The performance of polymer solutions in enhanced oil recovery: studies on their rheological,interfacial, and porous media behaviors

Four polymeric solutions based on xanthan, high and low molecular weight sulfonated polyacrylamides, and hydrolyzed polyacrylamide were prepared in aqueous solutions and their behaviors in enhanced oil recovery applications were investigated. The effect of thermal aging on polymer solutions was evaluated through rheological measurement. Pendant drop method was also used for measuring the interfacial tension (IFT) between crude oil and brine containing different polymer solutions. Moreover, the zeta potential of the oil reservoir particles treated with oil and polymer was determined by electrophoresis method in a nano-zeta meter instrument. In addition, sand pack and core flooding setup were used for evaluating the effectiveness of the polymer solutions in porous media. Polymer solutions displayed non-Newtonian behavior in almost the whole range of the shear rate applied; a shear thinning behavior was seen. Furthermore, the aging of polymers in formation water decreased the shear viscosity of all the polymers. The oil/water IFT decreased by the addition of polymers to water. The effect of xanthan polymer on zeta potential value was greater than that of the three acrylamide-based polymers. According to sand pack tests, by increasing the polymer concentration, the incremental oil recovery initially increased up to a polymer concentration of 3,500 ppm and then started to fall. Recovery factor increased from 50 to 65 % using the polymer solution in core flooding experiments. By increasing the injection rate from 0.2 to 3 mL/min, the injected fluid had less time to sweep the pores and consequently the amount of recovered oil decreased.     

Viscosity behavior and surface and interfacial activities of hydrophobically modified water‐soluble acrylamide/N‐phenyl acrylamide block copolymers

In this study, the viscosity behavior and surface and interfacial activities of associative water‐soluble polymers, which were prepared by an aqueous micellar copolymerization technique from acrylamide and small amounts of N‐phenyl acrylamide (1.5 and 5 mol %), were investigated under various conditions, including the polymer concentration, shear rate, temperature, and salinity. The copolymer solutions exhibited increased viscosity due to intermolecular hydrophobic associations, as the solution viscosity of the copolymers increased sharply with increasing polymer concentration, especially above a critical overlap concentration. An almost shear‐rate‐independent viscosity (Newtonian plateau) was also displayed at high shear rates, and typical non‐Newtonian shear‐thinning behavior was exhibited at low shear rates and high temperatures. Furthermore, the copolymers exhibited high air–water and oil–water interfacial activities, as the surface and interfacial tensions decreased with increasing polymer concentration and salinity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2290–2300, 2003     

The investigation of a new moderate water shutoff agent: Cationic polymer and anionic polymer

Cationic polymers and anionic polymers were selected as a moderate water shutoff agent for water production control. Due to the adsorption of polymers on the sand surface, the adsorption capacity under static condition, in porous media, and adsorption morphology on mica were investigated through starch–cadmium iodide method, core flow test, and atomic force microscopy measurement. The adsorption quantity on the sand surface increased with the high polymer concentrations and long adsorption time. With the increase of temperature and shearing time, the adsorption capacity slightly decreased. In addition, the adsorption capacity under water wettability condition was significantly larger than that under oil wettability condition. Alternate injection of cationic polymer and anionic polymer caused larger adsorption capacity in the core test. An adsorption multilayer was formed through alternate adsorption of cationic polymer and anionic polymer confirmed by atomic force microscopy. The visual simulation experiment was also conducted to illustrate adsorption and enhanced oil recovery mechanism. The polymers preferentially entered the high permeability zone and adsorbed on the sand surface, thus enhanced oil recovery. Furthermore, alternate injection of cationic and anionic polymers as a moderate water shutoff agent was successfully applied for water production control in oilfield test. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39462.     

