Abstract: 3-D Structural and Stratigraphic Interpretation of VLA 68/96 Area Block I Field, Lake Maracaibo, Venezuela

Pinto, Jonny - Bureau of Economic Geology

This paper presents the results of a structural and stratigraphic interpretation of Area VLA 68/96 located in Block I, Lake Maracaibo. The survey covers an area of 210 sq. km.

The work involved during the interpretation started with data gathering of all available information (geology, petrophysics). This information was integrated with 3D seismic in an attempt to resolve the structural framework in the study area and to propose drilling locations.

Structurally, the area is bounded east and west by inverse transcurrent faults striking north-west. North and South, the area is characterized by a series of small grabens showing structural closures. The major fault of the east area, Falla del Este, was originated during the tensional regime of the Jurassic, and was later reactivated during the compressional movements of late Eocene. The faults acts as a barrier for the hydrocarbons accumulation of the area. Seismic structural attributes such as dip and azimuth were used to validate the structural framework. These attributes proved very helpful in delineating the major fault pattern trends.

Production in the field comes primarily from the early to mid Eocene Misoa C sandstone. Stratigraphically, this study is centered around the Lower Eocene Misoa C-sands of the Misoa Formation (C4M — C5). These sands are of fluvial deltaic origin and were deposited during the Eocene. To map them, different attributes extraction techniques were compared. (1) Bounded attribute maps, to limit top and bottom surfaces, (2) Stratigraphic times slices, to detect subtle features and guide sand patterns, (3) Similitude maps, to combine non-lineal attributes at petrophisical level, and (4) Stratigraphic isochron slices, to divide the reservoir in equal layers of thickness of amplitude. The C4M package reservoir, is characterized by a series of continuous to non-continuous reflectors. These reflections are due to velocities and densities contrast between sand and shale which vary along the area and generate attributes that makes amplitude analysis a valuable tool for lithologic indicators. Most of the maps, are characterized by seismic amplitudes anomalies related to sand thickness. This correlation was established using statistical analysis and was interpolated using Kriging algorithms (Standard Co-Kriging). Finally, probability maps were generated and used in combination with petrophysical cut-off to delineate areas of interest.

There are already 15 wells drilled in the area and evidence of hydrocarbon to the south. The integration of the interpretation of 3D seismic with Geology and Petrophysics has recognized field development opportunities to the south of the study area, allowing the location of one appraisal well which will increase the remaining reserves by at least 10 MMSTB. The future development of the area should take into consideration the possibility of drilling at least two more locations in the area.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil