Summary
Reservoir flow simulation involves subdivision of the physical domain into a
number of gridblocks. This is best accomplished with optimized gridpoint
density and a minimized number of gridblocks, especially for coarse-grid
generation from a fine-grid geological model.
In any coarse-grid generation, proper distribution of gridpoints, which form
the basis of numerical gridblocks, is a challenging task. We show that this can
be achieved effectively by a novel grid-generation approach based on a
background grid that stores gridpoint spacing parameters.
Spacing parameter (L) can be described by Poisson’s equation
(∇2L = G), where the local density of gridpoints is
controlled by a variable source term (G). This source term can be based
on different gridpoint density indicators, such as permeability variations,
fluid velocity, or their combination (e.g., vorticity) where they can be
extracted from the reference fine grid. Once a background grid is generated,
advancing-front triangulation (AFT) and then Delaunay tessellation are invoked
to form the final (coarse) gridblocks. The algorithm produces grids varying
smoothly from high- to low-density gridpoints, thus minimizing use of
grid-smoothing and -optimization techniques. This algorithm is quite flexible,
allowing choice of the gridding indicator, hence providing the possibility of
comparing the grids generated with different indicators and selecting the
best.
In this paper, the capabilities of approach in generation of unstructured
coarse grids from fine geological models are illustrated using 2D highly
heterogeneous test cases. Flexibility of algorithm to gridding indicator is
demonstrated using vorticity, permeability variation, and velocity. Quality of
the coarse grids is evaluated by comparing their two-phase-flow simulation
results to those of fine grid and uniform coarse grid. Results demonstrate the
robustness and attractiveness of the approach, as well as relative
quality/performance of grids generated by using different indicators.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
11 December 2008
- Meeting paper published:
15 March 2009
- Revised manuscript received:
7 July 2009
- Manuscript approved:
4 September 2009
- Published online:
3 March 2010
- Version of record:
17 June 2010
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