Hydrolyzed Polyacrylamide Gel Research Articles

The effect of NaCl and HPAM solution concentration on HPAM gel structure degradation by ultrasonic waves

AbstractThe present study evaluated the impact of ultrasonic waves on the degradation of partially hydrolyzed polyacrylamide (HPAM) gel structures, focusing on the effects of sonication time, NaCl concentration, and HPAM solution concentration. Results showed that both sonication time and salinity levels play a crucial role in the degradation of HPAM gel, with an increase in sonication time leading to a decrease in the remaining gel and the presence of NaCl in the solution decreasing the residual time required for degradation. The results also revealed that higher levels of salinity expedite the degradation of the gel. In addition, the study discovered that a rise in polymer solution concentration usually results in a reduction in gel degradation. The research suggests there might be an ideal combination of polymer solution and NaCl concentration for achieving the greatest decrease in the degradation rate. For 2‐min sonication, as the salinity of the HPAM solution, with a concentration of up to 5000 ppm, increases, the accumulated energy remains relatively constant. However, when the polymer solution concentration is increased, the accumulated energy becomes more sensitive to changes in salinity. The results of this study provide valuable insight into the interplay between polymer solution concentration, salt concentration, and the energy required for gel degradation, which can be applied in various fields including the oil and gas industry, petroleum processing, and environmental remediation.

Exploring Potential of Gellan Gum for Enhanced Oil Recovery.

Extensive laboratory and field tests have shown that the gelation response of gellan gum to saline water makes it a promising candidate for enhanced oil recovery (EOR). The objective of this mini-review is to evaluate the applicability of gellan gum in EOR and compare its efficiency to other precursors, in particular, hydrolyzed polyacrylamide (HPAM). At first, the "sol-gel" phase transitions of gellan gum in aqueous-salt solutions containing mono- and divalent cations are considered. Then the rheological and mechanical properties of gellan in diluted aqueous solutions and gel state are outlined. The main attention is paid to laboratory core flooding and field pilot tests. The plugging behavior of gellan in laboratory conditions due to "sol-gel" phase transition is discussed in the context of conformance control and water shut-off. Due to its higher strength, gellan gum gel provided ~6 times greater resistance to the flow of brine in a 1 mm-width fracture compared to HPAM gel. The field trials carried out in the injection and production wells of the Kumkol oilfield, situated in Kazakhstan, demonstrated that over 6 and 11 months, there was an incremental oil recovery of 3790 and 5890 tons, respectively. To put it into perspective, using 1 kg of dry gellan resulted in the incremental production of 3.52 m3 (or 22 bbls) of oil. The treatment of the production well with 1 wt.% gellan solution resulted in a considerable decrease in the water cut up to 10-20% without affecting the oil flow rate. The advantages and disadvantages of gellan compared to HPAM are analyzed together with the economic feasibility of gellan over HPAM. The potential for establishing gellan production in Kazakhstan is emphasized. It is anticipated that gellan gum, manufactured through fermentation using glucose-fructose syrup from Zharkent and Burunday corn starch plants, could be expanded in the future for applications in both the food industry and oil recovery.

Phenolic resin gel suitable for medium-temperature and high-salinity reservoirs

Gel has been widely applied as a plugging agent for enhanced oil recovery. In this study, partially hydrolyzed polyacrylamide (HPAM) or co-polymers of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid (AM-AMPS) cross-linked with water-soluble phenolic resin (WSPR) forming two phenolic resin gels with mineralization of 41529 mg/L at 90 °C. The properties of the two gels were systematically evaluated in this work. Under the same dosage of polymer and cross-linker conditions, HPAM gel exhibits a faster crosslinking rate and higher strength than AM-AMPS gel, but is less thermal stable than AM-AMPS gel. Part of the two phenolic resin gels was prone to premature syneresis at higher crosslinker dosages, which has not been reported in published literature. Severe syneresis was observed in the HPAM gel with the cross-linker concentration ranges from 0.8∼1.0 wt% when heated up to 60 days. Fortunately, stable gels were developed when the loading of HPAM and cross-linker in the gelant ranges from 0.8∼1.0 wt% and 0.4∼0.6 wt% respectively. Besides, the dehydration ratio of some stable HPAM gels was still less than 8% when these gels aged for 150 days. For AM-AMPS gel, syneresis was observed in the gels with 0.8∼1.0 wt% cross-linker and 0.4 wt% polymer when heated up to 120 days. Luckily, when the polymer dosage is over 0.4 wt%, the crosslinker loading had little effect on thermal stability, so some stable AM-AMPS gels can be acquired. Premature syneresis of higher cross-linker loading gels, which is counter to our goal of increasing crosslinker dosage to improve the crosslinking density and further enhance thermal stability. Based on XPS, FT-IR, and Cryo-SEM testing results, two syneresis mechanisms of the higher crosslinker gels were proposed, which ascribes to the decrease in hydrophilicity and excessive crosslinking of gel systems. A piece of advice should bear in mind when design a phenolic resin gel: keep the cross-linker dosage appropriate to avoid overloading it. As a result, our findings may guide the development of stable phenolic gels under similar conditions, and part of the two gels could provide a solution for plugging in medium-temperature and high-salinity reservoirs.

