US2634961A - Method of electrothermal production of shale oil - Google Patents

Description

Patented Apr. 14, 1953 METHOD OF ELECTROTHERMAL PRODUC- TION OF SHALE OIL Fredrik Ljungstrom, Fiskebackskil, Sweden, as-

signor to- Svenska Skilferolje Aktiebolaget, Orebro, Sweden, a corporation of Sweden Application June '24, 1947,, Serial No. 756,625 I I.

In Sweden January 7, 1946 Section 1, Public Law 690, August 8, 1946 a Patent expires January 7, 1966 g 1 In my copending application Ser.,No. 756,624, of even date I suggest to heat shale rocks in their ,natural condition by means of electrical heating elements thrust into channels bored in the rocks so as to cause pyrolysis therein. The oil gasesand other gases thus produced are drawn off through special exhaust passages in the rocks to be collected and recovered through condensation and other processes.

-It isone of the objects of this invention to carrythis heating process into effect, in a manner such that the energy required for the same is :obtained at a lower cost than hitherto, in order-thus to out down the cost of producing the oil. Another object is to provide a heating process, wherein the shale rocks serve, so to speak, as, an,accumulator for cheap electric energy, which is consequently recovered in the form of heat, to be utilized for the benefit'of a pyrolysis carried into effect on a later occasion. A further object is to bring about a preparatory treatment of the shale rocks, so that leakage of the products recovered in the pyrolysis is effectively prevented. Further objects and advantages of the invention will be apparent from the following description considered in connection with the accompanying drawing, which forms a part of this specification, and of which:

Fig. l is a vertical sectional view of a shale rock, and

; Figs. 2 and 3 represent two diagrams.

In the drawing, I designates an oleous shale layer, which may have a layer oflimestone rock 12 and an earth layer I4 superimposed on the same. ,Thrust into vertically bored channels are a great number of electrical heating elements It adapted to heat the shale layer [0. My above mentioned patent application is referred. to for a closer description of the construction and arrangement of said heating elements andv of the exhaust passages. The heating elements It are connected to an electric power system 20 by means of branch conduits l8, so that low-voltage current is supplied to the heating elements. As

will also appear from said application, the heating. Oijthe shale rock is carried into effect in such manner that a horizontally travelling heat front is created, the direction of-which is denotedy 22 in Fig. 1.

In accordance with the invention, the heating of the shale rock is divided into two stages, a preheating stage and a subsequent stage for heating to the ultimate temperature, the latter beingcalled the pyrolysis heating in the following, In the heatingoi the shale, an oil produc 7 Claims. (Cl. 2623) 2 ing pyrolysis occurs at a temperature exceeding 250 0., and only in the proximity of 300 C. will there be anything like an appreciable production of oil gases and other hydrocarbon gases. The liveliest pyrolysis proceeds between 300 C. and 400 C., for example, that is to say, substantially all of the oil and gas quantities produced during the electro-thermal oil production isextracted within the said range. In the embodiment illustrated in the drawing, the preheating is carried out within a range of the shale rock confined between the dash anddot lines 24, 26, the heating elements located within this region being connected to the electrical power line 20. The temperature is thus caused to increase gradually by successively connecting further rows of heating elements [6 into the circuit, the rise of the temperature taking place according to thecurve 30 in Fig. 2, the abscissa of which indicates the hori-. zontal extent of the shale field according to Fig. 1 in the direction of the heat front, whereas the ordinate of said curve indicates the tempera-v ture in the shale rock. During the preheating process, the shale rock is heated to a temperature corresponding to theline 32 in Fig. 2, where no appreciable pyrolysis has set in as yet, said temperature amounting for instance to 240.-280 C. The pyrolysis heating is carried into efiect within a portion of the rock limited by thelines 34, 36, which portion is separated from the pre-. heating portion. During the pyrolysis heating, the temperature of the rock is increased in steps according to thecurve 38 to'the final temperature according toline 40, which temperature may amount to 360-420 C. Upon the lapse of a certain time, the preheating may have reached thecurve 30 and the pyrolysis heating thecurve 38 Thus there are two separate heating zones in the shale rock which progress forwardly in the same direction.

During the preheating period, approximately two-thirds of the requisite quantity of heat is supplied to the shale rock, while only about a third thereof is supplied during the pyrolysis heating, in the example presented above. While the preheating may be periodical, the pyrolysis heating takes place as continuously as possible, which has an advantageous effect on the produc-, tlon. As an example it may be assumed that. the. preheating only takes place during the half of the year. It is assumed that the same quantity of energy is always supplied to a heating element per unit of time. Inasmuch as two-thirds of the total quantity of heat is supplied during the preheating, obviously four times as many heating elements will have to be connected into the circuit as during the pyrolysis heating, which involves that double the quantity of heat is supplied inrhalf of the time. The travel rate of the preheating front confined by thelines 24, 26 will at the same time be double the rate of progress of the pyrolysis front between thelines 34, 36.

