US2973812A - Process and apparatus for in situ combustion - Google Patents

Description

March 1951 C. M SPORRAN 2,973,812

PROCESS AND APPARATUS FOR IN SITU COMBUSTION Filed April 21, 1958 VOLUME CHAMBER 62 AIR- FUEL GAS I 28 A FLUIE 6A5. g

INVENTOR. C. MACSPORRAN A TTORNE VS United States Patent PROCESS AND APPARATUS FOR IN SITU COMBUSTION Charles MacSporran, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Apr. 21, 1958, Ser. No. 729,855 12 Claims. (Cl. 166-11) verse or direct air drive whereby the heat of combustion "of a substantial proportion of the hydrocarbonin the stratum drives out and usually upgrades a substantial proportion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a borehole therein followed by injection of air through the ignition borehole in the stratum is a direct air drive process for effecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum combustion zone bec-ausea heavy viscous liquid bank of hydrocarbon collects in the stratum in advance of the combustion zone which prevents movement of air to the combustion process. To overcome this difficulty and to permit the continued progress of the combustion zone through the stratum, inverse air injection has'been resorted to. By this technique, a combustion zone is established around an ignition borehole by any suitable means. and

frequently plugs in front of the l air is fed thru the stratum to the combustion zone from one or more surrounding boreholes.

In operating with either direct or indirect air injection to produce hydrocarbons from a carbonaceous stratum by in situ combustion it is necessary to first ignite the carbonaceous material in the stratum around a borehole therein. A known method heater of the gas-fired type. When heating the stratum .in this manner it has been found that conventional heaters have heated the stratum only a portion of its thickness I or extent within the borehole so that ignition was effected at a restricted level in the stratum and not thruout its entire vertical extent, .which isnecessary if a combustion 'front extending from the top to the bottom ofthe stratum is to be' moved through the stratum to, other boreholes therein. p

Conventional downhole heaters frequently becomeIoVeI- heated, particularly, because of the fact that the heater is subjected to the highest temperature developed in the borehole. Some types of heaters burn off-at the supporting conduit comprising the feed line to the burner. The

instant invention is concerned with a downhole heater" and process for heating a borehole in a carbonaceous stratum to the ignition temperature of the carbonaceous material which avoids the problems of the prior art of of ignition comprises heating v the stratum around a borehole by means of -a downhole overheating the heater and of heating only alimited section of the borehole to be ignited. I

Accordingly, it is an object ,of the invention to provide an improved downhole heater arrangement and process for preheating and igniting a carbonaceous stratum around ICC improved heater and process for heating and igniting a carbonaceous stratum around a borehole therein which heats and ignites the entire section of the exposed stratum. A further object is to provide a process and arrangement of apparatus which permits control of the vertical extent of the flame or actual combustion zone associated with a downhole heater. It is also an object of the invention to provide an improved process and arrangement of apparatus for downhole'heatin'g of a carbonaceous stratum which prevents overheating of thedownhole equipment. A still further object is to provide a process and apparatus which avoids contact of the hot combustion gas from a downhole heater with the fuel-air feed line to the heater. Other objects of thejinvention will become apparent upon consideration of the accompanying disclosure.

The heater of the invention comprises an arrangement of feed and exhaust lines to and from the heater which are cooled by indirect heat exchange with a liquid coolant such as water. A feed line for a mixture of air and fuel gas extends thru the well head to a lowerleyel of the stratum surrounding a borehole therein and this feed line is surrounded by a concentric conduit also extending thru the well head to a lower level of the stratum. An exhaust conduit for withdrawing combustion gas from the borehole surrounds the aforesaid concentric conduit and extends thru the well head to a level adjacent the top of the stratum thereby providing an annulus around the inner adjacent conduit for withdrawal of combustion gases. The

annulus immediately surrounding the fuel-air feed line provides a passageway for the continuous stream of water from the lower section of the well bore thru the well head,

