Tricon offers customized workflows to address the complexity of your unconventional reservoir, any survey constraints or limitations, and budgetary considerations. Several options are available depending on the log data provided and the client’s requested deliverables. The schematic workflows are shown in Options 1, 2 and 3 followed by a detailed description. Each can be done in either the time or depth domain.
Time Domain (OVB PSTM)
Tricon proprietary Offset Vector Binning (OVB) is used to preserve offset and amplitude variation with azimuth during PSTM. Offset ranges are carefully selected so that the same fold is given to each offset bin, thus preserving offset vs. Amplitude information. By using regular offset and azimuth bins, gathers can more easily be cleaned and interpreted by the user than conventional OVT gathers (for which offsets and azimuths in the trace headers are somewhat random). The OVB workflow has proven to be reliable for gently-dipping geology.
Depth Domain (ES360 PSDM)
Paradigm’s Earth Study 360 is used to preserve angle and amplitude variation with azimuth during PSDM. Azimuthal tomography is used to make ultra-fine updates to the velocity field by adding the azimuthal moveout information. By trying all reflector dips during ray-tracing the gathers are pre-tilted to structure, meaning moveout sinusoids are due to HTI rather than residual VTI effects. Well-tie tomography to find VTI parameters also boosts HTI confidence. ES360 spiral gathers allow for post-migration spherical smoothing and arbitrary sectoring to condition gathers in a way that simultaneously enhances offset/angle and azimuth oriented signal. Both FastVel (volume-based) and Velocity Navigator (map-based) HTI residual moveout measuring tools can be used. The ES360 workflow has proven to be reliable in complex geology, provided wide-azimuth data with sufficient offset were acquired.
Option 1: HTI Flatten
This option is for the client that is concerned about HTI effects (non-flatness) on the gathers, but not particularly interested in fractures associated with the reservoir. Gathers are conditioned and cleaned to run FastVel (automatic velocity analysis) so that the RNMO-with-azimuth can be measured and then removed. Input data can be either OVB PSTM or Earth Study 360 PSDM gathers. Output is not converted to interval anisotropy nor compared with well logs or other geologic indicators. Time-varying trim statics can be applied to the gathers at client request to further flatten gathers.
- Flattened Gathers (with or without conditioning and trim statics)
- RMS Fast Azimuth Volume
- RMS Percent Anisotropy Volume
- RMS Fast Velocity Volume (OVB PSTM only – PSDM flow only works with interval velocities)
- RMS Slow Velocity Volume (OVB PSTM only – PSDM flow only works with interval velocities)
Option 2: HTI Flatten + Fracture Analysis (Velocity Variation with Azimuth – VVAZ)
Same initial workflow as Option 1, but with far more careful analysis to determine the presence of fractures. In-depth azimuthal fold analysis is performed to determine and measure areas of low confidence due to surface skips. World-Stress-Map.org and curvature maps are analysed to get a better understanding of the regional and local stress geomechanics. Interactive gather QC is used to double-check FastVel (automatic velocity analysis) parameters. After using a generalized Dix inversion to convert RMS to interval anisotropy, fracture logs are compared against interval values to verify inversion quality. If results are not telling a convincing fracture story, earlier work is adjusted and re-run to improve outcome. Finally, a detailed Fracture Report is prepared to help the client better understand their data.
Deliverables include (in addition to Option 1 deliverables):
- HTI Confidence Volume
- Interval Percent Anisotropy Volume
- Interval Fast Velocity Volume
- Interval Slow Velocity Volume
- RMS Fast Azimuth and Percent Anisotropy Velocity Navigator maps (ES360 PSDM only)
- Final Report with in-depth fracture discussion and images
Option 3: HTI Flatten + Fracture Analysis + TruLith
After performing VVAZ to determine fracture fast azimuth, we can run TruLith, our Amplitude Variation with Azimuth (AVAZ) workflow. TruLith takes the fast azimuth from VVAZ to create fast and slow azimuth gathers. TruLith gathers are essentially single-azimuth-sectored gathers for which the azimuth of the sector changes with depth/time to preserve amplitude variation with angle/offset along either the fast (fracture-parallel) or slow (fracture-perpendicular) azimuth. This allows us to perform pre-stack elastic inversion that is fracture-parallel and measures the host rock rather than fracture-contaminated rock properties. For instance, the Young’s modulus in rock with aligned fractures should be higher when measured only along the fast azimuth than with all of the azimuths summed. The first benefit of this workflow is a more accurate measurement of matrix rock properties. The second benefit is found when we perform the same inversion but on the slow azimuth gathers. The slow azimuth inversion products are corrupted by fractures (making the rocks seem weaker), but when compared with the fast azimuth inversion products, they can give a highly detailed volume of fracture density. Typically the best indicator of fractures is the poisson’s ratio comparison: (Poisson’s_Fast – Poisson’s_Slow)/Poisson’s_Fast.
Deliverables include (in addition to Option 2 deliverables):
- TruLith Fast Gathers
- TruLith Slow Gathers
- Fast Azimuth Inversion Products (AI, SI, Density, Young’s, Poisson’s, Brittleness)
- Slow Azimuth Inversion Products (AI, SI, Density, Young’s, Poisson’s, Brittleness)
- Fracture Density Volume (example – (Poisson’s_Fast – Poisson’s_Slow)/Poisson’s_Fast)
- Final Report