US3055423A - Controlling selective plugging of carbonaceous strata for controlled production of thermal drive - Google Patents

Description

Sept. 25, 1962 H. w. PARKER 3,055,

CONTROLLING SELECTIVE PLUGGING OF CARBONACEOUS STRATA FOR CONTROLLED PRODUCTION OF THERMAL DRIVE Filed May 4, 1959 2 Sheets-Sheet 1 AIR BRINE WATER BRINE PRODUCTION 9 RETORTED SHALE 4 25 24 E #7 /WATER \EVAPORATION 26 27 44 I COMBUSTION 2025). 22 L2 AIR A x x x F IG.

I M AIR\ 3 FLAME FRjiNT 66 r- 'VAM \yfi "m g Q 7 5 I2 i FIG. 4 i PRODUCTION I '5 innm SALT BLOCK BRINE BRINE INVENTOR. kAlR MRJ J H.W. PARKER BY f! 2;

A f TORNEVS p 1962 H w. PARKER 3,055,423

CONTROLLING SELECTIVE PLUGGING OF CARBONACEOUS STRATA FOR CONTROLLED PRODUCTION OF THERMAL DRIVE Filed May 4, 1959 2 Sheets-Sheet 2 PRODUCTION 5 HOT 52 BRINE GASES- SALT BLOCK "5; PRODUCED AREA FIG. 3

INVENTOR.

H. W. PARKER nyw w A TTORNEVS E FRONT United States Patent 3,d55,i23 Patented Sept. 25, 1962 hire CUNERQLLING SELELTEVEE PLUGGING (ll CAR- EQNAEEGUS STRATA FOR QGNTRGLLED PRO- DUQTHBN (BF THERMAL DRIVE Harry W. Par-her, Eartiesviiie, (Eda, assignor to Phillips Petroleum Company, a corporation of Delaware Filed May 4, 1959, Ser. No. 810,919 22 Claims. (Cl. 166-41) This invention relates to the production of hydro carbons by thermal drive. A specific aspect of the invention is concerned with selective plugging of the carbonaceous stratum while producing same by thermal drive.

In situ combustion in the recovery of hydrocarbons from underground strata containing carbonaceous material is becoming more prevalent in the petroleum industry. In this technique of production, combustion is initiated in the carbonaceous stratum and the resulting combustion zone is caused to move thru the stratum by either inverse or direct air drive whereby the heat of combustion of a substantial proportion of the hydrocarbon in the stratum drives out and usually upgrades a substantial pro-portion of the unburned hydrocarbon material.

The ignition of carbonaceous material in a stratum around a borehole therein followed by injection of air thru the ignition borehole and recovery of product hydrocarbons and combustion gas thru another borehole in [the stratum is a direct iair drive process for effecting in situ combustion and recovery of hydrocarbons from the stratum. In this type of operation the stratum usually plugs in front of the combustion zone because a 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 thru 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 air is fed thru the stratum to the combustion zone from one or more surrounding boreholes.

in situ combustion techniques are being applied to tar sands, shale, Athabasca sand and other strata in virgin state, to coal veins by fracturing, and to strata partially depleted by primary and even secondary and tertiary recovery method-s.

Strata containing hydrocarbon material in the form of solid and semi-solid and heavy viscous oil are often difiicult to produce because of their low permeability. Such strata include shales, heavy tar sands, and those containing semisolid hydrocarbons and/r highly viscous oils. In producing hydrocarbons from such strata around a Well therein by passing hot gas along the Wall of the well within the stratum, very little production can be eflected because of the difiiculty in flowing the hot gas into the stratum. After producing hydrocarbons from a relatively thin annulus around the well, the hot gases used in heating the stratum merely flow along the wall of the Well Without contacting the deeper solid, semi-solid, and viscous hydrocarbon material.

When producing hydnocarbons irom carbonaceous strata by thermal drive such as by in situ combustion wherein the stratum to be produced is ignited and the resulting combustion zone is driven thru the stratum, burning a portion of the hydrocarbon material and producing most of the balance as product, it is desirable in many instances to control the direction of the movement of the combustion front. Heretofore, no reliable method has been avail-able tor such control.

