US3254712A

US3254712A - Miscible phase displacement method of recovering oil

Info

Publication number: US3254712A
Application number: US183428A
Authority: US
Inventors: Lorld G Sharp
Original assignee: Socony Mobil Oil Co Inc
Current assignee: ExxonMobil Oil Corp
Priority date: 1962-03-29
Filing date: 1962-03-29
Publication date: 1966-06-07
Anticipated expiration: 1983-06-07

Description

United States ,atent Lorld G. Sharp, Irving, Tex., asslgnorto So'cony Mobil Oil Company, Inc., a corporation of New York. Filed Mar. 29, 1962, Ser. No. 183,428 Claims. (Cl. 166-9) This invention relates to the recovery of oil from reservoirs. More specifically, this invention relates to a miscible phase displacement method of recovering oil from subterranean earth formations.

Oil is most generally found in underground formations which possess inherent energy in the form of solution gas, gas trapped in caps within the formation, or natural water drive which forces the oil from the formation through production wells. When this native reservoir ens ergy is depleted to the extent that it is no longer economically feasible to utilize it for the purpose of forcing the oil from the formation, it is necessary, if further oil is to be recovered, to resort to a method of supplanting or supplementing the native energy. The various methods of adding energy to an oil formation are sometimes referred to under the general heading of secondary recovery, though they may be initiated prior to completion of primary recovery. One of the most efficient methods of secondary recovery currently known is miscible phase displacement. Miscible phase displacement includes injecting into a formation a fluid material which is miscible with the oil in the formation and thereafter driving the injected material through the formation whereby oil is displaced from the formation through production wells leading therefrom. One particular miscible phase displacement method commonly employed comprises in jecting a slug of hydrocarbon material such as liquefied, normally gaseous hydrocarbons generally known as LPG, or substantially pure propane, which is driven through the formation with a gas which maybe. separator gas, lean natural gas, flue gas, or air.

One of the problems inherent in a miscible phase dis placement process utilizing LPG or propane is that the viscosity of the injected material difiers appreciably from the viscosity of the petroleum oil which it is to displace from the formation. The result of this viscosity dilference is that the sweep pattern of the miscible material becomes extremely irregular with portions of the miscible material tending to slip by the oil in the formation, leaving a substantial portion of the oil behind. Long, fingerlike projections of the miscible material develop at the front edge of the material, causing early breakthrough of the miscible material and consequent reduction in the total amount of recovered oil. It is believed that this fingering action is due, at least in part, to the difference in viscosity between the reservoir or formation oil and the displacing material. Another problem which is encountered in the use of a miscible phase displacement process utilizing LPG or propane in a reservoir containing oil which is high in asphaltic material is that the asphalt is precipitated by the injected miscible hydrocarbons, causing a plugging of the formation by the substantially solid precipitated asphaltic material.

It has been suggested that the above-discussed problems with respect to the sweep pattern of a miscible phase displacement process utilizing liquefied, normally gaseous hydrocarbons may be solved by providing a gradation in the viscosity of the miscible materials injected. It has also been suggested that the problem of asphalt precipitation in such a process may be minimized by reducing the liquefied, normally gaseous hydrocarbon content of the forward portion of the miscible material injected.

It is one object of the present invention to provide a miscible phase displacement method of recovering oil wherein the sweep pattern of the miscible material is improved. It is another object of the invention to provide a miscible phase displacement method of recovering oil which may be effectively applied to a formation containing oil which is high in asphaltic content.

In accordance with the invention, formation oil is recovered through a production well by injecting into the formation through an injection well a succession of raffinate fractions of crude oil of decreasing density and decreasing viscosity and following the last of such fractions with a driving fluid. At least the first of such fractions is preferably deasphalted and may have removed from it any liquefied, normally gaseous hydrocarbons contained therein order to minimize the precipitation of asphalt from the formation oil upon contact by such fraction with the formation oil. The fractionating and deasphalting is preferably carried out at the lease site as a continuous process with crude oil which has been produced through the production well by primary production methods. It will be recognized, of course, that crude oil from nearby leases or from other sources may be employed in the method of the invention. If storage facilities are available, the fractions may be made in batches from either lease crude or crude from other sources. The preferred method of fractionating the crude oil is to contact the crude oil with the same liquefied, normally gaseous hydrocarbons which are employed in the latter steps of the method of the invention.

