Note the difficulty with the abbreviation "Mbbl," which means thousand
barrels in one system, and million barrels in the other.Epicentre makes a distinction that is often glossed over in the oil industry. That is the distinction between volumes and standard volumes.
A volume of (for example) oil could be measured in cubic metres (m3). (Whatever is said about "oil" also holds true for "gas".) Cubic metres is the SI unit of volume. More generally, it can be measured in barrels (bbl), which, in Epicentre, is a customary unit of measure.
But there is another unit of volume: the stock tank barrel (stb). Consider an experiment in which a given amount of oil is cooled (or heated) to 60 degF, and brought to atmospheric pressure. The original volume of oil is altered (usually reduced) to a different volume, due primarily to the removal of dissolved gas. This new volume is called a standard volume. The SI unit for a standard volume (introduced by POSC) is standard cubic metres at 15 degC (scm15C), and the customary unit is the stock tank barrel (stb60).
The initial reaction is to consider the scm15C to be another form of m3. I.e., they are both units of volume, and a distinction should not be made between them. This view fails for two reasons:
Thus, the standard volume really is a different quantity type, and requires a different unit of measure.
Consider the example of a barrel (bbl). For a well over a period of time, or for a field, it is more common to use "thousand barrels" or "million barrels" as the unit.
There is confusion over the abbreviations for these units.
| unit name | common abbreviation | SI type abbreviation |
|---|---|---|
| barrel | bbl | bbl |
| thousand barrels | Mbbl | kbbl |
| million barrels | MMbbl | Mbbl |
Note the difficulty with the abbreviation "Mbbl," which means thousand
barrels in one system, and million barrels in the other.
The AAPG came down hard on their authors. Many articles did not specify which system it was using, so the ambiguity of "Mbbl" remained in the article. In fact, the AAPG mentioned that both systems were occasionally used in the same article. The AAPG specified that all authors were to use the SI multiples.
The same pattern holds true for stock tank barrels
The table for "gas" is similar, except that the multiplier can get into billions or trillions. Consider the unit, cubic feet (cf) and its multipliers:
| unit name | common abbreviation | SI type abbreviation |
|---|---|---|
| cubic feet | cf | cf |
| thousand cubic feet | Mcf | kcf |
| million cubic feet | MMcf | Mcf |
| billion cubic feet | bcf | Gcf |
| trillion cubic feet | tcf | Tcf |
As with the oil, the same pattern holds true for the standard volumes.
Version 2.1 of Epicentre, and earlier versions, continue to use the common
abbreviations. However, there needs to be discussion on the matter.
If people feel there is a need to change to the SI multipliers (in line with
the AAPG, for example), Epicentre can change to these values.
Please send comments to John Bobbitt at
bobbitt@posc.org
The migration path within the databases is easy. All data can be written
out (as a PEF) with the conversion to the SI unit (cubic metres or standard
cubic metres at 15 deg C). The correct conversion will be applied. When it
is read into the new database with the new units, the correct conversions
for these units will be applied (since they are part of the reference data).
So the data will be updated.
Reference Homepage
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