3D Check shot Modeling for Time-Depth Conversion

Abstract

Time-depth conversion is one of the keys to successful drilling with a specific target. However, if the drilling target is incorrectly defined, it can cause significant material losses. For example, several cases found that the hydrocarbon depth was deeper than the expected target. As a result, the well will be considered dry even though it still has hydrocarbon reserves. In this study, we intend to develop 3D check shot modeling in which check shot and formation marker data are referred to and taken at the well to obtain a precise time-depth relationship to overcome this problem. The well data with check shot available that can be used for velocity modeling, for the time-depth conversion process is very limited. However, in development fields with dozens or even hundreds of wells, the time-to-depth conversion process becomes a challenge where it is not enough when using one single velocity. In addition, the velocity model must accommodate lateral heterogeneity so the depth structure map can match the well formation markers. On the other hand, seismic data can indirectly measure subsurface velocities vertically and horizontally. This research combines well-check shot data with seismic semblance velocity data to build a velocity model calibrated by well data. The time-to-depth conversion process with the calibrated velocity model has an average residual of less than 5 meters compared to only using check shot data, with an average residual is 25-meters.