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Seismic
Reservoir Characterization of a Gas Shale Utilizing
Azimuthal Data Processing, Pre-Stack
Seismic
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])
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 seismic
image in the presence of
anisotropy, find the sweet spots, and characterize fractures and reservoir
risk.
Seismic
azimuthal anisotropic
analysis determines the dominant direction of the fast and slow
seismic
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 anisotropy.
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 seismic
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 seismic
inversion and Ant Tracking provides a
superior tool to explore for gas in gas shale.
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n Finding the “porous” sweet spots n Drilling and completing effectively n accurate fault delineation required to avoid risk n Understanding the effects of anisotropy 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
Effective 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 More effective completions New drilling locations identified
Paddock,
Dave, Christian Stolte, Lei Zhang, Javaid Durrani, (Schlumberger Reservoir
Mattner, Joerg, 2002, Fractured
reservoir characterization from collecting data to dynamic
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