Polymer-flooding Produced Water Research Articles

Effect of hydrolyzed polyacrylamide on oil droplet stability in polymer-flooding produced water: variation of oil droplets diameter and oil–water interfacial properties

Hydrolyzed polyacrylamide (HPAM) in polymer flooding leads to stable oil-in-water emulsions, making the oil removal from polymer-flooding produced water (PFPW) more difficult. To elucidate HPAM’s effects on the oil separation performance of conventional physical separation process for PFPW, the stability, and diameter of oil droplets of simulated PFPW were accurately determined using the Turbiscan LAB expert. The results demonstrated that an increase in HPAM’s molecular weight and concentration led to a significant decrease in the diameter of oil droplets in simulated PFPW. When the molecular weight of HPAM increased from 6 to 18 MDa, there was a decrease in the Turbidity Scanning Index (TSI) values from 22.5 to 8.7, along with a significant decline in the diameter of oil droplets from 72.7 to 32.6 µm after a settling period of 40 min. Furthermore, a rise in HPAM concentration inhibited the enlargement of oil droplets. As HPAM concentration increased from 0 to 500 mg/L, the diameter of the oil droplets reduced by 42.1 µm after a 40 min settling period. HPAM's effect on restricting the growth of oil droplets remained relatively constant across oil concentrations ranging from 500 to 2500 mg/L. Moreover, increasing the molecular weight of HPAM from 6 to 18 MDa led to a 41.6% increase in PFPW's viscosity and a 38.9% decrease in oil-water interfacial tension, thereby inhibiting oil droplet coalescence. Our findings provide valuable fundamental guidance for the design of innovative separation methods for PFPW treatment.

Influence of suspended microcrystalline polymer system on characteristics of produced water from High Ca and Mg oilfields and corresponding oil removal methods

Suspended microcrystalline polymer flooding is a new promising EOR technology developed to improve oil recovery from high Ca and Mg reservoirs. However, as the technology is currently in the research and field experimental stage, the characteristics of its produced water and the corresponding water treatment methods are still not clear. In this study, the effects of polymer concentration on physical characteristics of the three simulated produced waters, namely, polymer flooding produced water (PFPW), high Ca and Mg PFPW (HPFPW) and suspended microcrystalline PFPW (SMPFPW), were investigated to understand the particularity of SMPFPW. Pattern of oil droplet diameters in SMPFPW exhibited a bimodal distribution with peak diameters at 4 and 150 μm. The viscosities of three waters are SMPFPW ≥ PFPW > HFPW in descending order. The absolute ζ potential of SMPFPW was 1.01 ∼ 2.42 times higher than that of HPFPW, but was substantially lower than that of PFPW due to high ionic strength. At same polymer concentrations (0 ∼ 300 mg/L), the oil content in SMPFPW is 1.78 ∼ 2.47 times that in HPFPW and 1.49 ∼ 1.87 times that in PFPW because of its unique spatial structure of polymers. From degreasing experiments, oil removal rate of SMPFPW by gravity sedimentation is higher than that of PFPW but slightly lower than that of HPFPW, polymer concentration play vital roles in oil-water separation. An inexpensive and practical routine, gravity sedimentation coupled with two-stage composite material filtration, for oil removal is proposed for SMPFPW on the basis of lab experiments.

Enhanced performance of porous forward osmosis (FO) membrane in the treatment of oily wastewater containing HPAM by the incorporation of palygorskite.

Since the emergence of forward osmosis (FO), low energy requirements, low fouling propensity and high-water recovery have made it one of the most promising water purification technologies. However, there have been few reports focusing on the treatment of polymer flooding produced water (PFPW) using FO technology up to now. In the present work, porous FO membranes with/without palygorskite (Pal) nanoparticles were utilized as the separation membrane to evaluate the potential of a porous FO membrane in the treatment of oily wastewater containing HPAM and the effect of Pal nanoparticles on the FO performance was investigated. When the loading concentration of Pal in the membrane was 0.75 wt%, the water flux could reach 37.67 L m−2 h−1 by using 4 g L−1 poly(sodium-p-styrenesulfonate) (PSS) as draw solution under a cross-flow rate of 18.5 cm s−1, which was much higher than that for pure polysulfone (PS) membranes. Besides, the comparison between ultrafiltration (UF) and FO performance in treating HPAM solution indicated that FO possessed better antifouling capacity, since less decline and higher recovery of water flux were observed during the FO process. Furthermore, recycling the draw solution gave an almost unchanged water flux, which suggested the feasibility of draw solute regeneration in the FO process. This work broadens the application field of porous FO technology and may pave a new way in the treatment of PFPW.

Experimental Evaluation of Anion Exchange Membranes for the Desalination of (Waste) Water Produced after Polymer-Flooding.

