Recent developments in pulsed neutron instrumentation open up new opportunities for petrophysical surveillance. Understanding the relation between a nuclear attribute and a recovery mechanism is a key element in selecting the appropriate running mode for a specific instrument. Developing a nuclear modelling capability allows us to screen various nuclear attributes for a given environment taking into account, specific rock, fluid and completion conditions to investigate the sensitivity of attributes to different recovery scenarios.

There are a limited number of experimental tests pits limiting our ability to replicate the complexity of nuclear attribute responses to the variety of fluid displacements and well completions. Imperfections with cement and gravel pack further complicate the nuclear attribute response and should be taken into account during the nuclear model process. Benchmarking the nuclear models against controlled environments (man-made defects) provide some confidence in utilising nuclear forward modelling to design the logging program ahead of the job. This allows us to optimise rig time and maximise the data acquisition during well work opportunities.

This method can be used in feasibility studies and petrophysical interpretation utilizing nuclear tools in different areas of petrophysical surveillance. Nuclear modelling can help to engineer gravel pack (specify the amount of Gadolinium enrichment), define the nuclear attributes that can be further used for gravel pack evaluation, and can also help in selecting the right tool from suppliers for monitoring multicomponent fluid saturations. In this paper we present some case studies to illustrate the application of nuclear modelling in the selection of attributes and tools for completion and reservoir surveillance.

The results from experimental tests provide us with confidence in the quality of results from nuclear modelling. A robust model requires detailed information from core, fluids and completion.

While all multidetector pulsed neutron instruments utilize the same physical principles and record similar basic measurements, there are differences due to tool geometry, electronics and interpretation algorithms. Screening nuclear attributes and selecting the appropriate tool for the job has a significant impact on rig time and acquiring quality data. Improving the quality of the acquired data will have a direct impact on the quality of the calculated results which will in turn lead to more effective well work and reservoir management.

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