1962 Paper L

NUCLEAR MAGNETISM LOG FIELD TEST RESULTS

BY

R. E. WYMAN

Shell Development Company (A Division of Shell Oil Company), Exploration and Production, Research Division, Houston, Texas - (Publication No. 299)

ABSTRACT

Nuclear magnetism measurements have been made on subsurface strata of different types. These field tests demonstrated that of the two independent parameters derived from the measurements, the free fluid index (FFI) was the more useful. The FFI indicated permeable zones generally without regard to borehole fluid, formation fluid, or formation rock. The magnitude of FFI is a value which approaches total porosity in clean formations but excludes porosity from clays. It was concluded that a positive FFI indicated that fluid was present and normally could be produced. Absence of a free fluid signal did not necessarily indicate that no permeable rock existed; the FFI signal could be reduced or eliminated opposite a reservoir by such factors as excessive ferromagnetic material in the formation, severe hole caving, or exceptionally heavy oil.

The other parameter measured by the nuclear magnetism log was the thermal relaxation time (T1). From these field tests it was concluded that a long T1 indicates hydrocarbons and (or) a very permeable formation.

Nuclear magnetism measurements are potentially useful because they provide an indication of permeable fluid-bearing zones which is not presently obtainable from any other logging tool. The limited number of nuclear magnetism logging tools available is a handicap in developing interpretation techniques.