Probing the Effect and Mechanism of Flue Gas on the Performance of Resorcinol/Hexamethylenetetramine-Based Polymer Gel in Flue Gas Flooding Reservoir

Abstract

Polymer gel plugging is an effective method for gas mobility control in flue gas flooding reservoirs. However, the effect and mechanism of flue gas on the performance of polymer gels have rarely been reported. In this study, a polymer gel was prepared by cross-linking hydrolyzed polyacrylamide (HPAM) and resorcinol/ hexamethylenetetramine (HMTA) to illuminate the influencing mechanism of flue gas composition on gel. The gel rheological testing results showed that flue gas promoted gelation performance, whereas it seriously threatened gel long-term stability, especially at high pressure conditions. The influence of CO2 on the polymer gel had the characteristic of multiplicity. The hydrodynamic radius (Rh) and the initial viscosity of HPAM solution decreased in the presence of CO2. Nonetheless, the dissolved CO2 expedited the decomposition rate of HMTA into formaldehyde, which promoted the cross-linking process of the HPAM, leading to a shorter gelation time. Oxidation–reduction potential (ORP) tests and Fourier transform infrared spectroscopy (FTIR) analysis indicated that O2 played a leading role in the oxidative degradation of HPAM compared to CO2 and threatened the gel long-term stability at elevated gas pressures. To address the adverse effects caused by flue gas, it is highly desirable to develop polymer gels by adding oxygen scavengers or strengthening additives.

Investigation of Polymer Gel Reinforced by Oxygen Scavengers and Nano-SiO2 for Flue Gas Flooding Reservoir

“…The mass fraction of the nanoparticles ranged from 0 wt% to 0.5 wt%. It can be seen that the flue gas curves the polymer molecule chains and decreases the R h , which is founded in our previous work [ 11 , 12 ]. After the addition of nano-SiO 2 , the interaction between nano-SiO 2 and polymer leads to an increase in R h ( Figure 4 a), and improves the viscosity of the polymer solution ( Figure 4 b).…”

“…However, the flue gas contains 3% O 2 , and under high pressure flue gas, O 2 will be continuously dissolved in large quantities in the gels. Our previous work shows that O 2 leads to polymer degradation and impairment of the polymer stability [ 11 , 12 ]. Hence, a sufficient amount of thiourea needs to be added to the gelant to meet the long-term stability of the polymer.…”

“…To study the influence of nanoparticles on the long-term stability of gels, the strength of gel under high-pressure flue gas is further investigated, as shown in Figure 6 . The strength of gel without the addition of nano-SiO 2 decreases to different degrees under different flue gas pressures and performs seriously with the increase in pressure due to the comprehensive effect of CO 2 and O 2 composed in flue gas [ 11 , 12 ]. In contrast, the strength of the gel in the presence of nano-SiO 2 is improved under different flue gas pressures.…”

“…High purity N 2 and flue gas (80% N 2 , 17% CO 2 , and 3% O 2 ) were supplied by Shanghai Shenkai Gas Co. Ltd., Shanghai, China. The polymer gels are prepared with formation water, and the composition was presented in the previously published paper [ 12 ].…”

“…O 2 leads to the degradation of the polymer, which in turn undermines the long-term stability of the gel. Thereafter, the performance of resorcinol/hexamethylenetetramine-based polymer gel in flue gas environments was studied [ 12 ]. The results show that flue gas promotes gelation performance while seriously threatening the long-term stability of gel.…”