# Types and Performances of Polymer Gels for Oil-Gas Drilling and Production: A Review
## 6 Conclusions  
Because of suitable viscoelasticity and deformability, polymer gels have been widely used for formation plugging, lost circulation control, profile control, and water shutoff in oil-gas engineering. Commonly used polymer gels can be categorized as in situ crosslinked gel and ground pre-crosslinked gel. According to the different formation conditions, the  
Figure 14: Comparison of preparation principle and performance of PAM/PEI and PAM/PEI-CFA gels. (**a**) SEM images of hydrogels with different CFA content; (**b**) synthesis route of the AM/PEI-CFA hydrogel; (**c,d**) swelling and rheological properties of hydrogels with different CFA contents. (Reprinted/adapted with permission from Ref. [81]. 2018, [PERSON], et al.).  
Figure 15: Preparation principle of intercalation polymerization of a composite gel and physical photographs of the compressive test. (Adapted from Ref. [82]. 2020, [PERSON], et al.).  
two kinds of polymer gels have different synthesis principles and preparation methods, and their temperature resistance, salt resistance, and mechanical properties are also different. The main advantage of in situ crosslinked polymer gel is that it can generate a high-strength bulk gel in in situ pores and fractures to achieve a high-strength plugging zone, and the main advantage of ground pre-crosslinked gel is that its particle size can be selected according to the size of pores and fractures, and it is less affected by formation temperature, salinity, and shear action.  
To expand the application range of polymer gels in response to high temperature and high salinity formation, we reviewed the strategies for increasing the high-temperature resistance, high salt resistance, gelation rheological, and mechanical strengths of polymer gels in terms of improving the polymer, crosslinker, and additive structures and types. Meanwhile, the action mechanisms of polymer gels for profile control and water shutoff in oil-gas reservoirs, in-depth profile control and displacement in formations, and lost circulation control during drilling were also analyzed. It provides theoretical and technical references for the development and optimization of polymer gels that may be suitable for different oil-gas drilling and production processes.  
Conceptualization, J.S.; methodology, S.L.; formal analysis, S.L. and K.L.; investigation, S.L. and J.Y.; resources, S.L. and Q.Z.; data curation, S.L.; writing--original draft preparation, S.L. and K.L.; writing--review and editing, S.L.; supervision, K.L.; funding acquisition, J.S. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Natural Science Foundation of China, grant number 52074327 and 51991361, and the Natural Science Foundation of Shandong Province, China, grant number ZR2020 QE107.  
Not applicable.  
All persons included have agreed to confirm.  
Thanks to the support of the National Natural Science Foundation of China, the Natural Science Foundation of Shandong Province, China, and the professional suggestions of reviewers.  
The authors declare no conflict of interest.