Article pubs.acs.org/IECR
New Insights into the Gelation Behavior of Polyethyleneimine CrossLinking Partially Hydrolyzed Polyacrylamide Gels Hu Jia,*,† Jin-Zhou Zhao,*,† Fa-Yang Jin,† Wan-Fen Pu,† Yong-Ming Li,† Ke-Xing Li,† and Ji-Mao Li‡ †
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu, People’s Republic of China ‡ Northeast Oil & Gas Branch of Sinopec, Changchun, People’s Republic of China S Supporting Information *
ABSTRACT: Using polymer gel is still the mainstream technique of the chemical method for water shut-off in mature oilfield development. The gelation performance of polyethyleneimine (PEI) cross-linking partially hydrolyzed polyacrylamide (HPAM) gel was systematically investigated in this paper by using three types of molecular weight (Mw) HPAM. Results show that the gelant solution (the fluid solution of cross-linker and polymer that exists before gelation) can slightly gel even at room temperature and form a rudimentary 3D network structure for protecting the subsequent gelling. The main factors, including HPAM, PEI concentrations, HPAM Mw, and total dissolved solids (TDS) to affect the gelation performance are also discussed. The gelation time is around 18−72 h at 65 °C, which is much longer than the commonly used chromium(III)-acetate crosslinking HPAM gel system. The gelation performance of the PEI/HPAM gel system is improved after flowing through porous media and shows the adverse law for a porous media sheared chromium(III)-acetate or phenol-formaldehyde cross-linking HPAM gel system. Atomic force microscopy (AFM) scanning results show that the microstructure of PEI/HPAM gel distributes a lot of cavities. Compared to the original premature gel (code B), the cavities are more uniform and regular after flowing through porous media. In addition, this study revealed that the presence of free oxygen in the uniform cavities of the weak crosslinked gel after flowing through porous media can accelerate the oxidation reaction to produce a darker brown gel. It also discusses how these new findings will affect the application of the gel system in the oil field. have achieved many worldwide successful field applications over the past decade.18−21 Recent results indicate that a variety of polymers containing acrylamide pendant groups react with PEI nitrogens through a transamidation reaction path way to provide gels.22 For the PEI/HPAM gel system, the gelation mechanism can be explained as an imine nitrogen from PEI attacking the carbonyl carbon attached to the amide group as shown in Figure 1.22 Many studies on PEI cross-linking acrylamide or polyacrylamide based copolymers have been focused on theoretical research and applications in moderate to high temperature
1. INTRODUCTION Excessive water production is a universal problem in the mature oil/and or gas reservoirs development. Worldwide, most of oil companies spend billions of U.S. dollars to address the high water cut problem in oil and/or wells.1−3 However, oil production is mainly dependent on various enhanced oil recovery (EOR) techniques.4,5 Injecting a polymer solution with a cross-linker, as a chemical method of EOR of forming a polymer gel in subterranean formation during a few hours to several days for water shutoff has been widely used in mature oilfield development.6,7 PAM (Polyacrylamide) or acrylamide based copolymers have been the most commonly used base polymers.8−11 They can be cross-linked either organically or inorganically. Inorganic crosslinkers including Cr3+, Al3+, and Zr4+ can cross-link HPAM.12,13 However, the cross-linking mechanism is done by ionic bonding between the negatively charged carboxylate groups and the multivalent cation, which has a low stability at high temperatures. Organically cross-linked polymers are known to have a higher thermal stability due to the covalent bonding cross-linking mechanism. Such organic cross-linkers as phenolformaldehyde, hydroquinone-hexamethylenetetramine, methenamine, terephthalaldehyde, and dihydroxy-naphthalene, etc. cross-linked HPAM gel systems have been reported widely in the literature.14−17 Nevertheless, some of these cross-linkers are toxic with limited uses in the field application. In consideration of environment protection, low toxicity organic PEI was introduced to obtain gels that are stable over a wider temperature range, and these PEI based polymer gels © 2012 American Chemical Society
Figure 1. Polymers containing acrylamide pendant groups react with PEI nitrogens through a transamidation reaction pathway to provide gels.22. Received: Revised: Accepted: Published: 12155
March 20, 2012 August 22, 2012 August 24, 2012 August 24, 2012 dx.doi.org/10.1021/ie301818f | Ind. Eng. Chem. Res. 2012, 51, 12155−12166
Industrial & Engineering Chemistry Research
Article
reservoirs (70−156 °C) because these high temperature reservoirs are often facing more of a challenge for water shutoff. However, polymer gel treatments in low temperature (
