Abstract:
A hybrid model for computing the radiation from a borehole while drilling has been developed. A model for modal propagation in a radially layered borehole is coupled with the OASES code for full wave modeling of the resultant seismic wave field. The coupling is performed using the concept of effective sources. First, an equivalent seismic source array that produces the same far-field radiation as the borehole is determined. This source array is then introduced into the layered earth model and the resulting seismic field is computed. Three propagating modes exist in the borehole in the presence of the drill-pipe. The individual modes radiate into the formation in a pattern that is dependent on geophysical properties, with the resulting radiation pattern being extremely complex and difficult to interpret physically. Here, visualization and animation in particular has proven to be an extremely useful tool. For example, animation allows the direct identification of the complex arrival pattern recorded on surface mounted geophones. The fundamental differences between the radiation patterns in fast and slow formations are also clearly demonstrated using computer visualization and animation.