The accompanying drawing illustrates diagrammatically in cross section a formation being produced by the method of the invention. The drawing also shows a preferred arrangement of surface-mounted equipment employed in the fractionation and deasphalting of the crude oil injected into the formation in accordance with the invention.

One particular embodiment of the invention is carried out in the following manner. This embodiment of the invention is based upon the recovery of a high asphaltic oil of gravity less than about 30 API. This particular lease crude is relatively low in low-boiling hydrocarbon content-in other words, the propane and lighter hydrocarbons.

The term high asphaltic oil" as used herein means an oil containing more than about 5 percent asphalt. The term liquefied, normally gaseous hydrocarbons as used herein shall include propane, butane, and liquefied petroleum gas, LPG, which usually contains trace amounts of methane, up to 10 percent ethane, 50 to percent propane, 10 to 40 percent butane, and less than 10 percent pentane and higher boiling parafiin hydrocarbons.

This particular embodiment of the invention is a continuous process wherein crude oil produced from the formation to which the method of the invention is applied is utilized in the preparation of the hydrocarbon fractions injected into the formation to effect recovery of the formation oil. The crude oil is continuously produced from the formation while the various injected fractions are prepared and injected into the formation. The injected fractions displace or aid in the displacement of the crude oil. The changes in the character of the fractions are made by changing the treating conditions of the crude oil, which changes may be made without interruptions in crude oil production.

Referring to the drawing, the reference numeral 5 designates the formation from which oil is recovered by the method of the invention. That portion of formation 5 containing the oil to be recovered is designated by reference numeral 6. Extending from the surface of the earth into formation 5 is a production well 10 which is provided at the surface with a wellhead l2.

tower 20 is in the 70 to 120 F. range.

A first quantity of formation oil is produced from portion 6 of formation through production well 10 into line 13 which is connected to wellhead 12. The forma- 15 open and valve 16 in line 17 closed the oil flows into deasphalting and fractionating column 20. The formation oil upon entry'into column 20 is at a temperature of 70 F. to 120 F..-prcferably about 100 F. The temperature in. the top of tower 20 may be as high a s 140? F. in precipitating this first fraction. For purposes of providing heat in the upper portion of tower 20, the tower is provided with a source of steam in a heat exchanger 2011, as illustrated. Within column 20, the formation oil is contacted countercurrently with liquid propane introduced to the tower through

lines

21 and 22 by means of pump 23 from storage tank 25, valve 24 in line 26 being closed and valve 27 in line 22 being open. The temperature of the liquid propane as introduced into The temperature of the propane may be increased by means of a heater 22a in line 22, or it may be heat exchanged with bottoms from tower 20. The relative amounts of the liquefied propane and the formation oil introducted into tower 20 range from about 1.0 to about 10 volumes of the liquefied propane per volume of formation oil introduced into the tower. Wllile propane is employed in this embodiment of the invention, it is to be understood that other liquefied, normally gaseous hydrocarbons such as butane, LPG, and mixtures of same may be used. Distribution of the oil and propane in tower 20 to obtain sufficient contact and avoid bypassing of the counterfiowing streams is accomplished by utilizing distributor plates or spargers (not shown in the drawing). If desired, packing such as raschig rings or berl saddles will also serve the purpose of effecting the desired liquid-to-liquid contact if installed in the upper part of the tower 20. if conditions are such with respect to the tower and the liquids introduced thereto that cooling rather than heating is necessary, a cooling medium rather than steam may be introduced into heat exchanger 20a in the upper portion of the tower.

The countercurrent contact of the propane with the formation oil within tower 20 results in a separating of the formation oil into a first rafiinate fraction and an extraction-fraction which includes the asphalt from the formation oil. The precipitated asphalt, which contains some of the propane, separated from the formation oil by interface 29, is withdrawn from tower 20 through line 30. The asphalt is heated by means of heater 31 as it passes through line to flash tower 32 in which the propane contained in the asphalt is removed from the asphalt and taken overhead through line 33 to compressor 34 where it is compressed and delivered to condenser 35 from which it flows as a liquid to tank 25. Between condenser 35 and tank 25, a line 36 is connected into line 33 for the purpose of allowing makeup propane to be introduced into the storage tank 25, if such is necessary. Asphalt is withdrawn from flash tower 32 through bottom drawoft' line 37 through which the asphalt is passed to storage means, not shown.

The first rafiinate fraction, which contains a major por-' .tion oil fiows from line 13 into line 14, and with valve 57, valve 58 in line 59 being closed. If there is no need to store this first rafiinate fraction, it may be injected directly into the formation in the following manner. Formation 5 is provided with an injection well 60 which extends from the surface into the formation as illustrated.

Secured at the surface on injection. well 60 is a wellhead 600 which in turn is connected to surge tank 55 by means of a line 61 provided with a pump 62. Line 61, as shown, is connected into line 56 by means of line 59 which is providcd with a valve 58. To directly inject the first raflinate fraction into the formation 5 through injection well 60, thus bypassing surge tank 55. it is pumped from in line 46 being open and valve 48 in line 49 being closed.

Within flash tower 50, removal of the propane from the first raffinate fraction is effected with the propane vapor from tower 50 passing overhead through line 52 into line 33. The propane vapor then passes through compressor 34 and condenser 35 into storage tank 25. The first raflinute fraction is withdrawn from flash lower 50 through bottom drawoff line 53 by means of pump 54 and is thence passed to a surge tank 55 via lines 56 and flush tower 50 by means of pump 54 through line 53 into line 56 and front line 56 through line 59, valve 58 being open. From line 59, the first raffinate fraction passes into line 61 through which it fiows to wellhead 60a and on into the injection well 60. It will be obvious from the drawing also that the first raifinate fraction stored in surge tank 55 may be withdrawn from the surge tank by pump 62 through line 61 and delivered to the wellhead 60a. While this fraction may be cooled before injection into well 60, preferably it is injected in heated condition in order to improve injection properties, particularly in the formation immediately adjacent to the injection well. The first raffinate fraction is introduced into the formation through injection well 60 until it has produced a radial band about the injection well which extends a distance of up to about 50 feet within the formation around the injection well. As indicated above, this first raffinate fraction is either passed through the surge tank 55 and then into the well, or passed directly into the injection well 60, the choice of passing it through the surge tank depending upon the operating conditions of the entire system at the time the oil is being processed. If conditions are such that the injection well is ready to take the first fraction, it is preferable that it be injected directly rather than passing it through the surge tank. Obviously, the surge tank may be filled and maintained as standby storage in the event that conditions should arise which would necessitate quick use of some makeup at this stage in the method.

After the first rafiinate fraction has been injected into formation 5 through injection well 60 to produce the radial band which extends a distance of up to about 50 feet around the injection well, production of formation oil is continued through production well 10 and the temperature of the formation oil and propane introduced into tower 20 is now raised to the F. to F. range. The top temperature of up to 160 F. is maintained by means of the heater 20a in the upper portion of the tower. The formation oil now being treated shall be, for purposes of reference, called the second quantity of formation oil. The procedure of introducing both the second quantity of formation oil and the propane into tower 20 is carried out in precisely the same manner as described above in connection with the production of the first rntlinate fraction. At equilibrium within tower 20, phase separation results in a bottom product or extract containing asphalt of the crude oil and also admixed therewith a part of the heavier nonasphaltic hydrocarbon components of the oil. Also as a result of the phase separation, there is produced a supernatant hydrocarbon oil or second raffinatc fraction containing the major part of the propane introduced to lower 20. The extract is passed to flash tower 32 where the propane is removed and delivered to storage tank 25 as described above. The oil fraction from which the propane has been removed is passed from the flash lower 32 through line 37 to either a pipe line or to storage facilities, not shown. The ratlinate fraction may be handled in several different ways. The fraction may be sent to flash tower 50 where the propane is removed to storage tank 25 and the demopanized fraction is then delivered to surge tank 55 or, in the alternative, it may be delivered directly into the injection well 60 in the same manner as described above in 'connection with the frst raflinatc fraction.