This invention is concerned with selective plugging of strata containing hydrocarbon material during a thermal drive process for producing the strata. Accordingly, it is an object 'of the invention to provide an improved process for th production of hydrocarbons from carbonaceous strata by controlled thermal drive. Another object is to provide a thermal drive process which is controllable as to direction and pattern. A further object is to provide a process for producing hydrocarbons from a can bonac-eou-s stratum around a single well therein by thermal drive thru a substantial section of the stratum. Other objects of the invention will become apparent to one skilled in the art upon consideration of the accompanying disclosure.

A broad aspect of the invention comprises plugging a selected area of a permeable stratum so as to control the pattern of a thermal drive process by heating the area to be plugged to a high temperature and injecting into the hot stratum a concentrated aqueous solution of a solid compound so as to vaporize water fnom the solution and deposit the compound in the pores of the stratum until plugging is effected. Any highly soluble compound not readily decomposable or volatilizable by heat is operable in the process. Preferred compounds are the relatively cheap and highly soluble salts of sodium and calcium such as sodium chloride and calcium chloride. Calcium chloride is preferred because of its greater solubility and hence its greater efficiency in the process. It has been 'found that the addition of a small quantity of glycerin in the solution greatly raids in rendering the resulting plug impermeable after cooling. A concentration of glycerin in the range of about 1 to 4 volume percent of the solution is eflective in aiding the plugging and rendering the plug impermeable.

A more complete understanding of the invention may be had by reference to the accompanying schematic drawing of which FIGURE 1 is an elevation in partial section thru a carbonaceous stratum; FIGURE 2 is a similar elevation showing another embodiment of the invention; FIGURE 3 is a similar elevation showing a third em.- bodiment of the invention; and FIGURE 4 is a plan View of an arrangement of wells nor production by in situ combustion illustrating another embodiment of the invention.

Referring to FIGURE 1, a stratum 10 is penetrated by a well 12, which is provided with casing 14- extending doWn approximately to the stratum 10 and capped by a well head. Within casing 14 are concentric conduits 16, I8, 20, and 22, extending to successively lower levels of the stratum. Packers 24, 25, 26 and 27 pack ofi spaces adjacent the ends of each of conduits 16, 18 and 20, respectively, for injection of brine in the upper and lower spaces and water in the intermediate space, all of these spaces being at an intermediate level of stratum 10. Line 30 connects with tubing 22 for injection of air or hot gas for effecting the thermal drive. Line 32 connects with conduit 20 for introducing brine to the lowermost packed oif space and line 34 connects with conduit 16 for introducing brine to the uppermost packed off space at the end of conduit 16. Line 36 connects with conduit 18 for introducing water into the intermediate packed oif space at the end of conduit 18. Line 38 connects with casing 14 and provides an efiluent line for produced gases collecting in the outer annulus of the well.

When the arrangement of FIGURE 1 is utilized for production by in situ combustion, a combustion front 40 is driven thru the stratum axially away from Well 12. Numerals 42 and 44 designate salt blocks at the upper and lower levels of the plugged ofl? area.

Referring to FIGURE 2, a stratum 10, which may be a shale or heavy tar sand, is penetrated by a borehole or well 12 which is provided with a casing 14 and a tubing string 22 extending to adjacent the bottom of the hole. A conduit '46 extends from the well head to an intermediate level of stratum 10 and the well is filled with sand 48 up to the top of stratum 10. A production line 50 connects with tubing 22 at the well head for removal of produced gases. Hot gases and/or air are introduced thru line 52 to casing 14 and the outer annulus of the well. A line 54 is connected with conduit 46 for introducing brine to the inner annulus. Numeral 56' designates a fracture formed around well 12, while numeral 58 designates a salt block in the stratum adjacent the fracture both above and below same.

