Abstract: 3-D Seismic and Offset VSP Data for Delineation of a Horizontal Well Trajectory: Bloque IV, Lake Maracaibo

C. Barrientos, S. Johnston, K. Leon, L. Stewart, I. D. Bryant

3-D seismic data were combined with well data to provide the broad structural framework necessary to define a horizontal infill well location in the Lower Lagunillas reservoir of Bloque IV; however, the low vertical resolution of the data precluded detailed interpretation of the thin (c. 30 ft) target horizon. Horizon slices through the 3-D volume indicated lineations that might represent faults or flexures that are below resolution of the data.

An offset VSP was recorded in the pilot well with a source location positioned so as to illuminate the planned well path. The frequency content of the VSP (up to 50 Hz) was much higher the dominant frequency of the surface seismic (10 Hz). The VSP provided indications of good reservoir continuity and possible improvement in reservoir quality downdip. The dip of the formation in the plane of the well path, a critical parameter for steering the well, was confirmed as close to 3 degrees. The well subsequently confirmed these indications.

It appears that offset VSPs offer the potential to significantly reduce drilling risks associated with horizontal wells in Lake Maracaibo, even when 3-D surface seismic is already available.

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