Near wellbore modeling method and apparatus

• US 20050015231A1
• Filed: 07/27/2004
• Published: 01/20/2005
• Est. Priority Date: 05/04/1998
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Edwards, David A., Fitzpatrick, Anthony J., Holmes, Jonathan A.
• Granted Patent: US 7,451,066 B2
• Time in Patent Office: Days
• US Class Current: 703/10
• CPC Class Codes: E21B 49/00 Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells

Abstract

A “near wellbore modeling” software will, when executed by a processor of a computer, model a localized area of a reservoir field which surrounds and is located near a specific wellbore in the reservoir field by performing the following functions: (1) receive input data representative of a reservoir field containing a plurality of wellbores, (2) establish a boundary around one specific wellbore in the reservoir field which will be individually modeled and simulated, (3) impose an “fine scale” unstructured grid inside the boundary consisting of a plurality of tetrahedrally shaped grid cells and further impose a fine scale structured grid about the perforated sections of the specific wellbore, (4) determine a plurality of fluxes/pressure values at the boundary, the fluxes/pressure values representing characteristics of the reservoir field located outside the boundary, (5) establish one or more properties for each tetrahedral cell of the unstructured grid and each cylindrical grid cell of the structured grid, (6) run a simulation, using the fluxes/pressure values at the boundary to mimic the reservoir field outside the boundary and using the fine scale grid inside the boundary, to thereby determine a plurality of simulation results corresponding, respectively, to the plurality of grid cells located inside the boundary, the plurality of simulation results being representative of a set of characteristics of the reservoir field located inside the boundary, (7) display the plurality of simulation results which characterize the reservoir field located inside the boundary, and (8) reintegrate by coarsening the grid inside the boundary, imposing a structured grid outside the boundary, and re-running a simulation of the entire reservoir field.

Claims

1. A method of modeling a reservoir field including a plurality of wellbores, comprising the steps of:

(a) receiving a data set which represents said reservoir field comprised of said plurality of wellbores, one of the plurality of wellbores being a specific wellbore,

(b) in response to the receiving step (a), modeling and simulating a region of said reservoir field located in an immediate vicinity of said specific wellbore without also simulating a remaining portion of said reservoir field thereby focusing substantially the entire said modeling and simulating step on said region of the reservoir field which is located in the immediate vicinity of said specific wellbore;

(c) in response to the modeling and simulating step (b), determining a first plurality of simulation results that are representative of said region of the reservoir field located in said immediate vicinity of said specific wellbore; and

(d) displaying said first plurality of simulation results representative of a set of earth formation characteristics in said vicinity of said specific wellbore.

2. The method of claim 1, wherein the modeling and simulating step (b) comprises the steps of:

(b1) establishing a boundary around said region of said reservoir field which includes said specific wellbore;

(b2) determining a plurality of fluxes or pressure values at said boundary, the fluxes or pressure values mimicing characteristics of said reservoir field located outside the boundary;

(b3) imposing a fine scale unstructured grid including a plurality of tetrahedrally shaped grid cells on said region of said reservoir field located inside said boundary and imposing a fine scale structured grid about a plurality of perforated sections of said specific wellbore; and

(b4) assigning one or more properties to each tetrahedral cell of the fine scale unstructured grid imposed on said region located inside said boundary.

3. The method of claim 2, wherein the determining step (c), for determining said first plurality of simulation results that are representative of said region of the reservoir field located in said immediate vicinity of said specific wellbore, comprises the step of:

(c1) in response to the assigning step (b4), running a first simulation, using said fluxes or pressure values at said boundary to mimic said region of the reservoir field located outside the boundary and using the fine scale grid inside said boundary, to thereby determine said first plurality of simulation results corresponding, respectively, to the plurality of grid cells located inside said boundary, said first plurality of simulation results being representative of a set of earth formation characteristics corresponding to said region of the reservoir field located inside said boundary and situated in said immediate vicinity of said specific wellbore.

4. The method of claim 3, further comprising the step of:

analyzing said specific wellbore in detail by importing a set of deviation surveys to improve a description of a welltrack of said specific wellbore.

5. The method of claim 3, wherein the running step (cl) of running a first simulation further comprises the step of:

determining a multi-segment well model by dividing said welltrack of said specific wellbore into a plurality segments and generating a plurality of sets of solution variables corresponding, respectively, to said plurality of segments of said specific wellbore.

6. The method of claim 3, further comprising the step of:

defining modified property zones located inside said boundary but outside and adjacent to said specific wellbore.

