US 3113620 A
Description (OCR text may contain errors)
Dec. 10, 1963 c. E. Hl-:MMINGER 3,113,620
PRocEss FOR PRODUCING vIscoUs oIL Filed July 6, 1959 /ze f22 sl-:PARATOR l 2| -VENT w TLSRSINE a A|R g l COMPRESSOR Y A'R OIL l BITUMINOUS DEPOSIT Chdr|esE.Hemminger Inventor United States Patent O 3,113,620 PROCESS FR PRODUCENG VISCGUS @EL Charles E. Hemmingen', Westfield, NJ., assigner to Esso Research and Engineering Company, a corporation of Delaware Filed .Iuly 6, 1959, Ser. No. 824,967 6 Claims. (Cl. 166-11) The present invention relates to an improved process for recovering viscous oil from subsurface deposits and, more particularly to a method for utilizing high energy explosives combined with in-situ combustion in a subsurface bituminous deposit containing viscous oil. Suitable deposits are subsurface strata containing hydrocarbons not naturally owable into a well bore traversing the deposit. In a most preferred process, according to the instant invention, oil is produced from oil shale reserves.
Control of the tremendous energy of nuclear devices for peacetime uses has, of late, become a subject of considerable interest. With the knowledge that such energy in the form of thermonuclear explosives should be available for a fraction of a mill per kilowatt-hour equivalent, numerous applications involving underground explosions have been proposed. Further, it has now been realized that ultra high energy explosions can be used in mining operations to break up formations, in the oil industry to increase or stimulate productivity by heating or raising the pressure of a reservoir, and in landscaping or earth moving techniques such as digging canals, making harbors, or removing troublesome obstacles.
The present invention is primarily directed to the production of oil. Further, it provides a method for preparing and utilizing an underground explosion chamber in a bituminous deposit suitable for the explosion of a high energy explosive charge. In accordance with the instant invention, oil is recovered from a subsurface bituminous formation by detonating an explosive within a well bore penetrating the formation and thereafter moving a combustion front downwardly through the formation adjacent the well bore. Oil is removed to the surface from the lower prtion of the formation through the single Well traversing the formation. In a preferred process, the above steps are repeated utilizing successively larger explosions until a cavity of approximately spherical dimensions is formed in the formation. Thereafter, an ultra-high energy explosive is detonated in the chamber formed to fragment a large volume of the bituminous formation and lill the cavity with broken and crushed material of the formation. The massive fragmented zone is then treated by conventional operations, such as in situ combustion or by water flooding With high temperature liquid phase Water in accordance with a process described in copending application S.N. 802,358, filed March 27, 1959.
Advantageously, in accordance with the present invention, nuclear energy can be released in an underground explosion of a thermonuclear device in a bituminous deposit containing hydrocarbons not naturally flowable into a Well bore traversing the deposit. Alternately, conventional molecular explosives can be employed. A particular advantage of the invention is that ultra-high energy explosives, either molecular or nuclear, can now be utilized by creating a specially prepared explosion chamber within the bituminous deposit. A cavity or explosive chamber is formed in a bituminous deposit which deposit contains substantial amounts of magnesium and calcium carbonates according to this invention by first detonating a small explosive charge in the well bore, then initiating combustion in the upper portion adjacent the well bore to establish a combustion front and thereafter injecting a combustion-supporting gas into the upper portion of the deposit to move the flame front downwardly and outwardly around the well bore, and then detonating a second explosion. By this method, the products of combustion remove substantially all organic material from an extended region in the vicinity of the Well bore, leaving a cavity in the deposit containing only a frail ash skeleton of rock. The second explosion detonated in the bore hole shatters the frail ash skeleton of rock, thus forming the cavity and at the same time causes additional fractures in the walls of the cavity. The in situ combustion step is repeated after each explosion, thereby forming another and larger area of frail ash skeleton of rock. Oil derived from the bituminous deposit by the combustion step can be removed to the Surface through the well bore extending through the bottom of the burned-out zone. By repeating the steps outlined, the cavity can be increased in size many fold.
