Understanding Gas-Condensate Reservoirs
How does a company optimize development of a gas-condensate ﬁeld, when depletion leaves valuable condensate ﬂuids in a reservoir and condensate blockage can cause a loss of well productivity? Gas-condensate ﬁelds present this puzzle. The ﬁrst step must be to understand the ﬂuids and how they ﬂow in the reservoir.
College Station, Texas, USA
Billy W. Harris
Wagner & Brown, Ltd.
A. (Jamal) Jamaluddin
Chevron Energy Technology Company
San Ramon, California, USA
Gary A. Pope
University of Texas
Curtis Hays Whitson
Norwegian University of Science and
Technology and PERA, A/S
For help in preparation of this article, thanks to Syed Ali, Chevron, Houston; and Jerome Maniere, Moscow.
ECLIPSE 300, LFA (Live Fluid Analyzer for MDT tool), MDT
(Modular Formation Dynamics Tester) and PVT Express are
marks of Schlumberger. CHEARS is a mark of Chevron.
Teﬂon is a mark of E.I. du Pont de Nemours and Company.
A g as-condensate reservoir can choke on it s
most valuable components. Condensate liquid
saturation can build up near a well because of
d rawdown below the dewpo i nt pressure,
ultimately restricting the ﬂow of gas. The nearwell choking can reduce the productivity of a well by a factor of two or more.
Th i s phenomenon, called condensat e
blockage or condensate banking, results from a
combination of factors, including fluid phase
properties, formation flow characteristics and
pressures in the formation and in the wellbore.
I f t h ese f acto r s a r e n ot u n de r stood a t t h e
beginning of ﬁeld development, sooner or later
production performance can suffer.
For example, well productivity in the Arun
f ield, in North S umatra, Indonesia, decline d
s igni f icantly about 1 0 y ears a f ter production
began. This was a serious problem, since well
deliverability was critical to meet contractual
o bligations f or gas delivery. Well studies ,
including pressure transient testing, indicated
t he loss was caused b y a ccumulation o f
condensate near the wellbore.1
1. Aﬁdick D, Kaczorowski NJ and Bette S: “Production
Performance of a Retrograde Gas Reservoir: A Case
Study of the Arun Field,” paper SPE 28749, presented at
the SPE Asia Paciﬁc Oil & Gas Conference, Melbourne,
Australia, November 7–10, 1984.
2. For a case study of the Karachaganak ﬁeld: Elliott S,
Hsu HH, O’Hearn T, Sylvester IF and Vercesi R: “The
Giant Karachaganak Field, Unlocking Its Potential,”
Oilﬁeld Review 10, no. 3 (Autumn 1998): 16–25.
Arun is one of several huge gas-condensate
reservoirs that together contain a significant
g lobal resource. Other lar g e g as-condensate
resources include Shtokmanovskoye ﬁeld in the
R ussian Barents Sea , K arachaganak field i n
K azakhstan , t he North field in Qatar that
becomes the South Pars field in Iran, and the
Cupiagua ﬁeld in Colombia.2
This article reviews the combination of ﬂuid
thermodynamics and rock physics that results in
condensate dropout and condensate blockage.
We examine im p lications for p roduction and
methods for managing the effects of condensate
dropout, including reservoir modeling to predict
ﬁeld performance. Case studies from Russia, the
USA and the North Sea describe ﬁeld practices
A g as condensate is a single-phase f luid a t
o ri g inal reservoir conditions. It consist s
predominantly of methane [C1] and other shortchain hydrocarbons, but it also contains longchain hydrocarbons, termed heavy ends. Under 3. Gas-condensate ﬂuids are termed retrograde because
their behavior can be the reverse of ﬂuids comprising
pure components. As reservoir pressure declines and
passes through the dewpoint, liquid forms and the
amount of the liquid phase increases with pressure
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