Viscoelastic behavior of hydrogel-based xanthan gum/aluminum lactate with potential applicability for conformance control

Gel systems composed of biopolymers can be used, which block the regions of high water permeability during a previously established period, through the in situ formation of a gel inside the rock pores. Among the biopolymers studied, xanthan gum has attracted the greatest attention due to its viscosifying power and good stability in reservoirs subject to severe salinity and temperature from 27 to 90°C. Xanthan chains have the ability to build up physical networks with metals such as aluminum lactate to form hydrogels. Therefore, the objective of this study was to prepare and evaluate, hydrogels made from xanthan gum (XG) cross-linked with aluminum lactate. Initially, the influence of the gel formulation (biopolymer concentration and cross-linker) and the reservoir conditions (pH, temperature, salinity) of the gel strength of the system and the injectivity of the gel systems was investigated through rheological tests. Subsequently, was analyzed the morphology of the systems for 30 days by scanning electron microscopy (SEM). The results showed that the systems based on xanthan gum cross-linked, were able to form strong gels at pH 8, temperature of 70°C and salinity of 29,940 mgL⁻¹ TDS. In general, the evaluated parameters (pH, temperature, salinity, polymer concentration, and cross-linker) had a direct effect on the initial strength of the gel. However, after aging for 30 days, a drop in gel resistance was observed, since all systems have similar tan (δ) values and these parameters no longer show significant influence The aging analysis of hydrogel systems by SEM showed a difference in the surface microstructure of the dry hydrogel over the 30 days.     

弱凝胶调驱体系性能评价研究

针对具有储层非均质性强、渗透率低和孔隙结构复杂特点的储层,在注水开发后期,含水率急剧上升,普通的水驱和聚驱方法很难将油驱替出。复合离子型聚合物凝胶有很好的储层适应性,与注入污水配伍性好,成胶时间可控,吸附、滞留能力强,抗冲刷性好。其注入能力强,波及范围大,既可以封堵储层大孔道("调"的作用),又可以驱替储层剩余油("驱"的作用),能够满足调驱体系大剂量注入的要求。本文针对复合离子型凝胶调驱体系进行配方优选并进行性能评价实验,实验结果表明,该调驱体系具有较好的抗盐性、抗剪切性、热稳定性和黏弹性。     

Adsorption behavior and shear degradation of ultrahigh-molecular-weight hydrolyzed polyacrylamide in a capillary flow

Ultrahigh-molecular-weight partially hydrolyzed polyacrylamides (HPAMs) are commonly used in polymer flooding to enhance oil recovery. However, the viscosity of the HPAM solution is susceptible to shear action. Viscosity change affects sweep range and displacement efficiency of the displacement fluid. Here, a macromolecular adsorption model in microcapillary is proposed to reveal the shear variation mechanism at low flow rates. The rheological behaviors of HPAMs with three different molecular weights are investigated using a stainless steel capillary. The shear rate distributions near contraction and within capillary are compared by numerical calculation using the laminar flow model. Experimental and numerical results show that the polymer solution was mechanically degraded at low flow rates, which is in agreement with the results predicted by the adsorption theory model. A new calculation method for the thickness of polymer adsorption layer at lower flow rates is proposed based on the adsorption model proposed in this study. It is found that the viscosity and adsorption of HPAM were changed with flow rate, and their changes are closely related to the displacement efficiency in the micropores of reservoirs. This study provides new perspectives for the selection of polymer injection flow rates and the water shutoff in reservoirs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48270.     

Thermoviscosifying polymer used for enhanced oil recovery: rheological behaviors and core flooding test

Polymer flooding represents one of the most efficient processes to enhance oil recovery, but the poor thermostability and salt tolerance of the currently used water-soluble polymers impeded their use in high temperature and salinity oil reservoirs. Thermoviscosifying polymers (TVPs) whose viscosity increases upon increasing temperature and salinity may overcome the deficiencies of most water-soluble polymers. A novel TVP was studied in comparison with traditional partially hydrolyzed polyacrylamide (HPAM) in synthetic brine regarding their rheological behaviors and core flooding experiments under simulated high temperature and salinity oil reservoir conditions (T: 85 °C, and total salinity: 32,868 mg/L, [Ca²⁺] + [Mg²⁺]: 873 mg/L). It was found that with increasing temperature, both apparent viscosity and elastic modulus of the TVP polymer solution increase, while those of the HPAM solutions decrease. Such a difference is attributed to their microstructures formed in aqueous solution, which were observed by cryogenic transmission electron microscopy. Core flow tests at equal conditions showed an oil recovery factor of 13.5 % for the TVP solution versus only 2.1 % for the HPAM solution.     

