US3286768A

US3286768A - Recovery of petroleum from a subterranean reservor

Info

Publication number: US3286768A
Application number: US309123A
Authority: US
Inventors: John P Heller
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1963-09-16
Filing date: 1963-09-16
Publication date: 1966-11-22
Anticipated expiration: 1983-11-22

Description

lab ld f3 FIPYElFf Nov. 22, 1966 J. P. HELLER RECOVERY OF PETROLEUM FROM A SUBTERRANEAN RESERVOIR Filed Sept. 16. 1963 5 Sheets-Sheet l PRIOR ART .JOHN P HELLER INVENTOR JNM 2". 99M

ATTORNEY I V- ,1966 J. P. HELLEE 3,286,768

- Filed Sept. 16. 1963 RECOVER! OF PETROLEUM FROM A SUBTERRANEAN RESERVOIR 3 Sheets-Sheet 2 a Blusz JOHN P/HELLER INVENTOR.

BYJMJ -A,

ATTORNEY Nov. 22-, 1966 J. P. HELLER 3,236,763

- RECOVERY OF PETROLEUM FROM A SUBTERRANEAN RESERVOIR Filed Sept. 1s. 1963 a Sheets-Sheet 5 JOHN RHELLER INVENTOR.

Of Mai ATTORNEY the number of injection and production wells.

'tionally, the injection and productionwells are arranged in regular, uniform patternsi While high areal sweep RECOVERY OF PETROLEUM FROM A SUBTERRANEAN RESERVOIR John P. Heller, Dallas, Tex., assignor to Mobil oll Corporation, a corporation of New York Filed Sept. 16, 1963-, Sen-No. 309,123 14 Claims. (Cl. 166-9) -terranean formations, or' reservoirs, as a result of gas pressure or natural water driveforcing the petroleum from the petroleum-bearing formation to a producing well and then to the surface of the earth. As recovery of petroleum from the formation continues, the reservoir energy gradually decreases. A major portion of the peltroleum still remains in the formation "and at any time after the reservoir energy begins to decline, secondary recovery methods may be initiated to increase the recovery of this remaining petroleum. Among these methods are those which involve flooding the formation with a liquid to displace the petroleum from the formation and drive it to at producing 'well. Flooding is also often employed initially for the production of petroleum where the formation does not containsuflicient reservoir energy to produce the petroleum. Y

In recovery methods. employing a displacing liquid, the

'shape of the displacement front, i.e., the advancing front of the displacing liquid'in the formation surrounding each injection well, is determined by various factors. Included among these are inhomogeneities -of the formation, the number and relative position of the injection and production wells, and the fluid properties of the displaced liquid and the displacing liquid. The shape of the area through which the displacement front has passed is termed the sweep pattern and the ratio of the area within the sweep pattern to the total area is termed the sweep efiiciency. Practical operations, from the standpoint of economy, require a maximum sweep efficiency commensurate with Convenelliciencies are obtained with these well patterns, and with others which do not have regularity or uniformity, still higher efiiciencies are desirable.

It is an object of this invention to improve the extent of recovery of petroleum from a subterranean formation.

It is another object of this invention to improve the sweep efliciency in an operation for the recovery of petroleum from a subterranean formation employing a displacing liquid.

It is another object of this invention to provide a method for controlling the shape of the displacement front passed through a subterranean formation containing petroleum.

Further objects of the invention will become apparent from the following detailed description,

In accordance with the invention, there is provided a procedure which involves the creation within a formation containing petroleum of an instability finger of a displacing liquid in a direction from the injection well to a production well in which the flow would normally be the slowest.

FIGURE 1 is a plan view of a portion of a petroleum field diagrammatically illustrating an arrangement of inectlon wells and production wells and the position and ,the shape of the displacement fronts of the displacing llquld in ected into the injection wells in accordance with conventional procedure.

F United States atone Patented Now-22, 1966 fronts of the. displacing liquid injected into the injection wells in accordance with the procedure of the invention.

FIGURE 3 is another plan view diagrammatically illustrating an arrangement of an injection well and production wells and diagrammatically illustrating a means for -creating an instability finger of displacing liquid.

FIGURE 4 is a sectional view of the injection well illustrated in FIGURE 3.

FIGURE 5 is a plan viewof another means for creating four symmetrically oriented instability fingers of a displacing liquid.

