水基纳米流体交替注气提高油湿碳酸盐岩油藏采收率的实验研究

Experimental Study on Improving Oil Recovery of Oil Wet Carbonate Reservoir by Alternate Gas Injection with Water-based Nanofluids

水交替注气(WAG)是一种常用的提高采收率方法,在世界各地的不同油藏中得到了广泛应用。该文提出了一种纳米流体交替注气(NWAG)的新方法,用以改善传统WAG工艺处理油湿碳酸盐岩储层的能力。在饱和原油的碳酸盐岩岩心上进行了水交替注气(WAG)和纳米流体交替注气(NWAG)的不同实验研究。采用两种不同粒径(11~14、30~40nm)的球形SiO_(2)纳米粒子来改善WAG注入法的性能。岩心驱油实验中的WAG过程是通过注入气体和SiO_(2)水基纳米流体进行的。此外,还进行了不同的表征研究,以研究纳米粒子对回收机制的影响。实验表明,纳米二氧化硅在岩石表面的吸附改变了储层岩石的润湿性,使其由油湿变为强水湿;纳米颗粒位于油水界面,导致油水界面张力降低。此外,通过向水相中添加SiO_(2)纳米颗粒,注入流体的粘度增加。增加粘度和改变润湿性会影响粘滞力和毛细管力,增加毛细管数,从而提高采收率。结果表明,粒径越小,回收率和效率越高。实验还表明,渗透率较低的岩心样品的采收率高于其它岩心样品。

Alternate water gas injection(WAG) is a common EOR method,which has been widely used in different reservoirs all over the world.This paper presents a new method of nanofluid alternating gas injection(NWAG) to improve the ability of traditional WAG process to treat oil wet carbonate reservoir.Different experimental studies on WAG and were carried out on carbonate cores of saturated crude oil.Two kinds of spherical SiO2 nanoparticles with different sizes(11~14 and 30~40 nm) were used to improve the performance of WAG injection method.The WAG process in core flooding experiment is carried out by injecting gas and SiO_(2)water-based nanofluids.In addition,different characterization studies were carried out to study the effect of nanoparticles on the recovery mechanism.The experimental results show that the adsorption of nano-Si02 on the rock surface changes the wettability of reservoir rock from oil wet to strong water wet;nanoparticles are located at the oil-water interface,resulting in the decrease of oilwater interfacial tension.In addition,by adding SiO_(2)nanoparticles to the aqueous phase,the viscosity of the injected fluid increases.Increasing the viscosity and changing the wettability will affect the viscosity and capillary force,and increase the capillary number,so as to enhance the oil recovery.The results show that the smaller the particle size,the higher the recovery and efficiency.The experiment also shows that the recovery of core samples with low permeability is higher than that of other core samples.