Water slug injection containing n polymers in porous media

Injection of water containing dissolved chemicals is an efficient oil recovery technique. One of the problems of this method is the loss of the chemical components due to interactions between rock and fluid. In polymer injection, adsorption may happen and lead to low process efficiency. The interaction between rock and fluid is governed by the adsorption isotherm, which relates the polymer concentration in water with the adsorbed amount on the rock. In this paper the problem of oil displacement by a water slug containing n chemical components that may be adsorbed is analyzed. The system of conservation laws is solved and the structure of the solution for the case of Henry's adsorption isotherm is completely described. The concentration profile of each component and the chromatographic cycle is calculated through simple expressions. The complete and detailed solution for the case of slug injection containing three chemical components is presented. The general solution developed can be used to model several Enhanced Oil Recovery techniques, in which the chemical components adsorb in porous media following Henry's adsorption isotherm.     

Improvement in adhesive‐free adhesion by the use of electrostatic interactions between polymer chains grafted onto polyethylene plates

The tensile shear adhesive‐free adhesion properties induced by electrostatic interactions between poly(acrylic acid) (PAA) and poly[2‐(dimethylamino)ethyl methacrylate] (PDMAEMA) chains grafted onto polyethylene (PE) with low‐density (LDPE) or high‐density (HDPE) plates were studied. PAA‐ or PDMAEMA‐grafted PE plates were immersed in a HCl or NaOH solution or water for 24 h, and their electrostatic properties were changed before they were overlapped with each other and heat‐pressed. The breaking of the substrate between the two plates with water‐swollen grafted layers was observed in the low range of grafted amounts in comparison with immersion in the acidic and basic solutions. The ability of the two plates with grafted polymer chains swollen in water to strongly bond with each other was a result of electrostatic interactions formed by positively charged PDMAEMA and negatively charged PAA chains. The breaking of the substrate in the case of adhesive‐free adhesion between quaternized PDMAEMA‐grafted and PAA‐grafted PE plates immersed in the basic solution occurred with lower grafted amounts of PAA. This came from the strong attractive force between dissociated anionic PAA chains and quaternized cationic PDMAEMA chains in the basic solution. In addition, the adhesive‐free adhesion strength of HDPE plates with the same grafted polymer chains encountered the breaking of the substrate with lower grafted amounts than that of LDPE plates. It was concluded that the grafting of polymer chains onto HDPE plates with high crystallinity was considerably restricted to the outer surface regions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2632–2638, 2006     

Adsorption behavior of cocamidopropyl betaine under conditions of high temperature and high salinity

The adsorption behavior of cocamidopropyl betaine (CAB) in aqueous solutions and on sandstone surfaces was studied under the conditions of high temperature and high salinity. In aqueous solutions, as temperature increased from 25 to 90°C and salinity increased from 0 to 115,200 ppm, surface tension and the critical micelle concentration (cmc) of CAB both decreased. In the solid/liquid system, when the CAB concentration of salt solutions reached 0.30 wt %, the static saturation adsorption amount on the surface of clean sands was 14.77 mg g^?1 at 90°C. Because of its noticeable saturation adsorption capacity, the adsorption of CAB on the solid/liquid interface agreed with multilayer adsorption. Also, the adsorption amount on the surface of oil sands was greater than on clean sands. Besides, the dynamic saturation adsorption amount and retention amount of 0.07 wt % CAB solution were less than the static adsorption amount. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40424.     

