Simultaneous thermal neutron decay time and shale compensated chlorine

Abstract

Earth formations surrounding a well borehole are repetitively bombarded with bursts of high energy neutrons. A radiation detector in a sonde in the borehole senses the gamma rays induced by the capture of thermal neutrons and sends representative signals to the surface. At the surface electronics, the population of thermal neutron capture gamma rays at two separate and distinct times is measured. The macroscopic thermal neutron capture cross section of the formation may be thus determined and logged. Further, two additional single channel energy analyzers, such as from 1.30 to 2.92 Mev and from 3.43 to 10.0 Mev, sense formation capture gamma ray response over a common time interval following each neutron burst. The measurements made in these two additional single channel analyzers are used to distinguish between the presence of salt water and hydrocarbons in the formation, which is also logged.