Effect of entanglement on rheological and ultimate properties of inorganic HPAM gels

The influence of the entanglement on the mechanical properties of partially hydrolyzed polyacrylamide gels is investigated. In the entangled gels, a power law, relating the plateau modulus and the polymer concentration, with an exponent of 2.3 is dominant. By contrast, the exponent of the power law is determined by the crosslinking density in the unentangled gels. On basis of the in-situ gelling method, the strain hardening characteristic of partially hydrolyzed polyacrylamide gels was observed. The strain hardening behavior is found to be controllable by the component of gels, but is insensitive to the frequency. In general, gels with higher polymer concentration exhibit a weaker tendency of stiffening and tend to fracture at lower strain. However, concentration dependence of the non-linear rheology and fracture properties is discontinuous around the entanglement concentration. The underlying mechanism is assumed to be relevant with the conversion of the crosslinking type, which is promoted from inter-crosslinking to intra-crosslinking due to entanglements. As a result, the fracture stress experiences a significant reduction as the polymer concentration exceeds the entanglements concentration. This article points out the significance of entanglements on the fracture toughness of polymer gels, and we hope it would provide suggestions for further studies.

Permeability reduction by gellan gum solutions

This paper summarizes the results of laboratory experiments with gellan gum. Gellan gum solutions demonstrated plugging in distilled water and brine saturated sand packs. Progressive plugging in distilled water saturated sand packs is explained by the presence of gel particles in the gellan gum solutions, whereas plugging in brine saturated sand packs is explained by the instantaneous gelation of gellan gum upon contact with brine. Gellan gum gel strength and its injectivity depend on brine salinity in the rage of 0–60 g⋅L−1. Gellan gum plugging behavior in porous media depends on polymer concentration, permeability, and temperature. However, in these tests internal pressure taps were not used, making conclusions impossible as to whether gellan gum solutions provide in-depth plugging in matrix rocks. Fracture models with an impermeable matrix and fractured sandstone cores were used in this study to compare gellan gum and hydrolyzed polyacrylamide gels. Alternating injection of gellan gum and brine demonstrated an effective way to plug 1-mm-height fractures. The plugging efficiency of polyacrylamide gel depends on the initial viscosity of the solution, if it is injected prior to gelation, and post flush salinity. Whereas in the case of gellan gum, these factors are not critical because the solution gels instantaneously upon contact with brine, with higher brine salinity improving gel strength. Although, maximal gel and post flush injection pressures were several times higher in the case of gellan gum, stabilized post flush injection pressure was higher in the case of hydrolyzed polyacrylamide gel placed as a mature gel in a sandstone fractured core.

Water shut off gel

Injection of Partially Hydrolyzed Polyacrylamide gels using inorganic crosslinking agents has proven to be one of the best methods for isolating water and enhancing oil recovery. Partially hydrolyzed polyacrylamide forms a gel structure in the presence of trivalent metal ions such as Cr3+, Al3+, which act as a crosslinker. In this case, a sequential injection of a polymer solution and a crosslinking agent is carried out into the formation and the gel is formed directly in the formation. Numerous successful examples of the implementation of this technology to reduce the water cut of the produced products were the basis for the development of a new gel composition, taking into account the disadvantages of the existing ones. The paper presents the results of laboratory studies on core material using the proposed gel composition based on a partially hydrolyzed polyacrylamide polymer and various crosslinking agents (note: thiourea / K2Cr2O7).

