凝析气非平衡雾态反凝析特征及其对采收率的影响

The characteristics of non-equilibrium fog-state retrograde condensation of condensate gas and its influence on recovery rate

摘要

凝析气藏衰竭降压速度直接影响反凝析伤害程度,控制和利用非平衡反凝析状态是提高凝析油采收率的关键。采用改进的长岩心实验装置及流程,开展不同降压速率的凝析气衰竭实验,验证岩心中渗流存在非平衡雾态渗流区,分析降压速率对采收率的影响,定量表征多个渗流区的持续压差范围及其对采收率的贡献程度,评价降压速率和多个渗流区对渗透率伤害的影响。结果表明:随降压速率的增加,露点压力、反凝析液量和非平衡雾态反凝析持续压差增大。凝析气在岩心中的渗流可分为纯气渗流区、雾态渗流区、气动油滞区和气油两相渗流区4个区域,其中雾态渗流区与气动油滞区的压力分界限主要取决于凝析油沉降压力。气油两相渗流区持续压差范围最大,对凝析油采收率的贡献程度最高,其次为雾态渗流区和纯气渗流区的,气动油滞区的最小。降压速率对凝析油采收率的影响高于对天然气采收率的影响。渗透率伤害率随降压速率的增加先降低后增大,最佳降压速率为3 MPa/h。反凝析伤害最大的阶段为雾态渗流区的中后期及气动油滞区的。该结果为合理利用雾态反凝析和提高凝析油采收率提供参考。

Abstract

The rate of pressure drop in condensate gas reservoirs directly affects the degree of retrograde condensation damage. How to control and utilize the non-equilibrium retrograde condensation state to improve the condensate oil recovery rate is the key to the efficient development of condensate gas reservoirs. Based on the understanding of the influence of pressure drop rate on non-equilibrium fog-state retrograde condensation and phase parameters in the bulk phase space, the existence of non-equilibrium fog-state seepage zones in the rock core was verified by improving the long rock core depletion experiment method. The influence of pressure drop rate on recovery rate was studied, and the continuous pressure difference range of multiple seepage zones and their contribution to the recovery rate were quantitatively characterized. The influence of pressure drop rate and multiple seepage zones on permeability damage was systematically evaluated. The research results show that with the increase of pressure drop rate, the dew point pressure, retrograde condensate liquid volume and the continuous pressure difference of non-equilibrium fog-state retrograde condensation increase. The seepage of condensate gas in rock cores can be divided into four zones based on the phase characteristics, produced gas components and the variation of oil and gas recovery rate: pure gas flow zone, fog-state seepage zone, gas-driven oil retention zone and gas-oil two-phase flow zone. Among them, the pressure boundary between the fog-state seepage zone and the gas-driven oil retention zone mainly depends on the condensate oil settling pressure. The gas-oil two-phase seepage zone has the largest continuous pressure difference range and the highest contribution to the condensate oil recovery rate, followed by the fog-state seepage zone and the pure gas seepage zone, while the gas-driven oil retention zone has the smallest contribution. The influence of pressure drop rate on the condensate oil recovery rate is higher than that on the natural gas recovery rate. Moreover, with the increase of pressure drop rate, the permeability damage first decreases and then increases, and the optimal pressure drop rate is 3 MPa/h. A smaller pressure drop rate will lead to earlier permeability damage, and the most severe damage stage mainly occurs in the middle and late stages of the fog-state seepage zone and the gas-driven oil retention zone. The research results provide a reference for the rational utilization of fog-state retrograde condensation and the improvement of condensate oil recovery rate.

关键词

凝析气 / 非平衡 / 雾态 / 反凝析 / 凝析油 / 渗流 / 采收率

Key words

condensate gas / non-equilibrium / fog state / retrograde condensation / condensate oil / seepage / recovery rate

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基金资助

中国石油天然气集团有限公司科技专项(2025E-4002)