High‐temperature performance and cross‐linking mechanism of different types of gel systems in saline environment

Abstract

Profile modification of injection wells or water plugging of production wells are the most common ways to improve oil recovery with the continuous development of oil reservoirs. For high temperature and high‐salt oil and gas reservoirs, the plugging agent is required to have certain stability under high temperature and high‐salt conditions. Polymer gel is one of the commonly used plugging agents in oil fields. This article conducted detailed experimental research and mechanism analysis on six gel systems composed by two types of polymer (hydrolyzed polyacrylamide [HPAM] and terpolymer L‐1) and three types of cross‐linker systems (phenol/hexamethylenetetramine [HMTA], resorcinol/HMTA and bisphenol‐A/HMTA). The mechanisms of cross‐linker systems and polymer were studied, and the experimental researches were done on their gelation process, long‐term thermal stability, salt resistance, microstructure observation, rheological properties, and so on. The number of high‐temperature resistant cross‐linking points determines the performance of the gel system formed by cross‐linker systems with the polymer. The cross‐linker systems of bisphenol‐A/HMTA have four high‐temperature resistant cross‐linking points, and its performance was the best. Due to the introduction of ATBS and NVP groups on the polymer chain, the performance of gel system formed by the terpolymer L‐1 was significantly more stable than that of formed by HPAM. This study shows that the bisphenol‐A/HMTA‐L‐1 gel has excellent long‐term thermal stability and salt tolerance, and can be used in ultrahigh temperature (150°C) and high‐salt oil and gas reservoirs to improve oil recovery.

Progress and Prospects of In Situ Polymer Gels for Sealing Operation in Wellbore and Near-Well Zone

“…Cross-linking mechanism of different types of cross-linker systems (adopted from Liu et al) (a) reaction mechanism of phenol, formaldehyde, and amide group; (b) reaction mechanism of resorcinol, formaldehyde, and amide group; (c) reaction mechanism of bisphenol-A, formaldehyde, and amide group. Reproduced with permission from ref . Copyright 2022 Wiley Online Library.…”

“…The dehydration rate usually quantifies the thermal stability of a gel: the higher the dehydration rate, the weaker the thermal stability of the gel. Liu et al 144 compared the thermal stability of gels formed by different combinations of cross-linkers. The dehydration rate was bisphenol-A/HMTA < resorcinol/HMTA < phenol/ HMTA, and bisphenol-A/HMTA had the best thermal stability, with a strength code of "D" for 120 days of aging at 150 °C, and the dehydration rate was only 1.6%.…”

“…Finally, the above reaction products undergo a dehydration/condensation reaction, forming a gel system with a three-dimensional network structure. 144 Liu et al 145 used AM/acrylamide-sodium tert-butyl sulfonate (ATBS)/NVP copolymer, HMTA, and bisphenol-A to prepare gels resistant to temperatures ranging from 150 to 200 °C. Chen et al 137 prepared a gel using AM/AA/AMPS polymers, hydroquinone, and hexamethylenetetramine, and the dehydration rate of this system was only 5% after aging at 130 °C for 120 days.…”

A gel system with long‐term high‐temperature stability for deep profile modification of high‐temperature oil and gas reservoirs

“…At present, there are a lot of research on hightemperature gel systems, but most of them are based on the research of gelation dynamic, static high-temperature resistance, and stability. 31,42,43 However, under actual reservoir conditions, the gel solution first flow in the formation porous media for a period before forming a highviscosity gel system. And there are few studies on the anti-shear properties of gel systems and the gelation properties of porous media.…”

“…Asghari 30 reported a foam gel using nitrogen as a blowing agent, which has a residual resistance coefficient of 64–180 and is good for blocking in high‐permeability layers. Based on previous studies, Liu et al 31 studied the gelation and long‐term stability characteristics of different polymers and crosslinked systems, analyzed their crosslinked mechanism, which provided a foundation for the development of gel systems.…”