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Study on a Novel Crosslinked Polymer Gel Strengthened with Silica Nanoparticles Yifei Liu, Caili Dai, Kai Wang, Chenwei Zou, Mingwei Gao, Yanchao Fang, Mingwei Zhao, Yining Wu, and Qing You Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01432 • Publication Date (Web): 30 Jul 2017 Downloaded from http://pubs.acs.org on August 10, 2017
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Energy & Fuels
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Study on a Novel Crosslinked Polymer Gel Strengthened with Silica
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Nanoparticles
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Yifei Liu1, Caili Dai1∗, Kai Wang2, Chenwei Zou1, Mingwei Gao1, Yanchao Fang1,Mingwei Zhao1,
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Yining Wu1, Qing You3∗
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1 School of Petroleum Engineering, State Key Laboratory of Heavy Oil, China University of Petroleum (East
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China), Qingdao, Shandong, 266580, People’s Republic of China, 2 China National Offshore Oil Corporation
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Research Institute, Beijing, 100028, People’s Republic of China, 3 School of Energy Resources, China University of
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Geosciences, Beijing, 100083, People’s Republic of China.
∗
Caili Dai
Email:
[email protected] Tel: +86-532-86981183
∗
Qing You
Fax: +86-532-86981161
Email:
[email protected] Tel: +86-010-82322754 1
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Abstract
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This paper studied the strengthening effects of silica nanoparticles on the polyacrylamide
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(PAM)/hydroquinone (HQ)-hexamethylenetetramine (HMTA) composite gel. Pure PAM/HQ-HMTA gel and
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PAM/HQ-HMTA gels containing silica nanoparticles up to 0.3 wt% were prepared at 110 °C. Influences of
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silica nanoparticles on gelation performances were systematically evaluated. By addition of silica
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nanoparticles, the gelation time became shorter and the gel strength was improved observably. Rheological
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measurements showed that silica nanoparticles enhanced both elasticity and viscosity of the gel significantly.
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Thermal stability of the gel was studied by differential scanning calorimetry (DSC) measurements. The
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maximum tolerated temperature of the gel was improved from 137.8 °C to 155.5 °C by addition of silica
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nanoparticles with a concentration of 0.3 wt%. Furthermore, to study the strengthening mechanisms of silica
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nanoparticles to the gel, the microstructure and existing state of water within the gel were investigated by
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environmental scanning electron microscopy (ESEM) measurement and DSC measurement. Micrographs of
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the gel showed that massive aggregations and arrangements of silica nanoparticles existed in uniformly
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distributed three-dimensional network structures of the gel, which greatly improved the structural strength of
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the gel. Moreover, mass fraction of bound water within the gel increased from 22.5% to 39.9% by addition
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of silica nanoparticles with a concentration of 0.3 wt%. The hydrogen bonds and electrostatic attractions
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between silica nanoparticles and water molecules/hydronium ions make higher bound water ratio, which
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contributes to better water holding capacity and thermal stability of the gel.
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Energy & Fuels
1. Introduction
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Global demand for crude oil as the important energy resource and chemical raw material is growing
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constantly with the increase of word economy.1 However, almost all reservoirs are heterogeneous, which
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leads to early water breakthrough into production wells along high permeability zones. The water
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breakthrough results in low sweep efficiency, high water cut, low oil recovery and high remaining oil
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saturation, which makes uneconomic water-flooding, high-cost sewage treatment and severe environment
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contamination.1-7 As reported, there is approximately 70% remaining oil left in the unswept zones of
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heterogeneous reservoirs.8 Thus, controlling water cut and increasing oil production is always the real
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challenge for field operators.8-10 And increasing sweep efficiency is the key to increasing oil production and
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reducing water production.1
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Until now, various crosslinked polymer gels are still the most commonly used techniques to improve
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sweep efficiency for enhanced oil production and reducing excessive water production.11, 12 In general, the
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crosslinkers used to prepare crosslinked polymer gels can be either metallic or organic.13 Metallic
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crosslinkers crosslink with polymers by ionic bonds, while organic crosslinkers crosslink with the polymers
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by covalent bonds. The metallic crosslinkers, such as Cr3+, Zr4+, and Al3+, are known to be toxic and
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environmentally unacceptable.14 Moreover, metallically cross-linked gels typically have poor thermal
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stability and short gelation time at temperatures higher than 60~70 °C, which are not suitable for high
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temperature reservoirs.15,
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polymer gels are with better thermal stability and longer gelation time, even at elevated temperatures.15 This
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owes to the covalent bonds formed by the polymers and organic crosslikers, which are with higher bond
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energy than ionic bonds.
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Compared with the metallically cross-linked gels, organically cross-linked
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Several organically crosslinked polymer gels have been reported in the literatures, among which the
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phenol-formaldehyde gel and polyethylene imine (PEI) gel draw more attention.17-21 The PEI crosslinker is
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nontoxic and environmentally friendly, however, the high price limits its application.22 In contrast, the 3 ACS Paragon Plus Environment
Energy & Fuels
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crosslinker composed of phenol-formaldehyde is cheap, but the main problem is that the phenol and
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formaldehyde are toxic, especially the carcinogenic character of formaldehyde.15 To overcome the above
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problem, researchers find the substitutes with lower toxicity for phenol and formaldehyde, such as
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hydroquinone (HQ) and hexamethylenetetramine (HMTA). Former studies have shown that the HQ-HMTA
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crosslinked polymer gels are with longer gelation time and better thermal stability than the other organically
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crosslinked gels, which have been successfully applied in four high temperature oilfields, among which the
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highest reservoir temperature is about 121 °C, for water shutoff treatment.13, 23
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In addition, the gels prepared with solid particles have drawn great attention in recent years due to their
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excellent performances compared with the gels unreinforced.24-28 Zhou et al.29, 30 developed a clay-gel for
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water shut-off in reservoirs with high permeability channels. The prepared gel showed high gel strength,
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good thermal stability and significant plugging effect. However, the gel system is only applicable for
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blocking fractures and wormholes, moreover, the salinity of the formation water has to be low (