thereby providingindirect heat exchange with the com- "Water column in the annulus surrounding the gas feed line to the heater, a continuous flow of water thru said annulus is effected and this, together with the circulation of water thru the jacket surroundingthe exhaustconduit, completely prevents overheatingof any of the downhole equipment. 7 p V A more complete understanding of the invention may be had by reference to the accompanying schematic drawing in which Figure 1 is an elevation partly in section of 'a preferred arrangement of apparatus associated with a borehole in a carbonaceous stratum for effecting the in-,

vention, and Figure 2 is a fragmentarypartial section of the lower end of a downholeburner arrangement in a borehole showing anotherv embodiment of the invention.

. Referring to Figure 1; a stratum 10 is penetrated by a well bore 12 and injection boreholes 14. Well bore 12 is provided with a casing 16 which extends substantially tothe upper level of stratum 10 and with a well head 18. A gas line 20 extends th-ru the'well head to a lower level of stratum 10 within borehole 12 andterminates in a gas distributor 22 which directs injected gas radially outwardly from the gas line thrua series of regularly spaced portsf23. A water line or. conduit 24 concentric with gas line 20 and ofsubstantially larger diameter so as to pro- ,vide an annulus. therebetween extends froma level just 5 g above distributor 22 thru the well head and connects with tank 26 which functions as a volume chamber and/or a back pressure control chamber.

' A concentric exhaust conduit 28 of larger diameter than conduit 24 extends Q i ,from a leveladjacent the top of stratum 10 thru the well 'a borehole therein. Another object :to provide an head and provides an annulus around conduit 24 forie'fliu- 9 eat combustion gas. An outer conduit 30 concentric with the inner conduits is closed at the lower end and extends thru the well head thereby forming a water jacket for exhaust conduit 28 substantially along its entire length. A water inlet line 32 connects with the lower end of the jacket and effluent water line 34 connects with the closure 36 on the upper end of the jacket. The structure thus far described provides a combustion zone 38 within the section of borehole 12 in stratum 10 extending substantially the full depth of the stratum. Combustion zone 38 may be shortened by raising the level of water 40 in the bottom of the well bore as described more fully below. An igniter 41, such as a heating element or spark plug connected by wires to a curent source not shown, is attached to conduit 24 for igniting the fuel-air mix fed to combustion zone 38.

A water conduit 42 extends from the ground surface thru a separate borehole to a level adjacent the bottom of borehole 12 and within a short distance thereof, such as a foot, and the underlying formation 44 is fractured at 46 by hydraulic pressure in conventional manner so as to provide a passageway for water into the lowermost section of the borehole. The water circulation system of the apparatus, in addition to conduit 42, fracture 46, borehole 12, conduit 24, and tank or chamber 26, includes a return water line 48 leading from tank 26 to conduit 42. A surge tank or vessel 50 is positioned in line 43 downstream of tank 26 and is provided with a liquid level controller 52 which is sensitive to the liquid level in an upper section of tank and in operative control of motor valve 54 in water line 56 which supplies replacement water for the process. A vent 57 from tank 59 allows escape of vapor from the tank. A pump 58 and a cooler 60 are provided in line 48 intermediate tank 50 and conduit 42. A liquid level controller 62 is provided on tank 26 and is in control of motor valve 64 in the return Water line 48.

The water circulation system for water jacket 30 comprises, in addition to feed line 32 and effluent line 34, a line 66 connecting line 48 with line 32. Motor valve 68 in line 66 regulates the flow rate of water thru jacket 30 to provide the desired amount of cooling. A valued waste water line 70 connects with line 34. p

A line 72 connects with the section of tank 26 above the water level therein to supply suitable air or other pressurizing gas to control the back pressure on the water in line 24. A motor valve 74 in line 72 controls the flow of gas into vessel 26 to maintain a selected pressure. A fuel gas line 76, provided with motor valve 78, and an oxygen (air) supply line 84), provided with motor valve 82, connect with gas feed line 20 and supply these gases in any desired ratio. A motor valve 84 in gas feed line 26 controls the flow rate of the premixed fuel gas-oxygen thru line 20. A motor valve 85 controls the back pressure on the flue gas egressing thru line 87 from conduit 28.

A pressure-controller instrument 86 is connected with the well anulus inside casing 16 by means of line 88 and is in control of motor valves 74, 84, and 85 so as to correlate the back pressure of the water in line 20 with the gas pressure within well bore 12 to maintain the proper liquid level 40 in the well bore.

Boreholes 14 are provided with a casing 90 extending to the vicinity of stratum and with a conduit 92 extending thru well head 94. An air line 96 and a fuel gas line 93 connect with conduit 92 for supplying air and/or an air-fuel gas premix to borehole 14 for the purpose of feeding the same thru stratum 10 to borehole 12 for initiation and maintenance of combustion of the carbonaceous stratum when it has been raised-to ignition temperature at borehole 12.

Referring to Figure 2, the heater arrangement comprises, in addition to the elements of Figure 1, including conduits 20, 24, 28, and 30, 'a water line 42 positioned within conduit 24 along with conduit 20. While conduits 20 and 4-2 are shown as nonconcentric, conduit 42 may be of larger diameter than conduit 20 and concentric therewith so as to provide an annulus with conduit 20 for supplying a stream of water to the bottom of the borehole and also an annulus with conduit 24 for an efliuent stream of water from the bottom of the borehole.

It is essential to the process of the invention to maintain a water level 40 above the lower end of conduit 24 so that water is continually forced out the annulus between conduit 24 and conduit 20. This effectively cools the assembly of conduits within the combustion zone 38, and also from the lower end of conduit 28 out thru the well head, because of the direct heat exchange of the water with the metal conduits. The lower end of conduit 24 is shown in Figure 1 below the bottom of stratum 10 which permits maintaining water level 40 as low as the bottom surface of stratum 10. By starting the preheating of the stratum with the level of water 40 at an intermediate section of the stratum, the heating of the stratum can be concentrated at an upper section thereof and, as the heating progresses, the level of water can be lowered either gradually or rapidly to a lower level so that the preheating with direct flame above the water of the borehole in stratum 10 is extended. This feature of the invention is particularly adapted to heating a carbonaceous stratum of substantial thickness, such as 20 to 30 feet or more. In heating thiner strata such as 5 to 15 or 20 feet the rate of introducing combustible mixture to line 20 can be sufficient to provide flame type combustion over the entire extent of exposed stratum within the borehole.

One of the advantages accruing to the process lies in the burning of the combustible mixture on the surface of the water in the borehole as it bubbles thru the water into the combustion area. This type of apparatus and operation avoids burning the combustible mixture thru burner orifices and therefore avoids the numerous burner problems involved in downhole burner equipment conventional in the art, such as corrosion, erosion, overheating, etc.

In operation of the process in accordance with the arrangement of apparatus illustrated in Figure 1, air and fuel gas are fed in a preferably stoichiometric ratio thru lines and 76, respectively, into line 20 thru motor valve 84 at a suitable rate to provide the desired amout of heating in the borehole. Water is injected at a selected rate thru conduit 42 by means of pump 58 so as to maintain a level of water 40 above the lower end of conduit 24. The injected combustible mixture of gas passes thru distributor 22 which directs the gas radially outwardly from conduit 24 so that it bubbles up thru the water into the combustion zone 38 and is ignited at the start of the heating process by igniter 41, thereby heating the wall of the borehole by direct contact of the resulting flame therewith and the hot combustion gases are exhausted thru the annulus between conduit 28 and conduit 24 into line 87, containing motor valve 85.

