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KIRTLAND AIR FORCE BASE ALBUQUERQUE, NEW MEXICO ...

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APPENDIX B<br />

collisions with hydrogen, neutron count rates represent the hydrogen content of the formation and can be<br />

interpreted in terms of porosity. This measurement can be compensated by using two different sourcedetector<br />

spacings and taking the ratio of these measurements.<br />

The neutron measurement uses a 1 or 3 curie AmBe-241 radioactive source. The neutron log can be<br />

presented in counts per second or porosity units. A casing collar locator measurement is a standard<br />

addition to the neutron log for well work.<br />

Borehole Video Survey<br />

The video survey utilizes a specialized closed-circuit system capable of visually inspecting boreholes.<br />

The picture image is recorded to a VHS videocassette through a professional video cassette recorder and<br />

then viewed for interpretation on a high-resolution monitor.<br />

The survey is usually performed from the surface downward in order to minimize the disturbance in the<br />

borehole fluid. Depth is recorded to the nearest one-tenth of a ft and displayed on the image. Logging<br />

speed is variable. A borehole video survey can be performed in an open well or in a cased well that is<br />

dry or contains clear fluid.<br />

Borehole Deviation<br />

Borehole orientation (azimuth and inclination angle) measurements are made with a magnetic based<br />

digital probe. The inclination angle is acquired with accelerometers and can be measured inside metal<br />

casing in addition to an open hole. The azimuth readings may be affected inside ferrous casing.<br />

Induction Measurement<br />

A small transmitter coil in the borehole probe induces eddy currents in the surrounding geologic material.<br />

The eddy currents generate a secondary magnetic field in the geologic materials. The strength of the<br />

magnetic field is controlled by the electrical properties of both geologic materials and groundwater. A<br />

receiver coil in the borehole measures the strength of the quadrature component of the secondary<br />

magnetic field and electronics in the instrument console convert the magnetic field strength to values of<br />

conductivity. A focusing coil in the borehole probe causes measurement sensitivity to peak about 12<br />

inches away from the borehole axis; consequently, borehole effects are minimized and the measured<br />

electrical conductivity responds to formation and groundwater changes.<br />

Drift and noise are typically less than 1 millisiemen per meter and conductivity changes of a few percent<br />

are easily resolved. The intercoil spacing resolves conductivity layers 20 inches thick. The system may<br />

detect layers that are thinner than 20 inches; however, the measured value is the product of conductivity<br />

contrast times layer thickness.<br />

The borehole induction system measures bulk conductivity resulting from the electrical properties of<br />

geologic materials and contained groundwater. In general, conductivity will increase as clay content<br />

increases and as ionic strength of groundwater increases. It may be difficult to identify contaminated<br />

groundwater in sediments that contain variable amounts of clay. In these environments, comparison of<br />

conductivity logs to natural gamma logs may enable discrimination between clayey sediments and zones<br />

of contaminated groundwater. However, it is important to note that very small variations in clay content<br />

may result in large changes in conductivity. These small variations in clay content may not be resolved<br />

with natural gamma log.<br />

Kirtland AFB<br />

SOPs for Field Investigations B-32 April 2004

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