A Natural Polymer-Based Cross-Linker System for Conformance Gel Systems

Abstract

Summary This paper describes a material derived from natural sources that can be used to crosslink a variety of acrylamide-based polymers over a broad temperature range to produce gels for conformance applications. Delayed crosslinked polymer systems have been used for many years in conformance applications. For the past decade, the most widely used system has been based on chromium (3+) crosslinked polyacrylamide. Organic crosslinkers, such as phenol/formaldehyde and polyethyleneimine (PEI) have also been used with a variety of polymers. However, these systems are being scrutinized by governmental agencies and have been scheduled for phase out in some countries. Because of these issues, a single, environmentally friendly crosslinker that could be used with a variety of polymers over a broad temperature range was the focus of this study. This paper details the laboratory development of an environmentally friendly, natural polyamine crosslinker system. This crosslinker can be used with a variety of polymers, such as polyacrylamide, AMPS/acrylamide, or alkylacrylate polymers. Gels ranging from stiff and "ringing" type to "lipping" gels have been obtained. The data illustrate a simple, commercially available system that can be applied to field operations. Potential crosslinking mechanism(s) of the system will be discussed. Introduction Water production in oil-producing wells becomes a more serious problem as the wells mature. Remediation techniques for conformance control are selected on the basis of the water source and the method of entry into the wellbore. Treatment options include sealant treatments and relative permeability modifiers (also referred to as disproportionate permeability modifiers). This paper primarily discusses water control with water-based gels for applications in wells in which the oil- and water-producing zones are clearly separated and can be mechanically isolated. Chromium(III) crosslinked polyacrylamide gels can be choice materials for matrix-fluid shut-off systems.1–4 The crosslinking reactions in these gel systems take place by the complexation of Cr(III) oligomers with carboxylate groups on the polymer chains (Fig. 1). Because of the nature of the chemical bond between Cr(III) and the pendant carboxylate groups, formation of insoluble chromium species can occur at high pH levels. Other problems with these systems include thermal instability, unpredictable gel times, and gel instability in the presence of chemical species that are potential ligands. The gel times are controlled by the addition of materials that chelate with chromium in competition with the polymer-bound carboxylate groups.5,6 Another popular water-based gel system for water-control applications is based on a phenol/formaldehyde crosslinker system for homo-, co-, and ter- polymer systems containing acrylamide.7–11 Depending on the polymer composition, these gels are thermally stable, and the gel times are controllable over a wide temperature range. The crosslinking mechanism involves hydroxymethylation of the amide nitrogen, with the subsequent propagation of crosslinking by multiple alkylation on the phenolic ring (Fig. 2).12,13 Several variations of the same technology were created to overcome the toxicity issues associated with formaldehyde and phenol. These processes generally involve replacing formaldehyde and phenol with less toxic derivatives that generate phenol and formaldehyde in situ, or are themselves active components of the crosslinking system. For example, formaldehyde can be replaced with hexamethylene tetramine (HMTA), glyoxal, or 1, 3, 5-trioxane. Substitutions for phenol included phenyl acetate, phenyl salicylate, or hydroquinone, among others.12,13 Extensive patent literature for this technology exists.14–22 Recently, a less toxic crosslinker was tested extensively in field trials worldwide and enjoyed a very high success rate.23–27 This system is based on PEI crosslinker and a copolymer of acrylamide and t-butyl acrylate (PA-t-BA). PEI is a low-toxicity material that is approved in the United States for food contact.28–31 PA-t-BA is a relatively low molecular-weight polymer. The low molecular weight is expected to provide rigid "ringing gels." The crosslinking is believed to take place in situ by amidation of the pendant ester groups on the base polymer (Fig. 3). Recent test results indicate that a variety of polymers containing acrylamide pendant groups react with PEI nitrogens through a transamidation reaction pathway to provide gels (Fig. 4).32 Because of recent changes in European environmental regulations, PEI is targeted for phase-out from the Norwegian section of the North Sea within the next few years. A search for biopolymers containing amino groups suggested that chitosan (Fig. 5) may react with acrylamide-based polymers in a manner similar to PEI. Chitosan is a polysaccharide obtained by de-acetylating chitin, a homopolymer containing ß-(1-4)-2-acetamido-2-deoxy-D-glucose (Fig. 6) that occurs in the shell or skin of anthropods or crustaceous water animals. Chitosan is also present in the environment, although in lesser amounts than the chitin. The degree of deacetylation in the commercially-available chitosan materials is usually in the 70 to 78% range. The chitosan solubility in acidified water, for example in acetic or hydrochloric acid, is in the 1 to 2% range. The viscosity of the solutions depends on the molecular weight of the polymer. If the pH of the solution is increased above 6.0, polymer precipitation occurs. This paper presents results using chitosan as an environmentally preferable crosslinker for use in combination with acrylamide- based polymers. Gel treatments using this material should contain a biocide. The advantage here is that if inadvertently discharged, the chitosan will biodegrade. Experimental Methods Preparation of Chitosan Solutions. Commercial solid chitosan samples were dissolved in fresh water solutions containing 1% acetic acid to make 1.0 to 1.5% polymer solutions. Chitosan lactate salt, which is also commercially available, can be dissolved directly in fresh water to prepare solutions with similar polymer concentration. The viscosities and clarity of the solutions depended on the polymer molecular weight and the degree of de-acetylation. Aqueous solutions of chitosan salts are also available commercially, which can be used directly for crosslinking base polymers. The preformed chitosan salts are insoluble in salt water or seawater.

Fabrication of ordered lamellar polyacrylamide/P123 composite membranes via solvent-evaporation-induced self-assembly

“…These were also demonstrated by the zeta potential data as shown in also has a negative zeta potential of −1.73 mV suggests that the p-PAM interacted with P123 and enwrapped the surface of the P123 micelles through hydrogen bonds between the amide groups and ethers. When the cross-linking reagent phenolic aldehyde was added into the p-PAM/P123 mixture solution, the p-PAM chains were cross-linked by phenolic aldehyde according to the mechanism from [19], as shown in Fig. 3.…”

High surface – Highly N-doped carbons from hydrothermally treated tannin

“…Moreover, it has been also proved that tannin, in the presence of a crosslinker such as formaldehyde, hexamethylenetetramine, glyoxal, or 1-, 3-, or 5-trioxane, is a very suitable material for preparing high-quality and low-cost gels and related carbon materials. Mimosa tannin is thus able to replace resorcinol, which is the standard reagent used to prepare the same kind of materials (Amaral-Labat et al, 2012, (Braghiroli et al, 2013). 2013b; Braghiroli et al, 2013;Grishechko et al, 2013;Reddy et al, 2003).…”

Supramolecular linear polymer formed by host–guest interactions of β-cyclodextrin dimers and polyacrylamide end-capped with adamantane

“…By introducing into the polyacrylamide main chain a certain amount of annular structure monomer (N-vinyl pyrrolidone (NVP) [1], styrene [2]), strong electrolyte (2-acrylamide-2-methyl propane sulfonic acid (AMPS) [3], sodium-p-styrenesulfonate [4]), hydrophobic monomer (stearyl methacrylate [5], dimethyl-dodecyl-allyl ammonium chloride [6], anionic long-chain alkyl [7] and so on ) or trace amount of crosslinking agent, the polymer's resistance to temperature, salt and shearing has been improved as a result. However, the introducing of these monomers has brought about some new issues such as decreased molecular weight and poor solubility.…”