An Assessment of Fundamentals of Nuclear-Based Alternatives to Conventional Chemical-Source Bulk-Density Measurement

作者：Badruzzaman Ahmed^*

来源：Petrophysics, 2014, 55(5): 415-434.

Key physics aspects of two proposed safer alternatives to Cs-137-based gamma-gamma density (GGD) concept, along with their interpretation and tool-design implications, are examined using Monte Carlo simulation of the attendant radiation transport. One alternative uses Bremsstrahlung X-rays from an electron accelerator (LINAC). The other injects neutrons from a 14-Mev neutron generator and uses gamma rays produced from inelastic scattering of high-energy neutrons. Each has exhibited distinct challenges in interpreting the bulk density thereby requiring complex design choices, corrections, or both. The paper studies the basic physics-based causes of the challenges, and explores the question: can these alternatives indeed replace the Cs-137-based GGD? The analysis reported in the paper indicates that the basic density response of Bremsstrahlung X-rays would be much closer to that of Cs-137-based gamma rays; both are based entirely on photon physics through Compton scattering. This illustrates that a direct-photon generator-based GGD can potentially replace the Cs-137-based GGD. The basic density response of inelastic n-gamma photons is significantly coupled to the underlying neutron physics and associated complexities, and thus is not fully Compton-like. The resulting inelastic n-gamma density is unlikely to be a general replacement of Cs-137-based GGD, but rather a pseudo-density, useful only in conditions where GGD is either unavailable or unobtainable, and that too, if the issues discussed in the paper are satisfactorily addressed.

• 出版日期2014-10