Upscaling Discrete Fracture Network Models via Cluster Segmentation
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Solution Overview
Problem
Existing upscaling methods for discrete fracture network models in the oil and gas industry, such as Oda's method and flow-based methods, often overestimate permeabilities or fail to accurately reflect fracture connectivity, leading to misleading flow simulation results and suboptimal development decisions.
Innovation Solution
A novel upscaling method that groups fractures into distinct clusters and assigns grid cells to these clusters, calculating effective permeabilities only within each cluster while ignoring fractures from other clusters, and incorporating inter-cluster flow impediment data to accurately represent fluid flow between clusters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If Oda's method is used to calculate effective permeability by adding weighted fracture permeabilities, then the calculation is simple and fast, but the permeability is over-estimated particularly in poorly connected fracture networks
Solution Approach 1:
The method segments the fracture network into distinct clusters based on physical connectivity. Each cluster is independently analyzed to calculate effective permeability, ensuring that only fractures within the same connected component contribute to the permeability calculation. This segmentation prevents over-estimation by excluding non-connected fractures that would otherwise be included in simple weighted averaging methods.
2Measurement precision
If flow-based methods are used to calculate permeability by computational flow simulations on each grid cell, then the permeability calculation is more accurate, but the computational effort is extensive and the result is sensitive to orientation and size of grid cells
Solution Approach 1:
The method segments the computational domain into fracture clusters, allowing permeability calculations to be performed independently for each cluster. This segmentation reduces the computational domain size and enables more efficient calculations compared to performing flow simulations on the entire grid cell, while maintaining accuracy by preserving the connectivity structure within each cluster.
Solution Approach 2:
The method performs preliminary clustering of fractures based on their spatial connectivity before the actual permeability calculation. This preliminary action organizes the fracture network into meaningful groups, which then guides the subsequent permeability calculation process. By pre-organizing the data structure, the method avoids the computational expense of analyzing all fractures simultaneously and reduces sensitivity to grid cell parameters.
3Ease of manufacture
If all fractures within a grid cell are considered for permeability calculation regardless of connectivity, then the calculation is simpler, but the fracture connectivity information is lost leading to misleading flow simulation results
Solution Approach 1:
The method segments the fracture network into connected clusters, ensuring that only fractures within the same cluster are considered together in permeability calculations. This segmentation preserves the connectivity information by maintaining the spatial relationships and intersection connections between fractures. The clustering algorithm identifies which fractures are physically connected through intersections, and this connectivity structure is preserved in the final permeability calculation.
Solution Approach 2:
The method applies local quality by treating different fracture clusters differently based on their connectivity characteristics. Each cluster is analyzed with its own specific fracture set and connectivity structure, rather than applying a uniform approach to all fractures. This allows the permeability calculation to reflect the actual local connectivity conditions in different regions of the reservoir, preserving important spatial variations in flow pathways.
Data Source
AI summary
A discrete fracture network model is upscaled to a simulation grid having effective permeabilities for each grid cell. Prior to computing the effective permeabilities, the grid cells are grouped in distinct grid cell clusters, such that flow via fractures is only possible between grid cells that mutually belong to the same grid cell cluster. This is achieved by grouping fractures into distinctive 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. Each grid cell is assigned to exclusively one fracture cluster. After defining the grid cell clusters, effective permeabilities are calculated for each grid cell using only the fractures of the fracture cluster to which the grid cell is assigned while fractures from other fracture clusters are ignored. Inter-cluster flow impediment data is assigned to selected grid cells.