7. The method of claim 3, wherein said plurality of tetrahedrally shaped grid cells of said unstructured grid imposed on said region of said reservoir field located inside said boundary consists of a first number of grid cells, and wherein said method further comprises the steps of:

(e) decreasing the number of said grid cells of said unstructured grid located inside said boundary from said first number of grid cells to a second number of grid cells, where said second number is less than said first number,

(f) imposing another grid on that part of said reservoir field which is located outside said boundary, said another grid also including a plurality of grid cells; and

(f) running a second simulation, without using said fluxes or pressure values at said boundary, to thereby determine a second plurality of simulation results corresponding, respectively, to a plurality of said grid cells enclosed by the entire said reservoir field, said second plurality of simulation results being representative of a set of earth formation characteristics corresponding to the entire said reservoir field; and

(g) displaying said second plurality of simulation results.

8. The method of claim 7, wherein the decreasing step (e) comprises the step of:

(e1) decreasing the number of said grid cells of said unstructured grid by a factor of “

n”

, said first number of grid cells being “

X”

in number, said second number of grid cells being “

X/n”

in number.

9. The method of claim 8, wherein “

n”

is selected from the group consisting of;

two point seven five (2.75), three (3), and four (4).

10. Apparatus responsive to a set of input data which includes a data set that further includes a reservoir field comprised of a plurality of wellbores adapted for modeling said reservoir field, said plurality of wellbores including a specific wellbore, comprising:

near wellbore modeling means for modeling a region of said reservoir field located in the immediate vicinity of said specific wellbore without simultaneously modeling a remaining portion of said reservoir field thereby focusing substantially the entire said modeling on said region of said reservoir field located in said immediate vicinity of said specific wellbore, said near wellbore modeling means including,

means for establishing a boundary around said specific wellbore of said reservoir field,

means for imposing a fine scale grid inside said boundary, said fine scale grid including a plurality of grid cells,

means for determining a plurality of fluxes or pressure values at said boundary, said fluxes or pressure values mimicing that part of said reservoir field located outside said boundary,

simulation means responsive to said plurality of fluxes or pressure values at said boundary for simulating that part of said reservoir field located inside said boundary without simultaneously simulating that part of said reservoir field located outside said boundary thereby generating a plurality of simulation results corresponding, respectively, to said plurality of grid cells of said fine scale grid inside said boundary, said plurality of simulation results being representative of characteristics of an earth formation located inside said boundary, and

display means for displaying said plurality of simulation results.

11. The apparatus of claim 10, wherein said grid imposed inside said boundary by said means for imposing comprises an un-structured grid including a plurality of tetrahedrally shaped grid cells, and wherein said near wellbore modeling means further comprises:

means for assigning properties to each tetrahedrally shaped grid cell of said un-structured grid,

said simulation means being responsive to said plurality of fluxes or pressure values at said boundary and to said properties assigned to each tetrahedrally shaped grid cell of said fine scale grid for simulating that part of said reservoir field located inside said boundary without simultaneously simulating that part of said reservoir field located outside said boundary thereby generating said plurality of simulation results corresponding, respectively, to said plurality of tetrahedrally shaped grid cells inside said boundary.

12. The apparatus of claim 11, wherein said input data includes well deviation surveys and wherein said near wellbore modeling means further comprises:

means responsive to said well deviation surveys for improving a description of a welltrack associated with said specific wellbore,

said simulation means being responsive to said plurality of fluxes or pressure values at said boundary and to said properties and to the improved description of said welltrack of said specific wellbore generated by the means for improving for simulating that part of the reservoir field located inside said boundary and generating said plurality of simulation results.

13. The apparatus of claim 12, wherein said specific wellbore includes a plurality of segments, and wherein said near wellbore modeling means further comprises:

solution variable generation means for generating a plurality of solution variables corresponding, respectively, to said plurality of segments of said specific wellbore,

said simulation means being responsive to said plurality of fluxes or pressure values at said boundary and to said properties and to said improved description of said welltrack and to said plurality of solution variables generated by said solution variable generation means for simulating that part of the reservoir field located inside said boundary and generating said plurality of simulation results.

14. The apparatus of claim 13, wherein said near wellbore modeling means further comprises:

modified property zone definition means for defining modified property zones located inside said boundary but outside and adjacent to said specific wellbore,

said simulation means being responsive to said plurality of fluxes or pressure values at said boundary and to said properties and to said improved description of said welltrack and to said plurality of solution variables and to said modified property zones defined by said modified property zone definition means for simulating that part of the reservoir field located inside said boundary and generating said plurality of simulation results.

15. The apparatus of claim 11, wherein said plurality of tetrahedrally shaped grid cells of said fine scale un-structured grid consists of a first number of grid cells, and wherein said apparatus further comprises:

means for reducing the number of tetrahedrally shaped grid cells of said un-structured grid located inside said boundary from said first number of grid cells to a second number of grid cells;

means for imposing another grid on that part of said reservoir field located outside said boundary, said reservoir field now including another plurality of grid cells,

said simulation means being responsive to said second number of the tetrahedrally shaped grid cells located inside said boundary and to said another grid imposed on that part of said reservoir field located outside said boundary for simulating the entire said reservoir field thereby generating a second plurality of simulation results corresponding, respectively, to said another plurality of grid cells located inside said reservoir field,

said display means displaying said second plurality of simulation results.

