Abstract - Flow simulators assume that the transmissibility between two cells is proportional to their connection area.
We show that this assumption is incorrect for partially connected cells, and assess the significance of this
previously ignored error.
Faulted reservoir flow simulation models built using corner-point geometry contain partially connected
cells across faults. Partial connections are an inevitable consequence of miss-alignments of grid-cells
resulting from the fault displacement, and it is not possible to eliminate them without compromising either
the sedimentary layering or the across-fault juxtaposition geometry. Across-fault cell connections vary in
shape from triangular to hexagonal, and have widely-varying fractional connection areas (the area of the
connection expressed as a fraction of the area of the cell face).
Using high-resolution flow simulation models of the volume between the centres of partially juxtaposed
grid-blocks, we examine systematically the magnitude of the transmissibility error. For two cells, the error
is greater when the fractional connection areas are smaller, and the kv:kh and cell length:height ratios are
larger. For a realistic cell aspect ratio of 60:1, kv:kh ratio of 0.1, and fractional connection area of 0.2,
tortuous flow within the cells results in a transmissibility that is about five times greater than the simulator
assumption. The errors decrease when fault rock is present between the cells, and when angular missalignments
between the cells are larger.
Analysis demonstrates that the transmissibility between partially juxtaposed cells is influenced not only by
the geometry and properties of the two cells in question, but also by the surrounding cells, and the error is
larger in more heterogeneous sequences. Because of the complexity of the dependencies there is no
analytical solution. A wider recognition of the problem, combined with our analysis of its magnitude, may
aid a better appreciation of fault-related transmissibility uncertainties.
Proceedings of ECMOR X1V: 14th Conference on the Mathematics of Oil Recovery, 1156-1169, ISBN: 978-1-63439-168-9.