BLAKE, BRUCE A., and DANIEL FIGUEROA
YPF/Maxus, Dallas, TX
Exploration in areas of complex geologic structures, such as the fold and thrust belt play of the southern Sub-Andean region of Bolivia, presents special problems in seismic data acquisition and interpretation. Several criteria are used in locating new seismic lines which relate directly to surface geology (i.e., topographic highs, age order of outcropping rocks, surface dips). These data alone are not sufficient to ensure the location of a prospect in the subsurface. We believe that a twostaged exploration effort of first shooting strike lines followed by well-positioned dip lines is a more cost-effective method.
We advocate first shooting strike lines (e.g., parallel to the outcropping formations) along the back limbs of thrust structures; later recording dip lines over culminations seen on the strike lines. The back limb strike lines are less expensive to shoot than either strike lines on the crests of the mountain ranges or dip lines that cross the mountains. Three dimensional seismic modeling shows that the subsurface position of the back limb strike lines is about the same as for the crestal strike lines. Data quality is better in the back limb strike over the crestal line mainly because the topography is flatter and the surface geology is Tertiary age. Data quality on the back limb strike line is better than dip line data mainly because the reflections are flatter and the ray paths less complex. Fore limb strike lines can be as useful as back limb lines in this type of exploration play.
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas