US3593787A - Interface advance control in secondary recovery program by use of gradient barrier - Google Patents

Abstract

The advance of the interface between driving and driven fluids in a secondary recovery operation toward a production well is delayed by the imposition of a gradient barrier of produced hydrocarbon fluids injected into the formation via a control well in line between an injection well and a production well, the recirculation of the formation hydrocarbon fluids providing a dynamic barrier.

Description

United States Patent Inventor Donald L. Hoyt Houston, Tex. 786,568

Dec. 24, 1968 July 20, 1971 Texaco Inc. New York, N.Y.

Appl. No Filed Patented Assignee INTERFACE ADVANCE CONTROL IN SECONDARY RECOVERY PROGRAM BY USE OF GRADIENT BARRIER 23 Claims, 12 Drawing Figs.

US. Cl 166/245, 166/263, 166/266, [66/268 Int. Cl E211) 43/20, E21b 43/22 Field of Search 166/245, 263, 268, 266

[56] References Cited UNITED STATES PATENTS 3.135.325 6/1964 Parker 166/266 Re. 24.873 9/1960 Lindauer 166/268 3,074,481 1/1963 Habermann 166/245 3,109,487 11/1963 Hoyt 166/245 3,215,198 11/1965 Willman 166/263 Primary Examiner-Ian A. Calvert Attorneys-16 E. Kavanagh and Thomas H. Whaley ABSTRACT: The advance of the interface between driving and driven fluids in a secondary recovery operation toward a production well is delayed by the imposition of a gradient barrier of produced hydrocarbon fluids injected into the formation via a control well in line between an injection well and a production well, the recirculation of the formation hydrocarbon fluids providing a dynamic barrier.

PATENTED M2!) B7! SHEET 2 OF 2 5 I 5 pg INTERFACE ADVANCE CONTROL IN SECONDARY RECOVERY PROGRAM BY lUSlE OlF GRADIENT BARRIER FIELD OF THE INVENTION This invention relates generally to the production of hydrocarbons from underground hydrocarbon-bearing formations, and more particularly, to a method for increasing the efficiency of the production of hydrocarbons therefrom.

DESCRIPTION OF THE PRIOR ART In the production of hydrocarbons from permeable underground hydrocarbon-bearing formations, it is customary to drill one or more boreholes or wells into the hydrocarbonbearing formation and produce hydrocarbons, such as oil, through designated production wells, either by the natural formation pressure or by pumping the wells. Sooner or later, the

flow of hydrocarbons diminishes and/or ceases, even though substantial quantities of hydrocarbons are still present in the underground formations.

Thus, secondary recovery programs are now an essential part of the overall planning for virtually every oil and gas condensate reservoir in underground hydrocarbon-bearing formations. In general, this involves injecting an extraneous fluid, such as water or gas, into the reservoir zone to drive formation fluids including hydrocarbons toward production wells by the process frequently referred to as flooding." Usually, this flooding is accomplished by injecting through wells drilled in a geometric pattern, the most common pattern being the fivespot.

When the driving fluid from the injection well reaches the production wells of a five-spot pattern, the areal sweep is about 71 percent. By continuing production considerably past breakthrough, it is possible to produce much of the remaining unswept portion. It would be a great economic benefit to be able to achieve a sweep of 100 percent of the hydrocarbonbearing formation. It would be an even greater benefit to be able to achieve it at breakthrough, so that it would not be necessary to produce large quantities of injected driving fluid.

It is understood that the failure of the driving flood in secondary recovery operations to contact or sweep all the hydrocarbon area is due to the development of a cusp at the interface between the driving and driven fluids, which advances toward the production well. If other portions of the interface could be made to keep up, or if the cusp formation were delayed, a more complete areal sweep would be possible. In the commonly assigned U.S. Pat. No. 3,393,735, issued to A. F. Altamira et al. on July 23, 1968 for Interface Advance Control in Pattern Flood by Use of Control Wells, there is disclosed how an increased amount of hydrocarbons is produced and recovered from an underground hydrocarbon-bearing formation by employing at least three wells, penetrating such a for' mation, which wells are in-line, to produce hydrocarbons from the formation via two of these wells including the middle well, as disclosed in the commonly assigned U.S. Pat. No. 3,109,487, issued to Donald L. l-loyt on Nov. 5, 1963 for Petroleum Production by Secondary Recovery. in both these cited patents, there is disclosed how a production control well is positioned between the injection well and the production well and is kept on production after the injected fluid reached it. In this manner, the cusp is pinned" down at the control well and while the area swept out by the injection fluid before breakthrough at the outer production well is increased, there is an unwanted handling of considerable quantities of injected fluid at the control well.

Another aspect to increase the sweep is disclosed in the commonly assigned U.S. Pat. No. 3,393,734, issued to D. L. Hoyt et al. on July 23, 1968 and involves the retardation of the development of the cusp toward a production well. The method of achieving more uniform advance is to control the flow gradients so that the interface is spread out. This can be done either by choosing a particular geometry of well posi' tions or by adjusting the relative production rates so that the velocity of advance is not predominantly in one direction. It can be done also by shifting the gradients frequently, in both direction and magnitude, thus preventing any one section of an interface from advancing too far out ofline.

SUMMARY OF THE INVENTION It is an overall object of the present invention to provide an improved secondary recovery procedure involving initially three wells in line as part of a well arrangement for exploiting a hydrocarbon-bearing formation, by changing the function of the wells at strategic times to gain maximum control of the flood front.

A three-well group is arranged in line so that an end well is completed for injection and the remaining two wells are offset and completed for production. Flooding is initiated at the end well by injection of an extraneous driving fluid, such as water or gas, thereinto and proceeds until breakthrough of the flood front occurs at the closer of the offset production wells, at which time injection via the end well to maintain flooding is suspended and the offset production wells are put on a standby basis, e.g., by being closed in. Then preferably, a small volume or slug of an extraneous fluid is injected into the formation via the closer production well, at which breakthrough occurred, to drive the flood front away from this well, injection at the end well and production from the other production well are resumed, while continuing to inject a portion of the produced formation hydrocarbon fluids into the converted production well. Examples of the extraneous fluid include produced formation hydrocarbon fluids, which may be treated with thickeners to increase the viscosity thereof, butane and propane, all being miscible with the formation fluids.

The continuous injection into the converted well establishes a system of pressure gradients which on one side of the well are directed opposite to the pressure gradients associated with the driving fluid. A point of equilibrium of forces is established wherever the components of pressure gradient directed away from the converted well are equal and opposite to the components directed toward that well. The locus of all such equilibrium points establishes a stable interface, typically teardrop shaped, around the converted well. The shape and size of this interface will depend upon the interrelationship of many factors, primarily, geometry of well positions, relative permeabilities and viscosities, and well rate distributions. Control of any of these factors can be used thereby to enhance the effectiveness ofthe method.

Since the injected driving fluid cannot penetrate this gradient barrier, it must travel a roundabout and longer flow path to reach the final production well, thereby delaying cusping into the end production well and allowing a longer period for the advance of the interface between the driving fluid and the formation fluids before breakthrough. When production at the end well is continued after breakthrough, the converted injection well is closed in and the continuing production results in recovery of the injected produced hydrocarbon fluids, along with remaining in place formation fluids.

Many variations of this basic procedure are possible, and some will be more advantageous than others for particular geometries of well positions, and reservoir and fluid parameters. But they will have certain things in common:

1. An intermediate well between an injection source and a production well either exists or is added.

2. At breakthrough into this intermediate well (or some time prior thereto), the injection is suspended and a volume of fluid, such as a portion of the produced fluid hydrocarbons, is injected into the intermediate well. This portion may be a percentage of the pore volume within the drainage radius of the well. A simple approximation of the drainage radius would be the average of the half distances to the nearest wells. This injection may be done with or without simultaneous production from other wells.

3. Injection of driving fluid is resumed at the principal injection well, and injection of the barrier fluid is continued into the intermediate well at a rate equal to a percentage of the production rates.

4. ,This continues, even though other existing wells may be captured" by injected driving fluid and closed in, until breakthrough of the injection fluid into the production well on the other side of the intermediate well.

5. At this time, or in some cases even before it, the injection of barrier fluid is stopped. Continued injection of driving fluid on one side and continued production on the other will move the barrier fluid completely into the production well if recovery of this fluid is desired (as, for example, if the barrier fluid used comprises produced hydrocarbon fluids).

Other objects, advantages and features of this invention will become apparent from a consideration of the specification with reference to the figures of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 disclosed four units of an inverted fivespot pattern;

FIG. la is illustrative of the interface advance in the form of a cusp toward a comer production well in one quadrant of such a five-spot pattern undergoing secondary recovery;

FIG. 2 disclosed one unit ofa ninewell diagonal pattern;

FIG. 2a, corresponding to FIG. la, illustrates cusp accentuation in one quadrant of a nine-well diagonal pattern unit, and FIG. 2b illustrates the effect of continued production from a control well to retard the advance of the interface toward a comer production well i.e. "pinning" the cusp, in one quadrant of a nine-well diagonal pattern undergoing secondary recovery;

FIG. 3 disclosed one quadrant of a nine-well diagonal pattern, illustrating the retreat of the cusp at the control well between the injection well and the corner production well resulting from injection of a small volume of produced fluid hydrocarbons into a control well, with all other wells temporarily shut in;

FIGS. 40, 4b and 4c illustrate the changes in well functions in accordance with the movement of the interface during the several phases of the production program in a 13-well pattern undergoing secondary recovery; and

FIGS. a, 5b and 5c correspond to FIGS. 4a, 4b and 4c during the production phases applied to a seventeen well pattern undergoing secondary recovery.

The objects of the invention are achieved by the use of control wells in combination with production wells to delay the breakthrough of injected driving fluid into the outermost production wells, typically in pattern units, by retarding the development of the usual cusp interface between the formation and injected fluids.

The specification and the figures of the drawings schematically disclose and illustrate the practice and the advantages of the invention with well patterns and areal sweep examples which are obtainable and have been observed both in secondary recovery operations and in potentiometric model studies which simulate secondary recovery operations. The model studies indicate a sweep obtained in an ideal reservoir, although the recovery from an actual sweep of a particular field may be greater or less, depending on field parameters.

Throughout the figures of the drawings, the same symbols will be maintained as follows: P P,and P represent respectively production wells at the comers, along the sides, and the interior control wells of a pattern or well arrangement; and, a solid circle indicates a production well, a crossed circle indicates a shut-in well, an arrowed open circle indicates an injection well, and an arrowed solid circle, a converted injection well. The diagonal x-x in FIGS. 2, 4a and 5a represents an axis of an injection well and a pair ofoffset production wells.

Referring to FIG. 1, there is disclosed four units of an inverted five-spot pattern wherein the corner wells of each pattern unit are production wells, while the inner central well is used for injection.

FIG. Ia illustrates the growth of the cusp in one quadrant of an inverted five-spot pattern unit, wherein the secondary flooding fluid is injected into the central well and production is maintained at the corner wells until breakthrough, to result in a sweep of approximately 71 percent.

Referring to FIG. 2, there is disclosed a nine-well diagonal pattern, essentially the five-spot pattern with control wells positioned on the diagonals between the central injection well and the corner production wells. The control wells should be spaced at least one-half the distance between the injection well and each corner production well, with the best results obtained when such control wells are positioned between threefourths and seven-eighths of the distance from the injection well toward the corner production wells. With such a pattern, the invention disclosed in the cited patent to Hoyt can be-cmployed with success to increase the sweep area over that mentioned for the basic five-spot pattern.

FIG. 2a illustrates cusp accentuation after breakthrough has occurred at an interior control well, P,, located midway between the central injection well and the corner production well, after which this well is closed in and production initiated and maintained at the corner production well until breakthrough thereat.

FIG. 2b illustrates the effect of a control well as it retards the advance of the cusp. As disclosed in the above-cited patents to Hoyt and to Altamira et al., the advance of the cusp has been pinned," thereby delaying the advance and accentuation of the pointed cusp interface, as illustrated in FIG. 2a, to produce an oblate cusp interface, resulting in a greater sweep. The procedure employed in achieving such a sweep requires providing the flooding or driving fluid to the central injection well and maintaining production, either concurrently or in turn, at both the control or interior wells and the corner production wells until breakthrough of the interface occurs at the corner production wells. The sweep in each instance is substantially the same, with differences in the amounts of injected fluid produced at the interior control wells.

