Chapter 12: Downhole Applications of Geophysics
Introduction Many geotechnical, environmental, and hydrological investigations require information about soil, sediments, bedrock and groundwater. Boreholes are drilled to investigate these materials in the subsurface, and borehole geophysical measurements are one of the primary methods for determining subsurface properties. Borehole geophysics provides measurements of subsurface properties under in-situ conditions, with no missing samples, and using several different physical measurements. Some of these measurements can be directly linked to noninvasive surface soundings, and a number of new borehole geophysical techniques are under development.
Figures & Tables
Near-surface geophysics uses the investigational methods of geophysics to study the nature of the very outermost part of the earth’s crust. Man interacts with this part of the earth’s crust: he walks on it; he drills and excavates into it; he constructs structures on and in it; he utilizes its water and mineral resources; and his wastes are stored on and in it and seep into it. The very outermost part of the Earth’s crust is extremely dynamic-in both technical (physical properties) and nontechnical (political, social, legal) terms-which leads to both technical and nontechnical challenges that are much different than the challenges faced by “traditional” applications of geophysics for regional geologic mapping and for oil and gas exploration (see Chapter 2).