A New Approach for Phase Behavior and Well Productivity Studies in the Deep Gas- Condensate Reservoir With Low Permeability

摘要

Deep gas-condensate reservoirs, with high temperature, high pressure, and low permeability, account for a high proportion in the recent years. Quite different with conventional gascondensate reservoir, this type of reservoir has smaller rock grains, prominent interfacial phenomena, and appreciable reservoir deformation. Consequently, it is necessary to study phase behavior and well productivity to model these deep gascondensate reservoirs more accurately. This paper considered both interfacial effect and reservoir deformation, and proposed a new method for calculating oilgas phase equilibrium in deep gas-condensate reservoirs. We introduced phase equilibrium calculation into fluid flow theory for condensate oil and gas system and then mathematically developed a physical-chemical flow model with consideration of interfacial effect and reservoir deformation. Gas well productivity was also studied and the corresponding equation was derived. Because flow behavior near wellbore is essentially important for a gas-condensate reservoir, we investigated fluid flow near wellbore and provided methods to determine retrograde condensate saturation, gas relative permeability, and pressure distribution. We applied to a real gas condensate reservoir and calculated well productivity, retrograde condensate saturation distribution, and gas relative permeability, particularly near wellbore. The results illustrated that interfacial phenomena and reservoir deformation made retrograde condensation appear much earlier and consequently aggravate formation damage. Therefore, the decrease of gas relative permeability and the drop of well production are faster than usual.