Delayed HPAM Gelation via Transient Sequestration of Chromium in Polyelectrolyte Complex Nanoparticles

Fundamental Studies on Fluids-Independent Regenerative Nanocomposite Hydrogels for Fracture Treatments of Conformance Control

Traditional granular hydrogels showed excellent injectivity, thermal integrity, and efficient remediation of heterogeneous reservoirs. However, granular hydrogels have demonstrated their inability to adapt to fractures due to the lack of sufficient interactions. Herein, we present new nanocomposite hydrogels consisting of cationic nanogelators and anionic granular hydrogels that can chemically in situ reform bulk hydrogels in the fractures. Interestingly, our granular hydrogels showed recross-linking independence on carrying fluids, contrary to prior reported fluid-dependent recross-linking granular hydrogels. The recross-linking of nanogelators and granular hydrogels can be accomplished from room temperature to 130 °C. The nanocomposite hydrogels displayed increased shear elastic moduli compared to pristine anionic granular hydrogels, probably due to the increased covalent cross-links formed by the homogeneous regenerative approach. We found that the granular hydrogels had high salinity tolerance even in the presence of 1000 ppm divalent ions of calcium (Ca2+) since Ca2+ ions often act as the cross-linker for partially hydrolyzed acrylamide-based hydrogels. Overall, we obtained new regenerative nanocomposite hydrogels based on cationic nanogelators and anionic granular hydrogels for fracture treatments.

Highly Robust Nanogels from Thermal-Responsive Nanoparticles with Controlled Swelling for Engineering Deployments

Regular nanogels have been demonstrated their inefficiency for subterranean oil recovery due to their intrinsic drawbacks of fast swelling within minutes, thermal instability, and salinity vulnerability. Prior deployment of swelling delayed nanogels mainly depended on the reservoirs at a relatively higher temperature. To address the issues encountered during engineering deployment, hereinwe devised an integrative approach to in situ form swelling delayed robust nanogels by introducing radically active monomers with thermally sensitive moieties. The nanoparticles with hydrophobic cores in brine in response to thermal input in situ generated well-dispersed hydrophilic nanogels, which showed a pronounced delayed swelling of a week compared to traditional nanogels showing swelling kinetics within minutes. Furthermore, the formation of swelling-delayed nanogels could occur at ambient temperature. This behavior was radically different from that of temperature-controlled labile cross-linkers containing nanogels, requiring temperatures greater than 50 °C for volume increase thanks to ester hydrolysis. In addition, the in-situ formed nanogels displayed long-term thermal stability and salinity tolerance under hostile media at temperatures up to 130 °C. The release of an acidic proton under aqueous conditions has been demonstrated to control the microenvironment for various scenarios. The nanotechnology of converting hydrophobic nanoparticles to hydrophilic nanogels could be applied in a wide range of practical applications such as plugging materials and foaming stabilizers for in-depth conformance control during water and CO₂ flooding.

Development of a High-Strength and Adhesive Polyacrylamide Gel for Well Plugging

Addition of melamine formaldehyde (MF) as a crosslinker containing hydroxymethyl to partially hydrolyzed poly(acrylamide) (HPAM) generated covalently crosslinked in situ gels through chemically nucleophilic attack by hydroxymethyl groups to amide in an HPAM backbone, which was demonstrated by FTIR spectrum analysis and rheological studies. NH4Cl could act as a catalyst to reduce the gelation time from 7 days in dilute water to 8 h in the presence of 0.8 wt % NH4Cl. Compared to high-temperature HPAM/phenol/formaldehyde and HPAM/Cr3+ gel systems, this gel has better adhesion and higher strength over a broad range of temperature from 60 to 100 °C under reservoir conditions with a denser and hook-like three-dimensional microstructure. Pressure-bearing capacity experiments demonstrated that the gel could efficiently plug high pressure from underneath to seal the wellbore, attributing to its high strength and good adhesion. This study could aid petroleum engineers in applying soft materials on controlling the pressure via polymer gels.

Progress of polymer gels for conformance control in oilfield

For the past decades, long-term water flooding processes have led to water channeling in mature reservoirs, which is a severe problem in oilfields. The development of better plugging ability and cost-effective polymer gel is a key aspect for the control of excess water production. Research on polymer gel applicable in a heterogeneous reservoir to plug high permeable channels has been growing significantly as revealed by numerous published scientific papers. This review intends to discuss the polymer gel techniques from innovations to applications. The related difficulties and future prospects of polymer gels are also covered. Developments of polymer gels to resist temperature, early gel formation, synergistic mechanisms and influence of pH, high salinity are systematically emphasized. The review provides a basis to develop polymer gels for future applications in oilfields to meet harsh reservoir conditions. It will assist the researchers to further develop polymer gels to improve the oil recovery from mature reservoirs under economic conditions to meet the requirements of future oilfields.

Fabrication and Characterization of Polysaccharide Metallohydrogel Obtained from Succinoglycan and Trivalent Chromium

In the present study, a polysaccharide metallohydrogel was successfully fabricated using succinoglycan and trivalent chromium and was verified via Fourier transform infrared spectroscopy, differential scanning calorimetry analysis, thermogravimetric analysis (TGA), field emission scanning electron microscopy, and rheological measurements. Thermal behavior analysis via TGA indicated that the final mass loss of pure succinoglycan was 87.8% although it was reduced to 65.8% by forming a hydrogel with trivalent chromium cations. Moreover, succinoglycan-based metallohydrogels exhibited improved mechanical properties based on the added concentration of Cr³⁺ and displayed a 10 times higher compressive stress and enhanced storage modulus (G′) of 230% at the same strain. In addition, the pore size of the obtained SCx could be adjusted by changing the concentration of Cr³⁺. Gelation can also be adjusted based on the initial pH of the metallohydrogel formulation. This was attributed to crosslinking between chromium trivalent ions and hydroxyl/carboxyl groups of succinoglycan, each of which exhibits a specific pH-dependent behavior in aqueous solutions. It could be used as a soft sensor to detect Cr³⁺ in certain biological systems, or as a soft matrix for bioseparation that allows control of pore size and mechanical strength by tuning the Cr³⁺ concentration.

Development of Greener D-Metal Inorganic Crosslinkers for Polymeric Gels Used in Water Control in Oil and Gas Applications

Crosslinkable polymers, such as polyacrylamide (PAM), are widely applied for water control in oil and gas reservoirs. Organic and inorganic crosslinkers are used to formulate a gel with PAM. Although chromium has a high level of toxicity, it has been implemented as an effective crosslinker combined with carboxylates because of the controllability of crosslinking time at low temperatures. The objective of this work was to develop greener d-metal inorganic crosslinkers based on cobalt, copper, and nickel to replace chromium for application at reservoir conditions. The obtained results showed that the gelation chemistry of the developed systems depends on the metal charge density. The gelation of PAM with d-metals depends on pH and temperature for low- and high-charge density, respectively. Cobalt (II) acetate (CoAc) was effective at high temperatures (130–150 °C) and forms (4% CoAc + 9%PAM) stable, and strong gels at a pH > 7 with a storage modulus exceeding 4300 Pa. However, Nickel Acetate and Cupper Acetate formed stable weak gels at low temperatures (50–70 °C) and a pH > 6 and gel decomposition was observed upon increasing the temperature. The developed formulations were compatible with low-salinity water (1000 ppm NaCl).

The advances of organic chromium based polymer gels and their application in improved oil recovery

In recent years, with the further development of old oilfields, in order to further improve the oil recovery, they must be conformance controlled. Among various types of conformance control methods, polymer gels composed of polymers and crosslinkers have attracted widespread attention because of their efficiency and low costs. Among them, organic chromium gels with their good formation adaptability and high stability have been fully developed in recent decades. This review introduces the different types of polymers and crosslinkers used in the preparation of organic chromium gels, and the mechanisms of affecting their performance are analyzed. On this basis, the organic chromium gels for different formation conditions are introduced, including nanoparticle-reinforced and compound organic chromium gels. At the same time, evaluation methods of organic chromium gels are introduced, while the focus is on the in-situ measurement method (mirco-rheology) of gel formation time developed in recent decades. Based on the currently developed organic chromium gel and the analysis of the development status in oilfields, future directions like the use of supramolecular organic chromium gel and shear organic chromium gel are suggested.

EDTA-Inspired Polydentate Hydrogels with Exceptionally High Heavy Metal Adsorption Capacity as Reusable Adsorbents for Wastewater Purification

Water pollution by heavy metal ions is a critical threat to public health. To remove the heavy metal pollutants from large waterbodies, we have synthesized a biocompatible, cost-effective, metal ion non-specific, and ethylenediaminetetraacetic acid (EDTA)-inspired polydentate hydrogel with exceptionally high adsorption capacity and reusability. The hydrogel was synthesized by the transamidation reaction between hydrolyzed polyacrylamide and branched polyethylenimine (BPEI). The mechanical strength of the synthesized hydrogel displayed an increasing trend with the wt % of the cross-linker (BPEI) and achieved a maximum storage modulus (G_max^') of 1093 Pa. Scanning electron microscopy revealed a porous network structure of the hydrogel (pore size: 30-70 μm), resulting in a very high swelling ratio of 5800%. The porous hydrogel manifested the maximum adsorption capacity of 482.2 mg/g when adsorbing from a mixture of metal ions (Cr³⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺), higher than any EDTA-grafted material known to date. The high adsorption capacity of the hydrogel was attributed to the existence of numerous EDTA-mimicking coordinating functional groups, as confirmed by X-ray photoelectron spectroscopy. In addition, the hydrogel showed the self-healing property and preserved more than 85% adsorption efficiency even after five cycles of reuse. Furthermore, the hydrogels showed no or moderate toxicity toward mammalian cells.

Boron removal by electrocoagulation: Removal mechanism, adsorption models and factors influencing removal

Boron (B), normally present in ground water and sea water, is a vital micronutrient for plants, but is also toxic in excessive amounts. Under typical conditions, aqueous boron is present as boric acid (H₃BO₃), which is uncharged, making B particularly challenging to remove by mechanisms commonly applicable to removal of trace constituents. Adsorption of B onto aluminum hydroxide solids (Al(OH)₃(s)) generated using aluminum-based electrocoagulation (EC) is a promising strategy for B removal. Infrared spectroscopy analysis indicated complexation of B(OH)₃ with aluminum hydroxide solids via surface hydroxyl groups, while X-ray and infrared spectroscopy results indicated that the structure of the Al(OH)₃(s) was influenced both by EC operating conditions and by water quality. A linear adsorption model predicted B removal well when initial concentrations were lower than 50 mg/L, but fit the experimental data poorly at higher initial B concentrations. The Langmuir adsorption model provided a good fit for a broader range of initial B concentrations (5-1000 mg/L). Factors affecting B adsorption during the EC process, including current intensity, Al dissolution rate, boron concentration, pH, and total dissolved solid (TDS), were investigated. Increasing current intensity initially led to a higher Al dissolution rate, and therefore higher B adsorption, but there was a limit, as further increases in current intensity caused rapid formation of Al(OH)₃(s) having a large particle size and a low capacity to complex B. Boron removal decreased as its concentration increased. The best removal of B occurred at pH 8, corresponding to a slightly positive zeta potential for aluminum hydroxide and a small but significant fraction of negatively charged B species. Higher TDS concentrations facilitated the use of higher current intensities, i.e., the limit on the effective Al dissolution rate increased with increasing TDS. Two real water samples (river water and oilfield produced water) spiked with B were treated using EC, resulting in up to 50% B removal from river water (C₀ = 10 mg/L, current = 0.2 A) in 2 h, and 80% B removal from produced water (C₀ = 50 mg/L, current = 1.0 A) in 2 h.

Delayed-Crosslink Hydrogel for Improving Oil Recovery in Differential Heterogeneous Reservoirs

Premature water production is an inevitable issue that results in loss of quantities of reserves in heterogeneous oilfields especially with large permeability ratios. Hydrogel treatments, preferentially plugging large channels, are efficient techniques to reduce excessive water circulation. In this work, a moderate delayed polyacrylamide hydrogel was fabricated applying in-depth plugging to promote oil production. Suitability tests of delayed hydrogel in the presence of quartz sand confirmed its mature delay over 10 days, providing the low-viscosity gelant sufficient time for entering the deep layer. Single sand-pack displacement tests demonstrated the excellent plugging ability in differential permeability layers to strongly promote the follow-up oil production. Aiming at heterogeneous reservoirs with three different permeability ratios, conventional displacements and hydrogel treatments were sequentially conducted. In comparison with water- and polymer-flooding that mainly performed exploitation at low-permeability-contrast layers (K _high/K _low = 3), the delayed hydrogel technique after polymer-flooding was capable of improving the oil recovery efficiency of unswept zones at high-permeability-contrast zones (K _high/K _low ≥ 10). Recovery in heterogeneous layers with permeability ratios (K _high/K _low) of 10 and 15 was enhanced to 48 and 59%, respectively from 18 and 0%. In addition, rheological behaviors and morphologies elucidated the delayed hydrogel with extruding deformation and high yield strength, facilitating water shutoff and improvement of oil production.

Nanotechnology Applied to Thermal Enhanced Oil Recovery Processes: A Review

The increasing demand for fossil fuels and the depleting of light crude oil in the next years generates the need to exploit heavy and unconventional crude oils. To face this challenge, the oil and gas industry has chosen the implementation of new technologies capable of improving the efficiency in the enhanced recovery oil (EOR) processes. In this context, the incorporation of nanotechnology through the development of nanoparticles and nanofluids to increase the productivity of heavy and extra-heavy crude oils has taken significant importance, mainly through thermal enhanced oil recovery (TEOR) processes. The main objective of this paper is to provide an overview of nanotechnology applied to oil recovery technologies with a focus on thermal methods, elaborating on the upgrading of the heavy and extra-heavy crude oils using nanomaterials from laboratory studies to field trial proposals. In detail, the introduction section contains general information about EOR processes, their weaknesses, and strengths, as well as an overview that promotes the application of nanotechnology. Besides, this review addresses the physicochemical properties of heavy and extra-heavy crude oils in Section 2. The interaction of nanoparticles with heavy fractions such as asphaltenes and resins, as well as the variables that can influence the adsorptive phenomenon are presented in detail in Section 3. This section also includes the effects of nanoparticles on the other relevant mechanisms in TEOR methods, such as viscosity changes, wettability alteration, and interfacial tension reduction. The catalytic effect influenced by the nanoparticles in the different thermal recovery processes is described in Sections 4, 5, 6, and 7. Finally, Sections 8 and 9 involve the description of an implementation plan of nanotechnology for the steam injection process, environmental impacts, and recent trends. Additionally, the review proposes critical stages in order to obtain a successful application of nanoparticles in thermal oil recovery processes.

