|Publication number||US3380526 A|
|Publication date||Apr 30, 1968|
|Filing date||Jun 28, 1966|
|Priority date||Jun 28, 1966|
|Publication number||US 3380526 A, US 3380526A, US-A-3380526, US3380526 A, US3380526A|
|Inventors||Altamira Anthony F, Hoyt Donald L|
|Original Assignee||Texaco Inc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (7), Referenced by (3), Classifications (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
April 30, 1968 A. F. ALTAMIRA ET AL 33 5 l9-WELL DOUBLE HEXAGON PATTERN FOR SECONDARY RECOVERY Filed June 28, 1966 4 Sheets-Sheet l -WW0 w April 30, 1968 A. F. ALTAMIRA ET AL 3,380,526
IQ-WBLL DOUBLE HEXAGON PATTERN FOR SECONDARY RECOVERY 4 Sheets-Sheet 2 Filed June 28. 1966 April 30, 1968 F, T R ET AL 3,386,526
lQ-WELL DOUBLE HEXAGON PATTERN FOR SECONDARY RECOVERY April 30, 1968 A. F. ALTAMIRA ET AL 3,380,526
l9-WELL DOUBLE HEXAGON PATTERN FOR SECONDARY RECOVERY Filed June 28, 1966 4 Sheets-Sheet 4 United States Patent 3,380,526 19-WELL DOUBLE HEXAGON PATTERN FOR SECONDARY RECOVERY Anthony F. Altamira and Donald L. Hoyt, Houston, Tex.,
assiguors to Texaco Inc., New York, N.Y., a corporation of Delaware Filed June 28, 1966, Ser. No. 561,146 9 Claims. (Cl. 1669) This invention relates generally to the production of hydrocarbons from underground hydrocarbon-bearing formations, and more particularly, to a method for increasing the overall production of hydrocarbons therefrom.
In exploiting underground hydrocarbon-bearing formations through a plurality of wells, it has been the general practice that when a production well yields an excessive amount of an extraneous fluid other than the hydrocarbons, e.g., water or gas, that production well is shut-in and the production of hydrocarbons is started and carried out at other production wells in the field. It is known that in such instances, a substantial amount of hydrocarbons is left behind in the hydrocarbon-bearing formation since such is not considered primarily recoverable economically.
Secondary recovery operations are now an essential part of the over-all program planning for virtually every oil and gas-condensate reservoir in underground hydrocarbon-bearing formations. Some of the operations developed include g-as repressuring and water, fire, steam and solvent flooding. Usually, they all employ some geometric pattern of injection and production wells, with injection of fluid into some of the Wells to displace hydrocarbons in the reservoir zone toward the production wells.
The front, or interface, between the injected and inplace fluids moves from injection toward production wells, changing shape as it progresses. Due to the pressure sinks around the production wells, a portion of the interface tends to accelerate and cusp into the production wells. Breakthrough of the injected fluid occurs when the interface reaches the production wells. The percentage of the entire reservoir which has been invaded by the injected fluid at that time is referred to as the sweep efficiency of the particular geometric pattern used.
The most commonly used well pattern is secondary recovery in the 5-spot pattern, with four injection wells at the corners of a square and a production well at the center. In a production field of 5-spot patterns, there are as many injection wells as production wells. Sweep efliciency for the S-spot pattern is about 71 percent. Other basic flood patterns sometimes used are the 7-spot, direct line and staggered line drives, with sweep efficiencies of 74, 57 and 78 percent respectively.
In field practice, injection usually will be continued well past breakthrough until the reservoir cannot be produced economically. In this way, some additional sweepout can be achieved, but often there will be large volumes of produced injection fluid to be handled, treated and re-injected. If sweepout prior to breakthrough in a pattern flood were improved, it is very likely that the ultimate recovery would be higher. The time and cost of the operation, to achieve comparable recoveries, would be reduced accordingly.
Accordingly, it is an object of the present invention to provide an improved method for the production and recovery of hydrocarbons, particularly liquid petroleum, from underground hydrocarbon-bearing formations.
Another object of this invention is to provide a method whereby the area sweep efficiency in pattern flooding is improved.
