Well productivity in an Iranian gas-condensate reservoir: A case study

摘要

This work is another step forward in our understanding of the dynamics of condensate buildup around wellbores in gas condensate fields. For this purpose one of the unique and huge Iranian gas condensate reservoirs is selected. The effects of condensate bank on the gas and condensate productivity and also the reservoir performance have been investigated throughout a simulation study. The productivity of the wells in the moderately rich gas condensate reservoir was observed to have initial rapid decrease and then reach a relatively constant value and after that a second decrease as the reservoir was depleted. Compositional simulation clarified the reasons for this uncommon productivity change. During early production, a ring of condensate rapidly formed around wellbore when the near-wellbore pressure decreased below the dew point pressure of the reservoir fluid. Moreover, relative permeability effects caused the saturation of condensate in this region to be considerably higher than the maximum condensate predicted by the PVT laboratory work. Gas productivity also decreased as the effective permeability to gas was severely reduced due to this high condensate saturation in the ring. After condensate formation throughout the reservoir due to pressure reduction below dew point, the gas flowing into the ring became leaner causing the condensate saturation in the ring to decrease. This increased the effective permeability of the gas. On the other hand, the reservoir pressure drop leads to less productivity which caused the gas productivity to reach a constant value. Changes in gas and condensate compositions in the reservoir also impacted gas productivity. As the result of this study it could be mentioned that the gas production rate may stabilize, decrease or possibly increase, after the period of initial decline. This is controlled primarily by the condensate saturation near the wellbore which would decrease in the near wellbore region because of the leaner gas entering this region and also partial vaporization. In addition to the gas production rate, the composition change should also be considered in the sale contracts.