Abstract: A reservoir in payrock in analysed using finite element simulation. A reservoir engineer selects an appropriate model from a set of template models, each including a set of polygons in plan and layers in elevation. The polygons are defined in objects instantiated from classes by control points and the layers as depth values of control points. A pattern object sweeps rotationally about a wellbore in a wellbore polygon to define a pattern of elements, fewer in number with distance from the wellbore. A polygon object also sweeps linearly from a generator line in the direction of a base line. The generator and base lines correspond to polygon boundaries. Finite element simulation is performed with the model so derived.