Solution and interfacial behavior of hydrophobically modified water-soluble block copolymers of acrylamide and N-phenethylacrylamide

Hydrophobically modified water-soluble block copolymers were prepared by aqueous micellar copolymerization of acrylamide and small amounts (2 and 3 mol %) of a hydrophobe (N-phenethylacrylamide) that is characterized by a long spacer that places the aromatic ring far away from the backbone, with the objective of investigating the copolymers' rheological behavior and surface and interfacial activities under various conditions such as polymer concentration, shear rate, temperature, and salinity. As expected, the block copolymers exhibit improved thickening properties attributed to intermolecular hydrophobic associations as the solution viscosity of the copolymers increases sharply with increasing polymer concentration. Additional evidence for intermolecular association is provided by the effect of NaCl, the presence of which substantially enhances the viscosity. An almost shear rate–independent viscosity (Newtonian plateau) is also exhibited at high shear rate and a typical non-Newtonian shear thinning behavior appears at low shear rates and high temperatures. Furthermore, the block copolymers exhibit high air–liquid surface and liquid–liquid interfacial activities as the surface and interfacial tensions decrease with increasing polymer concentration, indicating strong adsorption of the copolymer at the interface. The surface and interfacial tensions exhibited by the copolymers were found to be relatively insensitive to the concentration of salt (NaCl). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 467–476, 2001     

Rheological behaviour of polysaccharide aqueous solutions

Several data relative to the viscosity of water-soluble polysaccharide solutions were collected from the literature and processed by different rheological models. Some relationships between the viscosity of these polymer solutions, their molecular weight and their solution concentrations, were established and their validity checked. Thus, an accurate equation correlating the viscosity and both the shear rate and the solution concentration of different water soluble polysaccharides (xanthan, hyaluronan, carboxymethylcellulose) was deduced on the basis of Cross' model which suggests two domains in which the viscosity is constant, i.e. very low and very high shear rate ranges. Then, an expression relating the zero-shear viscosity (A) and the concentration of their solutions was proposed. Finally, an alternative equation to that of Mark–Houwink correlating the molecular weight and the intrinsic viscosity of the water-soluble polysaccharides studied in this paper was found.     

Novel fluorinated surfactants for enhanced oil recovery in carbonate reservoirs

Novel surfactant‐polymer (SP) formulations containing fluorinated amphoteric surfactant (surfactant‐A) and fluorinated anionic surfactant (surfactant‐B) with partially hydrolyzed polyacrylamide (HPAM) were evaluated for enhanced oil recovery applications in carbonate reservoirs. Thermal stability, rheological properties, interfacial tension, and adsorption on the mineral surface were measured. The effects of the surfactant type, surfactant concentration, temperature, and salinity on the rheological properties of the SP systems were examined. Both surfactants were found to be thermally stable at a high temperature (90 °C). Surfactant‐B decreased the viscosity and the storage modulus of the HPAM. Surfactant‐A had no influence on the rheological properties of the HPAM. Surfactant‐A showed complete solubility and thermal stability in seawater at 90 °C. Only surfactant‐A was used in adsorption, interfacial tension, and core flooding experiments, since surfactant‐B was not completely soluble in seawater and therefore was limited to deionized water. A decrease in oil/water interfacial tension (IFT) of almost one order of magnitude was observed when adding surfactant‐A. However, betaine‐based co‐surfactant reduced the IFT to 10^?3 mN/m. An adsorption isotherm showed that the maximum adsorption of surfactant‐A was 1 mg per g of rock. Core flooding experiments showed 42 % additional oil recovery using 2.5 g/L (2500 ppm) HPAM and 0.001 g/g (0.1 mass%) amphoteric surfactant at 90 °C.     

