52 SURFACE MACHINERY AND METHODS FOR OIL-WELL PUMPING.
electric motors are used at single wells to pump, clean, swab, and
In some oil fields it may be cheaper to install electric motors, power
lines, and transformers using electric power purchased from a power
company than to install and operate steam, gas, or oil engines.
Often the operators in an oil field could get cheaper power by erect-
ing a central electrical power plant, large enough to meet all of their
power requirements. This would save duplication of expense in run-
ning many smaller power units and would mean a smaller investment
cost per horsepower generated and a broader range of distribution
for maintenance charges and depreciation. It would ultimately
mean less cost per horsepower generated. However, before such a
plant is built, those contemplating its construction should be satis-
fied that the economies gained will provide for depreciation of plant
and the interest and dividends on the capital invested.
The ordinary type of slide-valve engine used for this service has
a low thermal efficiency as is shown in the following comparison of
gas consumed per horsepower-hour by it and other types of engines.'4
Cubic feet gas per
Type of engine. horsepower-hour.
Large natural-gas engine, highest type________________---------- 9
Ordinary natural-gas engine __.._-___ ____ ____ 13
Triple-expansion condensing steam engine _____ 16
Double-expansion condensing steam engine___________________________--- 20
Single cylinder and cut-off steam engine__ 40
Ordinary high pressure, without cut-off, steam engine____________________ 80
Ordinary oil-well pumping steam engine_________________________________ 130
A steam engine should have a boiler station close by in order to
minimize the steam loss due to exposed steam lines. However, the
steam engine is highly flexible and can be operated at 30 to 130 per
cent of the rated load at efficiencies close to the maximum efficiency
of the engine.
The writer recently saw a set of four 70-horsepower boilers, built
to furnish steam to the engines of 10 or 12 wells pumping on the
beam. Some of the 22-inch steam lines leading to the individual
wells were 1,600 or 1,800 feet long, but all were well insulated.
When asked for the reason for using steam engines instead of gas
engines in this oil field of ample gas supply, the general superin-
tendent gave the following information:
The wells in this particular field flow with great violence and as a result
enormous quantities of heavy wet gas settle in the canyons and behind the
small hills in dead air Spaces. This necessitates locating a central power
plant at a point on a hill less likely to be within this gas zone.
14 Westcott, Henry P., Handbook of natural gas. 1913, p. 596.
George, H. C. Surface Machinery and Methods for Oil-Well Pumping. Washington D.C.. UNT Digital Library. http://digital.library.unt.edu/ark:/67531/metadc12407/. Accessed May 5, 2016.