SIMPLE METHOD FOR DETECTING ANOMALOUS FLUID MOTIONS IN BOREHOLES FROM CONTINUOUS TEMPERATURE LOGS.

Above a critical Rayleigh number, the fluid in a borehole convects. The aspect ratio of the convective motions is commonly between four and ten as determined by temperature-time recordings at fixed depths in cased holes. Aspect ratios greatly in excess of this range indicate anomalous fluid-flow in the hole such as might be caused by exchange of fluid among aquifers. Such high-aspect ratios can be detected from a single continuous temperature-depth log by taking the difference between the temperature gradient over a short interval and that over a longer spanning interval and dividing this difference by the gradient over the longer interval. This provides a measure of the gradient error (GE) from which an aspect ratio (AR) can be calculated. GEAR logs are presented for a large and a small diameter hole and for a large-diameter partially cased hole containing a small-diameter tubing. Refs.