Influence of solution composition on fouling of anion exchange membranes desalinating polymer-flooding produced water

HypothesisAnion exchange membranes (AEMS) are particularly prone to fouling when employed to desalinate polymer flooding produced water (PFPW), an abundant sub-product from the oil and gas industry. The formation of fouling on an AEM will be affected by the composition of the solution, which includes various dissolved salts, partially hydrolyzed polyacrylamide (HPAM), crude oil, and surfactants. ExperimentsElectrodialysis experiments were performed to desalinate feed solutions with different compositions, aiming to distinguish between their individual and combined effects. The solutions contained diverse mono- and divalent ions. The analysis included data collected during the desalination and characterization of the fouled AEMs by diverse analytical techniques. FindingsHPAM produced the most severe effects in terms of visible fouling and increase of resistance. This polyelectrolyte fouls the AEM by adsorbing on its surface and by forming a viscous gel layer that hampers the replenishment of ions from the bulk solution. Ca and Mg have a large influence on the formation of thick HPAM gel layers, while the oily compounds have only a minimal influence acting mainly as a destabilizing agent. The membranes also presented scaling consisting of calcium precipitates. The effects of the gel layer were minimized by applying current reversal and foulant-free solution.

The effect of cations on gelation of cross-linked polymers

The effects of different cation concentrations and types on rheological property and stability of Guar, Xanthan, and Partially Hydrolyzed Polyacrylamide (HPAM) cross-linked gels were analyzed through experiments. Also, a new approach was developed to reduce the negative effects of cation by application of multi-walled carbon nano-tubes (MWCNTs). The presence of cations in cross-linked gel system will reduce the viscosity of gel, the higher the cation concentration is, the lower the viscosity will be. The bivalent cation has a greater viscosity reduction effect on gel than monovalent cation. The stability of cross-linked gels is worse with cations, this situation becomes more serious under higher salinity. MWCNTs were added to HPAM gel, cross-linked by (3-Aminopropyl) triethoxysilane (APTES), they surrounded cations and removed them from polymers and reduced the reaction possibility. This method enhances the viscosity and breakdown pressure of cross-linked gels, improves the stability of HPAM cross-linked gel under different operating conditions, and can be applied to related drilling projects.

Experimental and mechanism study: Partially hydrolyzed polyacrylamide gel degradation and deplugging via ultrasonic waves and chemical agents

Partially hydrolyzed Polyacrylamide (PHPAM) crosslinked by Cr+3 is frequently applied to plug thief zone for the better water management in matured oil reservoir. However, PHPAM gel may certainly cause inevitable formation damage nearby the wellbore. Although various kinds of chemical agents, such as hydrogen peroxide (H2O2), sodium hypochlorite (NaOCl), and chlorine dioxide (ClO2) were employed to mitigate the nearby wellbore damage. But, huge financial investment, poor degelation efficiency, environmentally insecure, corrosion problem, and long time span requirement persuade researchers to look for other effective technique. In this connection, ultrasonic waves is characterized by reliable, environment friendly, and cost effective technology. Current work involves comparative study of PHPAM gel degradation by the individual means of chemical agent and ultrasonic waves. Subsequently, the best-performed ultrasonic parameters and well-performed chemical agent were used independently and then simultaneously to deplug (PHPAM gel) the core sample. Results showed that 20 KHz frequency (1000 W) effectively reduced gel viscosity from original (2495 mPa.s) to 1.37 mPa.s after 10 min irradiation. This degradation is attributed to cavitation, heat energy, and hydroxyl radical (HO∙). However, after 2 min further exposure, the viscosity grew back to 3.29 mPa.s (18 KHz), 1.42 mPa.s (20 KHz), and 3.74 mPa.s (25 KHz). This adverse behavior is owing to hydroxyl radical (HO∙) annihilation. In chemical treatment, H2O2 among other chemicals efficiently degelled the PHPAM gel’s original viscosity to 2.64 mPa.s after 24 h reaction. Similarly, NaOCl and ClO2 brought down original viscosity to 6.5 mPa.s and 159 mPa.s respectively. SEM of the samples before and after treatment was performed for the better understanding of PHPAM gel morphology. Considering dynamic experiment, maximum 23.5% and 19.80% damaged permeability recovery (30 × 10−3 μm2 gas permeability) were obtained by applying ultrasonic waves (20 KHz, 1000 W, and 100 min irradiation) and chemical agent (H2O2) respectively. Permeability recovery was further increased to 40.90% by the simultaneous application of ultrasonic waves and chemical agent.

Evidence of the Gelation Acceleration Mechanism of HPAM Gel With Ammonium Salt at Ultralow Temperature by SEM Study

Summary Previously reported phenol-formaldehyde-based gel formulas with ammonium salt can provide a gelation time between 2 hours and 2 days at 25 °C, which has great potential to serve as water-shutoff or conformance-control agents in ultralow- to low-temperature reservoirs. The gelation performance can be adjusted by changing the concentration of hydrolyzed polyacrylamide (HPAM), crosslinker, and ammonium salt. Over the last decades, the working behavior of a gel system in a reservoir has been evaluated simply through the gelation-performance bottle test and the effectiveness of gel treatment at the macro level. However, the nature of a gel microstructure greatly dominates its working performance in subterranean reservoir conditions. The objective of this work is to investigate the relationship between gelation performance and microstructures of target gel by scanning-electron-microscope (SEM) analysis at different test conditions, including the effects of components concentration, aqueous-phase salinity, and porous-medium shearing, and to reveal evidence of the gelation-acceleration mechanism. Results show that ammonium salts act as bridging branch chains between polymer and crosslinker to accelerate the gelation progress. We reveal the gelation-process indicator through the discovery of several “coverings” that appeared among the polymer branch chains. The gelation-acceleration mechanism should be the embedding and growth of crystalline ammonium salts in the polymer skeleton to promote the extension of these coverings. The polymer skeleton covered by crystalline ammonium salts can increase the gel strength and salinity tolerance as a result of the unique structure of “crab's big claws.” The gelation performance is not seriously affected by the shearing effect in porous media, while the final gel strength still can reach Code I and exhibit a favorable long-term stability. Some application recommendations of the target gel are also discussed in this paper.

Low-Salinity Chase Waterfloods Improve Performance of Cr(III)-Acetate Hydrolyzed Polyacrylamide Gel in Fractured Cores

Summary Polymer gels are frequently applied for conformance improvement in fractured reservoirs, where fluid channeling through fractures limits the success of waterflooding. Placement of polymer gel in fractures reduces fracture conductivity, thus increasing pressure gradients across matrix blocks during chase floods. A gel-filled fracture is reopened to fluid flow if the injection pressure during chase floods exceeds the gel-rupture pressure; thus, channeling through the fractures resumes. The success of a polymer-gel treatment, therefore, depends on the rupture pressure. Salinity differences between the gel network and surrounding water phase are known causes of gel swelling (e.g., observed in recent work on preformed particle gels). Gel swelling and its effect on fluid flow have, however, been less studied in conjunction with conventional polymer gels. By use of corefloods, this work demonstrates that low-salinity water can swell conventional Cr(III)-acetate hydrolyzed polyacrylamide (HPAM) gels, thereby significantly improving gel-blocking performance after gel rupture. Formed polymer gel was placed in fractured core plugs, and chase waterfloods were performed using four different brine compositions, of which three were low-salinity brines. The fluid flow rates through the matrix and differential pressures across the matrix and fracture were measured and shown to increase with decreasing salinity in the injected water phase. In some cores, the fractures were reblocked during low-salinity waterfloods, and gel-blocking capacity was increased above the initial level. Low-salinity water subsequently flooded the matrix during chase floods, which provided additional benefits to the waterflood. The improved blocking capacity of the gel was caused by a difference in salinity between the gel and injected water phase, which induced gel swelling. The results were reproducible through several experiments, and stable for long periods of time in both sandstone and carbonate outcrop core materials. Combining polymer gel placement in fractures with low-salinity chase floods is a promising approach in integrated enhanced oil recovery (IEOR).

New Insights into the Gelation Behavior of Polyethyleneimine Cross-Linking Partially Hydrolyzed Polyacrylamide Gels

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 cross-linking 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 shear...

