The Kurunda Field, Tirrawarra sandstone is a low permeability, lean gas condensate reservoir located in the Cooper Basin of South Australia. Prior to production consideration was given to the need for gas cycling to maximize liquid recovery. Early long-term production tests, however, showed a much larger drop in liquid-gas-ratios than expected. A study was undertaken to determine the cause of this drop and the implications with respect to future operational policy.
A comparison of field observed performance and laboratory data indicated a reservoir fluid composition intermediate between that measured on two laboratory samples. Field observed performance together with results from a simplified model of retrograde gas condensate reservoir behavior further indicated that the observed liquid-gas-ratio correlated more closely to the bottomhole flowing pressure rather than the average reservoir pressure. This liquid-gas-ratio behavior was found to result from the near wellbore region of the reservoir acting as a separator and preventing the recovery of liquids originally entrained in the gas. This separation effect which continues for the life of the reservoir adversely effects liquid recovery for both primary and pressure maintenance operations, and prevents the economical application of the latter activity.