水驱后特低渗透油藏氮气驱驱油特性分析

Characteristics of Nitrogen Displacement in Ultra-Low Permeability Reservoir after Waterflooding

特低渗透油藏水驱采收率低,注入压力高,而氮气在特低渗油藏具有良好的注入性。本文在特低渗透岩心水驱后分别进行了常规的注氮气、水驱后水气交替、水驱后脉冲注氮气驱替实验。实验结果表明:特低渗储层微观非均质性导致气体在大孔道易形成窜流,水驱后常规注氮气提高采收率的效果有限。水气交替通过多轮次的注入使油藏中不同相态流体的分散程度提高,在优势流动通道中形成毛管阻力,促使后续注入气体进入局部致密区,可有效提高采收率16.37%;脉冲注气通过周期性注气方式,在局部高渗区和局部低渗区间形成压力扰动与交互渗流,使流体在地层中不断地重新分布,从而启动油层低渗区原油,提高采收率15.94%。此外,脉冲注气的注气压力比较低,与水气交替开采方式比较注入性提高。

Enhanced oil recovery by waterflooding is low and injected pressure is high in the ultra-low permeability reservoir, but nitrogen is easy to be injected. In this paper, core displacement experiments were conducted by the means of conventional nitrogen injection, WAG and pulse gas injection in ultra-low permeability reservoir after waterflooding. The experiment results showed that since the microanisotropy characteristic of ultra-low permeability reservoir, Nitrogen can crossflow easily in the big pore channel, therefore, injecting nitrogen normally after water flooding made an ineffective effort to enhance oil recovery. However, with using the WAG the dispersive degree of different fluid phase could be enhanced, and then, the capillary force could be formed in the advantage flow channel firstly, which made the later injected nitrogen come into partial dense area, oil recovery being enhanced effectively by 16.37%; The pulse gas injection could form pressure disturbance and interactive seepage between high-permeability zone and low-permeability zone which made the fluid redistributed in the reservoir, and finally the oil trapped in the low-permeability area was launched, thereby the oil recovery could be enhanced by 15.94%. Besides, the pulse gas injection pressure was low, and the gas injectivity was better than WAG.