US 3358756 A
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Dec. 19, 1967 .1. v. VOGEL 3,358,756
METHOD FOR 1N slTU RECOVERY OF SOLID OR SEMI-SOLID PETROLEUM DEPOSITS Filed March 12, 1965 l? le f 2o E HEAT I f H HEATER ExcHANGER :HITQ Il ISG i PRODUCT\ LINE SEPARATION HIS ATTORNEY United States Patent O 3,358,756 .METHOD FR I-N SITU RECGVERY F SOLID 0R SEMI-SOLID PETROLEUM DEPOSITS John V. Vogel, Houston, Tex., assignor to Shell Oil Company, New York, N.Y., a corporation of Delaware Filed Mar. 12, 1965, Ser. No. 439,169 3 Claims. (Cl. 166-7) ABSTRACT 0F THE DISCLOSURE This invention relates to the recovery of petroleum existing in a solid or semi-solid state from underground deposits, and more particularly, to a method of in situ recovery involving -a cracking operation for converting solid or semi-solid petroleum deposits into useful and recoverable hydrocarbon products.
' Substantial petroleum deposits exist in solid or semi- -solid form and these deposits, the so-called oil shale deposits, are the greatest oil reserves in the United States. These deposits were formed apparently from fresh water lakes in which organic matter, mostly of algal origin, collected with nely divided silt at the bottom of Y fresh water lakes. This organic matter subsequently dried, became compacted and was transformed into a laminated, impermeable organic-bearing mineral matrix known today as oil shale.
The existence of the petroleum in such a semi-solid vf orm is not conducive to economic recovery by .present day techniques but,` 'because of the extensiveness of these oilshale deposits they provide more than an adequate incentive to develop means of recovering the oil therefrom. For example, -the Green River formation, located midway between Denver and Salt Lake City, extends f o ver some 16,500 square miles, averaging 15 or more gallons of desirable shale oil per ton. This isv probably the worlds single largest known hydrocarbon deposit with estimated reservesuof over 150,000,000,000 barrels.
"Presently, there are two broad approaches to the re- `cover-y of shale oil from the organic-inorganic matrix lknown as oil shale. One is retort of mined Ashale and the other is in situ treatment of the shale. Most successful today of the two general types of processes is the treate ment. of mined shale by retort processes. The diculty with such a process is that a 50,000 barrel per day plant requires that 84,000 tons of raw, good grade, shale be :processed through the plant per day and that 71,000 tonsk of inorganic residue be-disposed of daily. Thus, the materials handling pro'blems in such a process is enormous.
Because the organic matter in oil shale exists largely .as an insoluble residue, often referred to as kerogen, having a molecular Weight of 3000 plus, it is dillcult to separate the organic matter from the inorganic matter without some modification of the kerogen. Heat converts it into a liquid or vapor form. This is the reason that retort processes mentioned -above are more successful than other types. These retort processes involving mining the oil shale, transporting the shale to a suitable processing v point, crushing and grinding the shale to a particle size permitting effective heat treatment and thereafter heating the resulting particles sufficiently to effect destructive distillation of the kerogen are not today economical.
Even though the potential recovery of shale oil may be as high as 50 to 75 gallons per ton, material handling problems have caused industry to look for other methods of recovering the oil products from oil shales. This has led to the second lbroad approach to the recovery of organic matter which involves attempts to heat the oil shales in situ to recover the useful organic matter. These latter techniques are much akin to the retort process and, in fact, many use in situ retort processes either burning the organic matter in the shale or providing fuel within the formation to develop sui-licient heat to cause destructive distillation thereby converting it to either recoverable liquid or vapor products.
While the in situ combustion processes eliminate the costly operations of mining, transportation and processing of the raw oil shale, the virgin oil shale is very strong and impermeable in its natural occurring state which adds other problems. It is difficult to establish in situ combustion and to maintain it once it has been initiated Another problem faced with in situ oil shale combustions When this art is used is that the produced gases are highly contaminated with nitrogen which may reduce their fuel val-ue almost to nothing. Another diculty with in situ combustions is the presence of both magnesium carbonate and calcium carbonate which begin to calcine from about 1100 to about l500 F. via an endothermic reaction Which is also undesirable.
Since both of the general techniques discussed abovehave their own unique problems, other approaches to the recovery of organic matter from oil shale have been sought. The present invention has resulted from efforts to find a better technique to recover the organic matter from the oil shale and avoid some of the serious drawbacks of the aforedescribed techniques.