In FIGURE 3 stratum is penetrated by a pair of spaced apart wells 12 and 13 each of which is provided with a casing 14- extending to about the level of the top of stratum 10, and with tubing strings 22 and 23, respectively. An air line 30 connects with tubing string 23 and a production line 50 connects with tubing string 22. A brine injection line 60 connects with the annulus of well 12 thru the well head. Packers 62 and 64 are positioned around tubing strings 22 and 23, respectively, at a selected intermediate level of stratum 10. A fire front 66 is shown intermediate wells 12 and 13, below the level of packers 62 and 64, moving toward well 13 countercurrently to air injected thru well 13 below packer 64. A salt block 58 is shown extending from well 12 toward well 13 as far as the approximate location of the fire front.

In FIGURE 4, air injection wells 13 are positioned in a ring around production well 12 with a flame front 66 being driven thru stratum 10 by inverse air injection thru wells 13. Production is recovered thru well 12. Brine injection wells are positioned intermediate air injection wells 13 and production well 12 outside the fire front in a selected location designed to block the movement of the fire front and seal off a selected section of the stratum to fiow of gases.

In producing hydrocarbons from shale, heavy tars, and other bituminous strata of little or no permeability around a single well, as illustrated in FIGURE 1, air or fuel gasair mixtures are injected thru tubing 22 to establish in situ combustion in the stratum around the Wall of the well. Of course, it is to be understood that hot gases such as steam, CO combustion gases, nitrogen, etc., may be utilized to retort hydrocarbons from the stratum adjacent the well. Without the use of the invention, it is possible to retort hydrocarbons from only a very thin annulus of the wellbore because of the difficulty of forcing the gases and/ or the combustion front deeper into the stratum and because heat transfer laterally thru the stratum is exceedingly slow. Naturally, unless some means is provided to force the air or other hot gas into the stratum, the same merely passes up the unobstructed borehole without penetrating the stratum to any appreciable depth. In the embodiment of the invention shown in FIGURE 1, two layers of brine are injected into the stratum together with an intermediate layer of water after the preliminary retorting and opening of the stratum around the wall of the well as deep as is possible in the open borehole. After this preliminary retorting, injection of air or hot gas is terminated to permit setting of the packers and conduits preparatory to injecting brine and water. Thereafter, the combustion zone is re-established below packer 27 by conventional means and injection of brine and water is initiated so as to commence plugging of the stratum at the upper level of the upper brine layer and lower level of the lower brine layer. The hot gases and hot rock in the area of injection of the brine evaporate water from the brine and leave in the pores of the rock or sand a solid salt block which forces the produced gases and combustion gas deeper into the stratum to bypass the salt block.

The function of the water is to prevent plugging across the advancing face or edge of the injected brine layers by continued evaporation of water from the brine. The injection of clear water dissolves any salt block which [might tend to form in the path of the advancing injected brine, thereby allowing forward movement of the brine into the stratum so as to continue forcing the produced hot gases deeper into the stratum.

The pressure applied to the injection of the brine and water is controlled in response to the hydrocarbon content of the produced gases. When the hydrocarbon concentration in the produced gases decreases below a normal production level, it is an indication that the brine and water are not being forced rapidly enough into the stratum to force the hot gases or combustion front farther into the stratum at a reasonable rate. By properly regulating the air injection rate and the pressure on the injected liquids, the movement of the salt block and the combustion zone thru the stratum can be controlled so as to drive the combustion front deep into the stratum from the ignition well and produce hydrocarbons from the section of stratum above and below the salt block. At any time during the process, upon termination of the injection of brine and water, the combustion zone may be driven around the end of the salt block and back to the well above the salt block. Of course, it is to be understood that the combustion zone may be driven from the well Wall above the salt block thru the stratum and back to the well wall below the salt block by injecting air thin line 38 and recovering production thru line 30. Indirect drive of the combustion front by inverse air injection is not operable in the embodiment of the invention shown in FIGURE 1 because it is necessary to drive the hot gases around the end of the injected brine and Water layers in order to open up the stratum to flow of gases and liquids.

The lower limit of the injection pressure on the brine is limited by the concentration of hydrocarbons in the produced gases. The block should be advanced at a rate sufiicient to cause the hot gases bypassing the block to retort hydrocarbons from the area in front of the advancing salt block rapidly enough to render the process economically feasible. However, advancing the salt block at any appreciable rate makes the process operable. The upper limit of brine pressure and rate of injection is determined and limited by the air compressors and permissible air injection pressures at the depth of the stratum being produced.

