低渗透油藏CO_2驱中后期提效方法研究

Efficiency improvement of CO_2 flooding in middle and later stage for low permeability reservoirs

为了解决低渗透油藏CO_2开发中后期因方向性气窜造成的开井时率低、整体开发效果差及存在安全隐患等问题,通过采用数值模拟和室内实验研究相结合的方法,对防控气窜、保障油井生产时率等技术方法展开了深入研究。结果表明:相对于周期注气、轮注轮采、连续注气等方式,水气交替方式CO_2气体波及较均匀,提高采收率效果更佳;月度CO_2注采比为1.7~1.8时,能同时兼顾保持混相能力和防止气窜,提高降水增油效果;针对油井的气窜特征,制定不同的流压控制标准,可最大程度地发挥CO_2驱的作用;通过周期采油方式来调整压力场变化,既可增加油气接触频率而促进混相,又可扩大CO_2波及体积,且一类见气井的周期采油效果要好于三类见气井的周期采油效果以及连续采油方式的采油效果;通过调整注采比控制合理生产压差,安装井口控套阀和设置井口单井罐定期泄压等措施,有效地保障了安全生产。研究结果可为吉林油田及国内其他同类地区开展CO_2驱试验与推广提供参考。

In order to solve the problems of low opening rate caused by directional gas channeling in the middle and later stages of CO2 flooding development in low permeability reservoirs,poor overall development results and potential safety issues,numerical simulation and laboratory experiments were used to analyze the effects of anti-controlled gas channeling,to ensure the production rate of oil wells and other technical methods.The results show that the CO2 of water-gas alternating is more uniform and the oil recovery efficiency is better than that of gas injection,wheel injection and continuous gas injection.When the monthly CO2 injection-production ratio is 1.7 to 1.8,it can simultaneously maintain the mixing capacity and prevent gas channeling,so as to decrease water cut and increase oil production.In view of gas channeling characteristics of oil well,different flow pressure control standards were formulated to maximize the CO2 flooding effect.The pressure field changes can be adjusted by periodic oil recovery,which can increase the frequency of oil and gas contact to promote mixed phase and expand the volume of CO2.The periodic oil recovery effect of typeⅠgas wells is better than that of typeⅢgas wells and the continuous oil recovery.The safety production is effectively guaranteed by adjusting the injection production ratio and controlling the reasonable production pressure difference,installing the wellhead control valve and setting up wellhead single well tank regular pressure relief.The results can provide technical reference for the development of CO2 flooding test and promotion in Jilin Oilfield and the same kind of oil reservoirs in China.