Abstract:

In order to further study the EOR effect of condensate gas reservoir in Zhongyuan Oilfield, the lower third member of Shahejie Formation of a block is taken as an example. Based on the theoretical support of material balance equation and state equation, laboratory experiments such as PVT phase state and physical simulation are carried out to reveal the development rule and deeply analyze the reasons of low production, even no production, of this gas reservoir, so as to recognizes the current situation. For the first time, a two-way EOR method by dry gas injection with pressure maintaining after plugging removing near wellbore area conforming to the geological characteristics of the condensate gas reservoir in this block is proposed. Physical simulation experiments of plugging removing by CO₂ flooding for natural cores at injection end and extraction end are conducted respectively. The corresponding permeability after plugging removing is 60.44 % and 63.15 %, showing that the effect of plugging removing by CO₂ injection is good. On this basis, experiment of core displacement with dry gas injection is conducted with the result that at the beginning, dry gas injection with pressure maintaining under the original formation pressure of 41.19 MPa for condensate gas reservoir can make the condensate oil recovery ratio up to 91.41 %; when the pressure decline to the plugging pressure of 21.14 MPa, using this method again, the recovery ratio can be 44.28 %. By the researches, the formation physical model of oil-water emulsification plugging, because that the near wellbore area pressure is lower than the dew point pressure in the development process, is further clarified, providing technical support for the benefit development of low permeability tight condensate gas reservoir in Zhongyuan Oilfield.

Key words: near wellbore area, condensate gas reservoir, low permeability, fluid model, EOR