Thermal degradation behavior of seawater based temporary plugging gel crosslinked by polyethyleneimine for fluid loss control in gas well: Kinetics study and degradation prediction

Abstract

Polymer gel served as a temporary plugging agent for fluid loss control during well completion and workover has received great attention in recent years. Gel breaking as well as flowback is the most concern after the downhole operations such as perforation, replace tubing. Using oxidative breaker as chemical method or jetting nozzle as mechanical strategy were mainly employed to remove gel. The former often fails to fully contact with the gel, and the gel breaking efficiency is not ideal. The latter, although effective, greatly increases the cost of operation. Thermal degradation of gel plug at reservoir temperature after the operation is more welcome. In this paper, we combined aging experiments, Fourier Transform Infrared Spectroscopy (FTIR) analysis, Scanning Electronic Microscopic (SEM) and Differential Scanning Calorimetry (DSC) experiment to reveal the degradation mechanism of seawater based temporary plugging gel crosslinked by polyethyleneimine (Abbreviated as “gel plug”). In addition, the fluid loss control ability and formation damage characteristic of the gel plug were evaluated through core flooding experiment. The dynamic process of gel degradation was studied by DSC technology, and the thermodynamic parameters were respectively calculated by Kissinger, Flynn-Wall-Ozawa, Horowitz-Metzger and Coats-Redfern model. According to the desired activation energy, Semenov equation and relevant data were used to derive the model for predicting gel degradation time. The developed model conforms to the aging experimental results with correlation coefficient of 0.988. This study provides knowledge for the optimization of temporary plugging gel technology in high-temperature gas wells.

Graphical Abstract

Keywords:

• Gel plug
• degradation kinetics
• polyethyleneimine
• fluid loss control
• sea water

Acknowledgments

Thanks for CNOOC Ltd. Shanghai Branch to provide seawater from East China Sea.

Additional information

Funding

This work is supported by State Key Science and Technology Project of China (Award No. 2016ZX05027-003-006), Distinguished Young Scholars Fund in Sichuan (Award No. 2019JDJQ0036) and Youth Science and Technology Innovation Team Fund of Southwest Petroleum University, China (Award No. 2018CXTD08).