Gas-condensate reservoirs are among the most difficult problems in practical Reservoir Engineering. In case the reservoir is saturated (which is the most frequent) it is impossible to obtain a representative reservoir fluid sample, because any production will create a draw down at well bore level, and some condensed liquid will be left in the formation.
On the other hand, behaviour of a gas-condensate reservoir is mainly controlled by fluid properties, and accurate knowledge of these PVT characteristics is required.
The former methods for PVT calculations (corresponding states law, K-value correlations) were rather tedious and of limited accuracy. The introduction of Equation of State and progress in computers has resulted in modern PVT packages which can accurately simulate fluid behaviour with a reasonable work involved.
The objective of this paper is to illustrate how such a modern PVT package can help in solving practical reservoir engineering problems on a gas-condensate field offshore Abu Dhabi.
Example shown includes:
Reconstitution of the original reservoir fluid using a sample obtained at flowing pressure below dew-point.
Calculation of initial gas composition change with depth in the reservoir, down to the gas-oil contact.
Condensate-gas ratios measured in various conditions during life of the reservoir can vary a lot: a PVT package helps in explaining these differences and selecting the best data.
Performance of lean gas injection into a depleted reservoir containing immobile condensed liquid, and how it improves condensate recovery.