Electrodialysis (ED) has been recently proposed to desalinate polymer-flooding produced water (PFPW), a byproduct stream from the oil and gas industry rich in charged polymers. However, process performance is limited by fouling occurring on the ion-exchange membranes, particularly on the anionic ones (AEMs). Thus, this study aimed to correlate the properties of different AEMs with their performance while desalinating PFPW, ultimately evaluating their significance when fouling is to be minimized and operation improved. Six stacks containing different homogeneous and commercially available AEMs were employed to desalinate synthetic PFPW during 8-days ED experiments operated in reversal mode. AEMs recovered from the stacks were analyzed in terms of water uptake, ion-exchange capacity, permselectivity, and area resistance, and compared with virgin AEMs. Relatively small changes were measured for most of the parameters evaluated. For most AEMs, the water uptake and resistance increased, while the ion-exchange capacity (IEC) and permselectivity decreased during operation. Ultimately, AEMs with high area resistance were linked to the fast development of limiting current conditions in the stack, so this property turned out to be the most relevant when desalinating PFPW.

Improving the performance of polymer-flooding produced water electrodialysis through the application of pulsed electric field

Concentration polarization and fouling hamper the desalination of polymer-flooding produced water (PFPW) via electrodialysis (ED). This water is an abundant by-product from the oil and gas industry. A common technique to mitigate both problems is the application of pulsed electric field (PEF), which consists in supplying a constant current during a short time (pulse) followed by a time without current (pause). Accordingly, this work evaluated the application of PEF during the ED of PFPW to improve the process performance and to reduce fouling incidences. The experimental work consisted in performing ED batch runs in a laboratory-scale stack containing commercial ion exchange membranes. Synthetic PFPW was desalinated under different operating regimes until a fixed number of charges were passed. After each experiment, a membrane pair was recovered from the stack and analyzed through diverse techniques. The application of PEF improved the ED performance in terms of demineralization percentage and energy consumption, the latter having reductions of 36% compared to the continuous mode. In general, the shorter the pulses, the higher the demineralization rate and the lower the energy consumption. Regarding the application of different pause lengths, longer pauses yielded lower energy consumptions, but also lower demineralization. Amorphous precipitates composed of polymer and calcium fouled most on the anion and cation exchange membranes, independently of the applied current regime, but in a moderate amount. Finally, the present study relates the observed effects of PEF application to the electrophoresis and diffusion of HPAM, and shows that PEF is a sound option to enhance the desalination of PFPW.

Demulsification of O/W emulsion using a novel polyether-polyquaternium copolymer: effect of the demulsifier structure and solution environment conditions

ABSTRACT A novel polyether-polyquaternium (PPA) demulsifier was prepared to dispose the alkali–surfactant–polymer flooding-produced water. The PPA replaced the sodium dodecylbenzenesulfonate (SDBS) on the oil/water interface and formed incompact interfacial film that destabilizes the oil droplets, making the oil/water separation easily achieved. Herein, we investigated the effects of the demulsifier structure and solution environment conditions (pH, temperature, and salinity) on the demulsification process. The highest demulsification efficiency reached 82.6% at pH of 6 and temperature of 60°C. These results impact the destabilization of O/W emulsion and provide new insight to enhance the demulsification performance of demulsifiers.

Interception Characteristics and Pollution Mechanism of the Filter Medium in Polymer-Flooding Produced Water Filtration Process

Polymer flooding enhances oil recovery, but during the application of this technology, it also creates a large amount of polymer-contained produced water that poses a threat to the environment. The current processing is mainly focused on being able to meet the re-injection requirements. However, many processes face the challenges of purifying effect, facilities pollution, and economical justification in the field practice. In the present work, to fully understand the structure and principle of the oil field filter tank, and based on geometric similarity and similar flow, a set of self-designed filtration simulation devices is used to study the treatment of polymer-contained produced water in order to facilitate the satisfaction of the water injection requirements for medium- and low-permeability reservoirs. The results show that, due to the existence of polymers in oil field produced water, a stable colloidal system is formed on the surface of the filter medium, which reduces the adsorption of oil droplets and suspended solids by the filter medium. The existence of the polymers also increases the viscosity of water, promotes the emulsification of oil pollution, and increases the difficulty of filtration and separation. As filtration progresses, the adsorption of the polymers by the filter medium bed reaches saturation, and the polymers and oil pollution contents in the filtered water increase gradually. The concentration and particle size of the suspended solids eventually exceed the permissible standards for filtered water quality; this is mainly due to the unreasonable size of the particle in relation to the filter medium gradation and the competitive adsorption between the polymers and the suspended solids on the surface of the filter medium. The oil concentration of the filtered water also exceeds the allowable standards and results from the polymers replace the oil droplets in the pores and on the surfaces of the filter medium. Moreover, the suspended particles of the biomass, composed of dead bacteria, hyphae, and spores, have strong attachment and carrying ability with respect to oil droplets, which cause the suspended solids in the filtered water to exceed the permissible standards and oil droplets to be retained in the filtered effluent at the same time.