In operating the embodiment of the invention illustrated in FIGURE 2, the wall of well '12 is first produced by retorting hydrocarbons therefrom with hot gases injected thru line 52 and with production being recovered thru tubing 22 and line 50. Brine is then injected thru line 54 and conduit 46 where it flows into the hot sand adjacent the end of conduit 46 and into the permeable stratum opposite the end of the conduit. The evaporation of water from the salt solution by the heat in the hot sand and rock forms a salt block at levels below and above the end of conduit 46 and in the stratum between these levels. The introduction of a salt block into the stratum opposite the end of conduit 46 forces the hot gases to flow deeper into the stratum in order to bypass the salt block and thereby produces more tar and hydrocarbon material from the stratum. The resulting salt block eventually blocks the injection of brine and, in order to overcome this difliculty, the brine injection pressure is increased until a horizontal fracture 56 is produced around well 12. This permits the brine to flow into the stratum thru the fracture but the flow of hot gases around the salt block and the injected brine produces more of the stratum in advance of the injected brine thereby rendering the same permeable and increasing the depth to which the brine can penetrate the stratum. The salt block can therefore be continually extended into the formation along the fracture and the fracture can be increased in radial depth as the injection process is continued, resulting in the production of more tar and other hydrocarbons from the stratum in front of the advancing fracture and salt block. It is feasible to either continually inject brine or to inject a large quantity of brine only when the injected gas-to hydrocarbon ratio becomes too high.

The embodiment illustrated in FIGURE 2 is similar to that illustrated in FIGURE 1 in all respects except the manner in which the continued injection of brine is assured. The injection of hot gases, including steam, is illustrated but it is also feasible to initiate combustion either above or below the salt block and drive the combustion front thru the stratum as in the embodiment illustrated in FIGURE 1. It is also feasible to utilize in the plugging step any liquid solution or slurry from which evaporation leaves a plugging or blocking residue. To illustrate, in FIGURE 2, the stratum may be fractured by any suitable means and a slurry of time clay particles may be used to plug the stratum adjacent the fracture and the sand adjacent the end of conduit 46.

The embodiment of the invention illustrated in FIG- URE 3 comprises initiating combustion in a selected selection of the stratum such as below the level of packers 62 and 64, driving the combustion front thru the stratum from well 12 to well 13 and injecting the solution effective in plugging thru line 60 to the annulus above packer 62 so that a salt plug 58 is formed along the upper boundary of the burned out area which progresses thru the stratum adjacent the combustion zone as the latter moves thru the stratum. This embodiment of the invention is applicable only to strata which are sufficiently permeable to allow the passage of gases from well to well. It is to be understood that well 12 may represent a central well with a ring of wells 13 surrounding same, or wells 12 and 13 may simply represent wells in a line of production and a line of injection wells, respectively. A combustion front 66 is moved thru the stratum by inverse air injection thru line 3t and tubing 23, while production is recovered thru tubing 22 and line 50.

In the embodiment illustrated in FIGURE 4, a stratum 10 is being produced by inverse air injection in a ring pattern of injection wells 13 around a central production well 12. It may be desirable to block the movement of the combustion front 66 in a given direction, such as along the edge of a cliff, to prevent escape of produced gases or air, or along the boundary of a field. Brine injection wells 15 are positioned in the vicinity of the desired blocking area and brine is injected so that the injected air and brine pressure force the brine into the combustion zone and the hot rock adjacent same whereby evaporation of the liquid from the brine deposits suflicient salt to effect plugging. This technique may also be desirable in converting a ring type combustion front to an in-line combustion front. In the process illustrated, the fire front in the area of the injected brine may be smothered for lack of oxygen, but there is suflicient heat in the hot stratum to vaporize enough water to effect plugging by salt deposition. Rough calculations show for typical conditions using sodium chloride in a given volume of rock after burning that there is sufficient heat to vaporize enough water so that percent of the pore space could be filled by salt crystallizing from a saturated solution. The movement of the resulting slurry further into the hot zone evaporates more water and thereby plugs the formation completely. More highly soluble salts such as calcium chloride are even more effective. It is also feasible to inject a slug of brine followed by injection of clear water, the brine quantity being sufiicient to effect the blocking and the water serving as the driving fluid. In some instances, the slug of brine may be driven to the desired location in the stratum by injecting gas.

