Application of the SI Metric System: Part 2 The Basic Units (includes associated papers 15141 and 15190 and 15329 and 15344 and 15844 and 15909)
- J.M. Campbell (Petrotech Consultants Inc.) | R.A. Campbell (Petrotech Consultants Inc.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- October 1985
- Document Type
- Journal Paper
- 1,801 - 1,805
- 1985. Society of Petroleum Engineers
- 2 in the last 30 days
- 131 since 2007
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Most of the customary units used in petroleum engineering are not used in the SI metric system. This article discusses the customary units, proposes the corresponding SI equivalent, and shows the conversion factors. When feasible, the new unit has about the same numerical value as the customary one. Subsequent articles will show the use of these and additional units in specific areas of expertise.
The language of petroleum engineering contains terms that have special meaning in the analysis of information and the communication of ideas. Some of these terms have been coined specifically for petroleum, while others have been borrowed. Through long-term usage these terms have become familiar and useful even though their scientific basis, or source, may be dubious. This introduces a "Catch 22." Attempting to eliminate these terms suddenly is difficult. It jeopardizes and delays acceptance. On the other hand, to delay implementing new terminology unduly is also counterproductive. It is much like learning a new language or expanding our vocabulary; we do not toss away old words when teaming new ones. SPE recognizes the problem and is attempting to convert to SI terminology in an orderly manner over a rather short time period. Some units are labelled "allowable," meaning they are temporarily acceptable but their use is discouraged. Although this policy satisfies no one completely, it is probably an intelligent compromise under the circumstances.
Length, Area, and Volume
The basic unit is the meter (m). In most applications, the length prefixes can he limited to kilometer (km), millimeter (mm), and, occasionally, micrometer ( m). The basic conversions for the meter are as follows.
1 ft=0.3048 m, 1 m=3.281 ft.
1 km=0.621 mile, 1 mile=1.609 km.
1 km = 1000 m, 1 m=1000 mm=1 (E + 06) m.
1 micron=1 m, 1 mil=25.4 m.
Depending on the units used in the original land survey, the hectare(ha) or km is the common unit for measuring large areas of land, as in reservoir engineering and geology. The m is the most common unit in other applications.
1 sq ft=0.0929 m, 1 m = 10.76 sq ft.
1 sq mile (section)=2.59 km.
1 ha= 10 000 m, 1 acre=4047 m
The cubic meter is the most common volume term, although the cubic decimeter (dm 3) or liter (L) is useful for small volumes. Gone is that old familiar liquid volume term, the API barrel (bbl), equal to 42 U.S. gal. Except for its familiarity, this unit of measurement possesses no redeeming features.
1 m3 = 35.31 cu ft = 6.29 bbl = 1000 L.
1 cu ft=0.028 32 m 3=7.481 U.S. gal=28.32 L.
1 bbl=0.159 m3 = 5.615 cu ft = 42 U.S. gal
=35 U.K. gal.
Standard Gas Volumes. It is common to specify a gas volume or rate in "standard" volumes at a specified temperature and pressure. This will be discussed in a later section.
The second is the basic time unit, but any other unit may be used. The use of the minute as a time unit is discouraged because of abbreviation problems. In the SI metric system the abbreviations are second (s), minute(min), hour (h), and year (a). Notice that "a" is used for annum instead of "y" for year.
Mass, Force, and Weight
This is an area where the ambiguity of the traditional customary unit system has led to confusion (and sometimes error). The SI metric system resolves this ambiguity by using different units for force and mass. These two quantities are related by the equation
(mass)(acceleration) force= . (conversion factor)
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