Anisotropy/Fracture Characterization

Tricon’s fracture characterization workflow entails a quantitative analysis of the fracture system to determine fracture orientation, fracture density, and brittleness. Through the integration of log-based petrophysical and rock physics analysis with anisotropic velocity and amplitude analysis performed on the seismic, Tricon can deliver an accurate, reliable representation of your fracture system.

Seismic Analysis of WAZ (wide azimuth) Surveys

The first phase of our seismic analysis workflow consists of analyzing the geometry of the processed CMP gathers and their amplitude fidelity at target. The processed PSTM gathers must meet minimum criteria for amplitude fidelity, azimuth and offset distribution at the target or we will recommend not proceeding with the analysis.

Histograms of the azimuth and offset distributions for the survey are displayed at each CMP. They help us assess whether or not it will be possible to process the seismic data as a wide azimuth survey using our offset vector tile formulation. Once we see that a WAZ processing flow can be used, the next step is to sort the source and receiver lines into cross-spreads, followed by the OVT binning and regularization based on the shots and receiver lines spacing.

The OVT formulation will include a set of constant offset and constant azimuth datasets appropriate for the isotropic migration. The offset vector tile migration preserves the azimuth in the trace headers. Once the migration by tile is completed, the 3D OVG (offset vector gather) volume is formulated for each CDP also preserving the azimuthal information in the trace headers. We typically define azimuthal ranges every 60 degrees. The OVG formulation includes reciprocity as did the migration so three azimuths are often sufficient.

In order to increase the signal to noise ratio prior to any azimuthal velocity analysis, 3D FXY deconvolution is applied to the OVG volumes. High density RNMO is computed in order to correct all residual NMO errors (RNMO) up to fourth order. Noise will be attenuated, still preserving relative amplitude. The updated interval velocity model by azimuth will enable the estimation of the HTI parameters.

A series of reservoir attributes related to kinematic and seismic amplitudes can be developed to characterize fractures and/or rock brittleness on both the full-azimuth gathers and individually on each of azimuth range selected. They include the following:

  • Stack and Coherence (HR Eigen, HR Semblance, Curvature and dip) for each azimuth range
  • FastVel to determine RMS and Interval Velocities
  • Azimuthal AVO (Intercept and Gradient)
  • Full simultaneous pre-stack inversion for each average azimuth range to estimate Poisson’s ratio and Young’s Modulus using a selected number of angle stacks.