Referring now to FIGURE 1, the numeral 10 designates a portion of a field having a formation containing petroleum. The field 10 is provided with injection wells for the injection into the formation of a displacing liquid and is provided with production wells for the recovery of the petroleum displaced from the reservoir by the injected flooding liquid.

Injection wells

11, 12, 13, and 14 and

production wells

15, 20, 21, 22, 23, 24, 25, 30, and 31 are shown. In a flooding operation for recovery of the petroleum within the formation the displacing liquid is injected into the injection wells 11, I2, 13, and 14.

In recovery methods employing a displacing liquid, the progress of the displacement process may be visualized in terms of the motion of displacement fronts. Surrounding each injection well, following injection of some of the displacing liquid, there exists a volume region of the formation within the pores of which the petroleum saturation is relatively low in consequence of the replacement of the petroleum by the displacing liquid in that region. Further out in the formation, there is a region in which the numerical value of the petroleum saturation is unchanged from that which obtained prior to the start of the injection. Lying between those two regions lies a transition zone in which the petroleum saturation depends relatively sensitively on position and on time as the displacement proceeds. The closed surface marking the median saturation within the transition zone is the displacement front.

The shape of the displacement front surrounding each injection well, as stated, is determined by various factors. First there are the various geometrical factors. These include the variations, from place to place in the formation, of porosity, permeability, native fluid saturation and surface properties of the rock matrix. These may be called the formation inhomogeneities, and may include random variations of the matrix, from microscopic poresized dimensions up to large scale trends in the rock properties over the gross dimensions of the formation. There may also be highly ordered variations in the rock parameters, such as a strong layered structure. A further set of geometrical factors involved in the determination of the shape of the displacement front are the relative positions of the injection and production wells and of the shape of the gross formation boundaries.

In addition to these geometrical determining factors, the shape of the displacement front may also be under the influence of the fluid properties. This will occur if there is a difference in mobility or density between the displaced liquid and the displacing liquid. Variations in frontal shape may then themselves effect changes in the velocity of fluid movement. The displacement front shape thus becomes unstable in the event the mobility of the displacing liquid is higher than that of the displaced liquid. In this case the displacement front develops extensions or fingers. As the displacement process or flood is continued, these will break through into the production well, diluting the produced liquid with displacing liquid and ldecreasing the lifetime of the field during which petroleum may be produced economically. Just after the start of the injection program, the displacement fronts surrounding the injection wells are relatively smooth and reflect the shape of the input boundaries which are injection well faces. This is the case even in floods wit-h an adverse mobility ratiothat is, in which the ratio of the fluid mobility of the displaced phase to that of the displacing phase is greater than unity, leading to the aforementioned instability fingering. As the flood progresses, however, the displacement front develops irregularities corresponding to the geometrical factors mentional above. in the unfavorable mobility situation these irregularities are amplified :by the instability mechanism and develop into finigers which reduce the sweep efliciency.

Assuming that the formation is more or less homogeneous and assuming furthermore that the displacement from i, 12,- 13, and 14 and the displacement front between the petroleum and the displacement front will 'be in t'he'fcrrn 'of a circle such as

circles

32, 33, 34, and 35. Further from the injection wells, the streamlines depart from their initially radial directions. The details of these deviations will depend upon the position of the production wells with respect to the'injection wells. More specifically, the position of the production wells with respect to the injection wells will determine the direction of the pathways of the greatest pressure differential between the injection well and each of the production wells. The liquid passed into the injection wells will flow in these directions at a rate greater than that in any other direction in the formation between the injection wells to the production wells.

Wit-h a homogeneous formation, the pathway of greatest pressure differential between injection and production wells will be in the direction of a straight line between the injection well and each of the production wells. As a consequence, the displacing liquid will flow at the highest rate from the injection well directly toward the production wells and at the lowest rate in a direction from the injection well to a point midway on a straight line between adjacent production wells. With continued injection of the displacing liquid, the pattern of the displacement front will thus have the form of the

patterns

40, 41, 42, and

43, for each of the injection wells 11 to 14, respectively. .With continued injection of the displacing liquid, breakthrough of the flooding liquid will eventually occur at the production wells and at breakthrough the displacement front will have the form of

patterns

44, 45, 50, and 51 for each of the wells 11 to 14, respectively.

