A computer implemented method of evaluating fracture abundance in a subsurface formation, the method comprising: a) defining a fracture network within a plurality of cells of a three-dimensional model of the subsurface formation using a plurality of geometric primitives, where the fracture network and the three-dimensional model are generated based on data obtained from a survey of the subsurface formation, wherein defining the fracture network includes expanding, within a respective containing plane, each of a plurality of two-dimensional polylines representing fractures in the subsurface formation, wherein: a two-dimensional polyline comprises one or more line segments that lie within a same plane; each of the plurality of geometric primitives is a triangular element; and expanding each of the plurality of two-dimensional polylines includes expanding, in the direction of the respective containing plane, first two-dimensional polyline among the plurality of two-dimensional polylines either into a substantially rectangular shape represented by first and second triangular elements defined by four nodes or into a substantially elliptical shape represented by twelve triangular elements defined by thirteen nodes; b) determining an area of the plurality of geometric primitives within at least a subset of the plurality of cells by summing areas of individual geometric primitives within each of the subset of cells, wherein the determining the area of the plurality of geometric primitives within the subset of the plurality of cells further includes: organising the plurality of geometric primitives within a spatially-organized data structure; accessing the spatially-organized data structure when summing areas of individual geometric primitives within each of the subset of cells to determine which of the plurality of geometric primitives are at least partially within each of the subset of cells; and clipping individual geometric primitives that are partially within each of the subset of cells; and c) determining a fracture abundance parameter for the fracture network from the determined area of the plurality of geometric primitives. a) defining a fracture network within a plurality of cells of a three-dimensional model of the subsurface formation using a plurality of geometric primitives, where the fracture network and the three-dimensional model are generated based on data obtained from a survey of the subsurface formation, wherein defining the fracture network includes expanding, within a respective containing plane, each of a plurality of two-dimensional polylines representing fractures in the subsurface formation, wherein: a two-dimensional polyline comprises one or more line segments that lie within a same plane; each of the plurality of geometric primitives is a triangular element; and expanding each of the plurality of two-dimensional polylines includes expanding, in the direction of the respective containing plane, first two-dimensional polyline among the plurality of two-dimensional polylines either into a substantially rectangular shape represented by first and second triangular elements defined by four nodes or into a substantially elliptical shape represented by twelve triangular elements defined by thirteen nodes; a two-dimensional polyline comprises one or more line segments that lie within a same plane; each of the plurality of geometric primitives is a triangular element; and expanding each of the plurality of two-dimensional polylines includes expanding, in the direction of the respective containing plane, first two-dimensional polyline among the plurality of two-dimensional polylines either into a substantially rectangular shape represented by first and second triangular elements defined by four nodes or into a substantially elliptical shape represented by twelve triangular elements defined by thirteen nodes; b) determining an area of the plurality of geometric primitives within at least a subset of the plurality of cells by summing areas of individual geometric primitives within each of the subset of cells, wherein the determining the area of the plurality of geometric primitives within the subset of the plurality of cells further includes: organising the plurality of geometric primitives within a spatially-organized data structure; accessing the spatially-organized data structure when summing areas of individual geometric primitives within each of the subset of cells to determine which of the plurality of geometric primitives are at least partially within each of the subset of cells; and clipping individual geometric primitives that are partially within each of the subset of cells; and organising the plurality of geometric primitives within a spatially-organized data structure; accessing the spatially-organized data structure when summing areas of individual geometric primitives within each of the subset of cells to determine which of the plurality of geometric primitives are at least partially within each of the subset of cells; and clipping individual geometric primitives that are partially within each of the subset of cells; and c) determining a fracture abundance parameter for the fracture network from the determined area of the plurality of geometric primitives.