Air or other pressurizing gas is injected into the back pressure chamber 26 above the liquid therein so as to maintain a suitable back pressure on the liquid in conduit 24 which pressure is regulated so that, when taken with the hydraulic head on the water in the borehole, it is less than formation gas pressure or pressure in borehole 12. Pressure in borehole l2 depends upon the back pressure maintained on the exhaust flue gas by valve in line 37 and the rate of injecting combustible gas as controlled by valve 84 in line 20, as well as the back pressure maintained in tank 26. Water is injected at a constant rate thru line 42 and the flow rates thru valves 74, 84, and 85 are correlated and controlled by pressure controller 86 which is connected with the well bore thru line 88 so as to be sensitive to pressure therein.

The water level 'in tank 26 is controlled by level controller 62 which operates motor valve 64 and the water level in tank 50 is controlled by level controller 52 operating valve 54 so as to supply make up water as required. Tank 50 is vented to atmospher to obtain the cooling efiect of evaporation from this tank. This reduces the amount of cooling required in cooler 60 in line 48. It is desirable to avoid flashing of water in conduit 24 and it is therefore desirable to cool the water injected thru line 42 to about atmospheric temperature or lower in cooler 60. Cool water. from line 48 is also circulated thru lines 66 and 32 to jacket 30 for cooling the outside of conduit 28 above the exhaust inlet. Jacket water is returned to tank 50 via line 34 or to waste via line 70.

In order to establish combustion of carbonaceous material in stratum 10, the temperature of the stratum around borehole 12 is raised to the ignition point of the carbonaceous material therein and the same is contacted with air or other O -containing gas injected through the stratum to the borehole. It is feasible to contact the stratum with 0 during the latter stages of the preheating step, or the contacting may be initiated after ignition temperature has been reached. It is preferable to inject the air for ignition of the carbonaceous material thru boreholes 14 by means of conduits 92 and pressurizing the stratum so that air passes thru the permeable stratum to the ignition well bore. Boreholes 14 are positioned within a few feet of well bore 12, such as 2 to 25 feet or more, depending upon the permeability of the stratum. As the injected air reaches the hot stratum around borehole 12, ignition thereof is initiated and in situ combustion is established so that the resulting combustion front is moved laterally outwardly from borehole 12 toward the injection wells. When the combustion front reaches the air injection wells, advancement of the front may be continued by injecting air from a ring of boreho es outside of the ring of boreholes represented by boreholes 14.

In accordance with one embodiment of the process, the injection of air thru boreholes 14 is commenced before preheating borehole 12 so as to flush out water and hydrocarbons present in the virgin stratum. The water and hydrocarbons driven in borehole 12 are then produced thru well tubing in conventional manner. In this manner the flow of air for initiating in situ combustion and the combustion itself are practically instantaneous when the stratum around borehole 12 has been heated to the desired level. During the initial phase of preheating, the flow of air is preferably terminated and renewed during the last phase of heating. Flow of air thru the stratum should be controlled so as to avoid excessive cooling of the stratum adjacent the borehole. It has been found advantageous to inject a small proportion of fuel as such as propane with the air thru line 98. This procedure hastens the combustion and reduces the time necessary to effect a sustained combustion of the carbonaceous material around the ignition borehole.

Etfecting the process with the apparatus shown in Figure 2 issubstantially the same as when utilizing the apparatus of Figure 1, the principal difference being in the injection of cooling water thru the well bore conduit 42 instead of thru this conduit placed in the formation.

After the in situ combustion has been established the downhole heater arrangement is withdrawn and hydrocarbons produced by the in situ combustion process are recovered by conventional means thru well 12. It is also feasible to leave the burner components in place and recover produced hydrocarbons thru any one or any combination of pipes 20, 24, and 28.