The shape of the displacement fronts as described above placing liquid. Thus, as shown in FIGURE 1, the

areas

52, 53, 54, and 55 have not been swept. Accordingly, the petroleum contained in the formation within these areas is not recovered at breakthrough. To the extent that this petroleum is not recovered, the efficiency of the flooding operation is diminished. Frequently, the efiiciency of the flooding operation, from the standpoint of the areas swept by the displacing liquid, maybe only about 50 percent.

By the procedure of the invention, the sweep efficiency of the displacing liquid is improved. With reference to FIGURE 2, the numeral 60 design-ates a portion of a field having a. formation containing petroleum. The field 60 is provided with

injection wells

61, 62, 63, and 64. Additionally, the field is provided with production wells 65,

70, 71, 72, 73, 74, 75, 80 and 81. Displacing liquid is passed into each of the injection wells 61 to 64. Howassumes, as mentioned, homogeneity of the formation and stability of the fronts. In practical operations, the formation may not the homogeneous. Further, as the result of an unfavorable mobility ratio and inhomogeneities in the formation, instability fingers of the displacing liquid can form. The early instability fingers are formed haphazardly in directions dictated by minor variations of rock properties. Their formation can result in premature breakthrough of the displacing liquid at any one of the production wells surrounding an injection well. The instability will also cause an earlier development of the enhanced flow along the diagonals between injection and production wells. Thus, the shape of the displacement fronts as described above will 'be changed. However, it can be considered that from an overall standpoint the shape of the displacement fronts will be more or less as described.

It will be seen from FIGURE 1 that, at breakthrough of the displacing liquid at the output wells, an appreciable ever, in the process of the invention, appropriately onenbed instability fingers of the displacing liquid are created within the formation. These instability fingers are created by introducing the displacing liquid from the injection well into the formation in those directions in which the flow of the displacing liquid from the injection well to the production well is normally the slowest. In the S-spot pattern of injection and production wells set forth in FIG- URE 2, the directions of lowest rate of flow of the displacing liquid from the injection well to each of the four production wells surrounding each injection well, assuming homogeneity of the formation, are to those points midway between adjacent production wells. Stated otherwise, the directions of lowest crate of flow of the displacing liquid are at the angle of 45 from the line joining the injection well with the respective production well.

In the embodiment set forth in FIGURE 2, four instability fingers are created within the formation for each of the injection wells 61 to 64. These fingers are created at an angle of with respect to each other and each is created in a direction on a line 45 from the line joining the injection well and each of the four production wells associated with the injection well. Thus, for each of wells 61 to 64, shortly after the beginning of injection of the displacing liquid, the shape of the displacement front will have the form of

patterns

32, 83, 84, and 85. Each of these patterns, with particular reference to pattern 82-as an example, will contain four

fingers

90, 91, 92, and 93. Thedisplacing liquid is continued to be injected into the formation in the direction of the lowest rate of flow and, with the continued injection of the displacing liquid, the shape of the fingers will become less clearly defined. However, the effect of the creation of the fingers along the direction of the lines of slowest flow of the displacing liquid in the formation will be maintained. The influence of the position of the production wells with respect to the injection wells on the direction of the flow of the displacing liquid from the injection well will become progressively greater as further displacing liquid is passed into the formation.

On the other hand, the initial formation of the instability fingers and continued injection of the displacing liquid would not otherwise have been swept. Accordingly, with placing liquid to sweep portions of the formation that continued injection of the displacing liquid, the displacement front will eventually have the shape of patterns )5, 100, 101, and 102. It will be seen from these patterns that the displacing liquid retains a tendency to flow in the direction of the created instability fingers. This tendency is a consequence of the adverse mobility ratio. The higher this ratio is, the greater will the tendency be. Eventually, however, the trend of movement of the displacing liquid in the direction of the created inst-ability fingers will be reversed so that the direction of greatest rate of fiow will be along the lines directly between the injection and the production wells. Thus, at break through, the pattern of the displacement front will have the shape of the patterns 103,104, 105, and 110. It

, and 132.

will be seen that, at breakthrough, the pattern of the swept area of the formation is greater than the pattern of the swept area indicated. in FIGURE 1. Thus, the

unswept portions

111, 112, 113, 115, 120, 121, and 122 of the formation are considerably smaller than the

unswept portions

52, 53, 54, and 55 in FIGURE 1. Thus, by the process of the invention, the area of the formation unswcpt by the displacing liquid may be only to 20 percent of the total area of the formation. Where the fingers from adjacent injection wells meet at or before breakthrough of the displacing liquid at the production wells, nearly complete sweepout would be expected.

