1965 Paper I-H

THE EFFECTS OF FLUID INVASION IN PULSED NEUTRON LOGGING

BY

L. S. Allen, W. R. Mills, and R. L. Caldwell Socony Mobil Oil Company, Inc. Field Research Laboratory Dallas, Texas

ABSTRACT

Multigroup neutron diffusion theory is used to study the effect of fluid invasion in pulsed neutron logging. The transient 3-group equations are solved numerically on an IBM 7090 digital computer. Two cases of fluid invasion are investigated: fresh water filtrate invading a salt-water-saturated formation and salt water filtrate invading a fresh-water-saturated formation. In both cases the formation is assumed to be a 20 per cent porosity sandstone. It is shown that the depth of investigation is significantly influenced by the type of filtrate invading the formation.