Polymer Gels Made with Functionalized Organo-Silica Nanomaterials for Conformance Control

Deep placement of gel in waterflooded hydrocarbon reservoirs may block channels with high water flow and may divert the water into other parts of the reservoir, resulting in higher oil production. In order to get the gel constituents to the right reservoir depths, a delay in the gelling time in the order of weeks at elevated temperatures will be necessary. In this work, a methodology for controlled gelation of partially hydrolyzed polyacrylamide using hybrid nanomaterials with functional groups as cross-linkers was developed. Two delay mechanisms with hybrid materials and polyelectrolyte complexes were designed and tested. Both mechanisms could significantly delay the gelation rate, giving gelling times ranging from several days to several weeks in synthetic sea water at 80 . Gelling experiments in sandstone cores showed that gel strength increased with aging time. For long aging times, strong gels were formed which resulted in almost no water permeability. A series of coreflooding experiments with polymer and deactivated nanomaterial were performed. In addition to differential pressures and concentration profiles, the experiments enabled calculation of retention and inaccessible pore volumes. A novel numerical model of 1D two-phase flow has been developed and tested with results from core flooding experiments. The model can track the age distribution and concentrations of the nanomaterial (and therefore water viscosity) throughout the porous medium at every time step. The model generated a good fit of experimental results.

Removal of copper ions from aqueous solution by the sodium salt of the maleic acid-allylpropionate-styrene terpolymer

The sodium salt of the maleic acid-allylpropionate-styrene terpolymer was used for recovery of copper ions from aqueous solution. Effects of contact time, sorbent weight and initial Cu²⁺ ion concentrations on removal efficiency were tested. The maximum experimental sorption capacity of the sorbent for copper ions is 0.71 g g^-1. The sorption isotherm of copper ions onto a prepared polymer sorbent has been studied and the equilibrium data were analyzed using Langmuir and Freundlich isotherm models. The adsorption isotherm data showed that copper ions adsorption on the sorbent was better fitted to the Langmuir isotherm model. The Lagergren pseudo-first- and pseudo-second-order kinetic models were applied to examine the kinetics of the copper ions sorption by the synthesized sorbent. The kinetic data are best described by the pseudo-second-order model. The calculated value of the maximum sorption capacity by the pseudo-second-order equation (0.62 g g^-1) corresponds well with its experimentally found value (0.71 g g^-1). Considering the obtained kinetic data, and the Fourier transform infrared spectroscopy (FT-IR) and UV-vis spectra of the sorbent after the sorption, it is possible to come to the conclusion that during the sorption process Cu²⁺ ions enter a complex with the carboxylic groups of the maleic acid units of the sorbent.

Engineering tenofovir loaded chitosan nanoparticles to maximize microbicide mucoadhesion

The objective of this study was to engineer a model anti-HIV microbicide (tenofovir) loaded chitosan based nanoparticles (NPs). Box-Behnken design allowed to assess the influence of formulation variables on the size of NPs and drug encapsulation efficiency (EE%) that were analyzed by dynamic light scattering and UV spectroscopy, respectively. The effect of the NPs on vaginal epithelial cells and Lactobacillus crispatus viability and their mucoadhesion to porcine vaginal tissue were assessed by cytotoxicity assays and fluorimetry, respectively. In the optimal aqueous conditions, the EE% and NPs size were 5.83% and 207.97nm, respectively. With 50% (v/v) ethanol/water as alternative solvent, these two responses increased to 20% and 602 nm, respectively. Unlike small size (182nm) exhibiting burst release, drug release from medium (281 nm) and large (602 nm)-sized NPs fitted the Higuchi (r(2)=0.991) and first-order release (r(2)=0.999) models, respectively. These NPs were not cytotoxic to both the vaginal epithelial cell line and L. crispatus for 48h. When the diameter of the NPs decreased from 900 to 188 nm, the mucoadhesion increased from 6% to 12%. However, the combinatorial effect of EE% and percent mucoadhesion for larger size NPs was the highest. Overall, large-size, microbicide loaded chitosan NPs appeared to be promising nanomedicines for the prevention of HIV transmission.