Pulsed neutron capture logs have long provided a means of determining water saturation and estimating porosity of formations behind casing. Recent technological advances in pulsed neutron logging have resulted not only in improvements in saturation and porosity data, but also in the capability to provide information regarding water entry and flow, lithology, and improved differentiation of gas-filled zones from tight formations. These advances provide greater accuracy in reservoir evaluation and monitoring as well as improved completion and production diagnostics.
Inelastic, capture, borehole, and background spectra are now utilized to enhance porosity estimates, identify water flow, and help determine lithology. Modular tool design allows the pulsed neutron tool to be combined with production logging tools for more reliable production diagnostics. Simple tool modifications permit quantitative measurements of water velocity and borehole oil holdup. The modular design also allows additional detectors to be placed in the toolstring for lithology identification and gravel pack evaluation.
This paper discusses this new pulsed neutron capture technology and gives an overview of the expanded range of pulsed neutron applications. Field examples of waterflow detection, gravel pack evaluation, oil/gas discrimination, and conventional analysis are presented from offshore wells in the Gulf of Mexico and from onshore wells in Mexico and the U.S.