geothermal resource potential of the safford-san simon basin, arizona

San Simon
Introduction
The San Simon area lies astride Interstate 10 in the southern Safford-
San Simon Basin and includes the small farming and railroad community of
San Simon.
Prior to extensive ground water withdrawal and attendant water table
lowering, the area had numerous thermal artesian wells, which were used for
irrigating crops.
Because the upper static water table was relatively deep
and the means for pumping from this aquifer was not feasible during the early
1900s, deep wells were drilled to tap an artesian aquifer, which was discovered
during drilling for water by the Southern Pacific Railroad.
Schwennessen
(1917) studied the geohydrology in this area and published data on these artesian
wells.
Thermal Regime
Schwennessen's data are used to determine the thermal regime of the area
prior to extensive ground water withdrawal. Figure 25 is a plot of well depth
versus surface discharge temperature of artesian wells reported by Schwennessen
(1917).
Wells with flow rates less than 10 gpm and an artesian head less than
3 m above the surface are not used. A linear relationship between the well
depths and the measured discharge temperatures exists, which has a slope or
temperature gradient of 46.6°C/km.
o
The surface intercept temperature is 18.5 C,
which is close to the mean annual temperature, l7 o C.
In the San Simon area,
these data indicate the general thermal regime of the basin is created by conductive
flow of heat through the basin-filling sediments.
This means that the
temperature of the confined aquifers increases systematically with depth.
69