20 C. E. VAN ORSTRAND 
formation in regard to the time required for a 2-inch diamond-drill 
hole to regain thermal equilibrium. The first curve represents the tem- 
peratures after drilling has been discontinued for about 30 days. The 
curves show clearly that the best records in a rotary hole are to be ob- 
tained a few hundred feet above the drill. This result is to be expected 
as the time during which the water has been in circulation is a min- 
imum in this portion of the well. 
Errors of an entirely different character appear in producing or 
depleted fields. Here the discharge of fluid from the producing sands 

SS 












tr 
\ 
CooL 
PS 
\ ~o4 
TEMPERATURE °FAMRENHE/T 





D Mean Annyal Temperature 
° Cc 
§ g 8 
DEPTH — FEET 

40 
250 
1500 
1,750 
2,000 
Fic. 4.—Depth-temperature curves. Diamond drill hole No. 79. Cop- 
per Range Consolidated Copper Company. Location, 1,740 feet south, 
2,340 feet east, NW. corner, Sec. 1, T. 53 N., R. 35 W., Houghton 
County, Michigan. 
tends to lower the temperatures immediately above and below the 
sand and to elevate those at the higher levels. Thus, wells that have 
been pumped rapidly for a long time, invariably show a marked rise 
of temperature near the surface of the ground. Furchermore, the re- 
placement of gas and oil in the sands with water may so completely 
alter the thermal conductivity and heat-generating properties of the 
sands that the original temperatures are never restored. 
RESULTS OF RECENT GEOTHERMAL SURVEYS 
The American Petroleum Institute (19) has completed’an exten- 
sive series of geothermal surveys extending over a period of about 5 
years. More than 400 wells were tested in the states of Kansas, 
542 
