STUDY ON ELIMINATING RETROGRADE CONDENSATE POLLUTION IN LOW-PERMEABILITY CONDENSATE GAS RESERVOIR

Abstract

With the decrease of pressure during the production process of low-permeability condensate gas reservoirs, different degrees of retrograde condensate pollution appear in the area near the wellbore, resulting in a rapid decrease in the productivity of gas wells. Due to the poor physical properties of low-permeability condensate gas reservoirs, conventional single measures such as circulating gas injection and huff and puff gas injection cannot effectively relieve the condensate pollution in the near-wellbore area. For this reason, this paper explores the WH1 gas well in the W low-permeability condensate gas reservoir and conducts research on the retrograde of reverse condensate pollution in a single well. First, 12 groups of inside evaluation experiments for the decontamination of retrograde condensates are carried out using the core of the condensate gas reservoir W and 6 different agents. According to the experimental results, methanol + CO<sub>2</sub> huff and puff are selected as the optimal agent for decontamination by retrograde condensate. Secondly, by analyzing the physical properties of the W low-permeability condensate gas reservoir and the production performance parameters of the WH1 well, a three-dimensional numerical simulation model of the single well of the WH1 gas well is established, and the PVT phase state matching and production performance history matching are carried out for the model. Finally, the single-well numerical simulation model of the WH1 gas well, combined with the experimental results, is used to simulate the obturation effect of CO<sub>2</sub> injection after methanol injection. Among them, the change of reservoir physical properties in the near-wellbore area after methanol injection is simulated by the method of local grid refinement. The research shows that after the simulated well is injected with 20m3 methanol when the CO<sub>2</sub> injection volume in a single cycle is 120 × 10<sup>4</sup> m<sup>3</sup>, the injection rate is 4 × 10<sup>4</sup> m<sup>3</sup>/d, and the well soaking time is 11 days. The reservoir pollution removal effect is the best in the area near the wellbore. From the change of liquid saturation in the near-wellbore area, it can be concluded that the damage of retrograde condensate is relieved by about 87.1%. This study has formed a set of efficient technical means for removing reverse condensate pollution in W low-permeability condensate gas reservoirs. It provides some technical guidance for the formulation of a rational development mode of condensate gas reservoirs.