Abstract: The Quest for Better Seismic Imaging in the Sub-Andean Thrust Belt of Southern Bolivia

John F. Dunn, Kenneth J. Nelson

Like many thrust belts around the world, the sub-Andean thrust belt of southern Bolivia is a difficult place to acquire good seismic data because of the challenges of complex geology, rugged topography, and remote access. This is further aggravated by the fact that we generally desire to image below the surface anticlines, where the conditions for acquiring good data are the worst. Near-surface, steeply-dipping beds also challenge some of the fundamental assumptions of seismic processing. Our approach has been to integrate detailed structural analysis of the surface and subsurface with the seismic interpretation.

Seismic imaging of structural geometry is a fundamental risk element in thrust belt hydrocarbon exploration. Acquiring high-quality seismic data in mountainous terraln has been a difficult, time consuming, and costly task. We have exerted considerable effort into finding innovative ways to improve data quality. After an initial round of acquisition in Bolivia, we designed a seismic test program to optimize acquisition parameters. We found that standard parameters were acceptable in the valleys, but larger dynamite charges yielded better results in the mountainous areas where imaging had previously been poor. Additionally, a swath line layout (three parallel receiver lines 200 m apart) helped improve the signal-to-noise ratio. Better static solutions, detailed velocity analysis, and ca eful structural modeling and depth migrations all help to yield better data and a more reliable interpretation.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela