Abstract: An underground logging tool is equipped with a gamma ray detector encircled by a rotatable shield featuring a collimator slot. After the fluid in a formation is activated by a neutron source, the detector is used to obtain radiation count information as a function of horizontal direction as the shield is rotated. Comparison of count rate data as a function of the shield slot orientation gives information concerning the direction of the formation fluid flow. Measurements at different time intervals following the activation of the fluid, made with the shield retracted from the detector, may also be interpreted in terms of speed of horizontal fluid flow past the tool.

Abstract: According to the method of the present invention a well cement having a high thermal neutron capture cross section is used when cementing the well casing in place. This, possibly together with the use of other high thermal neutron capture cross section materials in the borehole, such a highly saline borehole fluid and/or high thermal neutron capture cross section material sleeves on the well logging sonde, increases the effective depth of investigation of thermal neutron lifetime well logging instrumentation.

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.

Abstract: Disclosed is a system for nuclear well logging in which neutron pulse time duration for a high energy neutron generator and the frequency of pulses are selected downhole in the tool by use of a coded signal transmitted by the cable from the earth's surface. Separate channel systems are provided in the downhole tool for desired neutron pulse width and repetition frequency and are operated by a decoder system. Additionally, the accelerator voltage on a high energy neutron generator is controlled by a downhole switching system to selectively obtain different neutron output in response to coded signal transmissions. Moreover, provisions for obtaining different timing pulses to control gates for sampling signals generated in the tool are provided.