It is readily understood that there will be a portion of the shale rock of varying length between the two heating fronts. This portion has reached the temperature level according to theline 32, that is to say, it has been brought up to the temperature at which the pyrolysis may be commenced. When the preheating is interrupted, the distance between thelines 26 and 34 is reduced; again, when the preheating is started, said distance is increased.

This interruption in the heat supply to the shale rock, on its having reached thetemperature level 32, entails a number of very considerable advantages. While heat is supplied to a heating element It, the shale rock about the same is brought to varying temperatures, inasmuch as the temperature falls in a direction from the element, according to thecurve 42 in Fig. 3. In this figure, the abscissa corresponding to the curve. 42 is designated by it. After the electrical energy has been disconnected, the temperature will be equalized according to the curve 48. 9n account of the interval between the two heating periods, the shale rock will consequently show a more completed equalization of the temperature within, the heated portion of the rock. A shale rock has a coefiicicnt of heat expansion of about 0.00001. At the distances of 2-3 meters accurring between the various heating elements I, the expansions of different portions created by the heating will thus vary considerably within the shale rock at the diiierences in temperatureappearing from thecurve 42 in Fig. 3 (such as 200 0.), very irregular heat strains being thus produced within said portions of the rock. Gen erally, however, there is a tendency toward a swelling efiect by the heat in the horizontal direction created by the general heating of the rock. This swelling effectv tends to compress all vertical fissures occurring within the shale rock and, consequently, has a tightening effect on these fissures. However, during the preheating period partial zones are formed within the roclr, which tend to compress the above-mentioned fissures, whereas other zones are also formed where such compression is prevented. In the equalization of the temperature during the interval between the two heating periods, the compression of any fissures occurring becomes more general and thus more eiiective. The effect of the gases produced in the pyrolysis heating following non-desirable paths is thus counter-- acted to a very great extent by interruptions in the'hea't supply. Furthermore, the invention involves advantages as to the economical ultimate result in the electro-thermal recovery of oil. The preheating may be advantageously carried intoeifect during such times where cheap hydraulic power is comparatively amply available. The invention thus offers a favourable alternative fur the electric steam boilers in which, as is well known, electrical energy is used for the genera tion of steam The pyrolysis heating is carried into efiect at a relatively uniform supply of electrical energy. Preferably, the heat supply required for this purpose may constitute a small portion of the whole of the supplied quantity of heat as per above.

4 In electro-thermal production of shale oil, oilforming gases are extracted in part, which are recovered in a liquid state by condensation, while in part also other gaseous hydrocarbons and hydrogen, are formed, which can be condensed only with great difficulty at low temperatures, and which for this reason are called non-condensable gases hereinafter. Generally, these gases constitute the half of the quantity of all recovered hydrocarbons, and they have approximately the same effective combustion value as that of the liquid hydrocarbons. Thus for every liter of oil produced, approximately 1 cubic meter of gas is obtained at the same time. This gas is an excellent fuel, and when used in the proper manner it has a great commercial value equivalent to that of the oil, but with respect to the facilities of distribution and sales, it is not as manageable as the oil. A comprehensive network of gas conduits and great erection costs will thus accompany the distribution of the gas, and if all of the gas were to be distributed from a place where, say, 200,000 cubic meters of oil are produced yearly, considerable difiiculties are met with. If, for instance, constituents (sulphur and so forth) of the gas can not advantageouslybe recovered at the shale field, the same are instead preferably used as fuel in a central power station for the generation of electrical energy,

which is applied, according to the invention, if desired alternatively with other energy supplied, for instance from water power, for the pyrolysis heatingof the shale rock. On the other hand, a uniformly or nearly uniformly proceeding pyrolysis heating throughthe supply of electrical energy may be arranged from the gas-fired power station. By suitably determining the temperature to which the rock is heated during the preheating period the pyrolysis heating may thus be carried into effect without any external supply of energy in the form of hydraulic power.

The pyrolysis heating proceeds in such casecontinuously independently of the preheating,

which may be periodical and adapted, for instance, to excess power available from the hydraulic power stations. Obviously, the steam station is in this way loaded continuously and, if desired, uniformly, and, something of particular importance, the pyrolysis proceeds in a uni- 1 form and undisturbed process independently of the prevailing conditions relative tothe water power. However, the pyrolysis heating may be carried on at varying intensity during different periods and seasons, by a varying number of heating elements beingconnected into the network at the same time.

In a country, for instance of the size and nature conditions of Sweden, the invention under all circumstances renders possible an economically advantageous use of excess energy or so-called secondarypower from the hydraulic power stations for the production of liquid fuel. By the preheating, the shale rock here constitutes an accumulator recovering hydraulic energy in the form of heat, which may then, if desired, be -utii i-zed for the ultimate recovery of oil at a far later time.

