NEMETH, T., Chevron Petroleum Technology Company, New Orleans, LA; B. CORNISH, Halliburton Energy Services, Houston, TX; J. MINEAR, Consultant, Houston, TX; WILLIAM KEMPNER, Chevron USA Production Co, Bakersfield, CA; R. LANGAN, Chevron Petroleum Technology Company, New Orleans, LA
Vertical Seismic Profiles (VSPs) have been used on a limited basis for many years, both for early field development and the management of mature fields. Their frequency of application has been limited because of acquisition costs and the small reservoir volume imaged. The hope with VSPs is that one obtains more coherent and higher resolution images in a key area than is obtained with surface seismic 3-D data. Recent developments in borehole acquisition equipment (e.g., multilevel sensor arrays, permanent and portable) have made it more feasible to acquire 3-D VSPs.
Halliburton installed a permanent, 40-level, 3-C geophone string in a temperature observation well in Lost Hills in September 1998 (Cornish et al., this meeting). Their objective was to obtain time-lapse 3-D VSP data over nearby steam pilot. A direct comparison between the VSP and the surface seismic data is possible because the baseline surveys were acquired at the same time, using the same sources and recording system. A second 3-D VSP snapshot only was acquired in October 1999.
We have developed a prestack Kirchhoff depth migration algorithm tailored to 3-D VSPs. By applying imaging constraints within the algorithm, artifacts associated with a limited range of reflector illumination angles, the limited fold, and noise are reduced, and the computational efficiency of prestack depth imaging is increased. We have also developed a direct method for verifying the resolution of the migrated image for the given acquisition geometry, velocity structure, imaging constraints, and preprocessing effects.
AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California