Measurements from pulsed neutron devices have been available via wireline conveyance for more than three decades. Based on recent technology developments, their use has now been expanded to the logging while drilling (LWD) environments. Pulsed neutron generators (PNGs) are electronic devices that produce high energy neutrons without the use of traditional chemical sources. Measurements available for the first time from a commercial PNG-based LWD service include neutron-gamma density (NGD) for bulk density and density porosity.
Extensive testing for neutron-gamma density was conducted in a diverse range of environments. Therefore, NGD was put under a benchmarking process against traditional gamma-gamma density (GGD). Consequently, comparing results from both density measurements will allow us to assess the quality of NGD measurement and its limitations; and ultimately qualifying it. Factors such as the invasion and presence of gas or light hydrocarbons may influence the GGD-NGD comparison.
Results from various field testing of the NGD measurement while drilling that were recorded in a wide range of environmental conditions and formations indicate that in some cases, they require additional work to accurately characterize the measurement for quantitative analysis. Advantages and limitations of this measurement while drilling (NGD) technique will be highlighted and illustrated in the paper.