A Simple Method for Detecting Anomalous Fluid Motions in Boreholes from Continuous Temperature Logs

Abstract

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 hold 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 different 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) form which an aspect ratio (AR) can be calculated. GEAR logs are presented for a large and small diameter hole and for a large diameter partially cased hole containing a small diameter tubing. We attempted a preliminary assessment of the value and applicability of GEAR Logs to the detection of fluid flow in and about geothermal wells.