William Keller

Uncertainties in passive seismic monitoring

The use of passive seismic techniques to monitor oil- field completion and production processes is on the rise. Stress changes induced by such reservoir activities as hydraulic fracturing, water injection, or fluid extraction will often result in failure of the rocks with a concurrent release of seismic energy in the form of compressional (P) and shear (S) waves. Passive seismic monitoring is based on recording these emitted waves and then using their arrival times to estimate the location of the failure events.

Correlation of surface microseismic event distribution to water production and faults mapped on 3D seismic data: A West Texas case study

The use of microseismic techniques to map hydraulic fracture treatments has increased dramatically in recent years. During this time, microseismic monitoring has grown from a technical curiosity into an established method for determining the spatial distribution and therefore effectiveness of well completions in tight reservoirs. While both surface and downhole microseismic monitoring techniques are widely used throughout the industry, surface microseismic methods have typically been met with more skepticism. We present a case study from West Texas in which surface microseismic results from two adjacent wells are validated by both 3D seismic and production data.

Considerations in Azimuthal Processing and Velocity Inversion for Unconventional Plays

A tightly-sampled 3D land seismic survey from south central Texas was acquired atop the Austin Chalk near Giddings, Texas in 2015. A test subset of that survey was processed using an azimuth-friendly flow, and subsequent azimuthal velocity inversion (VVAZ) generated interval attributes which showed a remarkably strong correlation to historical gas production. Key elements of the azimuthally-AVO-compliant processing flow used to pre-condition the seismic data include (i) 5D interpolation onto a regularly-sampled set of output azimuth spokes; (ii) postmigration noise attenuation operating piecewise on these spokes; (iii) due care in estimating both the azimuthvariant time-shifts which form the input to the VVAZ inversion, as well as the maximum incident angle restricting the contribution of these time-shifts to the inversion; and (iv) testing the impact of the number of azimuths output from 5D interpolation on the quality of the final azimuthal interval velocity attributes. We posit that these key elements should be routinely incorporated into VVAZ inversion projects for unconventional plays worldwide.