Page 39 - Primer on Enhanced Oil Recovery

30 Primer on Enhanced Oil Recovery

Figure 3.1 Simplified imprecise water phase diagram.

critical point [pressure above approximately 218 atm (22 MPa)] and temperature

above 374 C (647 K) vapor and liquid are undistinguishable. This is so named
supercritical fluid and properties of it are outside of this book interest
Vapor is the material in a gas phase. Vapor exists below critical temperature and
can condense in liquid or solid state depending on the pressure. Vapor can be
formed from liquid (by evaporation or boiling) and from ice (by sublimation).
Transformation from liquid to vapor requires significant energy. This energy is
released when the vapor condenses back into water. This energy is approximately
six time bigger than the energy to heat water from 20 to 100 C. This is exactly

why water vapor is so efficient to deliver thermal energy to an oil formation.
In many cases water vapor term is interchangeably used with water steam term.
This is only correct if the steam is dry. In this case water gas (vapor, steam) is fully
transparent and it has lower density than air. If the steam is not dry then it contains
water droplets and it is translucent. Amount of thermal energy in a stem is signifi-
cantly affected by the temperature and amount of water in droplets. Ratio of water
droplets in the steam defines steam quality.
The bubble point is a temperature and pressure at which vapor starts to separate
from the liquid in a form of bubbles. At constant and high enough temperature this
will happen if the pressure is reduced. In everyday life this is can be observed when
a can with fizzy drink is opened (the pressure is reduced) and the liquid suddenly
becomes full of bubbles. The opposite is also true, if the pressure has increased the