Geometry and Gridding

Two models were simulated for this study. The first model consisted of nx=66, ny=70, and nz=12 grid blocks resulting in a total of 50,674 active cells. In the second model the number of blocks in the x and y directions were doubled to nx=132 and ny=140. The number of blocks in the vertical direction was kept at nz=12, leading to a total of 202,696 active cells. Active cells are cells with a porosity greater than 10^-6. Results of this second model were used in the seismic processing part of the study. Both models were gridded using a Cartesian geometry, with a denser grid at the center of the system (Figure ). The simulated area had an areal extent of 5 km $\times$ 5 km, and a thickness varying between 80 m and 120 m.

Two vertical faults were introduced in the yz-plane with an offset of 30 m. The faults were located at $x = 1,812.5~{\rm m}$ and $x = 3,375~{\rm m}$. To account for the proper connections across the faults a total of 1,260 non-neighbor connections were introduced in the 50,674-cell model and 2,520 non-neighbor connections in the 202,696-cell model. Non-neighbor connections are required when blocks which are neighbors in the i,j,k ordering used as input are not neighbors in the actual physical space as, for example, in the case of faults. Transmissibilities across the faults were then multiplied by 10 (at $x = 1,812.5~{\rm m}$)and by 10^-5 (at $x = 3,375~{\rm m}$), thereby increasing the transmissibility of the first fault while almost sealing the second fault. Figure  shows the areal view of the top layer and a xz-slice at $y= 2,270~{\rm m}$.

 

marcofig2
Figure 6 Areal and cross-sectional ($y=2270~{\rm m}$) meshing of the 50674-cell model, showing locations of faults and the gas-oil and water-oil contacts. The larger 202,696-cell model was constructed by doubling the number of grid blocks in the x- and y-directions.