To illustrate the invention a glass tube 9 inches long and %-inch inside diameter was packed with white sand which had a permeability of approximately 2.0 darcys. A /s-inch stainless steel tube was placed along the axis of the glass tube so that a sliding thermocouple could be used to measure the temperature of the sand. The central 6 inches of the glass tube was wrapped with an electric heating tape and covered with approximately Ai-inch of glass wool insulation. The sand was heated in this manner to a maximum temperature of 900 F. After the sand had been heated, brine was injected into the bottom of the tube. When the brine reached a position about 3 inches from the bottom of the tube sufiicient water had been evaporated to reduce the permeability IOGO-fold or more, and soon there was no further appreciable brine flow.

When cooled, salt blocks formed in this manner tended to leak a small amount of brine. The injected brine was not saturated therefore it dissolved the salt block. This difficulty was avoided by the addition of glycerine (2 ml./10fi in solution) to a calcium chloride solution (75 gr./ ml. water). The block formed by 24 hours of attempting to flow this solution into the hot sand remained after cooling of the apparatus.

In other tests the power to the heater was cut off when brine flow was started. In [these cases due to the high heat losses and small thickness of sand through which the solution flowed no stable permeability block formed. Tests showed the superiority of a calcium chloride solution (75 gr./ 100 ml.) over a sodium chloride solution (30 g./ 100 ml.) to form permeability blocks under adverse conditions. This is due to (the higher solubility of calcium chloride, and the higher viscosity of the resulting solution.

Various modifications of the invention will occur to one skilled in the art. For example, it is feasible to use as the plugging medium :a liquid which decomposes to a solid product when it reaches the hot zone, such as a solution of water glass (sodium silicate).

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

I claim:

1. A process for plugging a selected disc-like area of a permeable stratum around a well penetrating said stratum which comprises heating the area to be plugged to a temperature substantially above the boiling point of the hereinafter described solution at stratum pressure; and injecting thru said well a concentrated aqueous solution of a compound, solid and stable at said temperature, under pressure, radially into the hot area so as to iorce solution into the pores of said stratum, vaporize water therefrom, and precipitate said compound in the pores of said stratum in said disc-like area until plugging is effected.

2. The process of claim 1 wherein glycerin in the range of about 1 to 4 volume percent is incorporated in said solution.

3. The process of claim 1 wherein said compound is calcium chloride.

4, The process of claim 3 wherein glycerin in the range of about 1 to 4 volume percent is incorporated in said solution.

5. The process of claim 1 wherein said compound is sodium chloride.

6. The process or" claim 5 wherein glycerin in the range of about 1 to 4 volume percent is incorporated in said solution.

7. A process for plugging a selected area of a permeable stratum around a well penetrating same which comprises extending a conduit from the Well head to the level or" said area; filling ithe annulus around said conduit and the well below same with sand; heating said sand and said stratum at the level of said area so a temperature substantially above the boiling point of the hereinafter described solution at stratum pressure; and injecting thru said conduit radially in a disc-like pattern into the hot sand and hot stratum adjacent said level a concentrated aqueous solution of a compound, solid and stable at said temperature, so as to vaporize water therefrom and precipitate said compound in the interstices within said sand and in rthe pores of said stratum in said area until plugging is effected.

8. A process nor producing hydrocarbons from a carbonaceous stratum penetrated by a well, which comprises extending a first conduit from the well head to a selected intermediate level in said stratum; extending a second conduit from the well head llJO a lower level in said stratum; filling the annulus within said stratum between the well wall and said conduits with sand; passing hot gas along the wall of said well within said stratum via said annulus and said second conduit so as to fiuidize and drive hydrocarbons from the well Wall thereby increasing the permeability of an annulus of said stratum and heating same to a temperature substantially above the boiling point of the hereinafter described solution at stratum. pressure; thereafiter, continuing the passing of said gas thru said annulus and While said stratum is at said temperature, injecting thru said first conduit radially in a disc-like pattern into the hot sand adjacent the lower end thereof and into the adjacent hot stratum a concentrated aqueous solution of a compound, solid and stable at said temperature, whereby water vaporizes trom said solution and said compound is precipitated in said sand and in said stratum above and below the level of the end of said first conduit so as to form a block to upward and downward flow of said solution; continuing the passing of said gas thru said annulus and the injection of said solution deeper into said stratum so as to force said gas deeper into said stratum, thereby continuing the production of hydrocarbons; and recovering the produced fluids including hydrocarbons from said well.