In the event it is not desired to remove the propane from the second raflinate fraction, the fraction is delivered directly through

lines

49 and 56 into the appropriate line connected into injection well 60 or into the surge tank 55 from which fit it is pumped into well 60. in any event, production of v this second raffinate fraction is continued and injection of such fraction into the formation through injection well 60 is carried on until anamount is injected into the formation to provide" an annular ring extending a radial distance up to about 50 feet around the injection well. It will be readily recognized that as the second railinate fraction is injected into' formation 5 through the injection well the first raffinate fraction is driven outwardly through the formation toward the production well. Due to the increased temperature employed in the treatment of the crude oil from which the second raflinate fraction is produced in tower 20, the second fraction has a viscosity and density less than that of the first fraction injected.

After a sufficient quantity of the second raffinate frac tion is injected into the formation through the injection well to provide the above-described annular ring extending outwardly into the formation for a distance of up to about 50 feet, the production and treatment of a third raflinate fraction is commenced. Flow of formation oil comprising a third quantity of formation oil continues from production well through the lines provided into tower 20 as above described in connection with the previous fractions, with the temperature of the third quantity of formation oil being raised to within the range of about 150 F. to about 195 F. This temperature range under which the fractionating tower is now operating produces at equilibrium an extract fraction containing, as compared with the second fraction treated, a still higher proportion of relatively heavy nonasphaltic oil in admixture with asphaltic components of the formation oil and propane and third raflinate fraction of relatively low gravity, low viscosity oil and propane in admixture as a third fraction for injection. The extract is withdrawn from tower 20, passed to tower 32, and treated therein to separate the propane which is passed into storage tank 25. The bottoms from tower 32 are sent to a pipe line or pipe line storage facilities. The third raflinate fraction is removed overhead from tower 20 through line 40 and passed directly into the injection well 60 through

lines

40, 43, 45, 49, 56, and 59 to the wellhead. During this procedure, it will be obvious of course from the flow diagram that

valves

44, 47, a valve (not numbered) in line 53, and a valve in line 57, not shown, are closed while

valves

42, 48, and 58 are open. The third rallinate fraction need not have the propane removed from it and it may be injected in a quantity ranging up to about percent, preferably 2-5 percent, of the pore volume of the formation 5 which is to be swept by the method of the invention. If desired, this third raffinate fraction may be augmented by the addition thereto of additional propane front tank 25 which is introduced by means of pump 23 and line 21 into line 26 to the wellhead 60a.

Valves

24 and 27 are utilized to control the proportion of propane flowing through

lines

22 and 26, it being recognized that inasmuch as this is a continuous process there may be propane flowing to tower through line 22 to permit continued production of the third raflinate fraction while the earlier produced portions of the third raffinate fraction are being introduced into the formation through injection well 60. If desired, a portion of the miscible fluid now being introduced into the formation may comprise solely the third raflinate fraction and the propane mixed therewith, followed by pure propane injected from storage tank into injection well 60. In any event, the

.last phase of injection of miscible liquid into the formation through injection well 60 is carried out until the miscible liquid comprises up to about 15 percent, preferably 2-5 percent, of the pore volume of the formation to be swept. This last phase of miscible liquid may comprise solely the third rallinate fraction. it may comprise partly the third rallinutc fraction supplemented or diluted by propane introduced front storage 25, or it may comprise a first portion of the third raflinate fraction mixed with propane, followed by a second portion comprised solely of pure liquid propane from storage tank 25.

