THERMAL INJECTION TESTING OF
William M. Turner, Ph.D.
In the analysis of aquifer-performance test data, it is desirable to know which part
of the aquifer has the highest hydraulic conductivity and will yield water at the
highest rate to a well. Many workers have tried to develop in-hole flow meters based
on different principles. They all have drawbacks.
From the analysis of aquifer-performance-test data collected from an irrigation well
and a number of observation wells located at the village of Carrizal in the Santa Elena
Peninsula of Ecuador, AGW scientists suspected that, although 160 feet (49 m) of detrital
material was reported in the driller's log, the part of the aquifer contributing water to
the irrigation well was very thin. To gain additional information, a thermal
injection test was performed using the irrigation well. The well is screened
throughout the total thickness of the aquifer.
If water, at a temperature different from the temperature of water in a well column, is
introduced rapidly into the well bore, it displaces water in the well and forces it into
the aquifer. For a well, screened throughout the aquifer, the part of the aquifer with the
highest hydraulic conductivity will accept the greatest mass of water and will act as the
strongest heat source or heat sink, depending on the temperature of the injected water
relative to the natural temperature of the aquifer adjacent to the well. The part of
the aquifer which requires the longest period of time to reestablish thermal equilibrium
will be the zone of greatest hydraulic conductivity. Repeated temperature logging of
the well following injection of the slug of water will reveal this zone easily.
AGW scientists measured the temperature profile of an irrigation well at Carrizal using
equipment designed and built by AGW scientists. Our equipment can resolve 0.005
We filled a 3,000-gallon (11.4 m3) tank truck with shallow water from a hand-dug well
near the village of Barcelona about 2 km downstream from Carrizal on the Rio
Valdivia. We then flowed the water from the tank into the Carrizal well at an
injection rate of about 95 gpm (6 l/s).
Typical Injection Setup.
Temperature profiles measured after injection showed that a zone, beginning at the
water table and extending downward about 16 feet (5 m), required the longest period to
cool. We interpret that this zone has the greatest hydraulic conductivity. The
remaining 144 feet of alluvial material shown on the driller's log did not produce water.
The results of the thermal injection test confirmed the interpretation of the
aquifer-performance test and identified that the part of the aquifer which contributed
most water to the Carrizal well is very thin.