Mathematical models have been developed which successfully reproduce the response of the CNT-G neutron porosity tool to homogeneous formations. These models are based on the use of discrete ordinates and Monte Carlo techniques. This paper describes how the discrete ordinates models are being used to analyze CNT-G porosity response to:
bed boundaries between two semi-infinite homogeneous formations and
thin beds placed in otherwise homogeneous formations. Comparisons between bed boundary experimental measurements and corresponding calculations establish the validity of the modeling approach. In particular, features which occur at certain bed boundaries on field logs are accurately reproduced by the computations. The bed boundary calculations are repeated for several porosity contrasts to determine if the pattern of tool response is dependent on the magnitude of the contrast. The sensitivity of tool response to bed thickness is also investigated.
