Development of Neutron Generators to Replace AmBe Radionuclide Neutron Sources in Oil/Gas Applications

摘要

~(241)AmBe (α,n) radionuclide ("chemical") neutron sources are used extensively in the oil/gas industry for new and existing well exploration and evaluation for oil and gas. ~(241)AmBe sources pose several issues with respect to intentional or accidental diversion and/or use as a radiological dispersal device with a 433-year half-life. For this and several other reasons, development of an alternative source is needed as an option for eventual radionuclide source removal. Electronic neutron generators have been used in the oil/gas industry for many decades; however, they rely on the D-T reaction that produces a 14-MeV neutron that is far from the Am-Be spectrum and still require extensive licensing, insurance, security and disposal costs. This combined with the additional expense for detector tooling redesign and field re-calibration as inhibited adoption. A favored approach is going with a D-D reaction-based unit to avoid radioisotope issues and yield a softer neutron energy more comparable to the Am-Be spectrum for porosity tooling; however, this requires more power and/or vast increase in the reaction efficiency. Other reactions produce a spectrum much more like Am-Be, but require rethinking the approach. This paper discusses ongoing efforts partially-supported by prior DNDO and DOE projects to develop a non-radioactive, tritium-free neutron generator for oil/gas well applications to replace Am-Be radionuclide sources. Part of this effort is generating neutrons in excess of 4 MeV without the use of tritium. The primary approach is a le7 DD n/s generator that works in the 1-11/16" form factor for direct replacement of 4 Ci Am-Be sources in slimline applications for both oil/gas and environmental logging. Another for higher output and/or higher energy neutrons to better simulate the Am-Be neutron spectrum is larger, but consistent with existing 16 Ci tool dimensions.