Abstract
All unconventional gas plays rely on the presence of natural fractures to enhance or create permeability in the reservoir. Fractures cause significant, measureable changes in 3D seismic data. These changes appear as variations in seismic amplitudes and velocities with shot-receiver azimuth and are known as seismic azimuthal anisotropy.
Examples of the seismic identification of fractures are shown for a Mannville Coal and gas shale from Alberta, and the tight gas sands of the Pinedale Field in Wyoming, which is an analog to Alberta's Deep Basin. In the latter example, seismic fracture estimates are shown to be the best predictors of well EUR (Estimated Ultimate Recoverable) and therefore they are used to predict EUR in 3D.
The technology to measure seismic azimuthal anisotropy is now well developed and ready to be used to pinpoint higher producing areas of natural fractures in fractured unconventional gas reservoirs such as tight gas, gas shales and coalbed methane.
Seismic azimuthal anisotropy measurements have achieved a technical success rate for identifying fractures upwards of 80% in unconventional gas plays. This can significantly impact drilling success in areas where success rates are low. These measurements also indicate the probable fracture strike and so, by identifying where the gas is coming from, they can be used to avoid drilling into depleted pools.