Subsequent to the injection of the third raftinate fraction or the combinations of the third rafTtnate fraction and propane as above described, there is injected intothe formation through injection well a driving fluid which functions to displace all of the previously injected liquids and the formation oil from the formation through production well 10. The driving fluid preferably is a dry hydrocarbon gas, such as a separator gas, consisting in major part of methane with minor amounts of ethane and trace amounts of higher boiling hydrocarbons. The driving fluid may, however, be a flue gas or air. In some cases it may be desirable to drive the injected miscible liquids with an amphipathie liquid, followed by water. The amphipathic liquid is a material having a mutual solubility with water and a hydrocarbon fluid, such as an alcohol of 3 or 4 carbon atoms, an aldehyde. or a ketone. If separator gas, which is the preferred driving fluid, is employed, it is passed from storage tank through line 66 and compressor 67 into line 26 which is connected with wellhead 60a. lnjcction of the driving fluid is continued to ctl'cct displacement of formation oil from the formation 5 through production well 10 until either all of the formation oil has been displaced from the formation or until an uncconomical limit of the ratio of driving fluid and formation oil has been reached.

Subsequent to the injection of the driving fluid, the condition of the formation with respect to the formation oil, the various fractions of crude oil injected, and the driving fluid, is as diagranumttically represented in the drawing. The formation oil is being displaced toward production well 10 as illustrated by the po- 'tion of the formation indicated by reference numeral 6 The first, second, and third ratlinate fractions injected are represented, respectively, by

reference numerals

68, 69, and 70. As previously discussed, the fluid within the zone of the formation noted by reference numeral 70 may include the third rafhnate fraction, the third rafiinate fraction diluted by propane. or the third fraction per se followed by a quantity of pure pro ane. the total quantity of fluid oc cupying this zone formation indicated by reference numeral 70 comprising up to about 15 percent, preferably 2-5 percent. of the pore volume of the formation to be swe t. Filling zone 71 of the formation as shown on the drawing is the driving fluid.

in connection with the above description of the various steps of the invention. it has bccn indicated that only the first raftinate fraction of the formation oil need be depropnnizcd prior to injection. Of course, it is important that this first fraction have the propane removed from it in order to minimize asphalt precipitation within the formation. A decision as to whether or not to remove the propane from the further fractions, that is. those beyond the first one. depends upon several factors. If the available supply of propane is limited, it is preferable that the second and succeeding fractions of raflinate have the propane removed therefrom in order that it may be available for further use in lower 20 for the continuous fractionation of the formation oil. Also it may be desirable torcmove the propane or a portion of it in order to provide more accurate control of the viscosity and density of the fractions being introduced subsequent to the first fraction.

While the invention as illustrated above comprises the injection of three ratlinate fractions of crude oil, it is not intended that the invention be so limited. Depending upon the viscosity and density gradation necessary between the formation oil and the last of the miscible fluids injected, which may be,.for example, propane or LPG,

. 7 any number of raffinate fractions may be prepared in the manner above described and injected into the formation. Each succeeding fraction obviously should be of lower viscosity and density than its preceding fraction. The depropanization of the fractions, as indicated above, is dependent both upon the necessity for conserving the available supply of propane or LPG and the asphaltie condition of the formation oil.

While it has been indicated that crude oil from outside sources may be utilized in the preparation of the fractions to be injected, the invention finds particular advantage in its adaptability as a continuous process utilizing lease crude wherein continuous production of the lease crude is carried out while simultaneously portions of the lease crude are being fractionated and injected into the formation. It will be readily apparent that there is no necessity for the application of the invention to await the termination of primary production. The invention may be readily combined with primary production in order to facilitate a smooth and continuous transition from primary production to a miscible phase displacement form of secondary production. The equipment utilized in carrying out the invention may be of the portable form and skid mounted in order that it may be readily positioned on the lease site.

What is claimed is:

1. In a miscible phase displacement method of recovering oil from a subterranean earth formation provided with at least one production well and one injection well the steps which comprise:

(a) contacting crude oil with liquefied, normally gaseous hydrocarbons to produce from said crude oil a plurality of raflinate fractions, each of said fractions having a viscosity less than that of said crude oil and different from the others of said fractions, said contacting being conducted under conditions to deasphaltize at least the first of said fractions to be injected into said injection well;

(b) successively injecting said fractions into said formation through said injection well in an order of decreasing viscosity, the most viscous of said fractions being injected first;

(c) subsequent to the injection of the last of said fractions into said formation, injecting into said formation through said injection well a driving fluid miscible with the last of said fractions;

(d) driving said fractions by means of said driving fluid through said formation toward said production well; and v (e) producing oil from said formation through said production well.

