Xiong Chunming, Wei Falin, Li Weitao, Liu Pingde, Wu Yong, Dai Mingli, Chen Jun
Research Institute of Petroleum Exploration & Development, PetroChina, Beijing 100083, P. R. China.
Sichuan University, Chengdu 610044, P. R. China.
ACS Omega. 2018 Sep 6;3(9):10716-10724. doi: 10.1021/acsomega.8b01205. eCollection 2018 Sep 30.
A gel system composed of acrylamide (AM), ,'-methylenebisAM (BIS), and ammonium persulfate ((NH)SO) was developed and applied extensively in reservoirs to reduce water cut and increase oil production in mature fields. However, this gel system suffers from thermal stability loss and syneresis at high temperatures that reduces its ability to control water flow. It has been widely accepted that the loss of gel thermal stability can be explained via three aspects: the rupture of polymer chains, the breakage of cross-linker chains, and hydrolysis of polymer. The mechanism of hydrogel syneresis through polymer hydrolysis has been investigated extensively in other publications. However, research on the other two mechanisms is quite limited. In this article, we conduct a series of experiments to demonstrate how the rupture of polymer and cross-linker chains leads to the hydrogel instability at high temperatures. Viscosity and energy-dispersive system measurements suggested that polyAM chains were disrupted by the oxidation reactions involving free radicals. The method to measure the cross-linking degree was established and in combination with X-ray photoelectron spectroscopy measurements, the results showed that cross-linker chains were broken as a result of weaker C-N bond resulting from positively charged mesomethylene carbon and hydrolysis of amide groups on the cross-linker. Because of the application of deionized water in the experiments, nuclear magnetic resonance and FTIR measurements showed that the hydrolysis degree of polymer was weak. Hence, our results verified that breakage of polymer and cross-linker chains led to the rupture of the gel network at high temperature. Besides, cross-linker chains may play a more important role in the thermal stability of the gel, which explains some work into high-temperature-resistant gels.
一种由丙烯酰胺（AM）、N,N'-亚甲基双丙烯酰胺（BIS）和过硫酸铵（(NH₄)₂S₂O₈）组成的凝胶体系被研发出来，并广泛应用于油藏中，以降低成熟油田的含水率并提高原油产量。然而，这种凝胶体系在高温下会出现热稳定性丧失和脱水收缩的问题，从而降低其控制水流的能力。人们普遍认为，凝胶热稳定性的丧失可以从三个方面来解释：聚合物链的断裂、交联剂链的断裂以及聚合物的水解。关于通过聚合物水解导致水凝胶脱水收缩的机制，在其他文献中已有广泛研究。然而，对另外两种机制的研究相当有限。在本文中，我们进行了一系列实验，以证明聚合物和交联剂链的断裂是如何导致水凝胶在高温下不稳定的。粘度和能量色散系统测量表明，聚AM链被涉及自由基的氧化反应破坏。建立了测量交联度的方法，并结合X射线光电子能谱测量，结果表明，由于带正电的亚甲基碳导致C-N键变弱以及交联剂上酰胺基团的水解，交联剂链发生了断裂。由于实验中使用了去离子水，核磁共振和傅里叶变换红外光谱测量表明聚合物的水解程度较弱。因此，我们的结果证实了聚合物和交联剂链的断裂导致了凝胶网络在高温下的破裂。此外，交联剂链在凝胶的热稳定性中可能起更重要的作用，这解释了一些关于耐高温凝胶的研究工作。