These and other objects, advantages and features of ice this invention will become apparent from a consideration of the specification with reference to the figures of the accompanying drawings wherein:
FIG. 1 discloses a conventional 5-spot pattern unit in a field undergoing secondary recovery illustrating the interface of the injected fluid at breakthrough at the production wells;
FIG. 2 discloses the formation of a 19-well double hexagon pattern unit in a field of staggered equidistantly spaced wells;
FIGS. 3, 4 and 5 illustrate the movements of the interface of the injected fluid during the three phases of the exploitation plan in one 19-Well double hexagon pattern unit in a field undergoing secondary recovery; and
FIGS. 6, 7, and 8 illustrate the movements of the interface of the injected fluid during the three phases of an alternate exploitation plan in one 19-wel1 double hexagon pattern unit in a field undergoing secondary recovery.
In our copending, coassigned application for patent Ser. No. 517,052, field Dec. 28, 1965, for Interface Advance Control in Pattern Floods 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 formation, which wells can be in-line, to produce hydrocarbons from the formation via two of these wells including the middle well, as disclosed in the co-assigned US. Patent No. 3,109,487, issued to Donald L. Hoyt, on .Nov. 5, 1963.
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, in the interface, of a cusp 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, complete area sweep would be possible. In the above cited co-assigned application, a production control well is positioned between the injection well and the production well and is kept on production even after the injection fluid reaches 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 last production well is increased, there is an unwanted handling of considerable quantities of injection fluid at the control well.
Another aspect to increase the sweepout efli'ciency is disclosed in our copending, coassigned application for patent Ser. No. 516,891, filed Dec. 28, 1965, for Interface Advance Control in Pattern Flods by Retarding cusp Formation, and involves the retardation of the development of the cusp forward the 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 positions 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 of line.
The figures of the drawings schematically disclosed and illustrate the practice and the advantages of our invention with well pattern and areal sweepout examples which are obtainable and have been observed both in secondary re covery operations and in potentiometric model studies which simulate secondary recovery operations. The model studies indicate a sweepout obtained in and ideal reservoir, although the recovery from an actual sweepout of a particular field may be greater or less, depending on field parameters. The procedures to be described are based on the following set of experimental conditions and assumptions:
(1) All the units in any patern are balanced and produce at the same rate. This requires that wells on the edges of a pattern unit produce or inject at /6 or /2 of the rate of interior wells, depending inversely on the number of pattern units with which they are associated;
(2) The total amount of fluid injected must be equal to the fluid produced for each pattern unit, as well as for the whole pattern;
(3) The mobility ratio of the displacing to the displaced fluid is 1.0;
(4) The permeability and sand thickness of the formation is uniform; and
(5) Gravitational effects are not considered.
Throughout the drawings, the same symbolic indicators will be maintained as follows: R P P andl represent respectively, production wells at the corners, along the sides, medially and the center interior wells; and, a solid circle indicates a production Well, a crossed circle indicates a shut-in well, and an arrowed circle indicates an injection well.
FIG. 1, illustrates the interface of the injected fluid at breakthrough at the well of a single conventional S-spot pattern unit in a production field undergoing secondary recovery, wherein .the corner wells of each patern unit are injection wells, while the inner center well is used for production. Such a procedure will produce a sweepout of approximately 71%. In this pattern, the ratio of the distance between the rows of wells to the distance between the in-line wells is 0.5, i.e. d/a= /2.
Referring to FIG. 2, there is disclosed the formation of a 19-well double hexagon pattern, comprising six wells (P located at the vertices of an inner equilateral hexagon and a similar, concentric outer hexagon having wells (P located at the vertices thereof, and midway between these, wells (P on the sides of the outer hexagon, and a single central well (P,). The wells at the vertices and on the sides are part of a staggered equidistant well spacing, the ratio of the distance between the rows of wells to the distance between the in-line wells being 0.866, i.e. d/a=0.866. The wells at the vertices of the hexagons lie on common diagonals passing through the central well, with the wells (P at the vertices of the inner hexagon being located medially between the corner wells (P of the outer hexagon and the control well (P FIGS. 3, 4 and 5 disclose the interface shapes at the ends of the consecutive steps of the three phase, secondary recovery exploitation plan as used in the 19-well double hexagon pattern.
