Considerations Related to Drilling Methods in Planning and Performing Borehole-Geophysical Logging for Ground-Water Studies

摘要

The report reviews various aspects of drilling, sampling and borehole geophysicallogging that affect the effectiveness of well-log interpretation and the precision of well-log calibration using recovered samples, cuttings, or driller's logs. Because well logs are designed to measure the properties of geologic formations in situ, borehole conditions and the disturbances introduced by drilling are some of the most important factors controlling the effectiveness of geophysical logs in characterizing the hydrologic properties of rocks and sediments. The report reviews the operating principles and other factors related to commonly run geophysical logs that are likely to determine the accuracy and effectiveness of measurements made in boreholes. Geophysical logging tools discussed in detail are caliper, gamma, gamma spectral, gamma-gamma, neutron, electric, acoustic velocity, acoustic televiewer, temperature, and flowmeter tools. The report also reviews the various aspects of auger and hydraulic and air rotary drilling techniques that are most likely to affect logs, and lists some of the ways in which the drilling program can be modified to improve log quality in certain geological environments.