Applications Of The Compensated Spectral Natural Gamma Tool

Abstract

The Compensated Spectral Natural Gamma tool is a new generation natural gamma ray spectroscopy logging system which utilizes the complete energy spectrum to give information on the borehole environment as well as the concentrations of potassium (K), uranium (U) and thorium (Th) in the formation. The novel hardware and software features of the CSNG tool are demonstrated using log examples. The elemental concentrations are estimated from the window count rates using the method of weighted least squares which incorporates real-time compensation for borehole effects. This is accomplished by using an attenuation model which accounts for count rate reduction and spectrum shape changes due to borehole absorption and scattering. The value of this compensation technique is shown by logs which were made in wells both before and after casing was set. These examples show that the computed K, U and Th concentrations agree within the measurement uncertainties.