Nathaniel G. Tilander, Robert G. Mitchel
Overthrust areas represent some of the last frontiers in petroleum exploration today. Billion barrel discoveries in the Eastern Cordillera of Colombia and the Monagas fold-thrust belt of Venezuela during the past decade have highlighted the potential rewards for overthrust exploration. However the seismic data recorded in many overthrust areas is disappointingly poor. Challenges such as rough topography, complex subsurface structure, presence of high-velocity rocks at the surface, back-scattered energy and severe migration wavefronting continue to lower data quality and reduce interpretability. Lack of well/velocity control also reduces the reliability of depth estimations and migrated images. Failure to obtain satisfactory pre-drill structural images can easily result in costly wildcat failures.
Advances in the methodologies used by Chevron for data acquisition, processing and interpretation have produced significant improvements in seismic data quality in Bolivia, Colombia and Trinidad. In this paper, seismic test results showing various swath geometries will be presented. We will also show recent examples of processing methods which have led to improved structural imaging. Rather than focusing on "black box" methodology, we will emphasize the cumulative effect of step-by-step improvements. Finally, the critical significance and interrelation of velocity measurements, modeling and depth migration will be explored. Pre-drill interpretations must ultimately encompass a variety of model solutions, and error bars should be established which realistically reflect the uncertaintie in the data.
AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela