnish thereby a furnace the shape of a conic section rotated through 360, means for introducing into the annular space between said inner tube and said outer tube a combustible mixture of fuel gas and an oxygen containing gas, means for causing said combustible mixture to flow through the opening at the top of said furnace formed by the spaced relationship of said circular members, means within said furnace to initiate combustion of said combustible mixture, means for introducing cooling gas into the annular space between said outer tubing and said well bore, means for commingling said cooling gas with the products of combustion within said furnace, pumping means positioned in the lower portion of said inner tube, said inner tube being provided with circumferal perforations at a point above said pumping means, and separate means for withdrawing the discharge from said pumping means and the gases migrating through said perforations.

6. An apparatus for heating the oil contained in an oil-bearing formation which comprises a refractory lined furnace having a relatively smaller cross-sectional area at the top and a relatively larger cross-sectional area at the base, said furnace being inserted in a well bore and located in the region of the oil-bearing formation, means for introducing a combustible mixture of fuel gas and an oxygen containing gas into the top of said furnace, means within said furnace to ignite said combustible mixture, the difference in cross-sectional areas at the top and at the base of said furnace being sufficient to cause flame propagation at a point above the base of said furnace, means for introducing cooling gas into an annular space surrounding said furnace, means for commingling said cooling gas with the products of combustion from said furnace and means for withdrawing the resulting gaseous mixture from said Well bore.

7. An apparatus for heating the oil contained in an oil-bearing formation which comprises two concentric tubes to be inserted in a well bore,

one of which tubes carries at its lower end a refractory lined furnace having a relatively smaller cross-sectional area at the top and a relatively larger cross-sectional area at its base, means for introducing into the tube carrying said furnace a combustible mixture of fuel gas and an oxygen containing gas, means for causing said combustible mixture to ow into said furnace through an opening Iat the top of the furnace, means within said furnace to ignite said combustible mixture, the difference in the cross-sectional areas at the top and base of said furnace being sufcient to cause flame propagation at a. point above the base of said furnace, means for introducing cooling gas into an annular space imme diately surrounding said furnace, means for commingling said cooling gas with the products of combustion and means for withdrawing the resulting gaseous mixture from said well bore after contacting the oil-bearing strata.

8. An apparatus according to claim 7 in which the furnace is in the form of a cone attached to the base of the inner tube inserted in said well, said combustible mixture is introduced into said inner tube, said cooling gases are introduced into the annular space between said concentric tubes and the mixture of products of combustion and cooling gas is withdrawn through the annular space between the outer concentric tube and said Well bore.

CLYDE H. O. BERG. PHILIP H. JONES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,457,479 Wolcott June 5, 1923 1,473,348 Howard Nov. 6, 1923 1,626,940 Kreager May 3, 1927 2,188,737 Hixon Jan. 30, 1940 2,225,775 Garrett Dec. 24, 1940

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