Abstract: Normalization and/or Neutron-to-Porosity Transforms for Large Collections of Log Data

David J. Maness

Electric logs can be used to make many maps in addition to structure and isopach maps. Some of these include net and gross reservoir thickness, average gamma ray, and porosity-feet maps. Such maps are meaningful only if the log readings reflect geological and/or petrophysical variations and not tool variations. Normalization is a straightforward approach to correct for tool variations. Normalization requires identification of two uniform zones reflective of the endpoints of the log readings and determination of the normal values of each zone. The normal value may be a single number or may vary in a systematic manner across the geographic study area. Each zone in the log being normalized is shifted to its normal value and all other points are linearly interpolated and/or extrapolated a cordingly.

Conversion of old neutron logs to porosity logs is a variation of the normalizing process, where the two endpoint log readings represent a highly porous zone and a low porosity zone and the transform is from a linear to logarithmic scale.

Enhancement of an existing computer program now permits rapid normalization of large collections of logs. Maps made from the resulting normalized logs more accurately reflect geologic variations in the formations being investigated.

AAPG Search and Discovery Article #90984©1994 AAPG Annual Convention, East Lansing, Michigan, September 18-20, 1994