Naturally Fractured Tight Gas, Gas Reservoir Detection, Optimization. Quarterly report, October 1 - December 31, 1996

Data tapes were shipped from Western Geophysical for interpretation. The data tapes include wiggle trace data (two azimuth volumes of post stack time migration seismic data) and velocity data (2 azimuths stacking velocity cubes). The two azimuth volumes are those source receivers in the fast P wave velocity direction and the slow P wave velocity direction, as picked from super gathers that scanned over azimuth, termed azimuth bin gathers. Spatial variability in the direction of the fast P wave and the spatial variability in the magnitude of the difference of the two velocities are observed in the Rulison 3D dataset. The difference of interval velocity with azimuth is one of the more robust, and preferred, measures of seismic anisotropy. The stacking velocity cubes for each azimuth are used to determine the interval velocities of the two different azimuths. We also observed in the azimuth bin gathers significant azimuthal variations in amplitude (brightening and dimming) which were centered on the two chosen azimuths. This is very important because it indicates field data support that the amplitude anisotropy is oriented the same as the velocity anistropy. When the cause of the velocity anistropy is the same as the cause of the amplitude anistropy, then the velocity and amplitude anistropy will be aligned. The Western Geophysical Fractogram approach will further test the hypothesis (and the preliminary field data observation) that the two observations have the same orientation. However, if different causes exist for velocity versus amplitude anistropy, then the two effects need not be aligned