Abstract
A unique attribute of nuclear magnetic resonance (NMR) logging is the ability to measure a lithology-independent porosity. New NMR tools have generated renewed interest in measurements related to producibility, such as permeability and definition of water production potential. Industry discussion of those parameters has sometimes overshadowed the value of a lithology-independent porosity measurement. Such a porosity log can be easily understood by and utilized by non-specialists as well as log interpretation experts. The log reflects true porosity even in a complex lithology that changes over the well interval, such as limestone to dolomite transitions with evaporite inclusions. Similarly, since the log reads near zero in compacted shale, the measurement closely approaches effective porosity in clastic environments.
A new pad-type NMR logging tool produces such a porosity measurement with excellent vertical resolution. Investigation is focused within a volume whose vertical dimension is only 6 in. Examples from a number of wells illustrate excellent repeatability and resolution of thin reservoir components that are not visible with other NMR devices or conventional porosity logs. Logs are verified by core data and electrical images. The measurement is unaffected by borehole salinity, and the tool is combinable with other wireline tools.