Broadly, the invention involves a new method of recovering solid to semi-solid organic matter from underground formations, such as oil shale deposits, including the steps of penetrating the formation with at least one injection well and at least one production well, fracturing the formation between said wells, injecting a non-oxidizing heated vapor through the injection well, and recovering eflluents from the production well which includes organic materials formed from the solid to semisolid organic matter in the formation by a thermal cracking action.
This invention will be better understood by referring to the attached drawing showing an earthen formation, taken in cross-section, including an underground oil shale deposit and also the necessary surface equipment for practicing themethod of the present invention.
Because the present invention is particularly applicable to recovery of organic matter from oil shales, some of the characteristics of such shales should be considered. Generally, the inorganic material of oil shales is a laminated marlstone intimately mixed with clay and lesser quantities of sediment, plus other mineral constituents. The organic matter. in a semi-pure form (often referred to as kerogen) is a brown amorphous powder having a molecular weight of 3000 plus. Because of this high molecular weight, kerogen is insoluble in common petroleum solvents at ambient temperatures and structurally appears to be a molecular complex of saturated, basically non-benzenoid, condensed polycyclic ring systems loosely interconnected through -alkyl side chains which may include hetero atoms.
Because of this nature of oilshales, the only industrial successful process to date is destructive pyrolysis of crushed oil shale at temperatures in the order of 900 F. and at ambient pressures. In pyrolysis, about 66% of the organic matter is converted to a liquid oil and 9% is converted to light gases with the remaining 25% sticking to the inorganic matrix as a carbon-rich residue.
The process of the instant invention is specifically adapted to avoid the necessity of mining the oil shale and processing it in a retort as known commercially successful processes would require. Instead the instant invention uses a hot vapor circulated through a fracture between two wells to transfer heat underground. Heat is carried away from the hot fracture and into the oil shale formation by conduction, aided somewhat by convection. When sufficient heat has been transferred to raise the oil shale to a sufcient temperature, the organic matter undergoes thermal cracking. The vapor pressure of the hot newly formed products causes them to expand and be forced out of the shale and into the fracture, adjacent permeable zones and/or the producing well. This process is aided somewhat by a sweeping action of the hot vapor circulated as the heat carrying medium.
By properly controlling temperatures and withdrawal rates, the degree of cracking of the organic matter can be controlled so as to favor poduction of gas or oil. Generally speaking, gas products are favored -by higher temperatures and/or long exposure of the organic matter to the cracking temperatures.
It may be preferred, but is not essential that the hot vapor, or a portion thereof, be an organic material which, rwhile not miscible with the insoluble kerogen, is miscible with the cracked products obtained by circulating the hot vapor through the shale formation. Since the pyrolysis of the organic matter in the oil shale produces heavy cornponents Iwhich can be very viscous when in contact with cooler portions of the underground system, the misci'bility of the hot vapor with the liquid conversion products may tend to lessen their viscosity and allow them to drain more freely from the inorganic matrix into the fractures, adjacent permeable zones, and/or the producing well.
It is desirable that the vapor injected have good heat carrying capacity in the temperature range of 650 to l100 F. This eliminates superheated steam which is somewhat limited in its ability to carry heat and is nonmiscible with the oil products. Vaporous hydrocarbons, therefore, are especially desirable for carrying out the process. Further, an advantage is gained by using vaporous hydrocarbons since such hydrocarbons can be obtained on location for the use in the process which elirninates the requirement for large volumes of fresh water which would be difficult to find in the arid region where oil shales are common.
In the practice of this invention, it is desirable that light hydrocarbons which are themselves resistant to thermal cracking, be employed in the vaporous phase to recover the organic matter from the undergound oil shale deposits. Generally, suitable hydrocarbons are methane, ethane, propane, butane, kerosene, naphtha, gasoline, benzene, and the like. Benzene, butane and propane combine a high heat carrying capacity with good resistance to thermal crackin-g. Another suitable mixture of gases which is even more resistant to thermal cracking, although of somewhat lower heat carrying capacity, is the gas produced by the process itself as the 4kerogen undergoes .destruction distillation (hereafter termed shale gas). Because of the good heat carrying capacity of the hydrocarbons referred to above plus their miscibility with the liquid products formed from the thermal cracking, they are able to achieve better cracking efficiency and removal of products than immiscible superheated steam. Because the use of steam, especially at the temperatures involved, can cause unwanted tectonic changes to occur within the formation that are not likely to occur with the vaporous hydrocarbons, steam is not suitable in the instant invention.
Generally, it is desired that the vaporous hydrocarbons be injected into the formation at temperatures in excess of 700 F. In fact, it is very desirable to heat the hydrocarbon vapors to a temperature well above 700 F. in order to maintain the temperature in the area of central ow between the two spaced wells at a temperature of at 4 least 700 F. Generally, the upper limit to which the vaporous hydrocarbons can be raised is limited to that point at which they themselves undergo thermal cracking or suffer degradation and this will depend largely upon the particular hydrocarbon employed in the process.
For a better understanding of the invention, reference is made to the single accompanying gure showing an earthen formation in cross-section penetrated by two spaced wells. The earthen formation 1 is composed of a plurality of strata and includes a reservoir formation 2 composed principally of oil shale. In practicing this invention, at least one injection well 3 and at least one production well 4 are drilled through the earthen formation to penetrate the shale formation Z. The illustrated construction of both the injection well and the production well 3 and 4, respectively, is quite similar, each having a casing 5 positioned in the borehole and sealed with a sealant `6 to maintain its location therein. Inside each casing string 5 is an insulated tubing string 7 which is positioned in the casing string to leave insulating annulus therebetween which is sealed near the lower end of the tubing string 7 by packer 8.
Below packer 8, the casing string 5 is perforated in order to provide uid ingress and egress between the inside of the casing string 5 and the shale formation 2. It is generally preferred that the casing string actually be severed in the area of the perforations since this portion of the casin-g string will be subjected to high temperatures and this allows for expansion of the casing string.
Since, in all probability, the shale formation 2 will be impermeable, it will be necessary to fracture between the input well 3 and the production well 4. Fracture 9 can be established by the use of hydraulic fracturing fluids and can be propped with propping agents 10 to insure that it remains open during the injection of the hot hydrocarbon vapors. Not only may it be desirable to use propping agents 10, it may be necessary because of the expansion of the oil shale when heated which would tend to collapse the fracture if no propping agents are rpresent.
As it is desired that the hot hydrocarbon vapors be continuously recycled through the formation to etect the recovery of the organic matter therein, the discussion of the above ground equipment will begin with the effluents of production well 4 and terminate with the injection of the hot hydrocarbon vapors through injection well 3. At the wellhead 11 of casing string 5 of the production well, the vaporous eiuents are recovered through the insulated tubing string 7, pass through line 12 and go .directly to heat exchanger 13 and thence into a separating facility 14 in which the cracked products from the formation are separated from the hot hydrocarbon which was injected through the injection well 3 to recover these products. Depending on the particular hydrocarbon mixture used, the separation facility 14 may consist of simple conventional equipment for separating gases and liquids by gravity or may require somewhat more elaborate distillation and condensation equipment. The oil and gas products are recovered through product recovery lines 15 and 15a and the heat carrying hydrocarbon, which was injected in vapor form, is removed from the separating facility 14 by line 16 and goes directly to heat exchanger 13 and then through line 17 to pump or compressor 18. From pump or compressor 18, the hydrocarbon passes directly to a suitable heater 19 via line 20 wherein the hydrocarbon is raised to a temperature in excess -of 700 F.
From heater 19, the heated hydrocarbon vapors are routed via insulated pipe 21 to the wellhead 22 of the injection well 3. There the hot vaporous hydrocarbon travels down the insulated tubing string '7 of injection well 3 and proceeds via the tubing string and perforations 23 to fracture 9. From the perforations 23 in casing string 5 of the lower portion of injection well 3, the hot hydrocarbons enter fracture 9 and transmit their heat by conduction and/or convection to the oil shale formation adjacent to the fracture. As these hot hydrocarbon vapors ow through the fracture 9 to the production Well 4, some of the organic matter in the oil shale formation is thermally cracked to lower boiling products which are much less viscous. Once the cracked products from the organic matter in the formation are reduced to low viscosity products and/'or vaporized, they are forced out of their original position by expanding vapor pressure and swept along lwith the hot hydrocarbon to the production well from whence they are recovered via tubing string 7. As the circulation continues, the area of the shale formation 2 adjacent t-o fracture 9 will become depleted of much of the organic matter as indicated by the depleted zone 24. As the areas adjacent to fracture become depleted organic matter, it will become permeable to the hot hydrocarbon vapors allowing them to contact more virgin shale.
