The seismic reflection process in anisotropic media

Abstract

A study of the seismic reflection process in anisotropic media showed a number of results which have direct consequences in an exploration context. Using laminated blocks of an anisotropic material to simulate shale-type layering, the seismic wave propagation was observed to be dependent upon the lamination orientation and, hence, on the shale layering orientation in an exploration sense. The seismic waves were demonstrated to travel at a faster velocity in the direction parallel to the layering orientation. Stacks of conventionally recorded seismic lines parallel and across the layering resulted in a two-way travel time mis-tie at their tie-point. Time to depth conversion indicated that a severe depth mis-tie would occur. The implication for exploration is that mis-ties in 2-D land and marine data may indicate the presence of anisotropy, while 3-D land and marine data do not. 2-D recording is therefore a necessary requirement to indicate the presence of anisotropy prior to 3-D recording. Numerical modelling of equivalent seismic data showed that commercially available numerical modelling software is inadequate for modelling the effects of anisotropy.