2. The method of claim 1 wherein the liquefied, normally gaseous hydrocarbons remaining in the most viscous of said ratiinate fractions after production of said fraction in accordance with step (a) are substantially all stripped from said fraction prior to the injection of said fraction into said formation.

3. The method of claim 1 wherein said crude oil comprises the oil produced from said earth formation.

4. In a miscible phase displacement method of recovering oil from a subterranean earth formation provided with at least one production well and one injection well the steps which comprise:

(a) contacting crude oil with liquefied, normally gaseous hydrocarbons to produce from said crude oil a plurality of raffinate fractions, each of said fractions having a viscosity less than that of said crude oil and different from the others of said fractions, said contacting being conducted under conditions to deasphaltizc at least the first of said fractions to be injected into said injection well;

(c) adding to the last of said fractions prior to the injection of said fraction into said formation a quanlily of said liquefied, normally gaseous hydrocarbons;

(d) subsequent to the injection of the last of said fractions into said formation injecting into said formation through said injection well a driving tiuid miscible with the last of said fractions and said liquefied, normally gaseous hydrocarbons:

(e) driving said fractions and said liquefied, normally gaseous hydrocarbons by means of said driving flttid through said formation toward said production well; and

(f) producing oil from said formation through said production well.

5. In a miscible phase displacement method of recovering oil front a subterranean earth formation provided with at least one production well and one injection well the steps which comprise:

(e) following the injection of the last of said fractions into said formation, injecting into said formation through said injection well a quantity of said liquefied, normally gaseous hydrocarbons:

(d) following the injection of said liquefied, normally gaseous hydrocarlmns into said formation in accordance-with step (c) injecting into said formation through said injection well a driving lluid miscible with said liquefied, normally gaseous hydrocarbons;

(e) driving said fractions and said liquefied, normally gaseous hydrocarbons by means of said driving fluid through said formation toward said production well; and

(f) producing oil from said formation through said production well.

6. The method of claim 5 wherein the liquefied, normally gaseous hydrocarbons remaining in the most viscous of said rafiinate fractions after production of said fraction are substantially all stripped from said fraction prior to the injection of said fraction into said formation.

7. In a miscible phase displacement method of recovering oil from a subterranean earth formation provided with at least one production well and one injection well the steps which comprise:

(a) producing oil from said formation through said production well:

(b) continuously contacting said oil with liquefied. normally gaseous hydrocarbons while in stages raising the temperature of said oil and said liquefied, normally gaseous hydrocarbons to produce at each stage a raflinate fraction, said raflinate fractions being of progressively decreasing viscositics;

(c) continuously injecting said rnflinate fractions into said formation through said injection well in the order of the decreasing viscosities of said fractions;

(d) following the injection of the last of said raflinate fractions into said formation, injecting into said formation through said injection well a driving fluid miscible with the last of said fractions: and

(e) displacing said fractions by means of said driving fluid through said formation toward said production well to displace said oil from said formation.

8. in a miscible phase displacement method of recovering oil from a subterranean earth formation provided with i at least one production well and one injection well the steps which comprise:

(a) producing a first quantity of oil from said subterranean earth formation through said production well;

(b) flowing said first quantity of oi1 into a deasphalting and fractionating column;

(c) contacting said first quantity of oil within said column with liquefied, normally gaseoushydrocarbons to produce from said first quantity of oil a first raffinate fraction and an extraction fraction, the temperature of said liquefied, normally gaseous hydrocarbons and said first quantity of oil being maintained in the range of 70 F. to 120 F. during the produc tion of said fractions;

(d) flowing said first rafiinate fraction from said tower into said formation through said injection well;

