Systems, methods, and apparatus for transient flow simulation in complex subsurface fracture geometries

1. A method for simulating a subterranean region having fracture geometries, comprising:

a) obtaining by a processor data produced by a digital simulator module, the data representing a subterranean region and comprising a matrix grid and fracture parameters representing fractures in the subterranean region;

b) producing, by the processor, a computational domain separate from the digital simulator module;

c) inputting, by the processor, the data produced by the digital simulator module into the computational domain;

d) identifying, in the computational domain, gridblocks close to fractures in the matrix grid produced by the simulator module;

e) refining, in the computational domain, the size of gridblocks among the identified matrix gridblocks;

f) determining, in the computational domain, if the refined gridblocks meet a specified criterion;

g) repeating, in the computational domain, steps (d)-(f) if the criterion of step (f) is not met;

h) proceeding to step (i) if the criterion of step (f) is met;

i) calculating, in the computational domain, intersections between the refined gridblocks and the fractures;

j) inputting, by the processor, the calculated intersections from the computational domain into the digital simulator module; and

k) generating a simulation of the subterranean region with the digital simulator module using the calculated intersections.

2. The method of claim 1 , wherein the specified criterion is L n >L final , where L n is a gridblock length and L final is a defined gridblock length.

3. The method of claim 2 , wherein the specified criterion further comprises r L/d >r L/d,critical , where

r

L

⁢

/

⁢

d

=

L

n

d

g

-

f

,

L n is a gridblock length and d g-f is a minimum distance from a gridblock to a fracture, and r L/d,critical is a defined ratio.

4. The method of claim 1 , wherein the calculating intersections between the refined gridblocks and the fractures comprises identifying geometric relationships between created fracture cells and the refined gridblock.

5. The method of claim 1 , wherein the calculating intersections between the refined gridblocks and the fractures comprises identifying connections between fracture cells and the refined grid blocks.

6. The method of claim 1 , further comprising:

step (a) including obtaining data representing a subterranean region including wellbore parameters;

calculating a well index between created fracture cells and wellbore cells associated to the wellbore parameters; and

step (k) including using the calculated well index for generation of the subterranean region simulation.

7. The method of claim 6 , further comprising:

identifying geometric interactions between fractures and the wellbore cells; and

adding a well location to the created fracture cells for each segment of a fracture interacting with a wellbore cell.

8. The method of claim 1 , wherein the generation of a simulation of the subterranean region comprises generation of a geometry including at least one of: (i) a complex boundary, (ii) a complex surface, or (iii) a corner point.

9. The method of claim 1 , wherein the generation of a simulation of the subterranean region comprises a visualization of at least one of: (i) a fluid property, (ii) a reservoir property, or (iii) a pressure distribution.

10. A system for simulating a subterranean region having fracture geometries, comprising:

at least one processor;

a non-transitory memory linked to the processor, the memory having instructions stored therein, which when executed cause the processor to perform functions including to:

a) input data from a digital simulator module, the data representing a subterranean region and comprising a matrix grid and fracture parameters representing fractures in the subterranean region;

b) produce a computational domain separate from the digital simulator module;

c) input the data from the digital simulator module into the computational domain;

d) identify, in the computational domain, gridblocks close to fractures in the matrix grid produced by the simulator module;

e) refine, in the computational domain, the size of gridblocks among the identified matrix gridblocks;

f) determine, in the computational domain, if the refined gridblocks meet a specified criterion;

g) repeat, in the computational domain, steps (d)-(f) if the criterion of step (f) is not met;

h) proceed to step (i) if the criterion of step (f) is met;

i) calculate, in the computational domain, intersections between the refined gridblocks and the fractures; and

j) input the calculated intersections from the computational domain into the digital simulator module; and

k) generate a simulation of the subterranean region with the digital simulator module using the calculated intersections.

11. The system of claim 10 , wherein the specified criterion is L n >L final , where L n is a gridblock length and L final is a defined gridblock length.

12. The system of claim 11 , wherein the specified criterion further comprises r L/d >r L,critical , where

r

L

/

d

=

L

n

d

g

-

f

,

L n is a gridblock length and d g-f is a minimum distance from a gridblock to a fracture, and r L/d,critical is a defined ratio.

13. The system of claim 10 , wherein the function to calculate intersections between the refined gridblocks and the fractures comprises identification of geometric relationships between created fracture cells and the refined gridblocks.

14. The system of claim 10 , wherein the function to calculate intersections between the refined gridblocks and the fractures comprises identification of connections between fracture cells and the refined gridblocks.

15. The system of claim 10 , wherein the functions performed by the processor further include functions to:

input data from the digital simulator module representing a subterranean region including well parameters;

calculate a well index between created fracture cells and wellbore cells associated to the wellbore parameters; and

use the calculated well index for the generation of the simulation of the subterranean region.

16. The system of claim 10 , wherein generation of a simulation of the subterranean region comprises generation of a geometry including at least one of: (i) a complex boundary, (ii) a complex surface, or (iii) a corner point.

17. The system of claim 10 , wherein the generation of a simulation of the subterranean region comprises a visualization of at least one of: (i) a fluid property, (ii) a reservoir property, or (iii) a pressure distribution.

18. A method for simulating a subterranean region having fracture geometries, comprising:

obtaining by a processor data produced by a digital simulator module, the data representing a subterranean region and comprising a matrix grid and fracture parameters representing fractures in the subterranean region;

producing, by the processor, a computational domain separate from the digital simulator module;

inputting, by the processor, the data produced by the digital simulator module into the computational domain;

detecting, in the computational domain, geometrical intersections between matrix grid blocks and fractures in the data produced by the simulator module;

cutting, in the computational domain, the fractures into segments along matrix gridblock boundaries;

applying, in the computational domain, a pore-volume cutoff for small fracture segments;

calculating, in the computational domain, connections between segments inside a fracture and between connected segments belonging to intersecting fractures;

calculating, in the computational domain, intersections between well trajectories associated with the subterranean region and fracture segments;

computing, in the computational domain, transmissibility factors for non-neighboring connections and well indices associated with the subterranean region;

creating, in the computational domain, gridblocks in a grid domain and modifying the gridblock properties to represent fracture segments;

canceling, in the computational domain, connections and adding non-neighboring connections for the created gridblocks;

adding, in the computational domain, well perforations on the gridblocks;

inputting, by the processor, the gridblocks from the computational domain into the digital simulator module, and

generating a simulation of the subterranean region a with the digital simulator module.