Insights into the Effects of Salinity on the Transport Behavior of Polymer-Enhanced Branched-Preformed Particle Gel Suspension in Porous Media

Abstract

The branched-preformed particle gel (B-PPG) is a novel viscoelastic particle gel used for improving sweep efficiency and enhancing oil recovery in a heterogeneous mature reservoir. To improve the performance of B-PPG, partially hydrolyzed polyacrylamide (HPAM) is used to increase the viscosity and to prepare a homogeneous B-PPG suspension. Although some encouraging progress has been made in the application of polymer-enhanced B-PPG suspension, its transport behavior in porous media is still unclear, which is crucial for its application in enhanced oil recovery (EOR) in a heterogeneous reservoir. Due to the complex reservoir condition of different brine salinities, the physiochemical property of polymer-enhanced B-PPG suspension as well as its transport behavior in porous media can be affected, which may lead to unsatisfactory results. Understanding the effects of salinity on the transport behavior of polymer-enhanced B-PPG suspension in porous media is of vital importance in figuring out the flow behavior and improving the sweep efficiency in the mature reservoir. In this study, the effects of salinity on the swelling ratio, particle size, viscosity property, and suspension stability of B-PPG and polymer-enhanced B-PPG suspension were studied. Meanwhile, sand pack flow experiments were conducted to study the transport behavior of polymer-enhanced B-PPG suspension in porous media. The results show that when the brine salinity increases, the swelling ratio and particle size of B-PPG, as well as the viscosity and the suspension stability of polymer-enhanced B-PPG suspension all demonstrate a decreasing trend. In the range of 3550–10 651 mg·L–1, as the brine salinity increases, the resistance factor decreases and the transportation of polymer-enhanced B-PPG suspension in porous media becomes easier. In this case, the ratio of swollen B-PPG particle diameter to the pore throat diameter turns out to be the determining factor that governs the transport behavior. However, when the brine salinity is higher than 10 651 mg·L–1, with the increase of brine salinity, the resistance factor increases. As a result, the effects of viscosity and suspension stability of polymer-enhanced B-PPG suspension become more prominent.