IMAGING CAPABILITY OF CROSS-HOLE SEISMIC-REFLECTION SURVEYS

In seismic migration, it is important to sample a range of dips around the local structural dip at each image point. Meaningful images are o btained only where this condition holds. For cross-hole seismic reflec tion surveys, the distribution of dips sampled at each image point is controlled principally by the survey geometry, including source and re ceiver array lengths and their element spacings. Using a real data set as an example, we show how survey geometry can limit imaging capabili ty close to the boreholes and even in the middle of the section betwee n the boreholes. At the processing stage, effective removal of direct waves and accurate estimation of the velocity field are essential for optimizing image quality. For migration, we propose a generalized Berr yhill (GB) scheme which is based on the Kirchhoff integral and takes i nto account both the near-field and far-field terms. This should impro ve the ability to image close to source and receiver arrays, provided that the element spacing in the nearby array is small enough.