9. The process of claim 8 wherein said hot gas is passed thru said second conduit and hydrocarbons are recovered \tluu said annulus.

10. The process of claim 9 wherein said hot gas is produced by igniting said stratum below said intermediate level and injecting combustion-supporting gas th-ru said second conduit so as to effect in situ combustion.

11. The process of claim 8 wherein said compound is calcium chloride.

12. The process of claim 11 wherein glycerin in the range of about 1 to 4 volume percent is incorporated in said solution.

13. The process of claim 8 wherein said compound is sodium chloride.

14. The process of claim. 8 wherein said gas comprises steam.

15. The process of claim 8 wherein said gas comprises combustion gas.

16. A process for producing hydrocarbons from a carbonaceous stratum penetrated by a Well, which comprises establishing in said well at an intermediate level of said stratum an upper solution injection zone, an intermediate water injection zone, and a lower solution injection zone, each being separated and connected with a separate well conduit; heating an annulus of said stratum immediately surrounding said well to an elevated temperature substantially above the boiling temperature of the hereinafter described solution at stratum pressure by contacting same with hot gas, thereby producing hydrocarbons from said annulus; while said annulus is at said temperature, injecting a concentrated aqueous solution of a compound, solid and stable at said temperature, into said annulus tlu'u said upper and lower injection zones and simultaneously passing hot gas thru said annulus between an area above and an area below said injection zones, whereby water is vaporized from said solution and said compound is precipitated in the pores of said stratum to form solid rings of said compound so as to torce said gas deeper into said stratum; injecting water thru said water injection zone so as to provide tor flow of said solution deeper into said stratum while continuing the injection of said solution and the passing of hot gas thru the expanding annulus, thereby progressively extending said rings into said stratum and producing hydrocarbons from deeper in said stratum; and recovering the produced fluids including hydrocarbons from said well.

17. The process of claim 16 wherein said compound is calcium chloride and glycerine in the range of 1 to 4 Volume percent is incorporated in said solution.

18. The process of claim 16 wherein said compound is sodium chloride and glycerine in the range of 1 to 4 volnine percent is incorporated in said solution.

19. The process of claim 16 wherein said hot gas is produced by igniting an annulus of said stratum at a level spaced substantially from said intermediate level and passing combustion supporting gas directly into the ignited annulus from said well so as to force resulting hot gas thru said stratum around said rings into said well.

20. A process for producing hydrocarbons trom a restricted horizontal section of a stratum containing hydrocarbons which comprises igniting a selected vertically restricted area of said stratum around an ignition well therein; passing combustion-supporting gas to the ignited area so as to move the resulting combustion zone thru said stratum toward at least one other well therein and produce hydrocmbons trom said stratum; as said combustion zone is advanced radially outwardly from said ignition well injecting a concentrated aqueous solution of a compound, solid and stable at combustion temperature, into said stratum adjacent the horizontal boundary of said combustion zone so as to vaporize Water from said solution along said boundary and deposit said compound thereby iiorming a solid layer of said compound along said boundary; and recovery from one of said wells produced fluids including hydrocarbons.

21. The process of claim 20 wherein said compound is calcium chloride.

22. The process of claim 20 wherein said compound is sodium chloride.

References Cited in the file of this patent UNITED STATES PATENTS 2,390,770 Barton etal Dec. 11, 1945 2,874,777 Tadema Feb. 24, 1959 2,881,838 Morse ct a1 Apr. 14, 1959 2,903,065 Holbrook et al. Sept. 8, 1959 2,954,218 Dew et al Sept. 27, 1960

Images