The Capability of Pulsed Neutron Capture Logging To Determine Oil and Gas Saturations

Abstract

Abstract The capability of current pulsed neutron capture logging technology for determining oil and gas saturations has been investigated. The currently advancing technology provides more accurate saturation determination, leading to better reservoir management and hence more economic production than hitherto. Experiments have been carried out at our laboratory test facility with various commercially available logging tools. This has increased our understanding of the physical processes in pulsed neutron capture, such as the diffusion of thermal neutrons. The derived log value depends strongly on the way these effects are taken into account in the processing. Examples are shown of the results of various processing techniques. The comparison between different tools has led to recommendations for field applications. In addition to the experimental work, the basic tool response (the pulsed neutron decay) has been numerically simulated. With a Monte Carlo simulator, the detector count rates were modelled for several combinations of formation and borehole contents. In addition, the influence of porosity on the tool response has been investigated. In this way, the conclusions from the experimental results were extended. The details of a number of pulsed neutron capture tools were studied. As a result of these studies, a reprocessing technique was developed for one of these tools to simulate the log that would have been obtained by its predecessor. This enables time-lapse comparisons of the logs from the new generation of tools with previously obtained logs.