致密砂岩凝析气藏反凝析伤害评价及解除方法

Evaluations and removing methods of the retrograde condensate damage for the gas condensate reservoirs in the tight sandstone

凝析气藏反凝析伤害会严重影响气井产能,正确评价反凝析伤害程度,并有效解除反凝析伤害是凝析气藏开发中不变的主题。针对鄂尔多斯盆地苏里格凝析气田不同区块凝析气物性差异的特点,选择其中3个典型区块凝析气进行复配,基于PVT相态实验结果,采用各区块真实全直径岩心分别模拟了不同凝析油含量凝析气在衰竭开发过程中近井和远井地带的反凝析现象,并对其反凝析伤害程度进行了评价,同时开展了注CO 2吞吐、注甲醇段塞+干气段塞、注干气吞吐等3组解除反凝析伤害实验。实验结果表明:反凝析伤害程度随着凝析气中凝析油含量的增加而增大;随着凝析油含量的不断增加,近井、远井地带的反凝析伤害程度的差异在不断减小,同时近井地带的气相有效渗透率最大下降速度出现的时间越早,对应的压力也越大。3种解除反凝析伤害方法均能有效改善反凝析污染,但从气相有效渗透率恢复程度来看,注CO 2吞吐效果最佳,注甲醇段塞+干气段塞效果次之,注干气吞吐效果最差。

Retrograde condensation damage of condensate gas reservoirs may seriously reduce the productivity of the condensate gas well.Accurate evaluation of the retrograde damage degree and effective removal of the damage are the unchanged themes in the development of the condensate gas reservoirs.According to the characteristics of the condensate-gas physical properties in different blocks of Sulige condensate-gas field in Ordos Basin,three typical blocks were selected for the combination.Based on the results of PVT phase experiments,the retrograde-condensation phenomena of the condensate gas with different condensate-oil mass fractions near the well and far-well zones during the depletion development were simulated by using real full-diameter cores from each block.And moreover the degree of the retrograde condensation injury was evaluated,and three groups of the injury relief experiments were carried out:CO 2 injection huff and puff,methanol injection slug+dry gas slug and dry gas injection huff and puff.The experimental results show that with the increase of the condensate-oil mass fraction in the condensate gas,the retrograde-condensation damage increases,on the contrary,the difference of the degrees of the retrograde condensation damage between near the well and far well is decreased.At the same time,the earlier the maximal decline rate of the gas effective permeability near the wellbore occurs,the higher the corresponding pressure will be.The three removing methods of the retrograde condensation damage can further effectively control the retrograde condensation pollution,but from the viewpoint of the recovery degree of the gas effective permeability,the effects of CO 2 injection huff and puff are the best,the effects of the methanol injection slug+dry gas slug are the second,while the effects of the dry gas injection huff and puff are the worst.