An important feature of the present invention lies in the fact that, by creating an explosion chamber containing only a very friable skeleton of ash, many problems concerned with the shock wave created by the explosion are obviated. As most atomic devices release energy equivalent to that of a major earthquake, Without special precautions, shockwave can result in significant motion of the earths surface. In accordance with this invention, the loss of energy from an H-bomb or an A-bornb blast in the explosion chamber underground is substantially reduced due to transmission of shock wave energy through the skeleton ash material of the chamber. Therefore, substantially all the energy released can be utilized to provide sensible heat to raise the temperature of the fragmented rock which falls into the cavity following the expansion stage of the nuclear explosion.
Alternately, the very frail skeleton ash can be knocked down prior to the detonation of the ultra-high energy device simply by exploding a small charge or by utilizing a water Washing technique in accordance with conventional ooding practice in secondary recovery operations. The advantage of having a large, substantially empty cavity is readily apparent. The extremely large cavity from which the ash skeleton has been knocked down or removed, can be used to contain many tous of conventional molecular explosives. Further, it may be necessary to provide a suitable liner within the explosion chamber in order to avoid extensive contamination of underground formation materials and adjacent water tables by the radioactivity produced by the explosion of the device involving nuclear fission. In such cases extremely large cavities are required.
Broadly, bituminous deposits containing oil-shale can be produced in accordance With the method of the present invention. The process is suitable for rock formations known as oil shale which contain a combination of organic and inorganic sediments which have become hardened into impermeable rock. Suitable shales have a compressive strength in the range of 5000 to 30,000 p.s.i. The organic portion laid down in layers is a solid amorphous material generally known as kerogen which can be converted to oil under the application of heat. The oil recovered is a black viscous waxy substance which will not ow below about or 90 F.
Further objects and features of the invention and an exemplary manner in which it is 'toi lbe performed will be more readily apparent from the accompanying description taken in connection 'with the drawing in which .the
4single FIGURE shows schematically a method of'recovering viscous oil and at the saine time preparing a subsurface explosion chamber in a bituminous Vdeposit in which a high energy explosive device can be exploded `to* produce a massive fractured zone of rook for subsequent underground treatment.
Advantageously, the :method of the present invention is employed with bituminous deposits lying in the range of from to 20,000- feet below the surface of the earth.
The minimum ground cover `required is that necessary to insure complete containment of the explosion. This depends upon the energy yield of the explosive utilized. For nuclear devices, the minimum depth in feet is approximately equal to in the range of 250 to 450 times the cube root of the size of the device in kilotons. Thus, the explosion from a one kiloton nuclear bomb is completely contained if the device is exploded 250 to 450 feet below the nearest surface point. The maximum depth is limited only by the economic considerations involved in penetrating very deep lying formations with conventional drilling equipment.
Explosives suitable for use within a subsurface bituminous deposit are Well known in the ar-t. Due to the space limitation inherent in the process involving detonation of an explosive in a well bore, explosives having a high energy yield for their size are especially preferred. Most preferably, the explosion will have an energy yield equivalent to in the range of 0.1 kiloton to megatons of TNT. However, inexpensive chemical explosives such as ammonium nitrate can be employed. In one embodiment, the method of the present invention is carried out utilizing a thermonuclear device such as a hydrogen or atomic bomb. Suitable thermonuclear devices are now available for underground explosions; therefore, it is to be understood that the present discovery involves merely the use of a nuclear device in a novel and useful method `for exploiting oil deposits, and that the fabrication and manufacture of hydrogen and atomic bombs form no part of this invention.
