On the thermal instability of large diameter wells; an observational report

A fluid in a tube subjected to a thermal gradient will be stable as long as this gradient does not exceed a certain critical value. Observational evidence is presented that the fluid in large diameter wells, such as oil wells, subjected to the normal geothermal gradient is, indeed, unstable as predicted by the theory. Our independent observations support the evidence presented by Diment (1967) in a companion paper.