Page 17 - Primer on Enhanced Oil Recovery

8 Primer on Enhanced Oil Recovery

more heat during burning (as relative percentage of hydrogen is higher) and for this
reason command higher price when sold by the weight.
Concentration of some metals in oil (such as vanadium, titanium, nickel and so
on) in some heavy (bitumen) oil formations is so high that it merits industrial
extraction.
In the formation an oil is under higher than atmospheric pressure. The tempera-

ture is also usually higher than the room temperature (e.g. above 20 C). High pres-
sure allows oil to contain higher quantities of dissolved gas. All this leads to the
situation that oil properties, in substantial part affecting the extraction, in the forma-
tion are significantly different compared to the same liquid after extraction and pri-
mary separation from water and gases.
It is clear at this point that an oil has many properties, both physical and
chemical. One can count this as: chemical composition, molecular weight, den-
sity, viscosity, solidification and boiling points (temperatures), dissolved gas
content, saturated gas pressure, coefficients of thermal expansion, volumetric
coefficient and so on.
Oil volume as a rule is measured in barrels. One barrel volume is equal to 42
USA gallons volume at 60 F (15.5 C).

2.1.1 Natural gas

Natural gas is a mixture of hydrocarbon and other chemical molecules. Natural
gas in the formation can be in the form of free gas (gas cap) and/or it can be
dissolved in oil and in connate water. Natural gas at high pressure and a rela-
tively low temperature can be in the formation even in crystalline form (gas
hydrates). At room temperature and pressure natural gas is always in gaseous
phase.
Generally natural gas contains methane (CH 4 ) at concentrations in 70 98%, eth-
ane (C 2 H 6 ), propane (C 3 H 8 ) and butane (C 4 H 10 ). There is also admixture of hydro-
gen sulfide (H 2 S), carbon dioxide (CO 2 ), nitrogen (N 2 ) and helium (He). Some
other inert gases also can be presented as well as even mercury in some cases.
As with oil, the main physico-chemical gas parameters are numerous. On the
first place is, possibly, the molecular weight, as this inevitably leads to the amount
of produced heat. Then there are: density at atmospheric pressure, average critical
temperature and pressure, viscosity and so on.
Cleaned of impurities natural gas is odorless and colorless. To help in detection
of gas leaks some substances with unpleasant smell odorants are added into
natural gas before distribution to the end users.
The natural gas volume is usually measured in cubic feet (Ccf) in standard con-

ditions (60 F and 14.7 psi). Sometimes this changed to a measurement in metric

units cubic meters at room temperature (20 Cor 68 F).
The measuring customer units in many cases depend on the sales region or the
country. In the USA the sales are done in cubic feet (Ccf), in the Great Britain in
kilowatt-hours, in Russia in cubic meters.