WELL LOGGING METHOD FOR DETERMINING THE PRESENCE OF ALUMINUM AND MAGNESIUM

摘要

An activation well logging method for determining the presence and quantity of aluminum and magnesium in formations surrounding a borehole. The formations are irradiated with 14 mev neutrons which produce aluminum and magnesium activity with half lives of 20 milliseconds and gamma ray energy of 473 kev. The neutron source is turned on for a period of time sufficient to activate aluminum and magnesium and then turned off for 20 milliseconds. During the first 4 milliseconds while the source is off, no measurement is made. During the remaining 16 milliseconds, pulses are counted which fall in the amplitude range representing gamma ray energies from 450 kev to 500 kev. The rate of occurrence of these pulses is an indication of the aluminum and magnesium content of the formation. To correct for undesired background, the rate of occurrence of pulses in the energy intervals immediately above and below the 450 to 500 kev interval is determined and subtracted from the 450 to 500 kev measurement.