Figure 1 Velocity profile extracted
from in-line direction
The velocity cube for 1988 and 1994 3D surveys are provided by Wei He. The velocity was derived from the 4D seismic inversion impedance volume by using constant density 2. Since we are dealing a fairly small volume here which only includes reservoirs K8, K16, K40, L sands. Time-depth conversion tables from logs were used to convert two seismic travel time to the depth. Thus provided velocity cube is in depth but with Western 1994 seismic survey grid on X and Y, thus trace interval along X direction (E-W) is about 41ft and line interval along Y direction (S-N) is about 65ft.
Here we show 3 orthogonal slices extracted from derived velocity cube from inverted impedance cube. The figure 1 is the velocity profiles extracted from in-line direction, figure 2 is velocity profile extracted from the cross line direction and figure 3 is the velocity profile extracted from the depth direction. The derived velocity cube has grid size 41ft in X, 65ft in Y and 20ft in Z.
Figure 1 Velocity profile extracted
from in-line direction
Figure 2 Velocity profile extracted from cross-line direction
Figure 3 Velocity profile extracted
from depth direction
Since finite element method requires at least 10 grid points for the shortest wavelength propagated. Based on lowest velocity and domaint seismic frequency observed for 1988 and 1994 seismic survey, it was found maximum grid size for finite element modeling is about 20ft. The principal seismic frequency used in this first running is 25HZ. This requires two initial velocity cube to be interpolated in X and Y direction since sampling rate on X and Y are larger than 20ft. The 4D module volume interpolate is used to do interpolation because the interpolation honors continuity of seismic event which here is velocity interface very well. The X and Y direction are interpolated in two passes into 20ft.
Sampling interval in X, Y and Z are is 20ft.
In order to compare interpolated velocity cube with derived velocity derived from inverted impedance. We show 3 extracted velocity profile almost at the same position of Figure 1, 2, and 3. Figure 4, 5 and 6 are correponding extracted velocity profiles. The velocity cube has grid size 20ft in X, 20ft in Y and 20ft in Z.
Figure 4 Velocity profile (interpolated to 20ft) extracted from in-line direction
Figure 5 Velocity profile (interpolated to 20ft) extracted from cross-line direction
Figure 6 Velocity profile (interpolated to 20ft) extracted from depth direction
Stratigies
for modeling effortFrom the project description of interpolated velocity cube, we found number of cells in the cube is 329x206x131 which is 8878394 cells. This is still a challanging task for the current FDM program developed by Dr. Teng since program is still in serial execution fashion. It will take probably a full day to simulate acoustic case. Since velocity range is 7000-11000ft, based on lower velocity 7000ft/s and 25HZ principal frequency, sampling interval for model will be about 28ft. Based on higher velocity 11,000ft/s, the sampling interval for time will be about 1ms.