Abstract: Fracture and Lithology Delineation Using Mode Converted P-SV Reflections

Michelena Reinaldo, Elias Ata, Manuel Gonzalez, Jesus Sierra, Javier Perez

A 2-D, mode converted, P-SV data set recorded in south-west Venezuela was used to delineate fractures and to identify lithology within a carbonate reservoir located at a depth of 3000 m. The characterization of the fractures was needed to initiate the exploitation of the field using horizontal wells. P-SV converted waves exhibit amplitude and traveltime variations on both horizontal components that can be related only to azimuthal anisotropy effects. These effects appear to be caused by changes in the orientation and density of the fracture systems associated with the fault regime of the area. The results were calibrated with fracture orientations interpreted from formation micro-scanner logs.

Vp/Vs ratios were calculated using ts/tp ratios measured on migrated sections, after correlating P-wave reflections with converted P-SV wave reflections for different stratigraphic intervals. We found excellent correlation between Vp/Vs, gamma ray, and sonic logs, which allowed us to map lateral lithologic changes within the reservoir and to predict relative amounts of different rock types. To understand the relations between fracture density and rock type, we correlated lithologic maps obtained from Vp/Vs with fracture density maps obtained from the traveltimes differences between the horizontal components.

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