AVO Analysis

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Amplitude Variation with Angle or Offset

AVA / AVO behaviour in pre-stack seismic gathers is a classic direct hydrocarbon indicator (DHI) based on the principle that variations in amplitude of a seismic reflection with angle of incidence or source-receiver distance (offset) are caused by fluid and/or lithology changes in the reservoir.

Offset Synthetic Modeling

By examining the synthetic seismic response at the target, with varying porosity and saturation models, we can then look for similar seismic responses on the “real” seismic attribute volumes.  Systematically modeling varying rock properties highlights the sensitivity of seismic attributes to the rock property variations.  Offset modeling is also used to assess the feasibility of seismic inversion based reservoir characterization.

AVO responseFluid replacement modeling is performed to assess the sensitivity of elastic rock properties to pore fluid type in the reservoir.  Additionally, fluid and matrix properties are modeled from precise specification of a number of important reservoir parameters such as pressure, temperature, fluid gravities, salinity, GOR and matrix mineralogy.

Wedge modeling is performed to gauge the impact of thin bed tuning on the AVO response.  Modeled well logs, in addition to synthetic gathers are captured from any position in the wedge.

Oftentimes an AVO anomaly cannot be adequately modeled by changing one parameter at a time.  Another modeling technique is employed which systemically modifies two reservoir parameters simultaneously, one in the inline direction and one in the cross-line direction, resulting in a cube of synthetic gathers.

Reservoir Reconnaissance

Fluid and lithology anomalies are identified by analyzing AVO cross plots of the measured well data, modeled data and AVO attribute volumes, characterizing the different AVO classes.  The relationships of the hydrocarbon bearing zones to elastic properties and AVO attributes are then correlated to the seismic volume to identify similar reservoir seismic signatures.
Ultimately the goal of AVO analysis is to calibrate fluid effects seen or modeled from the well logs to the seismic data.  This calibration is also the goal of Seismic Inversion, but it is advisable to QC inversion results with a review of the seismic gathers and AVO analysis.

stress mapScope of Work:

  • Well to seismic ties
  • AVO well modeling
  • Obtain phase of the seismic data through well and seismic based wavelet extraction 
  • Rotate seismic to zero phase
  • Compare AVO response from synthetic and real (seismic gather) gathers at well location(s)
  • AVO background analysis
  • Produce AVO attribute volumes: Intercept (A), Gradient (B), Product (AB), Fluid Factor, and (Far-Near)*Far
  • Perform AVO analysis including cross plot analysis and maps of the key attributes

Deliverables:

  • AVO attribute volumes: Intercept (A), Gradient (B), Product (AB), Fluid Factor, (Far-Near)*Far
  • Near, Mid & Far angle ran
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A global-scale AVO-based pre-stack QC workflo...

Anna Rivet | Vimol Souvannavong | Celine Lacombe | Thierry C...
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