In the instant process, since the circulation of the hydrocarbon occurs in a closed circulatory system, little if any oxygen is available for actual in situ combustion which would occur at the temperatures in the formation if oxygen were present. Further, even if some oxygen is available within the formation, it is of little or no moment, since an extremely limited amount will be available to support combustion. Actual combustion in the formation is not desired since it could adversely affect permeability.
Though we have discussed the invention relative to the use of two spaced wells, one of which is the injection well and one of which is the production well, it should be appreciated that it would be possible to carry out the instant process in a single Well with dual insulated tubing strings and through a vertical fracture.
Further, it should be appreciated that the facilities located above the ground would all involve appropriate insulation in order to conserve thermal energy and the use of appropriate heat exchangers in order to recover the maximum amount of thermal energy from the eluents from the production well. In this way, the efficiency of the process can be improved and it can be operated on a commercial scale.
As the circulation of the hot hydrocarbons continues through the oil shale formation 2, the depleted zone 24 continues to expand as more and more of the organic matter is stripped therefrom. In some cases, it may be desirable to establish a fracture 9 at multiple levels in order to optimize the effects of this process in the formation and to allow for irregularities in the formation itself. When the fractures are employed at multiple levels, the hot hydrocarbons can be injected into the fractures separately or simultaneously but usually separately in order to avoid failure of the casing string resulting from a large segment thereof being exposed to the relatively high temperatures. To avoid simultaneous injections or exposing large areas of the casing to high temperatures, a lower packer 25 may be used in each casing 5.
In order that the invention can be better understood, the following example is illustrative of the instant invention and method of carrying it out.
Example I In a mathematical model, it was determined that 950 F. benzene vapors injected into a shale formation through an injection well and recovered at a production Well at 650 F. would give 55,000 B.t.u.s/bbl. to the formation. Calculated on four acre spacing with wells 300 feet apart and having liuid communication therebetween through the oil shale, an injection of 3260 barrels per day of 950 F. benzene vapors into fractures between the Wells will raise the temperature of a portion of the shale formation 25 feet on each side of the fracture to 750 F. within four years. The pressure drop will be 200l p.s.i. between the wells. If the shale has a richness of 30 gallons/ton of virgin oil shale, 442,000 bbls. of oil (or vaporous hydrocarbon equivalent) would be given out of the four acre- 50 foot interval during the four year period. An average of 300 bbls./day for the producing wells for the period.
The foregoing example is based on calculations and is not intended to limit the invention. Various changes in injection rates and temperatures will probably be necessary depending on the particular shale formations and the gaseous eiiluents (shale gas) recovered from the formation will probably be the most economical vapor to use in the instant process.
I claim as my invention:
-1. A method of recovering solid to semi-solid hydrocarbons from uniform underground oil shale reservoirs comprising the steps of:
(a) pentrating such a reservoir with at least one in- -jection well and at least one production well;
(b) horizontally fracturing and establishing iluid communication channels through said reservoir between said injection well and said production well;
(c) passing hot benzene through said reservoir by injecting it through said fractured injecting Well into said uid communication channels at a temperature in excess of 650 F. to convert solid to semi-solid hydrocarbon residues in said formation to mobile fluids;
(d) recovering said mobile uids from said production Well; and
(e) separating said mobile iiuids into liquid and gaseous hydrocarbon fractions.
2. A method according to claim 1 in which a conventional propping agent is added to the fractures.
3. A method according to claim 1 in which the ilow rate through the reservoir and the temperature of the hot benzene is controlled so that the solid to semi-solid hydrocarbons are substantially converted to hydrocarbon vapor and which are recovered above ground, condensed and fractionated into liquid hydrocarbon oil and hydrocarbon gases.
References Cited UNITED STATES PATENTS 895,612 8/1908 Baker 166-57 1,422,204 7/ 1922 Hoover et al. 166-11 2,813,583` 11/1957 Marx et al. 166-11 2,974,937 3/1961 Kiel 166--11 X 3,145,772 8/1964 Huitt 166-7 X 3,241,611 3/1966 Dougan 166-11 X 3,284,281 11/1966 Thomas 166--11 X STEPHEN J. NOV OSAD, Primary Examiner.