The process of the invention has been described above in connection with injection into a single injection well and production from four production wells equidistantly spaced from .each other and from the injection well. However, the process of the invention may also be applied where nhere are a different number of injection wells and a different number of production wells. Further, it may be applied where the wells, whether injection or production wells, are not equidistantly spaced from each other. Ordinarily, assuming homogeneity of the formation, the direction of the highest rate of flow of the displacing liquid from an injection well to a production well is that of a straight line between the injection well and the production well. Thus, ordinarily, still assuming homogeneity of the formation, the direction of the lowest rate of flow of the displacing liquid is that of a straight line rbisecting the angle from the injection well swept by a straight line from a production well toan intercepted production well. .For example, where there are one injection well and one production well, the angle from the injection well swept by a straight line from the production well to the next intercepted production well, i.e., the same production well, is 360". A straight line bisecting this angle will be oriented in a direction of 180 and therefore the direction of the lowest rate'of flow will be opposite to that of the highest rate of flow. Similarly, for example, in the emdirection of lowest rate of fiow is that of the line bisecting this angle.

It may occasionally be that the format-ion is not homogeneous. Where it is known that the formation is not homogeneous, the direction of the lowest rate of flow of displacing liquid will often also be known. In any case, the direction of the lowest rate of flow of displacing liquid may be determined. In accordance with another feature of the invention, prior to injection of the displacing liquid into the formation through the injection well, the direction of slowest flow of the displacing l-iquid'through the formation between the injection well and the production well is determined. Knowing the direction of the lowest rate of flow of the displacing liquid, the displacing liquid is injected into the formation in this direction.

Various methods for creating an instability finger of the displacing liquid may be employed. In a preferred embodiment of the invention, the instability finger can be created by injecting the displacing liquid through the injection well and into the formation through a direc- =tionally oriented void created within the formation from the wall of the well. In a particularly preferred embodirhent of the invention, the injection well is perforated employing conventional gun perforating means to create the directionally oriented void. FIGURES 3 and 4, re; spectively, illustrate this latter preferred embodiment of the invention.

Referring to FIGURES 3 and 4, injection well 123 penetrates a portion of the formation 124. The formation is provided with

production wells

125, 130, 131, Imaginary line 133 connects

wells

125 and 130, imaginary line 134 connects

wells

130 and 131. imaginary line 135 connects

wells

131 and 132, and

- imaginary line 140 connects

wells

132 and 125. For

purposes of illustration, well 123 is shown as being en larged with respect to the production wells.

Well 123 is provided with casing 141 extending to the bottom of the well wherein it is held in place by cement liner 142. The well is 'gunmerforated in four directions to provide four"-

voids

143, 144, 145 and 150. Void 144 is oriented as to point in the direction of the midpoint of line 133. Similarly, voids 145, 150, and 143 are oriented as to point in the direction of the midpoints of lines 134, 135, and 140, respectively. The voids penetrate the easing 141 and the cement liner 142 and enter into the forma' tion 124;. Upon injection of displacing liquid into well 123, the liquid passes from the well through the

voids

143, 144, 145, and into the formation and creates an instability finger oriented in the direction of the-midpoint of the lines joining the production wells.

Referring now to FIGURE 5, there is disclosed another means whereby an instability finger may be created in the formation in the desired direction of flow of the displacing liquid. Referring now to FIGURE 5, injection well 151 penetrates formation 152. Disposed longitudinallywithin the well is distribution tool 153. This tool 153 comprises an octagonally shaped casing 154 provided on its outer surface by

flow dividers

155, 160, 161, 162, 163, 164, 165, and 170. Each of these flow dividers is adapted to contact the wall of the well 151. Extending longitudinally through the distribution tool is a pair of pipes 171 and 172. Extending from pipe 171 are

flow conduits

173, 174, 175, and 180. Extending from pipe 172 are

flow conduits

181, 182, 183. and 184. In operation, the flow dividers 155, to 165, and separate the wall of the well 153 into eight segments. The tool 153 is oriented in the well such that four alternate segments are pointed into the direction in the formation in which it is desired to create the instability fingers. Depending upon the direction into which the instability fingers are to be created, the

displacing liquid is passed through either pipe 171 or 1721.