FIG. 3 discloses the interface shape at the end of the first phase, wherein driving fluid is injected into the formation through the wells (P along the sides of the outer equilateral hexagon, with production at the wells (P at the corners or vertices thereof until breakthrough of the injection fluid occurs thereat. The remaining wells of the pattern unit are shut in during this phase of the plan. At this breakthrough, a substantially hexamerous camlike area, having an outline of a spur gear, defined by the cusp formation ending at the producing corner wells (P remains, and is indicated by cross-hatching in FIG. 3, with an area sweepout of 30%. The ratio of the injected well rate to the production well rate is 2 to 3 i.e. there are two production wells for each three injection wells. Both injection and production are uniformly distributed.
FIG. 4 discloses the interface shape at the end of the second phase of the exploitation plan wherein injection is shifted from the side wells (P which are shut in now, to the corner wells (P of the outer hexagon, production is initiated both at the medial wells (P at the vertices of the inner hexagon and at the central well (P and maintained until breakthrough occurs at the medial wells (P of the fluid injected into the formation, the symbolic indicators being used as noted previously. An additional 38% sweepout is attained to give a sub-total of 68% sweep efficiency. The ratio of the injection rate to the production well rate is 7 to 2, i.e. there are seven production wells for each two injection Wells, with the injection and production rates being uniformly distributed.
The unswept area at the end of the second phase, as disclosed in FIG. 4, is hexagonal in shape with individual pairs of ear-like areas extending from the vertices thereof. The shift of injection from the side wells (P which are shut in, to the corner wells (P and the resultant production from the remainder of the wells in the pattern unit have extended greatly the interface so that at the end of the second phase, breakthrough at the medial wells (P occurs almost from two directions at the same time.
FlG. 5 discloses the interface shape at the end of the third phase of the exploitation plan. As in the second phase, injection is maintained at the corner wells (P of the outer hexagon with the sides wells (P thereof being shut in, production at the medial wells (P is stopped and and these wells are shut in, and production is maintained at the center well until breakthrough of the injection fluid thereat. The final shape may be described as a web of Y-shape areas, with the stems of the Y defining a hexafoil based on the center well. An additional 26% sweepout is attained to give a total of more than 94% sweep efiiciency.
FIGS. 6, 7 and 8 disclose the interface shapes at the ends of the consecutive steps of an alternate three phase, secondary recovery plan as used in the 19-well double hexagon patern, with both injection and production rates being uniformly distributed.
FIG. 6 discloses the interface shape at the end of the first phase of this alternate plan, wherein driving fluid is injected into the formation through the center well (P,), with production from the remaining wells of the unit, viz. at the wells (P P at the corners or vertices and midway along the sides of the outer equilateral hexagon, and at wells (P at the corners or vertices of the inner hexagon, until breakthrough of the injeoted fluid occurs at the latter. At this breakthrough, a substantially circular area defined by cusps ending at the medial wells (P has been swept out for a 25% sweep efficiency, resulting from an injection well to production well ratio of 1 to 11.
FIG. 7 discloses the interface shape at the end of the second phase of the alternate plan, wherein injection is maintained at the center well (P production from the corner wells (P P of both hexagons is stopped and these wells shut in, and production continued from the side wells (P of the outer hexagon until breakthrough thereat. At this breakthrough, a substantially hexamerous area defined by the cusp formations ending at the production side wells has been swept and the area remaining for sweepout is indicated by crosshatching in FIG. 7, for an area sweepout sub-total of 64%. The ratio of the injection well rate to the production well rate is 3 to 1, i.e. there are three production wells for each injection Well.
FIG. 8 discloses the interface shape at the end of the third phase of the alternate plan, wherein the center well (P and the medial wells (P at the corners of the inner hexagon are shut in, production from the side wells (P is discontinued and injection is initiated thereat, and production is initiated and maintained at the corner wells (P until breakthrough thereat. The unswept areas are indicated by crosshatching in the shape of fishtails based on the corner production wells, indicating a sweepout of over 88%. The ratio of the injection rate to the production rate is 2 to 3, i.e. there are two production wells for each three injection wells.
