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.

摘要

聚合物凝胶作为完井和修井过程中控制滤失的临时封堵剂，近年来受到了广泛关注。破胶和返排是穿孔、更换油管等井下作业后最受关注的问题。主要采用氧化破胶剂作为化学方法或喷嘴作为机械策略去除凝胶。前者往往不能与凝胶充分接触，破胶效率不理想。后者虽然有效，但大大增加了运营成本。操作后凝胶塞在储层温度下的热降解更受欢迎。在本文中，我们结合老化实验、傅里叶变换红外光谱 (FTIR) 分析，扫描电子显微镜（SEM）和差示扫描量热（DSC）实验揭示了聚乙烯亚胺交联的海水基暂堵凝胶（简称“凝胶塞”）的降解机理。此外，还通过岩心驱替实验评价了凝胶塞的降滤失能力和地层损伤特性。采用DSC技术研究凝胶降解的动态过程，分别采用Kissinger、Flynn-Wall-Ozawa、Horowitz-Metzger和Coats-Redfern模型计算热力学参数。根据所需的活化能，利用Semenov方程和相关数据推导出凝胶降解时间预测模型。开发的模型符合老化实验结果，相关系数为0.988。