Radiation Source Use and Replacement Abbreviated Version (2008) / Chapter Skim
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9 WELL LOGGING
9 WELL LOGGING
Pages 147-158
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From page 147... ...
As the string is raised, the sensors measure some or all of the following properties as functions of the depth: electrical resistivity, electron density, sound velocity, neutron moderation, thermal-neutron absorption, natural and artificial (induced) radioactivity, gamma-ray spectra, Compton scattering, borehole dimension, and occasionally nuclear magnetic resonance.
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From page 148... ...
to examine the earth formations surrounding the well and sensors to detect the media's response to interrogation tools. An analyst examines detector logs to look for some or all of the following parameters of the formation: formation water saturation, porosity, rock characteristics, carbon/oxygen ratio, and permeability.
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From page 149... ...
The tools are described in the sections that follow, first the nonnuclear well logging tools and then the nuclear well logging tools. NONNUCLEAR WELL LOGGING METHODS There are many nonnuclear well logging tools, including acoustic arrays, various resistivity tools, nuclear magnetic resonance tools, and formation pressure logs.
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From page 150... ...
SOURCE: Provided by committee. Occasionally, a dielectric constant tool, which measures the electrical permeability of the formation materials, is also used to help in identifying formation water content and rock types.
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From page 151... ...
The technique is effective in measuring properties related to fluids, including the saturated porosity of the formation and the size of the pore spaces containing fluids, which in turn provide information about the permeability of the formation. Because of the dropoff in magnetic field amplitude over distance, the attenuation of fields in geologic media, and the mud on the walls of the borehole, nuclear magnetic resonance gathers data only on media in very close proximity to the well bore.
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From page 152... ...
Radionuclide neutron sources are typically used for measurements of porosity and elemental analysis logs. The carbon to oxygen ratio (C/O)
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From page 153... ...
The neutron moderation tool and the mineral or elemental analysis tool typically use the radionuclide neutron sources because these tools are more effective if the initial neutron energy is lower. Neutrons emitted by Am-Be sources have energies substantially lower than D-T fusion neutrons (average energies around 4 MeV versus 14.1 MeV)
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From page 154... ...
Changing the sealedsource part of the accelerator is an added expense for oil-well logging companies, but this expense is justified because the pulsed, high-energy neutron source is advantageous. Note that there are some liabilities associated with accelerator sources, including the need to keep two tools on hand at any job site in case of tool failure and the regulatory and logistical burden caused by the dual-use nature of the D-T neutron generators (see Sidebar 9-1)
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From page 155... ...
can be used as a trigger for a nuclear explosive device, it is dual-use nuclear equipment and subject to the Export Administration Regulations, administered by the Department of Commerce. Federal regulations impose requirements on both domestic and international shipments and use of these accelerator-based neutron sources.
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From page 156... ...
. Even with the high cost of Am-Be sources, both the D-T accelerator neutron source and the californium-252 neutron source face a significant obstacle to being adopted more broadly within the well logging industry: The analyses of well logging data rely on a large body of data that has been accumulated for the porosity logs using Am-Be sources.
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From page 157... ...
such as the Nuclear Logging SIG, to address the technical obstacles to implementing replacements for the americium-beryllium sources used in well logging and the challenges of data interpretation. The group should decide what obstacles are most important, but the issues might include development of new reference standards for these replacement tools, examination of the response of these tools relative to the americium-beryllium tools, and exploration of any differences in response when the replacement tools are used in combination with other nuclear and nonnuclear well logging tools.
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