注CO_(2)改善页岩凝析气藏反凝析伤害效果评价

Effect evaluation of CO_(2) injection on mitigat retrograde condensate damage of condensate gas in shale gas reservoir

为解决常规反凝析伤害评价方法中忽略近井地带反凝析叠加效应和远井地带单相凝析气渗流特征导致评价效果失真的问题,基于长岩心驱替实验,建立了一种考虑叠加效应和远井单相流的反凝析伤害评价新方法,模拟了实际页岩储层衰竭开发中的反凝析伤害,评价了注甲醇、干气和CO_(2)解除反凝析的效果,研究了CO_(2)注入体积和注入压力对反凝析伤害评价指标的影响。结果表明:当压力降至最大反凝析压力时,气相渗透率伤害率达到80.2%~83.1%,驱替压差由5 MPa快速增至15 MPa,气相渗流阻力提高幅度约达200%;CO_(2)注入后气相渗透率提高倍数达3.2,气油比变化率达到23.1%,岩心压差降低率达到36.1%,说明注CO_(2)效果最好,其次是甲醇,注干气效果最差;CO_(2)最佳注入压力9 MPa,注入量0.15 PV,油气平衡时间9.9 h。研究成果为高效开发页岩凝析气藏和解除反凝析伤害提供了思路和方法。

In order to overcome the evaluation distortion of conventional evaluation method for retrograde condensate damage,which ignores near-wellbore retrograde condensate superposition effect and far-wellbore single phase condensate gas flow characteristics,based on long-core displacement experiment,a new evaluation method is established considering superposition effect and far-well single-phase flow,simulating retrograde condensate damage of shale reservoir in actual depletion development and evaluating retrograde condensate removing effect of the injections of methanol,dry gas and CO_(2).Influence of CO_(2) injection volume and injection pressure on evaluation indexes of retrograde condensate damage is studied.The results show that,when the pressure drops to the maximum retrograde condensate pressure,gas permeability damage rate is 80.2%~83.1%,with displacement pressure difference rapidly increasing from 5 MPa to 15 MPa and gas flow resistance increasing by 200%.After CO_(2) injection,gas permeability increases by 3.2 times with gas-oil ratio changing rate of 23.1%and core differential pressure decreasing rate of 36.1%,verifying that CO_(2) injection has the best effect,followed by methanol,and dry gas injection has the worst effect.The optimal injection pressure of CO_(2) is 9 MPa with injection volume of 0.15 PV and oil-gas equilibrium time of 9.9 h.The research provides ideas and methods for efficient development of shale condensate gas reservoirs and retrograde condensate damage removal.