EVIDENCE OF TWO EXTREME FLOW REGIMES OPERATING I N THE PRODUCTION ZONE OF DIFFERENT WELLS FROM LOS AZUFRES Page: 4 of 10
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CONF-850107-38
between deep wells of the northern sec-
tion and the shallower wells of the
southern section.
Giggenbach (1980) and D'Amore and Celati
(1983) have devised similar methods to
calculate the fractional molar contrib-
ution of equilibrium reservoir steam
phase to the total discharge produced by
a well. This parameter has come to be
known as the "y value" (Giggenbach,
1980), steam fraction (D'Amore and Cela-
ti, 1983) or excess steam (Truesdell et
al, 1984; Nieva et al, 1982), and has
been interpreted by some authors as an
estimate of the reservoir's in situ
steam molar fraction, from which the
steam quality could be readily obtained.
Heretofore this parameter shall be re-
ferred to as excess steam, and expressed
as a percentage rather than as fraction.
In this contribution we will describe a
modification to the procedure of Gig-
genbach (1980) that makes it applicable
to the case of a well with a high con-
tent of non-condensable gases in its to-
tal discharge. The variability in total
discharge compositions from Los Azufres
will be interpreted in the light of the
concept of excess steam, and the ques-
tion of the relation between excess
steam and in situ steam quality will be
addressed.
THE CONCEPT OF EXCESS STEAM.
The excess steam or "y value" is calcu-
lated from the apparent distortion in
the relative proportions of species par-
ticipating in the Fischer-Tropsch reac-
tion (or any reaction purported to be in
equilibrium in the uperturbed reservoir),
assuming that the total flow entering
the wellbore is made up of a mixture of
reservoir liquid and steam phases, each
having kept the chemical composition ithad at equilibrium (Giggenbach, 1980).
To further clarify this concept, use
will be made of Figure 1 where two hy-
pothetical cases are presented. In the
first case it is considered that a unit
mass of reservoir liquid is transported
to the wellhead. Even though a steam
phase would develop because of decom-
pression, as long as the chemical com-
position of the unit mass remains un-
changed, one would calculate an excess
steam value of zero. In the second
case it is considered a unit mass
composed of 10% (w/w) steam and 90%
(w/w) liquid, each phase having the
chemical composition corresponding to
reservoir equilibrium conditions. Again,
if this unit mass reached the wellhead
without any change in its chemical com-
position (although with a change in the
relative proportions of steam and liquid
phases) one would calculate an excess
steam value of ten percent. These exam-
ples might lead to the belief that the
calculated excess steam is indeed a
measure of steam saturation in the res-
ervoir. However, as will be discussed
later, it is probably incorrect in most
cases to assume that a unit mass could
be transported to the wellhead without
any change in its chemical composition.
CONCEPT OF EXCESS STEAMRESERVOIR
CASE RESULTING IN NO EXCESS STEAM:
UNIT MASS OF UN-
DISTURSED LIQUID
PHASEWELLORE ENTRANCE
STEAM
LIQUID
2HAS EMIXURE
CITH ALL ORIGINAL
COMPONENTSCASE RESULTING IN 10% EXCESS STEAM:
STEAM
LIQUID
UNI AS COM-
POSED OF 901 LIQ-
UID PHASE AND 101
STEAM AT EQUILIB-
RIUM
Figure 1. Idealized schematic transfer
of unit mass from reservoir
to wellhead.-234-
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Nieva, D.; Gonzales, J. & Garfias, A. EVIDENCE OF TWO EXTREME FLOW REGIMES OPERATING I N THE PRODUCTION ZONE OF DIFFERENT WELLS FROM LOS AZUFRES, article, January 22, 1985; United States. (https://digital.library.unt.edu/ark:/67531/metadc883772/m1/4/: accessed April 22, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.