Determination of Foliation and its Influence on the Fracture System in Basement Rocks using Borehole Image Log Data.

Christian Rambousek¹ and Kurt Decker^2
1Fronterra Integrated Geosciences
²University of Vienna

Foliation describes a pervasive planar feature within a rock. It does not occur as an individual feature such as fractures but rather affects the entire host rock. (Milnes et al., 2006). The anisotropy of rocks caused by foliation as well as the influence of foliation to the fracture network has been dramatically underestimated in the past. By analyzing borehole image data of over 25 wells in fractured basement reservoirs, we could show that this influence is evident and that anisotropy effects caused by foliation do have an effect on the mechanical properties of the rock mass. Anisotropy: It is assumed that an intact, non-foliated rock is isotropic and therefore will have the same stiffness (Young’s Modulus) regardless of directional stress. Since foliation adds anisotropy to the rock, the Young’s Modulus and strength values will change depending on the direction of stress relative to the foliation.

AAPG Search and Discovery Article #90152©2012 AAPG Southwest Section Meeting, Fort Worth, Texas, 19-22 May 2012