CO_2做低渗气藏储气库垫层的气水边界稳定性分析

Stability analysis of gas-water interface using carbon dioxide as cushion gas for gas storage in low permeability gas reservoir

将低渗透枯竭气藏改建为地下储气库的关键问题之一是气水界面的稳定性.为分析以CO_2做垫层气的低渗透气藏改建储气库在扩容建库和季节调峰时气水界面的稳定运移,根据枯竭气藏储层的特点,建立基于低渗透微裂缝储层的双重孔隙介质模型.以中原油田文23改建储气库的地下储层为研究对象,讨论扩容建库时CO_2垫层气的注入方式对气水界面稳定性的影响,以及储气库季节调峰时气水界面的运移特性.研究表明:在扩容建库阶段,CO_2连续注气驱水能快速扩容,但降低了气水界面和储层内压力场稳定性;间歇注气扩容方式在4个周期后扩容速率降低了4.8%,但更好地保证气水界面的稳定运移和储层内压力场的稳定;在季节调峰阶段,溶解态和超临界态CO_2的相互转换更好地保证气水边界和储层内压力场的稳定,同时提高储层空间利用率.

One of the key technique problems of reconstructing underground gas storage （ UGS ） using low permeability depleted gas reservoir is the stability of gas-water interface （ GWC） . To analyze the stable migration of GWC in gas storage reconstructed from low permeability gas reservoir using CO2 as part of the cushion gas during capacity expansion by gas injection and seasonal peak shaving of UGS, a dual-porosity numerical model was established based on the characteristics of low permeability micro fractured reservoir. Taking the reservoirs of Wen-23 gas storage reconstructed, the Zhongyuan Oilfield, as research objects, the effects of CO2 injection method on capacity expansion of UGS and migration behavior of GWC when peak shaving were simulated and discussed. The results showed that the method of continuously CO2 injection increased capacity expansion speed but reduced the stability of GWC and reservoir pressure field during capacity expansion. The method of CO2 injection at intervals reduced the rate of capacity expansion by 4.8% after 4 cycles, but could ensure stable migration of GWC and the stable of reservoir pressure field. Besides, the stability of GWC and reservoir pressure field were better ensured by the transformation between dissolved state and supercritical CO2 during seasonal peak shaving of USG, and the utilization of reservoir space were increased, simultaneously.