AVO & Inversion

Overview Library

All AVO and inversion work is consistent with well log and VSP data. Integration of all types of data-seismic, geological, borehole, rock physics, and petrophysics-is the cornerstone of our AVO and inversion process.

Amplitude variation with offset (AVO) has been used extensively in hydrocarbon exploration over the past two decades. Traditional AVO analysis involves computation of the AVO intercept, gradient, and higher-order AVO term from a fit of P-wave reflection amplitude to the sine square of the angle of incidence. This fit is based on the approximate P-wave reflection coefficient formulation in intercept-gradient form, given by Bortfeld (1961) and Shuey (1985) among others. Under the assumption of a background PS velocity ratio, the AVO intercept and gradient values can also be combined to obtain additional AVO attributes such as pseudo-S-wave data, Poisson's ratio contrast, and others. AVO intercept and pseudo-S-wave data are also used in conjunction with prestack waveform inversion (PSWI) in a hybrid inversion scheme. Hybrid inversion is a combination of prestack and poststack inversion methodologies. Such a combination allows efficient inversion of large data volumes in the absence of well information.

Multi-measurement reservoir definition workflows include the following components

  • Reservoir Synthetic Modeling
    Forward modeling to generate pre-stack synthetics from geological models
  • Anivec (prestack elastic modeling)
  • Prestack Waveform Inversion (PSWI)
    Full waveform prestack inversion is a non-linear inversion process that estimates elastic model (Vp, Vs, and density) from prestack seismic data using a genetic algorithm.
  • AVO Modeling and analysis
  • AVO Conditioning
    Conditions angle band stacks prior to performing AVO analysis
  • AVO Inversion
    Elastic impedance modeling and inversion from angle band cubes
  • Space-adaptive Inversion
    Space adaptive wavelet processing and inversion to relative seismic impedance
  • Elastic Impedance Inversion
    Combining low frequency trends with seismic relative inverted impedance cubes to generate absolute impedance
  • Integrated Rock Physics Modeling
    Fluid and rock property analysis, modeling and substitution
  • Rock Property Calibration
    Generating rock properties from seismic using transforms derived from petrophysical analysis of well data.
  • Lithology Classification
    Lithology classification defines the elastic signature of lithology and fluid types using rock physics analysis and well data through Bayesian estimation theory.

The outputs are high-resolution absolute acoustic and shear impedance and density volumes consistent with the seismic data and the well-log data. The inverted elastic parameter volumes are used for detailed interpretation of lithofacies and pore-fluid content in the subsurface. Combined with rock physics modeling and rock property mapping through lithology classification (Bachrach, et al., 2004) and joint porosity-saturation inversion, the method provides a powerful tool for quantitative reservoir description and characterization. The results are the most-probable litho-class, porosity, and saturation with uncertainties of prediction at every sample point in the 3-D volume.

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Quantitative Reservoir Description and Characterization

The result of inverting a seismic panel into relative acoustic impedance. Note the excellent tie with the well.
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