The boreholes of Figure 1 illustrate both a ring type arrangement of boreholes around a central borehole and a row of in-line ignition wells 12 having positioned on each side thereof a row of in-line injection boreholes 14. The process and apparatus disclosed are applicable to the ignition and'in situ combustion of any carbonaceous stratum which is permeable or which is impermeable and amenable to fracturing or other means of rendering the stratum permeable. Coal veins can be horizontally or vertically fractured around boreholes therein so as to permit in situ combustion thereof and most oil sands are sufficiently permeable to be produced by in situ com bustion without fracturing. Tar sands are usually sufficiently permeable while shales require fracturing in order to render them sufficiently permeable to produce by in situ combustion.

Certain modifications of the invention will become apparent tothose skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

1 claim: a V p 1. Apparatus for heating a subterranean stratum containing combustible carbonaceous material around a well bore therein comprising in combination av casing in said well bore having a wellhead at its upper end and extending to a level above said stratum; an eflduent water line extending thru said well head to a lower level of said stratum; gas conduit means within said water line extending from said well head to a lower level of said stratum; means on the lower end of said gas conduit means for delivering gas outside of said water line to the annulus between said stratum and said water line; an exhaust conduit surrounding said water line and extending from said well head to adjacent the level of the top of said stratum; a water jacket around said exhaust conduit extending downwardly from the wellhead; means for supplying water to the bottom of said well bore; and means for igniting a combustible mixture of O and fuel gas in said annulus delivered thru said gas conduit and said means on the lower end thereof.

2. The apparatus of claim 1 including a closed pressure-control chamber on the upper end of said water line having a level control for maintaining a selected water level therein; a water return line from said chamber to the well bore below the desired water level therein as said means for supplying water; a flow control valve in said return line controlled by said level control; and means for circulating water thru said water jacket.

3. The apparatus of claim 2 further comprising a gas pressuring line having a motor valve therein connected with said chamber; a fuel line and an air line connected with said gas conduit means; a motor valve in said gas conduit means downstream of said air and fuel lines; a motor valve in said exhaust conduit; a pressure-controller sensitive to the gas pressure in said well bore and in operative control of each of said motor valves.

4. The apparatus of claim 2 further comprising a surge vessel in said water return line downstream of the flow control valve therein having a vent to atmosphere; a liquid-level controller on said surge vessel; a water supply line connected with said vessel having a motor valve therein controlled by said liquid-level controller; and a pump and a cooler in said return line intermediate said surge vessel and said well bore.

5. The apparatus of claim 1 wherein said means for supplying water comprises a conduit leading to the bottom of said stratum adjacent said well bore.

6. A process for initiating combustion in a carbonaceous stratum around a well bore therein which comprises maintaining a selected waterlevel in said well bore at a lower level of said stratum; introducing a combustible mixture comprising fuel gas and 0 below said water level so that said mixture bubbles up thru said water into said well bore; burning said mixture in a combustion zone above said water level adjacent said stratum so as to heat the walls of said well bore to ignition temperature of the carbonaceous material therein; exhausting combustion gas out of said well bore; and feeding O to the resulting hot stratum so as to ignite same.

7. The process of claim 6 wherein O is fed to said stratum thru at least one borehole therein spaced close to said well bore so as to cause the resulting combustion zone to move outwardly from said well bore countercurrently to flow of O 8. The process of claim 6 further comprising continuously introducing water to said well bore below said water level; continuously passing a stream or" water up said well bore from the water below said level; and cooling efiiuent combustion gas above said stratum by indirect heat exchange with the effluent stream of water.

9. The process of claim 8 wherein said combustion gas is exhausted thru an annulus around said stream of water and wherein an annulus of water is circulated around the combustion gas annulus in indirect heat exchange therewith.

10. The process of claim 6 wherein the extent of said combustion zone is regulated during the heating of said stratum by varying said water level.

11. The process of claim 6 wherein the water level is lowered during the heating step.

References Cited in the file of this patent UNITED STATES PATENTS 2,506,853 Berg et a1. May 9, 1950 2,584,606 Merriam et a1. Feb. 5, 1952 2,793,696 Morse May 28, 1957

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