Summary
Certain fluid properties are required for studies related to management of
gas/condensate reservoirs or prediction of condensate reserves. Often these
studies must begin before laboratory data become available, or possibly when
laboratory data are not available. Correlations to estimate values of these
properties have been developed that are based solely on commonly available
field data.
These properties are the dewpoint pressure of the reservoir fluid, changes in
the surface yield of condensate as reservoir pressure declines, and changes in
the specific gravity of the reservoir gas as reservoir pressure declines. No
correlations based solely on field data have been published for any of these
properties.
The field data required are initial producing gas/condensate ratio from the
first-stage separator, initial stock-tank liquid gravity in °API, specific
gravity of the initial reservoir gas, reservoir temperature, and selected
values of reservoir pressure.
The dewpoint pressure correlation is based on data of 615 samples of gas
condensates with worldwide origins. The other two correlations are based on 851
lines of constant-volume-depletion data from 190 gas-condensate samples, also
with worldwide origins.
Introduction
Correlation equations for gas condensates based on readily available field
data have been developed. The correlations can be used to predict dewpoint
pressures, decreases in surface condensate yields after reservoir pressure has
decreased below dewpoint pressure, and decreases in reservoir-gas specific
gravity at reservoir pressures below dewpoint pressure.
A value of dewpoint pressure is essential data for any reservoir study. A
reasonably accurate estimate of dewpoint pressure for a specific reservoir
fluid is necessary in situations in which laboratory data are not available or
before laboratory data are obtained. Laboratory measurements of dewpoint
pressure and other gas properties of 615 gas condensates with worldwide origins
were used to develop a dewpoint-pressure correlation based on initial producing
gas/condensate ratio, initial stock-tank oil gravity, and specific gravity of
the original reservoir gas. This is the first proposed dewpoint-pressure
correlation that does not require some laboratory-measured quantity.
Estimation of decreases in producing yields after the reservoir pressure
drops below the dewpoint pressure is necessary for accurate prediction of
condensate reserves. The reduction in surface yields can be as much as 75%
during the primary production of a gas condensate. This reduction must be taken
into account in the prediction of ultimate recoveries of condensate. A
surface-yield correlation has been developed that is a function of a selected
reservoir pressure, initial stock-tank oil gravity, specific gravity of the
original reservoir gas, and reservoir temperature. The data set included
laboratory studies of 190 gas-condensate samples. This is the first proposal
offered in petroleum literature of a correlation to estimate the decreases in
surface yield.
© 2007. Society of Petroleum Engineers
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History
- Original manuscript received:
6 July 2005
- Meeting paper published:
21 November 2005
- Revised manuscript received:
12 February 2007
- Manuscript approved:
18 March 2007
- Version of record:
20 December 2007
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