Autocorrelogram migration: IVSPWD test

We present the results of applying autocorrelogram migration to inverse vertical seismic-while-drilling (IVSPWD) profile data collected in the Austin Chalk formation. The seismic reflections were excited by a drill bit moving along a horizontal well at a depth of 2800 m. The data were recorded by a receiver array on the surface. There were 609 twenty-second traces recorded at each of 10 three-component stations. After preprocessing, the traces were autocorrelated and migrated. Two imaging conditions were examined. The ghost-reflection imaging condition produced a reflectivity section that agreed with a nearby common-depth-point section. The migration section obtained with a primary-reflection imaging condition produced a reflectivity section inferior in quality to that of the ghost image. A possible explanation is that the drill-bit location was not precisely known, which can be shown to induce weak errors in the ghost-imaging condition but stronger errors in the primary-reflection imaging condition. Ghost migration images reflections not only below the drill bit, but also above the drill bit. This investigation is one of the first examples of successfully imaging the earth's reflectivity section from horizontal drill-bit data, and it offers a potentially useful method for seismic imaging from drill-bit data.