Page 75 - Primer on Enhanced Oil Recovery

66 Primer on Enhanced Oil Recovery

possible to say that thermal methods are most used techniques in EOR worldwide.
Two methods are most widely employed steam injection and internal combus-
tion. We have to stress at this point that when we are talking about steam injection
we are exclusively talking about water steam injection.

8.1 Steam injection

First experiments with steam stimulated oil extraction were conducted by Stovall at
around 1930. On the modeled formation at around 98% Original-Oil-In-Place
(OOIP) was extracted by the steam stimulation. This immediately has been fol-
lowed by the industrial application to an oil field in Texas. In 1939 Lapuck has
published first review of works on steam injection. Next wave of work in this direc-
tion started after Second World War when in 1951 Winkler conducted stem injec-
tion oil extraction in Leoprechting (Austria). Injected steam temperature (in the

well on the ground level) was in the region of 200 220 C. It was shown that the
method was economically feasible.
Wide utilization of steam injection started at around 1960 both in the USA and
USSR. It is still possible to say that the stem injection is most widely used EOR
method for high viscosity oils.
Continues steam injection consists of steam injection into the well at around
80% steam saturation. This stem, after reaching oil, condenses and transfers the
latent heat to the formation. Released thermal energy rises the formation tempera-
ture and lowers oil viscosity. At the same time at the elevated temperature light
hydrocarbons separate from the oil in form of gas. This gas moves in front of prop-
agation hot water water steam front and increases oil mobility and, ultimately,
oil displacement towards production wells.
Cyclic stem injection as also used, it is named huff and puff method. In consists
of utilizing production wells for first injection of steam (huff phase), soaking period
and production period (puff phase). During steam injection some volume of forma-
tion is heated by the injected steam. Soaking allow to utilize injected energy more
economically. During both those phases oil viscosity is reduced and partial oil
upgrading is reached. Then during the huff phase more mobile and partially
upgraded oil is extracted.

8.1.1 Detailed description
Continuous steam (water vapor) injection is used in oil formations with low temper-
ature and high oil viscosity. The injection usually proceeds through especially
devoted steam injection wells. Water steam has high hidden energy of condensation
(this is energy released during steam condensation into water liquid phase).
Moreover some energy is released during steam itself cooling from injection to con-

densation temperature. As the result during cooling from, for example, 230 Cat
the injection point to cooling down to formation temperature, let us say at around