FIGURE 4 Example of Multilinear Regression To Fill Monopole Shear 'Gaps' FIGURE 5 Top-Level View of Entire Lateral FIGURE 6 Third Segment (Middle Part of Lateral) step is to visualize the environment. Often, the only sonic data available are what has been acquired in the lateral itself. While workflows exist to use these data, the results can be improved (and interpretation time greatly reduced) by integrating additional data. The two best sources of visualization data are vertical well logs and the geosteering model. In the ideal scenario, the analyst would have sonic data from a vertical pilot well and a geosteering model based on multiple vertical offsets. The two can be combined to make a geosteering model with sonic velocities of each layer (by correlating the gamma ray/sonic in the vertical with the gamma ray-based geosteering model). Anisotropy (on both compressional and shear velocities) must be accounted for when using vertical sonic data to create a sonic-geosteering model. If no vertical sonic data exist from the pilot hole or nearby offsets, a "pseudo-geosteering" model can be created from the compressional data and density log. If sonic data in the lateral were acquired with a tool that stores the individual receiver array data, a dip image can be created by picking the compressional slowness from each azimuthal receiver array and combining the four measurements to create an azimuthal image. If the density measurement (which is dominated by the low side of the hole) is combined, it can aid in determining whether the wellbore is very close to a nearby bed or straddling two beds. The compressional image can help greatly in understanding where the wellbore is with respect to the nearby beds when a geosteering model is not available for correlation. Figure 3 shows an interval where the wellbore is in a shale with a limestone below (red boxed zone). From the sonic data alone, it is not clear if the wellbore is actually touching the lower formation or only close to the carbonate. However, the density tool response confirms measurements too low for the carbonate lithology response. The carbonate density can be seen just below this interval when the wellbore does enter the zone. Second Workflow Step The second step in the workflow is determining the "correct" compressional and shear velocities. This workflow focuses on determining a single set of compressional, vertical shear and horizontal shear velocities to be used in one-dimensional geomechanical models. Any time a shale 38 THE AMERICAN OIL & GAS REPORTER