低渗透油藏氮气-低矿化度水交替驱油特征及机制

Characteristics and mechanisms of N 2/low-salinity water alternate flooding in low permeability reservoirs

氮气-低矿化度水交替驱是将气-水交替驱中的水段塞替换为低矿化度水段塞。通过试验研究氮气-低矿化度水交替驱驱油特征和提高采收率的机制。结果表明:氮气-低矿化度水交替驱过程中,气体可以进入水难以波及的细小含油孔道,低矿化度水可以增强地层岩石水润湿,促进岩石壁面原油剥离,同时抑制氮气窜流,提高驱替压差,有效提高波及体积和驱油效率;随着渗透率降低,驱替达到稳定状态需要注入的流体体积逐渐增加,提高采收率幅度减小;非均质条件下氮气-低矿化度水交替驱可以有效降低高渗岩心窜流,扩大波及范围;在渗透率级差2~12.3范围内,其采收率较氮气驱提高2.05%~8.08%,较低矿化度水驱提高1.92%~3.97%;随着渗透级差的增大,氮气-低矿化度水交替驱的流动调控能力减弱。

N 2/low-salinity water alternating injection is to replace the water slug in gas-water alternate flooding with a low-salinity water slug.In this paper,the characteristics of N 2/low-salinity water alternating injection and its mechanisms for enhanced oil recovery were investigated experimentally.The results show that N 2/low-salinity water alternating flooding has both the advantages of low-salinity water enhancing the water wetting of formation rocks and the inhibition of water slug on N 2 channeling,which can promote the stripping of crude oil and effectively improve the displacement pressure difference.The injected N 2 gas can enter the small oil-bearing pores that are difficult to be swept by water,increasing the sweeping volume and oil displacement efficiency.As the effective permeability decreases,the volume of fluid injected to achieve a stable state increases,and the enhanced oil recovery amplitude decreases.Under heterogeneous conditions,N 2/low-salinity water alternating flooding can control the channeling of high permeability layers and expand sweeping area.In the range of permeability level difference 2-12.3,the recovery efficiency of the N 2/low-salinity water alternating injection increases by 2.05%-8.08%compared with N 2 injection alone,and 1.92%-3.97%compared with low-salinity water injection.With the increase of permeability level difference,the flow regulation ability of the N 2/low-salinity water alternating flooding is weakened.