Experimental and numerical study of huff-n-puff gas injection to re-vaporize liquid dropout in shale gas condensate reservoirs

The complex flow behavior of a gas condensate reservoir is caused by the compositional changes and the creation of condensate blockage around the wellbore. Once the pressure is lower than the dew point pressure, liquid dropout is formed in the reservoir. This liquid dropout reduces gas relative permeability. As a consequence, gas production is decreased and liquid dropout-condensate, a valuable resource, remains in the reservoir. In this paper, the re-vaporization mechanism of huff-n-puff gas injection is investigated from both experimental and numerical work. In huff-n-puff gas injection, when pressure is increased to be higher than the dew point pressure, part of the condensate can be re-vaporized and flows to the production well with gas during the puff process. Since there is only one well in the huff-n-puff process, the condensate region is near the well. When gas is injected into the reservoir, the pressure of the condensate region will be increased rapidly. Very limited research has been conducted on the re-vaporization of condensate, especially for shale gas condensate reservoir. Both experimental work and simulation study have confirmed the mechanism of condensate re-vaporization by huff-n-puff gas injection. The work from this paper indicates that huff-n-puff is an effective way to re-vaporize the condensate and enhance the condensate recovery.