鄂尔多斯盆地致密砂岩凝析气藏合理高效注气开发方式

Reasonable and high-efficiency gas injection mode for the tight sandstone condensate-gas reservoirs in Ordos Basin

凝析气藏反凝析伤害严重影响气井产能,注气能够有效改善反凝析伤害,提高凝析油采收率。针对鄂尔多斯盆地苏里格致密砂岩凝析气藏,基于PVT相态实验结果,在最大反凝析压力下开展岩心注气驱替实验,辅以在线CT扫描技术,深入研究了连续注气、注气吞吐和脉冲注气3种不同注入方式下凝析油采出程度和岩心中平均凝析油饱和度变化特征,优选出提高凝析油采收率最佳注气方式。实验结果表明:当注气量小于1 HCPV时,吞吐式注气岩心中凝析油饱和度下降最多;当注气量大于等于1 HCPV时,脉冲式注气凝析油采出程度最高。3种注入方式能够形成3种不同的油气渗流和分布特征:连续注气以驱替为主,与凝析油接触时间短,易于形成气窜;注气吞吐以扩散和抽提为主,与凝析油接触时间长,能够有效改善近井地带的反凝析伤害;脉冲式注气兼具了吞吐和连续注气的优点,减缓气窜的同时还能建立驱替体系,适用于多轮次下的注气开发。

The retrograde condensation damage of condensate gas reservoirs seriously influence the productivity of the gas wells.Gas injection can effectively improve the retrograde condensation damage and enhance the condensate oil recovery.In the light of the results of PVT phase state test of Sulige tight-sandstone gas reservoirs in Ordos Basin,supplemented by the online CT scanning technique,the core gas-injection-displacing experiment was carried out under the maximum retrograde-condensation pressure.The condensate recovery and the varied characteristics of the average condensate saturation in the core were deeply studied in three different injection modes,containing continuous gas injection,huff-puff gas injection and pulse gas injection,and the best gas injection mode for improving the condensate recovery was optimized.The experimental results show that when the gas injection volume is less than 1 HCPV,the condensate saturation in the core of the huff-puff gas injection decreases most;when the gas injection volume is more than or equal to 1 HCPV,the condensate recovery of the pulse gas injection is the highest.The three injecting modes can form three different oil-gas seepage and distribution characteristics,the continuous gas injection is mainly characterized by the displacement and the contact time with the condensate is rather short,so the gas breakthrough is easy to form;while for the huff-puff gas injection,the diffusion and extraction are main forms,the contact time with the condensate is pretty long,thus the retrograde condensation damage near the wellbore can by effectively improved;for the pulse gas injection,it has the advantages of both the huff-puff and continuous gas injections,so it can slow down the gas channeling and establish the displacing system at the same time,which is suitable for multi-round gas injection development.