Fracture Detection

AVAZ/VVAZ Analysis

Rocks often exhibit different properties along paths of maximum and minimum stress and/or along paths parallel and perpendicular to fractures. This information is manifest on seismic data through azimuthal variations in both stacking velocity (VVAZ) and/or amplitude-versus-offset (AVAZ). Through use of proprietary algorithms, Arcis can analyze the prestack data volume to glean information that may helpful in understanding the fracture and/or stress regime and therefore lead to improved drilling results.

P-wave fracture detection flow

Key elements of Arcis’ P wave fracture detection flow are:

a) 5D interpolation to improve the data sampling prior to azimuth-limited PSTM

b) AVO vs azimuth curve fitting as per the Ruger equation

c) Velocity versus azimuth curve fitting as per Tsvankin's elliptical NMO equation

 

Arcis’ technical staff possesses a full understanding of all the elements of a complete production P-wave fracture detection flow, including aspects of acquisition geometry QC, incorporation of client horizon information, 5D interpolation QC, and fracture attribute visualization. Moreover, on the data pre-processing side for AVAZ, AVO-compliant processing is paramount, and Arcis' processing group has much experience in that area.

Through collaboration between our Processing and Reservoir Services groups, Arcis can offer the unique ability to co-display AVAZ/VVAZ/curvature. Such a joint analysis has been rarely performed to-date in the industry, and going forward we are confident that a combined interpretation of these three disparate attributes (all ostensibly aimed at the same objective of fracture characterization) will result in more robust estimates of fracture characterization.

 

The following are 4 independent approaches to P wave fracture detection:

1. Fracture delineation via curvature analysis 

Fracture delineation via curvature analysis   

 (NE British Columbia; rose diagram in inset)

  

2. Fracture intensity via azimuthal velocity analysis

Fracture intensity via azimuthal velocity analysis

(Central Alberta; misfit QC in inset)

  

3. Fracture intensity via AVAZ

  

(Central Alberta)

4. VVAZ fracture intensity (Western Canada shale gas play). Fracture trends picked on the VVAZ intensity plot from a thick interval immediately above the producing formation show good correlation with faulting within the formation proper as seen on the time structure map (not shown). This observation supports the hypothesis that formation structure is in part controlled by overlying salt dissolution collapse and associated fracturing.