Gas-Condensate Well-Test Analysis with and without the Relative Permeability Curves

PENUELA, GHERSON

Based on an analytical analysis of the steady-state theory and its application to well test interpretation in gas-condensate reservoirs, two simplified models are proposed when relative permeability curves are not available. They allow the reservoir engineer to have relative permeability curves as functions of bottomhole pressure from constant composition experiments. Step-by-step procedures explained in the paper rely on the suitability of the steady-state assumptions. Comparisons are made using actual field data and discussions on applicability are also presented. One of the methods is applicable when very low capillary number can be assumed, and immiscible relative permeability curves can be used for pressure transient interpretation. This method is recommended to be used in pressure buildup data analysis. The other proposed method is recommended for pressure drawdown data analysis and is based on the assumption that miscible flow regime controls the fluid flow in the near wellbore region. It is concluded that, although it depends on several factors, miscible relative permeability curves are generally good approximation for pressure drawdown data analysis.An additional method is also discussed. It relies on the ability to simulate properly the near-wellbore fluid flow with accurate fluid and flow models. Using output data from a compositional simulator, it was shown that it is possible to numerically model fluid bank impairment, while analytically, it is possible to obtain reservoir properties, usually shadowed in current methods for condensate buildup.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California