Study on the Dynamic Rheometry and Swelling Properties of the Polyacrylamide/Laponite Nanocomposite Hydrogels in Electrolyte Media

Polyacrylamide/laponite/chromium triacetate nanocomposite (NC) hydrogels were prepared by incorporation of the laponite nanoparticles in partially hydrolyzed polyacrylamide followed by cross-linking of their aqueous solutions with chromium triacetate. Influence of nanoparticle, cross-linker, polymer concentrations, and gelation media (water) temperature, salinity, and rheometer frequency on the viscoelastic behavior of the NC hydrogels were studied by probing the network properties. In addition, swelling behaviors of these NC gels in tap and oil reservoir water were evaluated. According to dynamic rheometry of the gelation process, the limiting storage modulus of the NC gels increased with increasing laponite content. The addition of laponite into the polyacrylamide gelling system increased their viscous properties more strongly than the elastic properties. The ultimate elastic modulus of the NC gels increased with increasing water salinity and temperature. Increasing rheometer frequency during gelation retarded the sol–gel transition and decreased the ultimate elastic modulus. The equilibrium swelling ratio of the NC hydrogels in tap water decreased with increasing laponite content. The salt sensitivity of the NC gels in oil reservoir water slightly decreased with increasing laponite content. These results suggest the superiority of the hydrolyzed polyacrylamide (HPAM)/chromium acetate/laponite NC hydrogels for water shut-off applications in oil reservoirs as compared with unfilled HPAM gels.

Influences of Fracture Aperture on the Water-Shutoff Performance of Polyethyleneimine Cross-Linking Partially Hydrolyzed Polyacrylamide Gels in Hydraulic Fractured Reservoirs

In previous study, we have discussed the gelation performance of the polyethyleneimine (PEI) cross-linking partially hydrolyzed polyacrylamide (HPAM) gel system. The major goals of this paper are to investigate the conventional application performance of the PEI cross-linking HPAM gel system, including injectivity and sealing charactersic through core flowing experiments. Results show that polymer gels formualted with a combination of 2.0 wt % HPAM (Mw = 8000 kDa) and 0.35 wt % PEI can achieve the critical pressure gradient above 500 psi/ft on average and with a maximum at 1136.38 psi/ft through the core flowing experiments with apertures ranging from 0.080 to 0.200 cm. The pressure gradient and brine permeability reduction factors (Frrw) are also attractive. The gradient pressure is inline with expectations of the gradient pressure predicting curve obtained by Seright for the chromium(III) acetate cross-linking HPAM gel. A strong adhesive force of stretching 2 cm width rather than breakage in fracture pr...

Rheological and swelling behavior of semi‐interpenetrating networks of polyacrylamide and scleroglucan

AbstractPreparation and characterization of novel semi‐interpenetrating polymer network (semi‐IPN) hydrogels based on partially hydrolyzed polyacrylamide (HPAM) and scleroglucan solution crosslinked with chromium triacetate are described. Effects of scleroglucan concentration on the gelation process and swelling behavior of synthesized hydrogels in different media were investigated using dynamic rheometery and swelling tests, respectively. Oscillatory shear rheology showed that the limiting storage modulus of the semi‐IPN gels increased with increase in scleroglucan concentration. It was also found that the viscous energy dissipating properties of the semi‐IPN gels decreased with increase in the crosslinker concentration of the gelation system. In addition, the loss factor slightly decreased by increasing the scleroglucan content, indicating that the viscous properties of this gelling system decreased more than its elastic properties. The swelling tests showed that the equilibrium swelling ratio (ESR) of the semi‐IPN networks decreased with increase in scleroglucan content, due to the decrease of ionic groups of polyelectrolyte hydrogel. However, the semi‐IPN gels showed lower salt sensitivity in synthetic oil reservoir water as compared with HPAM gels. Therefore, these semi‐IPN hydrogels may be considered potentially good candidates for enhanced oil recovery (EOR) applications. Copyright © 2009 John Wiley & Sons, Ltd.

Rupture of Polyacrylamide Gel in a Tube in Response to Aqueous Pressure Gradients

Hydro‐gel and the evolution of its strength as the gel matures from the state of aqueous fluid to the state of viscoelastic solid provides opportunity to employ hydro‐gel in certain critical applications, such as sealing of fractures or high permeability streaks in a hydrocarbon reservoir. The mature gel, inside the channel, helps in diverting the injected water into an un‐swept oil bearing zone. For the gel treatment to be effective, the gel layer inside the channel has to resist failure under water pressure. This article describes evaluation of the strength of Cr(III)–partially hydrolyzed polyacrylamide gel, formed in transparent tubes. A pressure gradient was imposed on the gel by injecting water on one end of the tube, leaving the other end open to atmosphere. Pressure gradient that increased with time caused shear deformation, and bulging of gel at the outlet end of the tube. At a threshold pressure, the deformation culminated to a rupture at the center of the gel, and subsequent burst of water through the outlet. Rupture was visualized using colored water that fingered through the center of the gel, leaving the rest of the gel intact. Rupture pressure, similar to the ultimate strength of a material, is defined for the gel layer. The rupture pressure was found to increase with the length, and decrease with the width of aperture. A theoretical model in support of this trend is presented here. When the pressure was built up fast, the rupture took place at a much smaller pressure. In case of pressure build‐up over a long period of time, rupture pressure became independent of the duration of build‐up. The effect of the rate of pressure build‐up is analyzed using the concept of viscoelasticity. Also, the rupture model is extended to the situations where the porous media hinder the free movement of gel at the outlet, and allow partial movement of gel laterally through the surrounding wall.

