Writing in the journal Energies, a team of researchers from China has published a paper investigating the synthesis of graphene oxide doped polyacrylamide gels. The research has potential benefits for the petrochemical industry.
Study: Synthesis and Mechanical Properties of Polyacrylamide Gel Doped with Graphene Oxide. Image Credit: Jarek_Sz/Shutterstock.com
Improving Oil Field Exploitation
Oil fields are finite resources with diminishing returns over time for exploitation and extraction. Petrochemicals have made modern industry possible, powering industry, energy generation, and transportation all over the world. Whilst there is a push toward net zero carbon emissions, oil and natural gas are still a necessary part of modern industry and society, at least in the short-to-medium term.
Enhancing the recovery of petrochemicals from deep resources is a key concern in the petrochemical industry currently. Several reservoirs suffer from problems with water ingress, and oil recovery decreases during the medium and late stages of reservoir exploitation and oil recovery.
Several strategies have been explored to improve oil recovery from low-permeability reservoirs and provide enhanced water control. Amongst the approaches proposed, polyacrylamide polymer gels have proven potentially beneficial. These materials are used to block water flow which can impede oil recovery from reservoirs.
The structure diagram of GO.Image Credit: Zhang, H-P., et al., Energies
Polyacrylamide Polymer Gels
These materials have several distinct advantages for this purpose. Benefits include controllability, selectivity, and easy injection. However, there are some challenges associated with them which hinder their potential use for improving oil exploitation in reservoirs.
Polyacrylamide polymer gels suffer from drawbacks such as insufficient thermal stability and high strength which cannot be properly controlled. This unfortunately limits their application in ultra-deep wells, where temperatures can typically exceed 150 oC and are at a depth of 5300-7000 m.
These reservoirs require gels with high temperature resistance and weak mechanical properties. The high strength of these gels makes it difficult to deploy them at such extreme depths. Thus, their efficiency for controlling water ingress is severely limited in such environments. As oil is increasingly being exploited in these ultra-deep reservoirs, this is a critical issue for the petrochemical industry.
Research has focused on strategies to improve the properties of polyacrylamide polymer gels, reducing their strength and increasing their temperature resistance to make them more suitable to ultra-deep reservoir environments. Currently, these materials are limited to shallow, low-temperature reservoirs.
Transmission electron microscope (TEM) picture of graphene oxide. Image Credit: Zhang, H-P., et al., Energies
Strategies to Improve Polyacrylamide Gels
Scientists have evaluated several innovative methods. Some researchers have grafted synthetic polymer and natural polysaccharide copolymers, such as starch-grafted polymers. Graft polymerization modifies the structure of natural polymers, making them suitable for a wide range of applications. Additionally, modified nanoparticles have been used to improve the physical properties of gels.
Modified nanoparticles can further improve properties such as mechanical strength and thermal stability in hydrogels compared to starch-grafted polymers, leading some researchers to concentrate on the incorporation of nanoparticles into hydrogels. Moreover, research has indicated that this strategy improves beneficial properties such as elasticity and ductility, making the approach suitable for deep oil reservoir applications.
One research paper by Shamlooh et al. evaluated the effects of SiO2 nanoparticles of different concentrations and sizes on cross-linked polyacrylamide/PEI gels and properties such as viscoelasticity and stability. A 2 wt.% SiO2 incorporation improved gel strength by more than three hundred percent. However, whilst these strategies have demonstrated potential, challenges still exist with high strength.
Photos of PAM/PEI/GO gels with 2.0 wt.% PAM, 0.1 wt.% PEI, and various GO concentrations. (a) Without GO; (b) 0.006 wt.% GO; (c) 0.08 wt.% GO; (d) 0.12 wt.% GO. Image Credit: Zhang, H-P., et al., Energies
The Study
The authors have investigated the benefits of using graphene oxide to improve the properties of polyacrylamide gels for deep-reservoir oil exploitation. Graphene oxide has emerged in recent years as a viable alternative to other modification strategies, with several studies focusing on this material.
Graphene oxide possesses many advantages for this application. The material has a vast number of hydrophilic epoxy and hydroxyl groups and can be easily peeled and dispersed in stable aqueous solutions, making it suitable for the production of composite hydrogels with excellent mechanical and physical properties.
Modification is made easy by the presence of numerous active sites due to the material’s large surface area. This makes it possible to incorporate functional characteristics into graphene oxide.
A novel cross-linked nanocomposite polyacrylamide gel was prepared in the study to understand the effects of graphene oxide on thermal stability and mechanical properties. Characteristic group changes within the gel matrix due to modification with graphene oxide nanosheets were analyzed using FT-IR, XRD, and Raman spectroscopy.
Yield stress, viscoelasticity, and creep recovery were measured to study rheological properties. SEM and differential thermal analysis were employed to analyze the changes in thermal stability and 3D network structure.
Improved mechanical properties were observed in the prepared nanocomposite graphene oxide/cross-linked polyacrylamide gels. PAM, the main agent, was responsible for the gel’s increased toughness and strength. Increased graphene oxide content reduces the gel’s stiffness, and gelation time increased with greater graphene oxide content.
Differential scanning calorimetry revealed that graphene oxide improved bond strengths in the prepared composite polyacrylamide gel due to the presence of carboxyl and hydroxyl groups. This enhanced the composite gel’s thermal stability.
Based on their analysis of this novel composite graphene oxide/polyacrylamide gel, the authors have stated that it has the potential to be used for water control in high temperature, ultra-deep oil reservoirs.
Further Reading
Zhang, H-P., et al. (2022) Synthesis and Mechanical Properties of Polyacrylamide Gel Doped with Graphene Oxide Energies, 15(15), p. 5714 [online] mdpi.com. Available at: https://www.mdpi.com/1996-1073/15/15/5714
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