The displacing liquid flows through the flow conduits associated with the pipe and enters alternate segments formed by the flow dividers; The liquid then enters the formation from the segments" to create the four instability fingers.

In the practice of the invention, thedisplacing liquid has a mobility higher than the mobility of the petroleum in the formation. relative permeability of the formation to the liquid to the viscosity of the liquid.- With the displacing liquid having the higher mobility, the mobility ratio of the displacing liquid to the displaced liquid is such as to impart instability to the displacement front and maintain the of the created instability fingers.

The procedure of the invention may be employed in connection with flooding operations in which the displacing liquid is miscible with the petroleum in the formation. For example, the procedure of the invention may be cmploycd .in connection with the injection of liquefied petroleum gas (LPG) or other light hydrocarbon which is miscible with the petroleum in the formation. In these operations, following injection of the displacing liquid miscible with the petroleum in the formation, a driving fluid is employed to drive the miscible displacing liquid through the formation from the injection well into the direction of the production wells. The driving fluid, which may be a gas, can be miscible with the displacing liquid.

The procedure of the invention may also be employed where the displacing liquid is immiscible with the petroleum in the formation. Thus, for example, water may be injected into the formation to drive the petroleum through the formation from the injection well to the production well.

The displacing liquid injected into the formation from By mobility is meant the ratio of the the injection well, whether miscible or immiscible with the petroleum in the formation, is also capable, as previously mentioned, of forming haphazard instability fingers.

,T'hese haphazard instability fingers are of higher wave number. While the formation of these more closely spaced haphazard instability fingers in the present process fingers can be prevented by avoiding large viscosity gradicnts between the petroleum in the formation and the displacing liquid. These large viscosity gradients may be avoided by employing as the displacing liquid a mixture of petroleum from the formation and a conventional flooding liquid such as liquefied petroleum gas. As this displacing liquid is injected into the formation, the proportion oil with respect to the amount of liquefied petroleum gas or other conventional displacing liquid is continually reduced so that at the completion of injection of a graded zone" of displacing liquid, the displacing liquid is substantially or completely all liquefied petroleum gas. More specifically, the flooding operation may be carried out employing at the beginning of operation a mixture of 9 parts of petroleum from the formation and 1 part of liquefied petroleum gas. Subsequently, the displacing liquid will L consist of 8 parts of petroleum and 2 parts of liquefied petroleum gas. Thereafter, the viscosity of the displacing liquid may. be reduced further by reduction in the proportion of petroleum by 1 volume and increase in the proportion of liquefied petroleum gas by 1 volume until the displacing liquid is all liquefied petroleum gas. Where a fluid immiscible with the petroleum in the formation is employed, various types of thickening agents may be added to the liquid to effect a gradation in viscosity and thus avoid large viscosity differences within the formation between the liquid therein and the displacing liquid.

Having thus described my invention, it will be understood that such description has been given by way of illustration and example and not by way of limitation, reference for the latter purpose being had to the appended claims.

I claim:

1. In a process for the production of petroleum from a formation penetrated by an injection well and a production means including at least one production well by injection of a displacing liquid into said formation through said injection welland displacement of said petroleum by said displacing liquid in the direction of said production well, the improvement comprising injecting said displacing liquid into said formation from said injection well only in a direction in which flow on the displacing liquid would normally be the slowest from said injection well to said production well.

2. The procedure of claim 1 wherein said displacing liquid has a mobility higher than the mobility of said petroleum in said formation.

3. The procedure of claim 1 wherein said displacing liquid is immiscible with said petroleum in said formation.

4. The procedure of claim 1 wherein said displacing liquid is miscible with said petroleum within said formation.

5. The procedure of claim 1 wherein said formation is penetrated by an injection well surrounded by four production wells.

6. The procedure of claim 1 wherein said injection well is subjected to gun-perforation prior to injection of said displacing liquid to create a void into said formation from said well oriented in a direction in which flow of the displacing liquid would normally be slowest from said injection well to said production well and injecting said displacing liquid into said formation through said void.