Gelation and Swelling Behavior of Semi-Interpenetrating Polymer Network Hydrogels Based on Polyacrylamide and Poly(vinyl alcohol)

Novel semi-Interpenetrating Polymer Network (semi-IPN) hydrogels based on partially Hydrolyzed Polyacrylamide (HPAM) and Poly(Vinyl Alcohol) (PVA) were prepared by solution crosslinking using chromium triacetate. Effects of PVA content on the gelation process and swelling behavior in tap water and different electrolyte solutions were investigated. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the semi-IPN gels decreased with increasing PVA content. It was also found that increasing the PVA content increases the loss factor, indicating that the viscous properties of this gelling system increase more strongly than the elastic properties. The swelling ratio of the semi-IPN gels in tap water decreased as the concentration of the PVA increased. However, the semi-IPN gels showed lower salt sensitivity factor in synthetic oil reservoir water as compared with HPAM gels. Therefore, they are potentially good candidates for enhanced oil recovery applications.

Study on gelation of partially hydrolyzed polyacrylamide with titanium(IV)

The gelation of metallic crosslinking agent titanium(IV) (Ti(IV)) with partially hydrolyzed polyacrylamide (HPAM) is reported. Factors affecting the crosslinking reaction are discussed and the dynamic properties of the gel are examined. The results indicate that crosslinking of Ti(IV) with HPAM is delayed at low concentrations of polymer and titanium tartrate. The gelling of Ti(IV)–HPAM is a strong function of titanium/tartaric acid molar ratios, HPAM concentration, initial solution pH value, solution salinity, and the hydrolysis degree of HPAM. The gel strength depends on Ti(IV) concentration in a particular way; after a maximum Ti(IV) concentration is reached gel strength decreases. The salt NaCl can accelerate the gelling rate of Ti(IV)–HPAM. A crosslinking mechanism of Ti(IV) with HPAM is proposed. Ti(IV)–HPAM gel can hold its strength at moderate temperature (50°C) for a long time making it suitable to be used in a moderate temperature oil reservoir.

Slow Gelation of Titanium(IV) with Partially Hydrolyzed Polyacrylamide. Crosslinking Reaction and Gel Properties

The gelation of metallic crosslinking agent titanium(IV) (Ti(IV)) with partially hydrolyzed polyacrylamide (HPAM) is studied. Factors effecting the crosslinking reaction are discussed and the dynamic properties of gel are examined. The results indicate that crosslinking of Ti(IV) with HPAM is delayed at low concentrations of polymer and the titanium tartrate. The gelling of Ti(IV)–HPAM is a strong function of titanium/tartaric acid molar ratio, HPAM concentration, initial solution pH value, solution salinity, and hydrolysis degree of HPAM. The gel strength depends on Ti(IV) concentration in a particular way, after a maximum Ti(IV) concentration is reached gel strength decreases. The salt NaCl can accelerate the gelling rate of Ti(IV)-HPAM. The crosslinking mechanism of Ti(IV) with HPAM is proposed. Ti(IV)-HPAM gel can hold its strength at moderate temperature (50°C) for a long time which is suitable to be used in a moderate temperature oil reservoir.

Adsorption Properties of Trivalent Metal Ions onto Hydrolyzed Polyacrylamide Gel.

In a previous paper (Morohashi et al., 1990), we focused the attention on quantitative consideration of the adsorption mechanism of divalent metal ions onto the hydrolyzed polyacrylamide gel, which was based on the adsorption equilibrium of the metal ions. In this study, adsorption properties of the trivalent metal ions, Fe 3+ , onto the gel were investigated in the buffer solution. It was reported that the relationship between concentration of metal complexes adsorbed and that of hydrogen ions was explained fairly well by a model according to the adsorption equilibrium of the trivalent metal ions.