Z.M. ZAAFRAN
Dept of Petroleum Engineering
Riyad University
Saudi Arabia
ABSTRACT
Investigations carried out in the laboratory on horizontally and vertically oriented sandstone specimens collected from two different areas in England and Saudi Arabia have indicated a distinct anisotropy of the formation resistivity factor. It is suggested that this anisotropy effect may be an indication of attributable orientation of the specific conducting minerals. The derived layer thicknesses as obtained from the quantitative interpretation of resistivity logging and surface soundings were found to have been overestimated by a factor equal to the coefficient of anisotropy, when they were compared with borehole data.
In the light of the foregoing, some degree of caution therefore needs to be exercised before a quantitative evaluation of reservoir rocks is considered.