Initially, `when a thermonuclear device is exploded in an underground oil deposit, an isothermal ball of fire is produced, which produces a very high pressure and temperature. The intensity of energy absorbed from the shock wave is sufficiently high near the fireball to vaporize rock and increase the size of the explosion chamber, then melt rock outside the vaporized sphere, and crush more rock outside the melted liner. The cavity, at much higher than equilibrium ground pressure, is held back by the inertia of the surrounding rock but then expands to equalize the cavity pressure with ground pressure pushing the crushed but -unvaporized rock ahead of it, more or less isotropically. Almost immediately the cavity is collapsed and the crushed bituminous rock caves into the void which has been created, forming a massive fractured zone which is then exploited by a conventional process such as the hot water process already referred to. In this process, oil is recovered from the fragmented zone by supplying high pressure water, steam or brine to the zone through an injection well or injection wells at a temperature in the range of 550o to 800 F. to supply the hea-t to decompose the bituminous material and carry out the oil ythrough a production well. Sufficient pressure is employed to maintain the high temperature water in dense phase. Recovery efficiencies approaching 100% can be achieved at reasonable rates of water injection suicient to advance the heated zone at a velocity in the range of 0.1 to 5 feet per day. The flood water at a temperature in the range of 550 to 800 F. is supplied to the fragmented zone by injecting water, steam or brine or a mixture of these at high temperature at the top of the crushed zone. Where water is injected through the injection well through a casing set to the top of the fragmented Zone, oil can be produced by the action of the water from the bottom of the zone through a production well `set `to the lower most region of the fractured zone. Alternately, an in-situ combustion process can be employed.
Referring to the drawing in detail, reference character 1 designates a bituminous oil shale deposit which does not produce itself under natural conditions. This deposit can be an oil-shale having essentially no permeability and containing non-mobile oil in the form of kerogen, laid down in the Irock in layers. It is isolated by adjacent strata 2 and 3. Within bituminous deposit 1 which, for example, can be of the order of 1000 feet thick there has L been formed :a substantially spherical explosion chamber 4- containing a peripheral friable skeleton of ash 5 left in place following the combustion step.
Reference character 11 designates a well bore extending downwardly from the sunface 12 through formation 2- and terminating in formation 1. It will be understood that the weli bore actually extends through a plurality of subsurface formations and that only a total of three formations are shown in 4the drawing for simplification. A well `casing 13 extends downwardly through the well bore 11 and into the bituminous deposit l1 to be exploited. The upper end 14 of the casing is capped or closed off above the surface and a conduit 15 communi- Cates with the casing above the surface for purposes which will be hereinafter set forth. By drilling from the top of formation 1 to a predetermined depth a single string of tubing 16 is placed concentrically in casing 13 and terminates beiow the lower end of casing '13 whereby oil which accumulates in the well bore, as will be more fully hereinafter set forth, can be removed to the surface. In the case of impermeable shale rock, gas communication is established from the well bore at the upper portion of the formation downwardly through the formation around the well bore and lback into the well bore in the lower portion of the formation by detonating an explosive charge. Redrilling for setting casing 16 is usually required after the fracturing operation.
In practicing the present invention, the casing 13 is cemented to the walls of the well bore 11 through the central portion of the oil bearing formation 1 as indicated by the reference character 17. Thus, Ifor-mation 1 is in direct communication with the casing throughout the 11pper portion of the formation and the formation is in direct communication with tubing string `16 through the lower end portion of the formation.
Air mixed with hydrocarbon fuel is forced through conduit 15 downwardly through the annulus between the casing 13 and tubing 16 and outwardly into the upper portion of the formation 1. As the high pressure fuel and air mixture is supplied, combustion can then be initiated by any suitable means. The flame front resulting from the combustion is driven by air injection downwardly and outwardly through the formation 1 around the well bore in the directions indicated by the arrows. Also, the gases of combustion will be forced downwardly through the formations by the high pressure incoming fuel-air mixture and will enter tubing 16 to be carried to the surface.
As will be apparent, oil containing materials and oil entrained in formation 1 around the well bore will be moved and directed into the lower portion of the well bore by the heat of combustion together with the resultant gas drive and will be carried up the tubing string 16 together with the gases of combustion or can be removed by any desired articial lifting means. In some formations the amount and the pressure of the gas discharging into the lower portion of the well can be suhcient to provide removal of accumulated oil along with the combustion gases through the tubing.
Oil removed to the surface is separated from the combustion gases in separator 21. These gases are then sent by line 22 to a gas turbine 23 where they provide the energy to compress the air fed to the air compressor through line 26. To give economical operation of the gas turbine compressor combination the back pressure in line 22 is of the order of 15 to 100 p.s.i. Additional air can be admitted through line 27 from other compressors as needed. Fuel in the form of suitable hydrocarbon gases is introduced through line 2S and can be mixed if desired with compressed air coming through line 24 into the formation through line 15. The gas turbine can be started up by means of natural gas or other fuel admitted by line 28 and is vented through line 30.
In order that those skilled in the art may better understand how the present invention can be practiced, the following example is given by way of illustration. In-
itially, a well having a diameter of about 12 inches is drilled into an oil-shale deposit having a thickness of about 1000 feet, the top of the formation lying at a depth of about 1000 feet. In some instances it may be desirable to drill a bore hole having a diameter of the order of 4 feet. This will depend on the size and type of explosive to be employed. Generally holes in the range of 12" to 4 can be drilled with ordinarily available equipment.
In the oil-shale, which has a richness averaging about 25 gal. per ton, 1 ton of TNT is detonated to cause the initial fracturing and establish gas communication to the lower regions of the formation. The explosion will open up some permeability and allow the downward movement of a flame front.
Following the explosion (l ton equivalent), a 4" tubing string is placed to the bottom of the bore hole to serve as an internal exit pipe. Combustion is then initiated at the top of the formation. For approximately 20 days, 50,1000 cubic feet per minute of air mixed with 5 c.f./min. of 1000 B.t.u. gas is injected through the annulus between the exit pipe and the casing into the top of the formation with an inlet pressure of about 100 p.s.i.g. Thereafter, the 4 exit pipe is withdrawn and a second explosive charge is actuated in the formation.
The second explosive charge is preferably larger than the irst and in this example a charge of tons of TNT is employed. A suitable hole is drilled into the bottom of the formation and the 4 exit pipe is again placed as an exit pipe for the recovery of produced oil. Again combustion is initiated and for 40 days 100,000 c.f./min. of air with 10 c.f./min. of 1000 B.t.u. gas is injected into the upper portion of the formation.
Once again the 4" exit pipe is withdrawn and 100 tone of TNT is exploded in the central portion of the formation being produced. The explosion not only knocks down the peripheral layer of rock Skelton left in the cavity which has been formed but also brings about new fracturing of the formation. Combustion is initiated in the usual manner and a flame front moved downward through the newly fractured formation enlarging the chamber once more. This time 100,000 c.f./min. of air is injected with no fuel gas for a period of 40 days.
After the third explosion, and combustion steps, oil production begins to become significant and during the next 6010 days, 3000 barrels per day of oil can be produced by injecting 500,000 c.f./rnin. of air into the upper portion of the formation. This amounts to a total oil recovery by the 70th day of approximately 1.8 million barrels. During the same period, an average of 12 109 MM B.t.u./day of gas is available to run the gas turbines and auxiliary equipment at the surface.
Within the bituminous formation, combustion of air and shale or shale-oil vapors will reach local temperatures of about 1500 F. About 75% of the magnesium and calcium carbonates will be decomposed at these temperatures. Thus, the mass of the residual shale over and above the loss of about 10% by weight in the form of hydrocarbons will be substantially reduced by the carbon dioxide loss. In all, there will be approximately a 50% loss in mass within the portion of the formation exploited. Gases leaving the cavity will be at about 300 F. and will contain some oil in vapor form.
By the process described above, a cavity of roughly spherical dimensions will be created having a diameter of about 500 feet. This chamber can then be utilized according to this invention to explode an ultra-high energy explosive charge. While conventional explosives can be employed, it is preferable to utilize a thermonuclear device.
Any suitable atomic device such as a ssion or a fusion bomb known in the art can be used in accordance with the present invention. Suitable devices are those which release substantially all their available energy within not more than about 1 minute after the establishment of criticality by changes involving exoergic transformation. On the tiring of the 1-20 megaton device the release of energy creates an extremely high pressure within the bomb cavity which has been prepared. Almost immediately the roof of the cavity will collapse and fractured rock from above completely llls the explosion cavity forming a massive zone of fractured rock. Trapped heat from the explosion will raise the temperature of the shattered and crushed material from its original underground temperature of about F. to a temperature on the average which is in the order of 200 to 300 F. Thereafter, a single well is drilled into the fractured zone, casing is placed to the top of the zone, and a tubing string inside the casing is run to the bottom of the zone. Following this, a 50% mixture of saturated liquid and saturated vapor water at 700 F. and 3100 p.s.i. is injected through the casing of the well into the uppermost portion of the fractured zone. The steam and condensate is injected at a rate of approximately 2100 barrels per day for a period of time in the order of 3 years. Water and oil are produced through the tubing string from the bottom of the zone.
