--> ABSTRACT: Hydrocarbon Seals: A Seismic Perspective, by L. Liro, T. Smith, D. Quintanilla, P. Colton, and P. Anderson; #90906(2001)
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L. Liro1, T. Smith1, D. Quintanilla1, P. Colton2, and P. Anderson2

1Veritas Exploration Services, Houston, TX USA
2Veritas Exploration Services, Calgary, AB Canada

ABSTRACT: Hydrocarbon Seals: A Seismic Perspective

Seals are one of the most poorly studied elements of a petroleum system. Geologic and geophysical analyses tend to emphasize the determination and Previous HitevaluationNext Hit of reservoir and hydrocarbons, respectively, without specific regard to the presence of a sealing facies.

Geophysical Previous HitevaluationNext Hit of a shale Previous HitsealNext Hit is somewhat analogous to Previous HitevaluationNext Hit of sandstone reservoirs – while depositional criteria may suggest reservoir quality, this property may vary significantly due to other factors. For shale sealing facies, the competence of the Previous HitsealNext Hit is controlled by many factors, such as bulk composition, specific clay types, lithification, and presence of micro– or macro– scale fracturing due to post–deposition structuring. As with reservoir facies, it is critical to understand the petrophysical character and any variations within the shale Previous HitsealNext Hit, so that this information can be rigorously calibrated to the seismic signal.

A simple investigation of shale Previous HitsealNext Hit competence is an Previous HitevaluationNext Hit of variations in compressional seismic velocity (Vp). This Previous HitevaluationNext Hit is useful if Previous HitsealNext Hit competence is associated with significant lateral pressure variations or overpressure. Comparison of Vp with shear velocity (Vs) may identify the presence of overpressured section.

Other seismic techniques that may aid in Previous HittopNext Hit Previous HitsealNext Hit Previous HitevaluationNext Hit include well calibrated seismic inversion, seismic anisotropy and azimuthal AVO.

Previous HitFaultNext Hit seals are typically identified by significant lateral variations in seismic attributes across the Previous HitfaultNext Hit plane. Calibrated direct hydrocarbon indicators conforming to the Previous HitfaultNext Hit plane readily identifies Previous HitfaultNext Hit Previous HitsealNext Hit presence.

As with most seismic techniques, the degree of prediction accuracy is directly proportional to the amount and proximity of calibration data. Thus in rank exploration there may still remain significant uncertainty in the Previous HitsealTop competence prediction.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado