Insights into Polyacrylamide Hydrogels Used for Oil and Gas Exploration: Gelation Time, Gel Strength, and Adhesion Strength
Zhenghua Sun, Shiyuan Wang, Qi Zhu, Xiaoqin Cao, Kun Lv, Yujun Feng, Hongyao Yin
Abstract
Polyacrylamide hydrogels are widely used as lost circulation materials and plugging agents in oil and gas production engineering. In these practical applications, controllable gelation time, favorable gel strength, and interface adhesion strength are desirable properties for polyacrylamide hydrogels. However, there have been no systematic studies of these properties, particularly for adhesion behavior. This study aimed to investigate the influences of polymer molecular weight and concentration on gelation time, gel strength, and adhesion ability of the nonionic polyacrylamide (NPAM)/phenol–formaldehyde resin gelling system. It is demonstrated that increasing the NPAM molecular weight and concentration strengthens the degree of gel network entanglement, resulting in shortened gelation time and enhanced gel strength. For every million increases of NPAM molecular weight ranging from 485 × 10 4 to 1217 × 10 4 Da, the gelation time reduces by 1.7 h. The adhesion strength of NPAM hydrogels is mainly related to the number of hydrogen bonds between the rock and amide groups of hydrogel surfaces. By raising enrichment of functional groups, the adhesion strength increases from 1315 to 1913 Pa. In addition, adhesion behaviors of cationic and anion polyacrylamide hydrogels were also examined in contrast to NPAM hydrogels. Interestingly, cationic polyacrylamide hydrogels possess a higher interface adhesion strength but less bulk cohesion. These findings are helpful to comprehend molecular weight and concentration effect on polyacrylamide hydrogel performances and the relationship between hydrogel network structure and macroscopical properties.