7. The procedure of claim 1 wherein said displacing liquid has a graded viscosity with respect to said petrolcum in said formation whereby sharp viscosity gradients and the production of extraneous, closely-spaced instability fingers are avoided.

8. In a process for the production of petroleum from a-formation penetrated by an injection well and a. production means including at least one production well by injection of a displacing liquid into said formation through said injection well and displacement of said petroleum by said displacing liquid in the direction of said production means, the improvement comprising injecting said displacing liquid into said formation from said injection well only in the direction of a line bisecting the angle from said injection well swept by a line between said injection well and a production well to the first intercepted production well.

9. In a process for the production of petroleum from a formation penetrated by an injection well and a plurality of production wells equidistantly spaced from each other and from said injection well by injection of a displacing liquid into said formation through said injection well and displacement of said petroleum by said displacing liquid in the direction of said production wells, the improvement comprising injecting said displacing liquid into said formation from said injection well only in a direction to a point located midway on a line between adjacent production wells.

10. In a process for the production of petroleum from a formation penetrated by an injection well and four production Wells equidistantly spaced from each other and from said injection well by injection of a displacing liquid into said formation through said injection well and displacement of said petroleum by said displacing liquid in the direction of said production wells, the improvement comprising injecting said displacing liquid into said formation from said injection well only in a direction to a midpoint of each of the lines joining adjacent production wells.

11. In a process for the production of petroleum from a formation penetrated by an injection well and a plurality of production wells equidistantly spaced from each other and from said injection well lay-injection of a displacing liquid into saidformation through said injection well and displacement of said petroleum by said displacing liquid in the direction of said production wells, the improvement comprising the steps of creating a plurality of voids into said formation from said injection well in number equal to the number of said production wells,

12. In a process for the production of petroleum froma formation penetrated by an injection well and four production wells equidistantly spaced from each other and from said injection well by injection of a displacing liquid into said formation through said injection well and displacement of said petroleum by said displacing liquid in the direction of said production wells, the improvement comprising the steps of creating four voids into said formation from "said injection well, each of said voids being oriented in a direction only to a point midway of a line joining a different pair of adjacent production wells, and injecting said displacing liquid into said formation only through said voids.

13. In a process for the production of petroleum from a formation penetrated by an injection well and by a production means including at least one production well by injection of a displacing liquid into said formation through said injection well and displacement of said petroleum by said displacement liquid in the direction of said production well, the improvement comprising the steps of determining the direction of the lowest rate of liquid flow in said formation between said injection well and said production well and injecting said displacing liquid into said formation from said injection well only in said-direction of said lowest rate of liquid flow.

14. In a process for the production of petroleum from a formation penetrated by an injection well and by a production means including at least one production well by injection of a displacing liquid into said formation through said injection well and displacement of said petroleum by said displacing liquid in the direction of said production well, the improvement comprising determin- 1 ing the direction of the lowest rate of liquid flow in said formation between said injection well and said production well, creating a void from said injection well into said formation oriented only in said direction of said lowest rate of liquid flow, and injecting displacing liquid into said formation only through said void.

References Cited by the Examiner v UNITED STATES PATENTS 2,107,007 2/1938 Lang 166-10 CHARLES E. OCONNELL, Primary Examiner.

T. A. ZALENSKI, S. I. NOVOSAD,

- 7 Assistant Examiners.

Claims

1. IN A PROCESS FOR THE PRODUCING OF PETROLEUM FROM A FORMATION PENETRATED BY AN INJECTION WELL AND A PRODUCTION MEANS INCLUDING AT LEAST ONE PRODUCTION WELL BY INJECTION OF A DISPLACING LIQUID INTO SAID FORMATION THROUGH SAID INJCTION WELL AND DISPLACEMENT OF SAID PETROLEUM BY SAID DISPLACING LIQUID IN THE DIRECTION OF SAID PRODUCTION WELL, THE IMPROVEMENT COMPRISING INJECTING SAID DISPLACING LIQUID INTO SAID FORMATION FROM SAID INJECTION WELL ONLY IN A DIRECTION IN WHICH FLOW ON THE DISPLACING LIQUID WOULD NORMALLY BE THE SLOWEST FROM SAID INJECTION WELL TO SAID PRODUCTION WELL.