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.

Efficient removal of partially hydrolysed polyacrylamide in polymer-flooding produced water using photocatalytic graphitic carbon nitride nanofibres

In this work, graphitic carbon nitride (GCN) photocatalyst-incorporated polyacrylonitrile (PAN) nanofibres (GCN/PAN nanofibres) were successfully prepared using electrospinning technique. The physicochemical properties of the fabricated GCN/PAN nanofibres were analysed using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), elemental analyser, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and UV–vis–NIR spectroscopy. The photocatalytic degradation by GCN/PAN nanofibres exhibited 90.2% photodegradation of partially hydrolysed polyacrylonitrile (HPAM) after 180 min under UV light irradiation in a suspension photocatalytic reactor. The results suggest that the photodegradation of HPAM contaminant by GCN/PAN nanofibres was due to the synergetic effects of HPAM adsorption by the PAN nanofibres and HPAM photodegradation by the GCN. This study provides an insight into the removal of HPAM from polymer-flooding produced water (PFPW) through photocatalytic degradation of liquid-permeable self-supporting nanofibre mats as a potentially promising material to be used in industrial applications.

Removal of divalent ions from viscous polymer-flooding produced water and seawater via electrodialysis

The presence of multivalent ions in polymer-flooding produced water (PFPW) hampers its recycling mainly because i) they increase the risk of scaling and reservoir souring (sulfate), ii) they interfere with the viscosifying effect of the fresh polyelectrolyte. It is desirable to achieve the removal of most multivalent ions without completely desalting the stream. With the adequate process conditions, electrodialysis could help to achieve this goal, so this work focused on evaluating the removal of divalent ions from synthetic PFPW through varying operational conditions. The experimental work consisted on batch experiments run in an electrodialysis-stack composed of strong Neosepta ion-exchange membranes. Synthetic PFPW solutions containing a mixture of monovalent and divalent ions were desalted at four different current densities, and three different temperatures. Additionally, the effect of the dissolved polymer on the removal was assessed by performing half of the experiments on polymer-containing solutions and half of them on solutions without it. Our results demonstrate that it is possible to achieve preferential removal of divalent cations (calcium and magnesium) through electrodialysis, especially when employing low current densities (24 A/m2) and high temperature (40 °C). The removal of sulfate, a divalent anion, is also accelerated in these conditions. The presence of polyelectrolyte did not significantly affect the removal rate of divalent ions. Thus, it is concluded that meticulous application of ED to minimize concentrations of divalent ions in PFPW is a potential effective way for water and polymer recycling in enhanced oil recovery situations, as an alternative to the use of other non-selective desalination technologies.

Investigation of Cleaning Strategies for an Antifouling Thin-Film Composite Forward Osmosis Membrane for Treatment of Polymer-Flooding Produced Water

An optimized cleaning strategy of a thin-film composite membrane functionalized with zwitterionic poly(sulfobetaine methacrylate) brushes (TFC-PSBMA membrane) was investigated for a long-term forward osmosis (FO) treatment of polymer-flooding produced water (PFPW). Crude oil and anionic polyacrylamide (APAM) were used as the representative organic substances in the wastewater. The results showed that irreversible fouling was significantly aggravated by increasing the relative concentration of crude oil in the feed solution revealing it to be the major foulant. Then, five cleaning protocols were investigated such as deionized water washing, NaCl osmotic backwashing, chemical washing with acid, alkali, and surfactant cleaning, respectively. As the result, it was found that chemical cleaning with sodium dodecyl benzenesulfonate (SDBS) was the most effective method for removing foulants from the membrane surfaces. Meanwhile, PSBMA brushes grafted on the membrane exhibited excellent tolerance to the chemical s...

Electrodialysis-based desalination and reuse of sea and brackish polymer-flooding produced water

The reuse of polymer flooding produced water (PFPW) generated in oil and gas industry is limited by its salt content, making desalination by electrodialysis a promising treatment option. Therefore, this study aimed to 1) assess the technical feasibility of employing electrodialysis to desalinate PFPW generated in assorted scenarios, and 2) evaluate the reuse of the electrodialysis-desalted water to confect polymer-flooding solution. The experimental work involved desalting two kinds of synthetic PFPW solutions, one with relatively low salinity (TDS = 5000 mg/L, brackish PFPW), and another with high salinity (TDS = 32,000 mg/L, sea PFPW), at two different temperatures, and later reusing the desalted solution to prepare viscous solutions. For the electrodialysis runs, the effects of feed composition and temperature on water transport, energy consumption and current efficiency were analyzed. It was found that the presence of polymer did not significantly influence the water transport rate or the specific energy consumption for the seawater cases, but had a measurable effect when desalting brackish water at 20 °C. It was also found that some polymer remained in the stack, the loss occurring faster for the brackish PFPW. Still, both kinds of reused PFPW probed adequate to be employed as a basis for preparing n polymer solution.

