A new technique is presented for the development of a common equation of state (EoS) model for multiple petroleum reservoir fluid compositions counting heavy gas condensates, near-critical fluids and black oils. The basic idea is that the phase behavior of a reservoir fluid to a large extent is determined by its critical point. This is not only the case at near-critical conditions. An EoS model matching the critical point of a petroleum reservoir fluid will in general also provide a good match of routine and EOR PVT data for both gas condensates and black oils. A measured critical point will seldom be available, but can be estimated from other available PVT data. The new technique is exemplified through the development of a 9-component common EoS model for 21 H2S rich reservoir fluids, 3 near-critical fluids, and 18 black oils. All 21 fluids had routine PVT data and 11 had solubility swelling data. Using the available PVT data, an approximate critical point was determined for each reservoir fluid composition. The critical point and the saturation point pressure at the reservoir temperature were the only data tuned to when developing the common EoS model. With this simplified method, the time spent on developing a common EoS model for a large number of fluids can be significantly reduced. The method provided a good match of the PVT data for all 21 reservoir fluids including the shift from bubble point to dew point on the swelling curve for the black oil compositions that had solubility swelling data.

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