Abstract
In the oil field, exploration of the subsurface through well logging provides measurements of the characteristics of rock formations and fluids to help identify and evaluate potential reservoirs. Downhole nuclear measurements focus on formation properties such as natural radioactivity, formation density, and hydrogen content, as well as the identification of the elemental and mineralogical composition of the rock through spectroscopy. Accurate nuclear modeling is a fundamental part of nuclear well logging tool development, from concept through design to response characterization. Underlying the accuracy of nuclear modeling is a good knowledge of nuclear cross sections of the elements in the tool, borehole, and subsurface formations. The recent focus on replacing tools based on radio-isotopic sources with those based on D-T neutron generators opens many opportunities for new measurements but highlights the deficiencies of current cross sections. For example, in neutron-induced inelastic and capture gamma ray spectroscopy, major obstacles come from a lack of or inaccuracies in the cross sections of essential materials.
Highlights
In the oilfield industry, exploration of the subsurface is essential to answer questions regarding location, type, and quantity of hydrocarbon as well as its producibility
With the introduction of pulsed neutron generators, new measurements have been developed such as capture and inelastic gamma ray spectroscopy, which directly measure elements in the formation including carbon
We focus only on the gamma-ray spectral shape as the absolute amplitude of neutron capture and inelastic cross sections are of secondary importance for this application
Summary
Exploration of the subsurface is essential to answer questions regarding location, type, and quantity of hydrocarbon as well as its producibility. The downhole drilling environment can be severe: these tools must work at temperatures that may exceed 175 oC, are exposed to repeated shocks of 100 g or more, and must be protected by housings withstanding downhole pressures of 2000 atm or more. In these difficult environments, delivering accurate and reliable measurements is a challenge [1]. The latest major release of the evaluated nuclear reaction data (ENDF) library [4] has major changes in neutron reaction cross sections for isotopes of interest in well logging
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