Influence of salts, anion polyacrylamide and crude oil on nanofiltration membrane fouling during desalination process of polymer flooding produced water

The effective management of polymer flooding produced water (PFPW), co-produced in the process of polymer flooding oil extraction, will become a subject to solve urgently. To study membrane fouling properties, a commercial NF membrane (NF90) was adopted to treat model PFPW in this work, with different kinds of salt, anion polyacrylamide (APAM) and crude oil as target foulants. AFM, SEM-EDS, ATR-FTIR and contact angle were employed to analyze various membrane autopsies. The results showed that the membrane fouling was dominantly induced by APAM, as well as salts and crude oil. Various mutual influences between ions and APAM including charge screening, complexation, molecule coiling up and anti-scaling effect would aggravate or mitigate fouling in different combinations. The hydrophilic APAM could produce a “shielding effect” against crude oil because of its rapid adhesion on membrane surface under the strong hydrogen binding and complexation assisted by calcium. Membrane fouling induced by the three target foulants could improve salt rejection by strengthening size exclusion. In addition, the Donnan effect caused by APAM and nonpolar action caused by crude oil can also contribute in salt removal. Finally, fouling mechanism was proposed and some suggestions were put forward.

Reclaiming polymer-flooding produced water for beneficial use: Salt removal via electrodialysis

This paper discusses the use of electrodialysis (ED) to remove salts from polymer-flooding produced water (PFPW) in order to meet confecting polymer solution standards. Specifically, the ED treatment of PFPW with total dissolved solids (TDS) concentrations and varying cations and anions distributions was evaluated at three voltage settings. The removal rates of cations, anions, and TDS increased rapidly with time at the same voltage; their removal rates also simultaneously increased with voltage. With Neosepta® CMX-SB/AMX-SB membranes, cations and anions were generally found to be removed in the following order (from the fastest to the slowest): Ca2+ > Mg2+ > K+ ≈ Na+ and Cl- > SO2- 4 > CO2- 3> HCO- 3. The viscidity of the polymer solution confected by treated PFPW was found to be superior compared with the polymer solution confected by fresh water.

Development of a four-grade and four-segment electrodialysis setup for desalination of polymer-flooding produced water

An electrodialysis (ED) setup with an 11 m 3/h water treatment scale was designed based on a small experimental device. The setup adopts four-grade and four-segment (four-GS) reversal electrodialysis (EDR) technology to desalinate polymer-flooding produced water (PFPW). The removal rate of total dissolved solids (TDS) with different flow rates was measured with different grades and segments. The operating performance of this setup was determined to meet design standards. The maximum treatment capacity and the optimal operation conditions of the tested setup were studied. The design standards were met only by adopting a four-GS ED setup. The maximal capacity of the four-GS ED setup for treating PFPW was 5 m 3/h. The optimal operating condition and results were at an operating electric current of 86 A, 62.5% production rate of diluted treated PFPW, 0.89 kW∙h/m 3 energy consumption, and 78.7% TDS removal rate. Under optimal conditions, the treated PFPW has two beneficial uses. First, the diluted treated PFPW is feasible for preparing polymer solutions. Second, the concentrated treated PFPW is feasible for replacing the original PFPW as the injecting water in the water-flooding process for high permeability layers.

Reclamation of the Polymer-Flooding Produced Water

In order to resolve the discharge problem of the polymer-flooding produced water (PFPW) in crude oil ex-traction, the PFPW was treated by a four-grade and four-segment (four GS) electrodialysis reversal(EDR) set-up. The testing results show that the treated PFPW has two kinds, one is the diluted treated PFPW, the total dissolved solids (TDS) of the diluted treated PFPW is less than the original PFPW, the diluted treated PFPW is feasible for confecting polymer solution; another one is the concentrated treated PFPW, the TDS of the concentrated treated PFPW exceeds the original PFPW, the concentrated treated PFPW is feasible for replacing the PFPW as the injecting water in the water-flooding process for high permeability layer. This treatment technology can not only decrease environment pollution resulted by the PFPW discharge, but also achieve closed-circuit of the water resource during crude oil extraction by using polymer flooding technology.