16. The apparatus of claim 15, wherein said means for reducing reduces the number of tetrahedrally shaped grid cells of said un-structured grid located inside said boundary by a factor of “

n”

, said first number of grid cells consisting of “

X”

grid cells, said second number of grid cells consisting of “

X/n”

grid cells.

17. The apparatus of claim 16, wherein said “

n”

is selected from a group consisting of;

two point seven five (2.75), three (3), and four (4).

18. A program storage device for storing instructions which, when executed by a processor of a computer, conducts a process comprising the steps of:

modeling a reservoir field including a plurality of wellbores, the modeling step comprising the steps of;

(a) receiving a data set which represents said reservoir field comprised of said plurality of wellbores, one of the plurality of wellbores being a specific wellbore,

(b) in response to the receiving step (a), modeling and simulating a region of said reservoir field located in an immediate vicinity of said specific wellbore without also simulating a remaining portion of said reservoir field thereby focusing substantially the entire said modeling and simulating step on said region of the reservoir field which is located in the immediate vicinity of said specific wellbore;

(c) in response to the modeling and simulating step (b), determining a first plurality of simulation results that are representative of said region of the reservoir field located in said immediate vicinity of said specific wellbore; and

(d) displaying said first plurality of simulation results representative of a set of earth formation characteristics in said vicinity of said specific wellbore.

19. The program storage device of claim 18, wherein the modeling and simulating step (b) comprises the steps of:

(b1) establishing a boundary around said region of said reservoir field which includes said specific wellbore;

(b2) determining a plurality of fluxes or pressure values at said boundary, the fluxes or pressure values mimicing characteristics of said reservoir field located outside the boundary;

(b3) imposing a fine scale unstructured grid including a plurality of tetrahedrally shaped grid cells on said region of said reservoir field located inside said boundary and further imposing a fine scale structured grid about perforated sections of said specific welbore; and

(b4) assigning one or more properties to each tetrahedrally shaped grid cell of the unstructured grid and to each grid cell of the structured grid imposed on said region located inside said boundary.

20. The program storage device of claim 19, wherein the determining step (c), for determining said first plurality of simulation results that are representative of said region of the reservoir field located in said immediate vicinity of said specific wellbore, comprises the step of:

(c1) in response to the assigning step (b4), running a first simulation, using said fluxes or pressure values at said boundary to mimic said region of the reservoir field located outside the boundary and using the fine scale grid inside said boundary, to thereby determine said first plurality of simulation results corresponding, respectively, to the plurality of grid cells located inside said boundary, said first plurality of simulation results being representative of a set of earth formation characteristics corresponding to said region of the reservoir field located inside said boundary and situated in said immediate vicinity of said specific wellbore.

21. The program storage device of claim 20, further comprising the step of:

analyzing said specific wellbore in detail by importing a set of deviation surveys to improve a description of a welltrack of said specific wellbore.

22. The program storage device of claim 21, wherein the running step (c1) of running a first simulation further comprises the step of:

determining a multi-segment well model by dividing said welltrack of said specific wellbore into a plurality segments and generating a plurality of sets of solution variables corresponding, respectively, to said plurality of segments of said specific wellbore.

23. The program storage device of claim 22, further comprising the step of:

defining modified property zones located inside said boundary but outside and adjacent to said specific wellbore.

24. The program storage device of claim 20, wherein said plurality of tetrahedrally shaped grid cells of said unstructured grid imposed on said region of said reservoir field located inside said boundary consists of a first number of grid cells, and wherein said process further comprises the steps of:

(e) decreasing the number of said grid cells of said unstructured grid located inside said boundary from said first number of grid cells to a second number of grid cells, where said second number is less than said first number,

(f) imposing another grid on that part of said reservoir field which is located outside said boundary, said another grid also including a plurality of grid cells; and

(f) running a second simulation, without using said fluxes or pressure values at said boundary, to thereby determine a second plurality of simulation results corresponding, respectively, to a plurality of said grid cells enclosed by the entire said reservoir field, said second plurality of simulation results being representative of a set of earth formation characteristics corresponding to the entire said reservoir field; and

(g) displaying said second plurality of simulation results.

25. The program storage device of claim 24, wherein the decreasing step (e) comprises the step of:

(e1) decreasing the number of said grid cells of said unstructured grid by a factor of “

n”

, said first number of grid cells being “

X”

in number, said second number of grid cells being “

X/n”

in number.

26. The program storage device of claim 25, wherein “

n”

is selected from the group consisting of;

two point seven five (2.75), three (3), and four (4).