While in the foregoing, there has been shown and described the preferred embodiment of the present invention, it is to be understood that minor changes in details of construction, combination, and arrangement of parts may be resorted to without departing from the spirt and scope of the invention as claimed.
What is claimed is:
/1. A process ffor producing oil from a bituminous formation consisting essentially of an oil shale deposit containing appreciable amounts of calcium and magnesium carbonate depo-sits and containing hydrocarbons not naturally flofwable into a well bore traversing said formation, which comprises fracturing said formation adjacent said well bore by detonating a first explosive charge therein, initiating combustion in the upper portion of said [formation adjacent said well bore to establish a combustion front, injecting into said upper portion of said formation a combustion-supporting gas to move said combustion front downwardly and outwardly around said well bore and leave only a frail ash skeleton of rock in the wake of said combustion front, detonating a second explosive charge in said well bore to knock down said ash skeleton of rock, thereby forming a chamber and fractur-ing additional portions of said formation proximate said well bore substantially unaffected by said iirst explosion and said combustion, thereafter again establishing a combustion front in the upper portion of said formation, and moving said front downwardly through said formation and said chamber, wherein said combustion steps are carried out at temperatures up to about 1500" F., and removing to the surface from the lower portion .of said formation in said chamber oil produced by the combustion within said formation in said chamber.
2. The process of claim Il wherein said chamber is made larger by repeated explosion of increasingly larger explosive charges and thereafter fol-lowing each explosion, mowing a combustion front downwardly through the region fractured by the explosion.
3. A process for producing oil from a subsurface bituminous formation consisting essentially of an oil shale deposit containing appreciable amounts of calcium and magnesium carbonate deposits and containing hydrocarbons not naturally ilowable into a well bore penetrating said formation, which comprises creating within said formation an explosion chamber of approximately spherical dimensions having a diameter in the range of about 10 to 1500 feet, said explosion chamber being prepared by (l) drilling a well bore into said formation, (2) fractuning regions of said formation adjacent said Well bore by detonating an explosive charge within said well bore, (3) initiating combustion in the upper portion of the formation to establish a combustion front around said well bore, (4) injecting air into sa-id upper portion of said formation to move said combustion front downwardly through said formation leaving only a frail ash skeleton of rock in the wake of said combustion front, (S) then detonating a second explosive in said well bore shattering said ash skeleton of rock, thereby forming a cavity and producing additional fractures in said surrounding formation and again carrying out the combustion step, said combustion steps being carried out at temperatures up to about 1500 F., repeating this procedure until an explosion chamber of the desired size is obtained and (6) then detonating a high energy explosive in said explosion chamber rto form a massive fragmented zone within said formation and fill said chamber with fragments formed by said explosion, oodng said fragmented zone with Water at a temperature in the range of 550 to 800 F., and removing to the surface oil extracted from said zone by said Water.
4. The process according to claim 3 characterized further in that a single Well is drilled into said fractured zone with a casing set to the top olf said Zone and a pro- Iduc'tion tubing string Within said casing, set to the bottom portion of said zone, and said Water is injected into said zone 'through the annulus between `said Casing and said production tubing string.
5. The process according to claim 3 wherein said high energy explosive produces an underground explosion hav- 5% ing an energy yield equivalent to at least 0.1 kiloton of TNT.
6. The process according to claim 5 wherein said high energy explosive is a molecular explosive.
References Cited in the le of this patent UNITED STATES PATENTS 1,422,204 Hoover July 11, 1922 1,457,479 Wolcott June 5, 1923 2,780,449 Fisher Feb. 5, 1957 2,788,071 Pelzer Apr. 9, 1957 2,819,761 Popham et a1. Jan. 14, 1958 3,001,775 Allred Sept. 26, 1961 OTHER REFERENCES