Modelling mach wave propagation between boreholes in layered media

Abstract

Crosshole seismic experiments often yield data containing arrivals which are difficult to understand and explain, due in part to the location of the sources and receivers in boreholes. In order to use the data from these experiments to infer properties of a petroleum reservoir, an improved knowledge of the effects of source and receiver boreholes on the waves propagating in these experiments is therefore very useful. An example of this type of problem is the interpretation of the energy radiated from tube waves propagating in the source well, since in slow formations where the tube wave velocity is larger than the formation shear wave velocity, this energy can result in the recording of large amplitude Mach waves, or shock waves, in the receiver well (Meredith 1990 ; de Bruin and Huizer 1989). This phenomenon typically will occur in shallow, low velocity sedimentary layers . The conical Mach waves will not only have an amplitude much larger than that predicted for radiation directly by the source, but will also have a linear moveout velocity which cannot be explained by radiation directly Erom the source.