--> Seismic Reservoir Characterization of a Gas Shale Utilizing Azimuthal Data Processing, Pre-Stack Seismic Inversion, and Ant Tracking, David Paddock, Christian Stolte, Lei Zhang, Javaid Durrani, John Young, and Pat Kist, #40310 (2008).
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Previous HitSeismicNext Hit Reservoir Characterization of a Gas Shale Utilizing Azimuthal Data Processing, Pre-Stack Previous HitSeismicNext Hit Inversion, and Ant Tracking*

 

David Paddock1, Christian Stolte1, Lei Zhang1, Javaid Durrani1, John Young1, and Pat Kist1

 

Search and Discovery Article #40310 (2008)

Posted October 30, 2008

 

*Adapted from oral presentation at AAPG Annual Convention, San Antonio, Texas, April 20-23, 2008 and from 2007 WTGS paper of the same title by essentially the same authors.

 

1Schlumberger, Houston ([email protected])

 

Abstract

 

Prospective hydrocarbon-bearing zones in the subject gas shale are characterized by gas entrapped in the sediment matrix with some additional open-fracture component. This gas is economically recovered by horizontal drilling and fracturing. We show the results of an integrated workflow to get a good Previous HitseismicNext Hit image in the presence of Previous HitanisotropyNext Hit, find the sweet spots, and characterize fractures and reservoir risk.

 

Previous HitSeismicNext Hit azimuthal anisotropic analysis determines the dominant direction of the fast and slow Previous HitseismicNext Hit velocities indicative of maximum horizontal stress and/or fracture orientation and intensity. Corrections for HTI (horizontally transversely isotropic) medium were applied prior to VTI (vertically transversely isotropic) anisotropic Kirchhoff pre-stack time migration (KPSTM). Data processing created a pre-stack volume as input for inversion and a stacked volume as input for Ant Tracking.

 

Simultaneous inversion of the pre-stack data determined acoustic impedance (AI) and Poisson’s ratio (PR). A blind test of the inverted attributes is very encouraging. Sweet spots may be areas of anomalously low Poisson’s ratio (PR), away from faults, with high velocity Previous HitanisotropyNext Hit.

 

Ant Tracking reduces the risk of drilling near faults (a reservoir risk due to expected mineralization) by providing a high resolution image of fractures and faults beyond what can be interpreted from conventional Previous HitseismicNext Hit data. Faults were expected to be mineralized, with some mineralization extending out into the surrounding shales.

 

The resulting integration of Poisson's ratio, fractogram, and Ant Tracking provides effective delineation of areas with superior porosity and charge, areas with open fractures, and areas with faulting, outlining likely sweet spots as well as areas to be avoided in drilling.

 

Integration of anisotropic data processing with pre-stack Previous HitseismicNext Hit inversion and Ant Tracking provides a superior tool to explore for gas in gas shale.

 

Selected Figures

¨ Abstract

¨ Figures

¨ Challenges

¨ Conclusions

¨ References

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

¨ Abstract

¨ Figures

¨ Challenges

¨ Conclusions

¨ References

 


 

Measuring fractures with Previous HitseismicNext Hit (from Mattner, 2002).

 

Fractogram: Vfast-Vslow. Map view at target, displaying azimuthal variations in Previous HitanisotropyNext Hit.

 

Previous HitSeismicNext Hit profile, prestack inversion, migrated conventional Previous HitseismicNext Hit; sweet spots in gas shale reservoir in purple.

 

Previous HitSeismicNext Hit profile, Poisson’s ratio from prestack inversion, showing improved reservoir delineation.

Integration for the bigger picture. Fractogram - reservoir and completion risk; Previous HitSeismicNext Hit Inversion - rock property delineation;  Ant Tracking - subtle fault identification; Sonic Scanner – calibration.

 

Challenges of Gas Shales

 

n  Finding the “porous” sweet spots

n  Drilling and completing effectively

n  accurate fault delineation required to avoid risk

n  Understanding the effects of Previous HitanisotropyNext Hit

n  reservoir rock physics and delineation of structure

n  Quantifying the fracture storage of gas

n  Understanding the fracture system

n  Prior to this study, two unsuccessful wells drilled

 

Conclusions

 

Effective Previous HitseismicNext Hit gas shale workflow

n  Azimuthal velocity analysis improved delineation and understanding of fracture and stress regimes

n  Prestack inversion delineated sweet spots and areas to be avoided

n  Ant Tracking identified subtle faults that had been overlooked on conventional Previous HitseismicNext Hit

More effective completions

New drilling locations identified

 

References

 

Paddock, Dave, Christian Stolte, Lei Zhang, Javaid Durrani, (Schlumberger Reservoir Previous HitSeismicNext Hit Services), John Young, Pat Kist, (WesternGeco), 2007, Previous HitSeismicNext Hit reservoir characterization of gas shale utilizing azimuthal data processing, prestack Previous HitseismicTop inversion and Ant Tracking: WTGS publication.

 

Mattner, Joerg, 2002, Fractured reservoir characterization from collecting data to dynamic modeling: Course, GeoTech Consulting, slide (as part of presentation).

 

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