As in the case of the preferred exploitation plan as depicted in FIGS. 3, 4 and 5, the unswept areas are located around the production wells, in areas having the strongest flow gradients. Thus, further production may be continued after breakthrough with comparatively less production of the injected fluid than in the ordinary production following breakthrough, to give sweepouts greater than those indicated above.
It is recognized that any of the increased sweepouts obtained by the use of 19-well double hexagon pattern exploited as disclosed herein is an idealization, as in the case for the sweepouts for the 5- and 7-spot patterns. None of the values is likely to be achieved in the field, but the relative superiority of the sweepouts thereover obtained by the use of the 19-well double hexagon pattern is clear and is independent of inhomogeneities.
The basic technique employed to increase sweep efliciency controls the advance of the front in the pattern to achieve large areal coverage, by shifting and adjusting the geometric position, direction and magnitude of the flow of pressure gradients. If the positions of the wells in the pattern are favorable, by changing the wells used for injection and production, high flow gradients can be made to cover most of the pattern, The pattern and procedures disclosed herein have high sweep efliciency leaving the unswept areas at breakthrough in the regions of strong flow gradients adjacent the production wells, and thus readily swept by production past breakthrough.
The sweepout and volumes of injected fluid produced vary from one pattern to another, and also appear to be functions of rate distribution and distance parameters within a given pattern.
In evaluating the performance of a flood pattern, or in comparing performances of different patterns, there are three main considerations:
(a) Percentage of sweep (b) Volume of injection fluid handled (c) Time to achieve the sweep.
For a given total field production rate, it will not be possible generally to obtain an increase in sweepout without at least a proportionate increase of time, which is to be expected. However, if the extra time involved is disproportionately long, the gain in sweepout may not be economically worthwhile.
Any pattern and/or rate distribution which retards the development, or the advance, of a cusp towards the production wells will increase the sweepout of a field. As mentioned previously, two principal means of doing this are: (a) pinning down the cusp by locating production wells between the injection source and the outer production wells, and keeping these 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 it to proceed toward the corner production wells of a pattern unit, as disclosed in our above cited coassigned applications.
The spreading out of the cusp is in general a more advantageous procedure. It yields as good or better sweepout with less production or injection fluid. Further, a higher rate distribution on corner wells of pattern units generally results in much less overall production of injection fluid, but also in less sweep (although exceptions can be found in more complicated patterns).
The advantages of the methods disclosed above are evident. Fewer injection wells are required, more reservoir fluid is recovered prior to breakthrough of injection fluid, and so more ultimate recovery is obtained, as compared with other methods generally employed in secondary recovery operation.
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 fluid or displacement fluid, the advantages obtainable in the practice of this invention are also realized in primary hydrocarbon production operations wherein the hydrocarbon-bearing formation is under the influence of a water drive 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.
As will be apparent to those skilled in the art, in the light of the accompanying disclosure, other changes and alternatives are possible in the practice of this invention without departing from the spirit or scope thereof.
1. A method of producing hydrocarbons from an underground hydrocarbon-bearing formation involving a pattern unit of wells located at the vertices and on the sides of a hexagon and wells located therewithin including a central well which comprises introducing fluid into said formation via the wells located on the sides of said hexagon, and producing hydrocarbons from said formation via the wells located at said vertices of said hexagon until breakthough of the fluid introduced into said formation thereat, thereupon ceasing introducing fluid via said side wells and introducing fluid into said formation via the Wells at said vertices of said hexagon and producing hydrocarbons via said wells within said hexagon until breakthrough of said fluid introduced into said formation into said last mentioned wells producing hydrocarbons other than said central well, and thereafter ceasing producing hydrocarbons at the breakthrough wells while continuing producing hydrocarbons via said central well until breakthrough of the introduced fluid thereat.
2. In the method of producing hydrocarbons as defined in claim 1, the rates of introducing fluid into said formation and producing hydrocarbons from said formation being controlled so that the breakthrough of the fluid introduced into said formation at the producing wells occurs simultaneously.
3. In the method of producing hydrocarbons as defined in claim 1, said wells located at the vertices of said hexagon defining an outer equilateral structure, said wells located therewithin other than said central well defining an inner similar hexagon.
4. In the method of producing hydrocarbons as defined in claim 3, said wells located at said vertices and on said sides of the outer hexagon being spaced equally from each other on each of said sides, said central well being located equidistantly from the vertices of said inner similar hexagon, the wells in said pattern unit totaling 19 in number.
5. In the method of producing hydrocarbons as defined in claim 4, the wells located at said vertices and on said sides of said outer hexagon and therewithin being spaced apart and aligned in rows whereby the ratio of the distance between the rows of wells to the distance between the in-line wells is 0.866, defining a double hexagon pattern unit in a production field.
6. The method of producing hydrocarbons from an underground hydrocarbon-bearing formation involving wells located at the vertices and on the sides of similar concentric hexagons and a central well located therewithin which comprises injecting fluid into said formation via the wells located on the sides of the larger of said hexagons, and producing hydrocarbons from said formation via the wells located at said vertices of said larger of said hexagons until breakthrough of the fluid injected into said formation thereat, thereupon ceasing introducing fluid via said side wells and introducing fluid into said formation through the wells at end vertices of said larger of said hexagons and producing hydrocarbons from said central Well and the wells defining the smaller of said hexagons until breakthrough of said fluid injected into said formation in said last mentioned wells producing hydrocarbons other than said central Well, and thereafter ceasing producing hydrocarbons at the breakthrough wells while continuing producing hydrocarbons at said central well until breakthrough of the introduced fluid thereat.
7. In a method of producing hydrocarbons from an underground formation involving a pattern unit a production field comprising similar equilateral hexagons and a center well, with the outer of said hexagons having a well on each of its sides equally spaced from the vertices adjacent thereof, the steps of injecting fluid into said formation throughout said center well and producing formation hydrocarbons from the remaining wells of said pattern unit until breakthrough of the injected fluid at the production wells defining the vertices of the inner of said hexagons, thereupon ceasing production thereat and at the vertices of the outer of said hexagons while continuing injecting fluid through said center well and producing formation hydrocarbons from the wells located on said sides of said outer hexagon until breakthrough of injected fluid thereat, and thereafter ceasing injecting fluid at said center well and producing formation hydrocarbons from the side wells of said outer hexagon and initiating injecting fluid at said side wells and initiating producing formation hydrocarbons from the wells at said vertices of said outer hexagon until breakthrough of said injected fluid thereat.
8. In the method of producing hydrocarbons as defined in claim 7, the rates of introducing fluid into said formation and producing hydrocarbons from said formation being controlled so that the breakthrough of the fluid introduced into said formation at the producing wells occurs simultaneously.
9. In the method of producing hydrocarbons as defined in claim 7, the wells located at the vertices of said hexagons and on each of the sides of said outer hexagon and said center well being spaced apart and aligned in IO'WS whereby the ratio of the distance between the rows of wells to the distance between the in-line wells is 0.866, defining a double hexagon pattern unit totaling 19 wells in number.
References Cited UNITED STATES PATENTS 2,885,002 5/1959 Jenks 1669 3,113,616 12/1963 Dew et al 1669 3,113,617 12/1963 Oakes 1669 3,113,618 12/1963 Oakes 1669 3,120,870 2/ 1964 Santourian 1669 3,143,169 8/1964 Foulks 1669 3,205,943 9/ 1965 Foulks 1669 CHARLES E. OCONNELL, Primary Examiner.
D. H. BROWN, Assistant Examiner.
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|US3113616 *||Mar 9, 1960||Dec 10, 1963||Continental Oil Co||Method of uniform secondary recovery|
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|US3120870 *||Aug 4, 1961||Feb 11, 1964||Phillips Petroleum Co||Fluid drive recovery of oil|
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|US3205943 *||Aug 20, 1959||Sep 14, 1965||Socony Mobil Oil Co Inc||Recovery method for petroleum|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US4085797 *||Dec 22, 1976||Apr 25, 1978||Phillips Petroleum Company||Progressive displacement of residual water past shut-in wells preparatory to tertiary oil recovery|
|US4182416 *||Mar 27, 1978||Jan 8, 1980||Phillips Petroleum Company||Induced oil recovery process|
|US4375302 *||Mar 3, 1980||Mar 1, 1983||Nicholas Kalmar||Process for the in situ recovery of both petroleum and inorganic mineral content of an oil shale deposit|
|International Classification||E21B43/00, E21B43/30|