In FIG. 3, the invention illustrates the improvement provided by one embodiment of this invention over the disclosures of the prior art in FIGS. 1, la, 2, 2a and 2b. With injection of the driving fluid via the central well of a nine-well diagonal pattern, production is maintained via the interior control well, P (or also via the corner production well, P until breakthrough thereat, to form the interface indicated at A,P,A in FIG. 3, to yield a sweep of 57 percent. The control well, P,, is located on the ,diagonal through the injection well and the corner production well, P about three-fourths of the distance from the central injection well. If the production well at P, were closed in to avoid handling any of the injection driving fluid and production were initiated (or continued) and maintained till breakthrough at the corner well, P the sweep (not indicated) would increase by 9 percent, for a total sweep of 66 percent.

Instead, a volume of produced formation hydrocarbon fluids equal to a predetermined value, e.g. about 15 percent of a pattern unit volume, is injected through the interior control wells, P,-, from which production has ceased, and the cusp driven back by the resulting injected bubble of hydrocarbon fluids, as shown in section at C FIG. 3, and the interface distorted as indicated by the dashed outline at A A the point of the cusp being driven back from the control well, P while the flanks advance from the line A,P A,. The changes in the shapes of the cusp have been exaggerated for purposes of clarity.

When production is initiated (or resumed) at the corner well, P and with about 50 percent of produced formation fluids being injected continuously into the formation via well P the cycling hydrocarbon fluids form a stable teardrop bubble, as indicated in section at C FIG. 3. The envelope of this bubble represents the surface of equilibrium of pressure gradient forces.

By the time the driving fluid gets around the gradient barrier to achieve breakthrough at the corner production well, P the sweep of the formation fluids has been increased 31 percent,

as indicated by the interface at 13 F 8 for a total sweep of 88 percent.

Finally, if production at P, is continued after breakthrough with the control well P, closed in, maximum gradients are reestablished along the axis of the wells, and virtually all the injected produced hydrocarbon fluids can be recovered quickly along with additional formation fluids miscible therewith, bringing total sweep to over 90 percent before an appreciable percentage ofinjected driving fluid is produced.

The sweep can be increased either by forming a larger initial bubble or using a greater fraction of the produced fluid hydrocarbons for injected back into the formation via the cow verted control well.

FIG, la discloses the basic nine-spot pattern modified by the addition of four interior control wells, which can be positioned on the diagonals of the pattern for best advantage as indicated previously. it can be visualized also as a four-unit fivespot pattern, wherein the injection wells of the inverted fivespot pattern units have been converted to production wells, and the innermost production well of the foununit live'spot pattern has been converted into an injection well. li t ith such a conversion, the positions of the control wells have been predetermined and may not be situated for best effect.

As illustrated in one quadrant ofthc pattern, the first phase of the production method requires injecting driving fluid via the central well and production initiated and maintained at the remaining 12 wells of the pattern until breakthrough is achieved at the four interior control wells, as shown in FIG.

4a, the clear area being the sweep and the right diagonals indicating the unswept in-place fluids. Then these interior production wells are converted to injection wells for receiving produced formation fluid hydrocarbons while production is continued from the corner wells P and the side wells P, until breakthrough thereat, as illustrated in FlG. ll), the left diagonals in the teardrop-shape section indicating the returned fluid hydrocarbons. As indicated in H6. ts, the four side wells are closed in, production is continued at the corner production wells 1P," until breakthrough occurs thereat. By the illustrated phases of this method when applied to the nine-spot pattern as modified by the addition of four interior control wells, a sweep of approximately 87 percent follows. if production after breakthrough at the corner wells is continued, the teardrop bubble can be recovered in approximately 8 percent of the time required for the third phase, bringing sweep to 93 percent, leaving slivers of unswept areas adjacent the corner production wells.

