Modelling the Effect of Composition Change during Condensate Dropout in a Horizontal Gas Well.

摘要

This paper presents a mathematical model describing the behavior analysis for a two-phased gas-condensate system narrowing down on the three zone method.udThe three zone method accounts for the composition change in the reservoir and is based on modeling the depletion by three main flow regions:ud• A near wellbore region (Region 1) where the oil saturation is important allowing both phase, vapor and liquid to be mobile.ud• Region 2 where condensate and gas are present but only the gas is mobile.ud• An outer Region 3 exists when the reservoir pressure is greater than the initial gas dew point and contains only gas. udThis research proposed a fourth region (Region I) which is the immediate vicinity of the well where accumulation of liquid buildup at high rates which yielded from an increase of liquid saturation and a probable decrease in gas relative permeability. The existence of the fourth region or flushed zone is particularly important as it represent the total skin effect: mechanical skin, rate dependent two-phase skin and skin due to gas condensate blockage. The calculated well deliverability rate using the modeled equation for gas condensate reservoir showed a relatively high difference when compared to other known equations. This significant difference is as a result of the effects of the proposed Region I. The developed correlation confirms that as the pressure drops below dew point there occurs condensate banking which when the critical saturation is reached becomes mobile and leads to a reduction in gas flow rate in the reservoir.