Method of upscaling a discrete fracture network model

A computer readable medium having stored on it a set of computer instructions that when loaded in a computer is capable of carrying out steps comprising:

• receiving a discrete fracture network model of a subsurface fractured hydrocarbon bearing reservoir formation, said discrete fracture network model comprising a plurality of fractures as input;
• grouping all fractures of the plurality of fractures into fracture clusters, whereby all fractures that are physically connected with each other by intersection, either directly or indirectly via a number of other physically connected fractures, exclusively belong to one fracture cluster such that no fracture within one fracture cluster is physically connected with any fracture of any of the other fracture clusters;
• assigning a unique fracture cluster number to each of the fracture clusters;
• overlaying a three dimensional simulation grid over the discrete fracture network model, consisting of a three dimensional array of grid cells in three directions;
• attributing a grid cell cluster number to each grid cell in the simulation grid, which grid cell cluster number uniquely maps to the unique fracture cluster number of exclusively one fracture cluster that intersects with the grid cell;
• computing an effective permeability for each grid cell and for each of the three directions using the fractures that are inside the grid cell and that form part of the fracture cluster that has the fracture cluster number to which the grid cell cluster number of the grid cell is uniquely mapped, whereby ignoring other fractures that are inside the grid cell but that form part of a fracture cluster having a fracture cluster number that does not map to the grid cell cluster number of the grid cell;
• and
• assigning inter-cluster flow impediment data to selected grid cells reflecting flow impediment barriers between neighboring grid cell clusters;
• outputting a table containing grid property data for all grid cells, wherein the grid property data for each grid cell comprises the cluster number assigned to the grid cell, and one effective permeability number for each of the three directions;
• and
• outputting inter-cluster flow impediment data.

A computer system programmed to carry out steps comprising:

• receiving a discrete fracture network model of a subsurface fractured hydrocarbon bearing reservoir formation, said discrete fracture network model comprising a plurality of fractures as input;
• grouping all fractures of the plurality of fractures into fracture clusters, whereby all fractures that are physically connected with each other by intersection, either directly or indirectly via a number of other physically connected fractures, exclusively belong to one fracture cluster such that no fracture within one fracture cluster is physically connected with any fracture of any of the other fracture clusters;
• assigning a unique fracture cluster number to each of the fracture clusters;
• overlaying a three dimensional simulation grid over the discrete fracture network model, consisting of a three dimensional array of grid cells in three directions;
• attributing a grid cell cluster number to each grid cell in the simulation grid, which grid cell cluster number uniquely maps to the unique fracture cluster number of exclusively one fracture cluster that intersects with the grid cell;
• computing an effective permeability for each grid cell and for each of the three directions using the fractures that are inside the grid cell and that form part of the fracture cluster that has the fracture cluster number to which the grid cell cluster number of the grid cell is uniquely mapped, whereby ignoring other fractures that are inside the grid cell but that form part of a fracture cluster having a fracture cluster number that does not map to the grid cell cluster number of the grid cell;
• and
• assigning inter-cluster flow impediment data to selected grid cells reflecting flow impediment bathers between neighboring grid cell clusters;
• outputting a table containing grid property data for all grid cells, wherein the grid property data for each grid cell comprises the cluster number assigned to the grid cell, and one effective permeability number for each of the three directions;
• and
• outputting inter-cluster flow impediment data.