Regular and Irregular type grids in reservoir simulation

[ibtisam01]

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As I am beginner to Reservoir Simulation, therefore my questions some times can be childish.

My Question is related to two figures that are attached with this thread. Fig 1 shows regular grids and fig 2. shows irregular grids.

I can understand that irregular grids are designed on the basis of subsurface structures, but how these irregular grids are made in Eclipse simulator??? Whenever I input any number of grids in data file, always regular shaped grids are formed. I am curious about this.

[link Point to another website Only the registered members can access]

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Any help in this matter please.

Thanks..........