Measuring the temperature in a well is useful for determining the Earth's gradient at that location. Reviewing the gradient (change in temperature over the change in depth) gives clues as to what is happening underground. When comparing multiple wells in a close proximity, the subtle movements of water, gas, air and the transfer heat are noticeable.
Certain patterns are identifiable once there is an understanding of how temperature reacts to different mediums and situations. The following sections give examples of how temperature -depth curves can differ and what these differences mean.