FIG. 5a discloses a 17-spot pattern which is formed by drilling a single injection well in a center of a 4X4 well square. In this l7-spot pattern, there are four corner production wells, two producing side wells on each side of the 4X4 well square, and four interior control wells located on the diagonals of the pattern and positioned between the central injection well and the corner production wells.

in FIGS. 5n, db and 5c, there are illustrated in one quadrant of the pattern, using the same symbolism as in M63. do, ll; and ile, three steps or phases of the production method as applied to the l7-spot pattern. lit the first phase, illustrated in FIG. 5a, with injection maintained at the central injection well, production is initiated and maintained at the four interior control wells, the eight side wells and each ofthe corner wells until breakthrough is achieved at the control wells. in the second phase, as illustrated in PM}. 5b, while production is maintained at the corner production wells and the side wells, the interior control wells are converted from production to injection of produced formation fluid hydrocarbons until breakthrough occurs at the side wells. Thereupon, the side wells P, are closed in, while production is maintained until breakthrough at the corner production wells, lP injection of the driving fluid is continued at the central well and injection of produced fluid hydrocarbons is continued also via the interior control wells, P interface positions at breakthrough into the corner well, P are indicated in H6. fie. Again the favorable position of the injected fluid hydrocarbons is sweep before interface breakthrough. Clearly, the wider the barrier can be made, the better will be the sweep.

Factors which will cause such a barrier to be wide are: A. higher viscosity of the control well fluid than of the driving lluid;

B. high control well injection rates as a percentage of production;

C. production from side wells during the control well injection phase;

D. dual control wells straddling the axis through the injection and production wells to form a wider bubble, depending on the spacing between the straddle wells, such spacing being in the range of 0.1 to 0.2 of the distance between the injection and production wells, (not shown in the drawing for purposes ofclarity).

Any pattern and/or rate distribution which retards the development, or the advance, of a cusp towards production wells will increase the sweep of a field. Two principal means of doing this have been cited above, viz. (a) pinning" down the cusp by locating production wells between the injection source and the outer production wells, and keeping such inner (or control) wells on production after breakthrough; and (b) spreading" out the cusp by pulling the front toward side wells until breakthrough thereat before allowing the interface to proceed toward the corner production wells ofa pattern unit.

lillerein has been disclosed another method of delaying the advance of the interface in the form of a cusp toward an outer production well by locating a dynamic barrier of produced fluid hydrocarbons between an injection well and the outer production well.

Although emphasis has been placed in this disclosure on the practice of this invention as directed to a secondary recovery operation, particularly employing water or other similar aqueous fluid as the injection displacement fluid, the advantages obtainable in the practice of this invention are also realized in primary hydrocarbon production operations wherein the hydrocarbonbearing formation is under the influence of either a water or gas drive, or both a water and a gas drive, and also in the instance of a secondary recovery operation wherein a gas, such as natural gas, is employed as the injection fluid. Moreover, the invention is applicable particularly to an arrangement of a pair of production wells in line with an injection well under the influence of an active water drive.

l claim:

l. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation which comprises penetrating said formation with at least an injection well and an offset production well, injecting an extraneous driving fluid comprising natural gas into said formation via said injection well to displace fluids including hydrocarbons in said formation toward said production well, producing said formation fluids including hydrocarbons from said formation via said production well until said extraneous driving fluid has reached a predetermined intermediate position therebetwcen, thereupon injecting into said formation an extraneous fluid miscible with said formation fluids via an intermediate well between the injection and production wells and continuing such injecting to form a dynamic barrier in said formation therebetween, and maintaining producing fluids including hydrocarbons from said formation via said offset production well while injecting extraneous driving fluid and that fluid miscible with said formation fluids into said for-. mation via said injection and intermediate wells respectively.

2. In a method as defined in claim 1, said intermediate well being one of a pair of wells straddling the diagonal between said injection and production wells and spaced apart from each other by a distance from 0.1 to 0.2 of the distance between the last-mentioned wells.

3. in a method as defined in claim I, the extraneous fluid in-' jected via the intermediate well being selected from the group consisting of butane, propane and produced hydrocarbon fluids.

4. In a method as defined in claim 3, the intermediately injected extraneous fluid being recovered from produced formation fluids via said production well and returned to said formation via said intermediate well until breakthrough of said extraneous driving fluid at said production well.

5. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing for mation under the influence of an active aquifer which comprises penetrating said formation with a pair of production wells in line with the direction of advance of said aquifer, producing formation fluids including hydrocarbons displaced by said aquifer until breakthrough of the interface between the formation fluids and said aquifer at a production well, thereupon ceasing producing formation fluids thereat and injecting thereinto an extraneous fluid of predetermined volume, starting initially with a percentage of the reservoir volume and continuing with a percentage of the produced formation fluids from the other of said pair of production wells to provide a dynamic gradient barrier at the interface where said breakthrough has occurred, and producing formation fluids including hydrocarbons from said formation via the other of said pair of production wells, while maintaining said gradient barrier.

6. In a method of producing formation fluids including hydrocarbons as defined in claim 5, said extraneous fluid being selected from the group consisting of butane, propane and produced hydrocarbon fluids.

7. in a method of producing formation fluids including hydrocarbons as defined in claim 6, said predetermined volume amounting to percent of the reservoir volume affected by the production well where said breakthrough has occurred.

8. In a method of producing formation fluids including hydrocarbons as defined in claim 5, ceasing producing from said pair of wells while injecting said extraneous fluid.

9. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation which comprises penetrating said formation with at least three wells, a first well, a second well and a third well, said wells being substantially in line and the second and third wells being on one side of said first well with said second well closer thereto, injecting an extraneous driving fluid into said formation via said first well to displace fluids including hydrocarbons in said formation toward said second and third wells, producing said formation fluids including hydrocarbons from said formation via said second well, recovering formation hydrocarbon fluids from produced formation fluids, ceasing producing said formation fluids and then injecting some of the recovered formation hydrocarbon fluids into said formation via said second well, and producing said formation fluids including hydrocarbons from said formation via said third well and injecting extraneous driving fluid and some recovered formation hydrocarbon fluids into said formation via the first and second wells respectively, the injecting of fluids into said formation via said first and second wells continuing until breakthrough of said extraneous driving fluid at said third well, thereupon ceasing injecting fluids via said second well while continuing producing said formation fluids via said third well. 10. in a method as defined in claim 9, injecting recovered fonnation hydrocarbon fluids into said formation via said second well prior to breakthrough of said extraneous driving fluid thereinto.

11. In a method as defined in claim 9, injecting recovered formation hydrocarbon fluids into said formation via said second well upon breakthrough of said extraneous driving fluid thereinto.

12. In a method of producing formation fluids as defined in claim 9, concurrently initiating and maintaining producing said formation fluids from said second and third wells.

13. In a method of producing formation fluids as defined in claim 9, initiating producing formation fluids from said third well after starting injecting of recovered formation hydrocarbon fluids into said formation via said second well.

14. In a method of producing formation fluids as defined in claim 9, said three wells in line being part of a l3-well pattern, wherein the central well of said pattern is said first well and the remaining pattern walls are production wells arranged in equal numbers along the sides and on the diagonals of a quadrilateral, including said second and third wells arranged therealong and eventually producing formation fluids therefrom.

15. In a method of producing formation fluids as defined in claim 14, simultaneously initiating producing said formation fluids via all of said production wells.

16. in a method of producing formation as defined in claim 14, producing formation fluids via said wells located on the diagonals of said pattern adjacent said injection well and continuing producing therefrom until breakthrough of said extraneous driving fluid occurs, thereupon converting said aforementioned diagonal wells into injection wells and injecting recovered formation hydrocarbon fluids into said formation via such converted wells and initiating and continuing producing from the side wells of said pattern until extraneous driving fluid breakthrough occurs thereat, thereupon continuing injecting recovered formation hydrocarbon fluids into said formation via said converted wells and initiating and maintaining producing said formation fluids via the corner wells of said pattern until extraneous driving fluid breakthrough occurs thereat.

17. in a method of producing fluids as defined in claim 9, said three wells in line being part of a 17-well pattern, the central well being said first well and the remaining wells being production wells located in equal numbers along the sides and on the diagonals of a quadrilateral including said second and third weils arranged therealong, and eventually producing formation fluids therefrom.

18. In a method of producing fluids as defined in claim 17, continuing injecting said extraneous driving fluid via said central well and producing simultaneously from all of the remaining wells of the pattern until said extraneous driving fluid breakthrough occurs at individual production wells on said diagonals, thereupon converting said individual production wells into injection wells and injecting recovered formation hydrocarbon fluids into said formation via the converted injection wells and continuing producing said formation fluids via the remaining production wells until extraneous driving fluid breakthrough occurs thereat.

