Abstract
Gas condensate reservoirs exhibit complex coupling between phase behaviour,
interfacial tension, velocity and pore size distribution. Appropriate
characterization of the in situ fluids and relevant flow testing can provide
valuable insight into gas condensate reservoir forecasting. The following
insights were obtained during the course of this testing:
- The importance of path dependence was shown to be significant when creating
equilibrium phases below saturation pressure for use in quantifying phase
interference. Differences, due to compositional path, in API gravity of liquids
in solution were quantified to be as much as 10 degrees, with molecular weight
differences over 110 daltons.
- End-point saturations, such as trapped gas and residual condensate
saturation, are sensitive to the level of interfacial tension (IFT). Critical
condensate saturation was less sensitive to IFT (pressure).
- The two-phase injection approach and the protocol whereby explicit
measurement of relative permeability is performed provide a very thorough
gas-condensate reservoir data set, which are amenable for use in simulation and
reservoir production forecasting.
Background
This paper discusses performance of gas condensate reservoirs.These reservoirs
have a reservoir temperature located between the critical point and the
cricondentherm on the reservoir fluid's pressure-temperature diagram. This is
the only unique and accurate means of identifying gas condensate reservoirs;
any other definition [condensate-gas ratio, C7+ molecular weight (MW) or C7+
API gravity] is specious and ersatz.
In these reservoirs, as the pressure drops, vapour and liquid phases
result.Capillary pressure causes phase interference which usually reduces gas
productivity. A cross-section of interesting topics that show the complexities
of gas-condensate reservoir production have been reported in the
literature(1-7). All of the relevant parameters, if well understood,
will lead to more accurate evaluation of the amount of hydrocarbon in place,
the rate at which the resource can be produced and the optimization strategies
as the reservoir matures.
Introduction
In this paper, retrograde condensate characterization and properties
measurement, explicit relative permeability and two-phase dynamic steady-state
measurements are discussed. Notwithstanding the very specific nature of this
paper in quantifying phase behaviour-fluid flow coupling in the laboratory, it
was considered important to provide a short commentary on sampling of gas
condensate fluids that form the foundation on which experimental gas condensate
testing is built. Extensive treatment of this theme was beyond the scope of the
current paper.
Retrograde Condensate Sampling
The bottomhole flowing pressure (PBHF) must be lower than reservoir
pressure to induce flow. If the PBHF is less than dew point pressure
then liquids drop out in the porous media around the production well. The gas
is much more mobile than the condensate and, therefore, the gas-condensate
ratios (GCR) exhibited at surface are commonly higher than that of the
reservoir fluid.
A further complication of this problem is that the composition of the surface
liquid also changes. When the PBHF is above dew point, the MW of the surface
liquid is the highest. Figure 1 shows the change in composition incident to
decreasing bottomhole pressure.
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
View full textPDF
(
1,010 KB
)
History
- Original manuscript received:
4 April 2006
- Meeting paper published:
13 June 2006
- Revised manuscript received:
21 April 2009
- Manuscript approved:
9 June 2009
View Cart
