Anisotropic Earth Models Improve Completion Design

Bratton, Tom
Schlumberger, Greenwood Village, CO

     Isotropic earth models have been the standard in the industry for more than 30 years; not because isotropy was a good assumption, but because 3-dimensional anisotropic logging measurements were unavailable. Today, 3D anisotropic measurements are available, and the derived anisotropic earth models are beginning to impact completion design. To illustrate the improvements, case studies from tight gas-sand plays in the Rocky Mountains will be presented. These case studies show how to identify and quantify anisotropy and how this new information should be used to improve the completion design.
     Laboratory measurements on recovered core often show differences between the horizontal and vertical rock properties. The corresponding horizontal and vertical elastic moduli can now be measured with new sonic logging techniques. This is leading to improved correlations between logs and core. In addition, zone containment is often breached when sandstones are stimulated. Isotropic stress models applied to anisotropic formations do not predict either the correct stress or the correct stress contrasts between layers. A calibrated anisotropic stress model provides a stress profile which better defines zone containment and changes the perforating and staging strategy. The primary application for this method is improved completion design. The technical contribution to the industry is a better quantification of stress profiles in anisotropic formations.

AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah