In recent years there have been increasing market pressures and hints of regulatory changes that would require the total elimination of traditional nuclear well logging sources for downhole applications. There are a number of reasons why replacement of isotopic sources would be desirable, and a considerable effort has been expended discussing and researching the possibilities. The dialog has taken place at every level from internal research and development activity at individual companies and laboratories, through discussions among larger groups at technology forums and special interest group meetings, all the way to congressional hearings and formal Nuclear Regulatory Commission reports to the President of the United States. The issue is not just the replacement of the Americium- Beryllium neutron logging source, but of the Cesium- 137 source as well. Various service-company and operating-company groups have been wrestling with this problem for at least 30 years, and yet no acceptable replacement for the traditional Cesium gamma-gamma density measurement has been fielded. There are some services that produce a density curve using pulsed neutron generators, but none of these provides the accuracy and precision of the traditional sourced measurement. The gamma-gamma density measurement is the most trusted porosity indicator for reserves estimation around the world, and the lack of a viable sourceless alternative creates a problem for the industry. The fact that formation density and neutron porosity measurements are used for much more than just formation porosity complicates the issue considerably. This paper examines some of the potential benefits of using neutron generators and high energy photon sources in well logging. Pulsed neutron generators can be used for a number of measurements in addition to neutron porosity, and these additional data can be significant going forward. The potential for high- energy electronically controlled photon generators is truly great if we can produce measurements of quality comparable to the traditional Cs-sourced tools, and if we can get them to work in the downhole environment. We will also examine some of the difficulties involved in making all of this happen. There are significant hurdles that must be overcome to produce the necessary enabling technologies required to provide the level of reliability, accuracy, and precision that we have become accustomed to with the traditional sourced tools. We will discuss some of these issues and attempt to suggest a course forward.
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