According to the invention, the steam power station may be fired either solely with gas from the pyrolysis process, or, the same may be fired with other fuelsdepending on the prevailing conditions on every particular occasion. Thus the gas may be readily disposed of during certain periods, for instance for the supply of gas to the cities in winter-time. In summer-time, when winter-time.

such gas consumption is less, the steam station may be fired solely with the gas or with a suitable combination of gas and other fuels. According to the invention, the non-condensable gas can thus also be utilized in a particularly favourable manner by the combination of a periodically heated shale-rock, on the one hand, where the preheating proceeds, and which accumulates and utilizes available cheap waterfall energy, and, on the other hand, pyrolysis heating effected solely with the non-condensable gas produced by the pyrolysis, this use of the gas also taking place periodically alternately with the employment of the gas for other purposes. In this case too, it is conceivable to vary the intensity of the pyrolysis heating by altering the number of active heating elements [6 to suit the oil or gas quantity produced per unit of time and the consumption of electrical energy to the price conditions. Generally, a periodic operation of the preheating may be carried into effect synchronously with the seasons. In summer, for example, there is as a rule an excess of electrical energy available, while in this season the gas consumption, for instance, in the cities is at the same time reduced often to less than the half of the quantity required in Through the preheating energy accumulated during the summer, the steam power stations may therefore, according to the invention, aid in winter toward the electrical energy supply by firing with fuels other than the gas, while the pyrolysis gas produced in the same time is used simultaneously in the gas distribution of the cities, where it is of a higher value than in the form of boiler fuel. According to the invention, the production, for instance, of

raw shale oil is rendered possible by electrothermal means out of shales, even of relatively poor in oil, at so good an economy that this oil can compete with oils, as far as cost is concerned.

The gas-fired power station may be provided with steam turbines or gas turbines or other modern heatpower motors.

While one more or less specific embodiment of the invention has been shown, it is to be understood that this is for purpose of illustration only, and the invention is not to be limited thereby, but its scope is to be determined by the appended claims.

What I claim is:

1. The method of recovering hydrocarbons from shale deposits in situ by electro-thermal pyrolysis which includes the steps of supplying electric energy to two horizontally spaced areas of a given deposit to provide a first zone heated to a preheat temperature lower than the final temperature at which recovery of hydrocarbons is effected and a second zone heated to pyrolysis temperature to effect the desired recovery of hy- 6 drocarbons, the electrical energy being supplied progressively to the different areas to cause the heat fronts of the two zones to travel horizontally in the same general direction.

2. The method as set forth in claim 1 in which the electrical energy is supplied differently with respect to time intervals to provide a varying horizontal distance between the said zones at different times.

3. The method as set forth in claim 1 in which a given area is first heated to preheat tempera-.- ture to accumulate heat therein at a temperature below that at which pyrolysis occurs and subsequently heated at a later time to pyrolysis temperature.

4. The method of recovering hydrocarbons from shale deposits in situ by the aid of a plurality of horizontally spaced heating elements located in a shale deposit which includes the steps of initially preheating a selected area to a preheat temperature lower than the temperature at which pyrolysis occurs to accumulate heat therein at a temperature below that at which pyrolysis occurs and subsequently heating the same area to pyrolysis temperature to effect recovery of the hydrocarbons in gaseous form.

5. Method as set forth in claim 4 in which the preheating is effected by supplying electrical energy to said heating elements intermittently and in which electrical energy is supplied to said elements for pyrolysis heating only after an appreciable time interval following the completion of the preheating whereby to permit substantial temperature equalization over the area preheated before pyrolysis heating is effected.

6. The process of recovering hydrocarbons comprising slowly preheating an extensive area containing shale and hydrocarbon by applying heat at a plurality of spaced locations in the area to a temperature below the temperature at which pyrolysis occurs to accumulate heat therein at a temperature below that at which pyrolysis occurs, subsequently progressively heating the same area to a temperature at which pyrolysis occurs and collecting the hydrocarbon products.

'7. The process according to claim 6 wherein the direction of treatment of the area by the preheating and the subsequent heating progress in the same general direction.

FREDRIK LJUNGSTROM.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 849,524 Baker Apr. 9, 1907 1,422,204 Hoover July 11, 1922 1,457,479 Wolcott June 5, 1923 1,510,655 Clark Oct. '7, 1924

Claims (1)

1. 4. THE METHOD OF RECOVERING HYDROCARBONS FROM SHALE DEPOSITS IN SITU BY THE AID OF A PLURALITY OF HORIZONTALLY SPACED HEATING ELEMENTS LOCATED IN A SHALE DEPOSIT WHICH INCLUDES THE STEPS OF INITIALLY PREHEATING A SELECTED AREA TO A PREHEAT TEMPERATURE LOWER THAN THE TEMPERATURE AT WHICH PYROLYSIS OCCURS TO ACCUMULATE HEAT THEREIN AT A TEMPERATURE BELOW THAT AT WHICH PYROLYSIS OCCURS AND SUBSEQUENTLY HEATING THE SAME AREA TO PYROLYSIS TEMPERATURE TO EFFECT RECOVERY OF THE HYDROCARBONS IN GASEOUS FORM.

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