Formation Evaluation Using Advanced Pulsed Neutron Tools

Abstract

Pulsed neutron log provides a valuable method of evaluating cased hole formations. It is commonly used to monitor reservoir performance and depletion over a long period of time. The tool can be used to monitor sweep efficiency during waterflooding and enhanced oil recovery stages. It can provide valuable data that can be used to fine-tune the simulation model predictions. Pulsed neutron tools are commonly run, in either capture or inelastic modes, to estimate time-lapse fluid saturation changes behind the casing they consist of one neutron generator and a number of gamma ray detectors at different distances from the neutron generator. The tools are run in different modes to investigate front movement and 2-phase/3-phase saturation profile under challenging borehole conditions. The older generation 2-detectors tool is highly affected by the borehole environment, and therefore saturation. The two new generation 3-detectors and 4-detectors tools seem better in detecting and quantifying the fluid saturation. Subsequently, the 3-detectors tool is seemingly the best in terms of delivering robust answers in complex and unknown borehole conditions. The log results from the new generation tools were useful for tracking the 2-phase/3-phase fluid front movement, identifying swept intervals. This paper compare the design and implementation of the different pulsed neutron tools generations, limitations and operational issues, and log results interpretation