Page 157 - Fundamentals of Enhanced Oil and Gas Recovery
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Thermal Recovery Processes
r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
@x Kgα
5 (5.29)
@t 2φΔS o mν s ðh 2 yÞ
y
As it is clear from the following equation, horizontal velocity is a function of y but
not t.
@x
x 5 t 1 x 0 (5.30)
@t
y
If SAGD interface develops vertically above the wells (x 0 5 0),
Kgα
r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
x 5 t (5.31)
2φΔS o mν s ðh 2 yÞ
Kgα 2
t
y 5 h 2 (5.32)
2φΔS o mν s x
SAGD-dimensionless interface shape is defined as follows:
r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
x y 0 t Kgα
X 5 Y 5 t 5 (5.33)
h h h φΔS o mν s h
2
0
1 t
Y 5 1 2 (5.34)
2 X
5.2.2 Cyclic Steam Stimulation Technique (Huff-and-Puff)
CSS is a technique for enhanced recovery of heavy oils at primary production phase.
The steam would assist the heavy oil to flow more easily through the formation into
injection or production wells. A specified amount of steam is injected to the drilled
well. Then process is stopped to give a chance to steam for heating the formation
around the well. Finally, the wells are allowed to produce and heat is exhausted with
the produced fluid. This process is called “huff-and-puff” and is repeated until there
would be a considerable amount of produced water. This process is then continued to
heat the oil and compensate the pressure decline in the reservoir to continue the pro-
duction. In this technique, some injection wells may convert to production ones and
the total number of production wells would increase.
This process is recommended due to its high rate of success and high investment
rate of return. However, from thermal point of view, SAGD process is two times
more efficient in comparison to CSS technique. Fewer damages would occur due to
lower pressures in comparison to CSS, and ultimately, SAGD is more economic for
thick reservoirs, in comparison to cyclic steam processes [13]. More recent studies in