19. in a method of producing fluids as defined in claim 17, continuing injecting said extraneous driving fluid into said formation via said central well and producing said formation fluids via said wells spaced on the diagonals of said pattern immediately adjacent the central injection well and continuing producing therefrom until extraneous driving fluid breakthrough occurs at such production wells, thereupon convetting such wells into injection wells and injecting recovered formation hydrocarbon fluids into said formation via the converted injection wells and initiating and maintaining producing from the side wells of said pattern until extraneous fluid breakthrough occurs thereat, thereupon continuing injecting recovered formation hydrocarbon fluids into said formation via the converted injection wells and initiating and maintaining producing at the corner production wells until said extraneous driving fluid breakthrough occurs thereat.

20. In a method as defined in claim 9, said injecting of recovered hydrocarbon fluids via said second well being of predetermined amount starting with about 15 percent of the pore volume within the drainage radius of said second well and continuing with about 50 percent of the production of formation fluids from said third well to provide a dynamic barrier therebetween.

2]. In a method as defined in claim 20, said recovered'formation hydrocarbon fluids being treated with thickeners to increase the viscosity thereof prior to injection into said formation via said second well.

22. In a method of producing formation fluids as defined in claim 9, said three wells in line being part of a nine-well diagonal pattern wherein the central well of said pattern is said

Claims (21)

1. 2. In a method as defined in claim 1, said intermediate well being one of a pair of wells straddling the diagonal between said injection and production wells and spaced apart from each other by a distance from 0.1 to 0.2 of the distance between the last-mentioned wells.
2. 3. In a method as defined in claim 1, the extraneous fluid injected via the intermediate well being selected from the group consisting of butane, propane and produced hydrocarbon fluids.
3. 4. In a method as defined in claim 3, the intermediately injected extraneous fluid being recovered from produced formation fluids via said production well and returned to said formation via said intermediate well until breakthrough of said extraneous driving fluid at said production well.
4. 5. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation under the influence of an active aquifer which comprises penetrating said formation with a pair of production wells in line with the direction of advance of said aquifer, producing formation fluids including hydrocarbons displaced by said aquifer until breakthrough of the interface between the formation fluids and said aquifer at a production well, thereupon ceasing producing formation fluids thereat and injecting thereinto an extraneous fluid of predetermined volume, starting initially with a percentage of the reservoir volume and continuing with a percentage of the produced formation fluids from the other of said pair of production wells to provide a dynamic gradient barrier at the interface where said breakthrough has occurred, and producing formation fluids including hydrocarbons from said formation via the other of said pair of production wells, while maintaining said gradient barrier.
5. 6. In a method of producing formation fluids including hydrocarbons as defined in claim 5, said extraneous fluid being selected from the group consisting of butane, propane and produced hydrocarbon fluids.
6. 7. In a method of producing formation fluids including hydrocarbons as defined in claim 6, said predetermined volume amounting to 15 percent of the reservoir volume affected by the production well where said breakthrough has occurred.
7. 8. In a method of producing formation fluids including hydrocarbons as defined in claim 5, ceasing producing from said pair of wells while injecting said extraneous fluid.
8. 9. A method of producing formation fluids including hydrocarbons from an underground hydrocarbon-bearing formation which comprises penetrating said formation with at least three wells, a first well, a second well and a third well, said wells being substantially in line and the second and third wells being on one side of said first well with said second well closer thereto, injecting an extraneous driving fluid into said formation via said first well to displace fluids including hydrocarbons in said formation toward said second and third wells, producing said formation fluids including hydrocarbons from said formation via said second well, recovering formation hydrocarbon fluids from produced formation fluids, ceasing producing said formation fluids and then injecting some of the recovered formation hydrocarbon fluids into said formation via said second well, and producing said formation fluids including hydrocarbons from said formation via said third well and injecting extraneous driving fluid and some recovered formation hydrocarbon fluids into said formation via the first and second wells respectively, the injecting of fluids into said formation via said first and second wells continuing until breakthrough of said extraneous driving fluid at said third well, thereupon ceasing injecting fluids via said second well while continuing producing said formation fluids via said third well. 10. In a method as defined in claim 9, injecting recovered formation hydrocarbon fluids into said formation via said second well prior to breakthrough of said extraneous driving fluid thereinto.
9. 11. In a method as defined in claim 9, injecting recovered formation hydrocarbon fluids into said formation via said second well upon breakthrough of said extraneous driving fluid thereinto.
10. 12. In a method of producing formation fluids as defined in claim 9, concurrently initiating and maintaining producing said formation fluids from said second and third wells.
11. 13. In a method of producing formation fluids as defined in claim 9, initiating producing formation fluids from said third well after starting injecting of recovered formation hydrocarbon fluids into said formation via said second well.
12. 14. In a method of producing formation fluids as defined in claim 9, said three wells in line being part of a 13-well pattern, wherein the central well of said pattern is said first well and the remaining pattern walls are production wells arranged in equal numbers along the sides and on the diagonals of a quadrilateral, including said second and third wells arranged therealong and eventually producing formation fluids therefrom.
13. 15. In a method of producing formation fluids as defined in claim 14, simultaneously initiating producing said formation fluids via all of said production wells.
14. 16. In a method of producing formation as defined in claim 14, producing formation fluids via said wells located on the diagonals of said pattern adjacent said injection well and continuing producing therefrom until breakthrough of said exTraneous driving fluid occurs, thereupon converting said aforementioned diagonal wells into injection wells and injecting recovered formation hydrocarbon fluids into said formation via such converted wells and initiating and continuing producing from the side wells of said pattern until extraneous driving fluid breakthrough occurs thereat, thereupon continuing injecting recovered formation hydrocarbon fluids into said formation via said converted wells and initiating and maintaining producing said formation fluids via the corner wells of said pattern until extraneous driving fluid breakthrough occurs thereat.
15. 17. In a method of producing fluids as defined in claim 9, said three wells in line being part of a 17-well pattern, the central well being said first well and the remaining wells being production wells located in equal numbers along the sides and on the diagonals of a quadrilateral including said second and third wells arranged therealong, and eventually producing formation fluids therefrom.
16. 18. In a method of producing fluids as defined in claim 17, continuing injecting said extraneous driving fluid via said central well and producing simultaneously from all of the remaining wells of the pattern until said extraneous driving fluid breakthrough occurs at individual production wells on said diagonals, thereupon converting said individual production wells into injection wells and injecting recovered formation hydrocarbon fluids into said formation via the converted injection wells and continuing producing said formation fluids via the remaining production wells until extraneous driving fluid breakthrough occurs thereat.
17. 19. In a method of producing fluids as defined in claim 17, continuing injecting said extraneous driving fluid into said formation via said central well and producing said formation fluids via said wells spaced on the diagonals of said pattern immediately adjacent the central injection well and continuing producing therefrom until extraneous driving fluid breakthrough occurs at such production wells, thereupon converting such wells into injection wells and injecting recovered formation hydrocarbon fluids into said formation via the converted injection wells and initiating and maintaining producing from the side wells of said pattern until extraneous fluid breakthrough occurs thereat, thereupon continuing injecting recovered formation hydrocarbon fluids into said formation via the converted injection wells and initiating and maintaining producing at the corner production wells until said extraneous driving fluid breakthrough occurs thereat.
18. 20. In a method as defined in claim 9, said injecting of recovered hydrocarbon fluids via said second well being of predetermined amount starting with about 15 percent of the pore volume within the drainage radius of said second well and continuing with about 50 percent of the production of formation fluids from said third well to provide a dynamic barrier therebetween.
19. 21. In a method as defined in claim 20, said recovered formation hydrocarbon fluids being treated with thickeners to increase the viscosity thereof prior to injection into said formation via said second well.
20. 22. In a method of producing formation fluids as defined in claim 9, said three wells in line being part of a nine-well diagonal pattern wherein the central well of said pattern is said first well and the remaining pattern wells, including said second and third wells, are production wells arranged in equal numbers on the diagonals of a quadrilateral, and eventually producing said formation fluids via all of said production wells.
21. 23. In a method as defined in claim 22, said second well being spaced away from said first well by at least three-fourths 035946706 of the distance between said first well and said third well.

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