(e) producing a second quantity of oil from said subterranean earth formation through said production well;

(f) flowing said second quantity of oil into said tower;

(g) contacting said second quantity of oil within said tower with said liquefied, normally gaseous hydrocarbons while maintaining the temperature of said second quantity of oil and said liquefied, normally gaseous hydrocarbons within the range of 110 F.

to 160 F. to produce from said second quantity of Y 011 a second rafiinate fraction and an extraction fraction;

(h) flowing said second raffinate fraction from said tower into said formation through said injection well;

(i) producing a third quantity of oil from said subterranean earth formation through said production well;

(j) flowing said third quantity of oil into said tower;

(k) contacting saidthird quantity of oil within said tower with said liquefied, normally gaseous hydrocarbons, the temperature of said third quantity of 10 oil and said liquefied, normally gaseous hydrocarbons being maintained within the range of F. to F. to produce a third raffinate fraction and an extraction fraction;

(1) flowing said third raffinate fraction from said tower into said formation through said injection well; (-rn) following the injection of said third raffinate fraction into said formation, injecting into said formation through said injection well a driving fiuid miscible with said third raflinate fraction.

(n) driving said raftinate fractions by means of said driving fluid through said formation toward said production well; and

(o) producing oil from said formation through said production well.

9. The method of claim 8 wherein the liquefied, normally gaseous hydrocarbons remaining in said first rafiinatc fraction after production of said fraction in accord ance with step (c) are substantially all stripped from said fraction prior to inject-ion of said fraction into said formation through said injection well.

10. The method of claim 9 wherein a quantity of said liquefied, normally gaseous hydrocarbons is injected into said formation through said injection well after the injection of the last of said raflinate fractions and before the injection of said driving fluid.

References Cited by the Examiner UNITED STATES PATENTS 2,234,207 3/1941 Thiele 208-87 2,867,277 1/1959 Weinaug 166-42 3,103,972 9/1963 Parker 166-9 JACOB L. NACKENOFF, Primary Examiner.

BENJAMIN HERSH, CHARLES E.- O'CONNELL,

Exmniners.

C. H. GOLD, T. A. ZALENSKI, Assistant Examiners.

Claims

1. IN A MISCIBLE PHASE DISPLACEMENT METHOD OF RECOVERING OIL FROM A SUBTERRANEAN EARTH FORMATION PROVIDED WITH AT LEAST ONE PRODUCTION WELL AND ONE INJECTION WELL THE STEPS WHICH COMPRISE: (A) CONTACTING CRUDE OIL WITH LIQIEFIED, NORMALLY GASEOUS HYDRACARBONS TO PRODUCE FROM SAID CRUDE OIL A PLURALITY OF RAFFINATE FRACTIONS, EACH OF SAID FRACTIONS HAVING A VISCOSITY LESS THAN THAT OF SAID CRUDE OIL AND DIFFERENT FROM THE OTHERS OF SAID FRACTIONS, SAID CONTACTING BEING CONDUCTED UNDER CONDITIONS TO DEASPHALTIZE AT LEAST THE FIRST OIF SAID FRACTIONS TO BE INJECTED INTO SAID INJECTION WELL; (B) SUCCESSIVELY INJECTING SAID FRACTIONS INTO SAID FORMATION THROUGH SAID INJECTION WELL IN AN ORDER OF DECREASING VISCOSITY, THE MOST VISCOUS OF SAID FRACTIONS BEING INJECTED FIRST; (C) SUBSEQUENT TO THE INJECTION OF THE LAST OF SAID FRACTIONS INTO SAID FORMATION, INJECTING INTO SAID FORMATION THROUGH SAID INJECTION WELL A DRIVING FLUID MISCIBLE WITH THE LAST OF SAID FRACTIONS; (D) DRIVING SAID FRACTIONS BY MEANS OF SAID DRIVING FLUID THROUGH SAID FORMATION TOWARD SAID PRODUCTION WELL; AND (E) PRODUCING OIL FROM SAID FORMATION THROUGH SAID PRODUCTION WELL.