Effect of microscopic aggregation behavior on polymer shear resistance

The study of polymer aggregation behavior effect on shear resistance shed light on the synthesis of antishear polymer for oil displacement and enhances the application effect of polymer flooding. The effects of mechanical degradation on the properties of polymer solutions were studied by using partially hydrolyzed polyacrylamide (HPAM), hydrophobically modified HPAM (HMPAM), and dendritic hydrophobic associative polymers (DHAP), which are characterized by “granular,” “chain,” and “cluster” aggregation behavior, respectively. The results show that mechanical shearing can dramatically reduce the performance of polymer solution. The shearing resistance can be effectively enhanced by improving the polymer aggregation behavior. After being strongly sheared, hydrophobically associating polymers can still partially restore its network through hydrophobic association, therefore rebuild the solution viscosity. For DHAP, the broken molecular chains distribute more evenly in solution after shearing. In addition, the strength of reconstructed network structure of DHAP is better than that of HMAPM, which implies a better shear resistance. Furthermore, the hydrophobic association of linear polymers will increase their static adsorption on quartz sand. Meanwhile, DHAP with stronger spatial structure has less static adsorption, which is beneficial to maintain a higher polymer concentration in solution. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48670.     

Hydrophobically modified melamine-formaldehyde sponge used for conformance control and water shutoff during oil production

Polymer or polymer gels have been widely used to control excessive water during oil production by homogenizing injection profile and reducing water cut in the produced fluids. However, the gels used are generally unable to selectively minimize water production, and face the challenge of syneresis of gels under high temperature and high salinity environment. In this work, melamine-formaldehyde sponge was modified with AlCl₃ solution, rendering a transition from hydrophilic to hydrophobic state with a water contact angle of 130° on the surface of the modified product. Filtration results show that mineral oil and water can be selectively separated with the hydrophobically modified sponge powders. Simulated water shutoff experiments demonstrated the blockage efficiency against water was 30% higher than that against oil, and the oil production was increased 7.4% after blocking. The parallel profile control tests confirmed that the fraction flow of high permeable channel decreased about 75%, accompanied with 60% rise of oil recovery factor. These results indicated that such hydrophobic materials can significantly reduce excessive water production, and this work provided a new idea to offer a low-cost hydrophobic material for conformance control and water shutoff during oil production.     

Acidic Heavy Oil Recovery Using a New Formulated Surfactant Accompanying Alkali–Polymer in High Salinity Brines

The strength of a newly formulated surfactant with an alkali and polymer (AS/ASP) to improve an acidic heavy oil recovery was laboratory evaluated by various flooding experiments. The comparative role of the parameters like chemical nature, surface wettability, salinity, temperature and injection scheme were explored at high temperature and pressure on Berea sandstone rocks. According to the results the anionic surfactant is capable of providing proper oil displacement under high salinity conditions around 15 wt%. Continuous monitoring of differential pressure response and effluents’ state clearly represented the formation of an emulsified oil in high saline solutions with both alkali and surfactant. Adding sodium metaborate to the surfactant solution reduced the interfacial tension (IFT) to ultra low values and decreased the surfactant emulsion generation capability at higher salinities. Besides, adding Flopaam AN113SH to the chemical slug increased the residual oil removal owing to lower mobility ratios. So, while high capillary number and an emulsion phase were generated by the A/S slug phases, adding polymer could further enhance the performance of these chemicals. On the other hand, chemical flooding through the oil-wet medium resulted in shorter break through time, lower differential pressure, finer emulsion formation, and lower oil recovery in comparison to the similar water-wet cases.     

耐盐型双子表面活性剂驱油体系研究

对一种新型双子表面活性剂GA12-4-12进行了研究。该表面活性剂在矿化度为2.5×10^5mg/L、氯化钙浓度为1.5×10^4mg/L的水溶液中表现出良好的表面活性,其临界胶束浓度为538.6mg/L。GA12-4-12溶液与稀油间的油水界面张力随着盐含量的增加（60～250g/L）而降低。在高矿化度模拟地层水条件下,GA12-4-12及其与聚合物复合体系SP的油水动态界面张力均能达到超低值（10^-3mN/m）。进行模拟驱油实验表明,GA12-4-12与SP复合体系提高水驱采收率分别为6.25%、10.67%。     

Significance of polymer on emulsion stability in surfactant‐polymer flooding

The influence of polymer on stability and shear rate on droplet size of emulsion is evaluated in the laboratory, microstructure of the emulsion is observed under a microscope, and the pore distribution of the cores is analyzed through mercury injection experiments. In the process of surfactant‐polymer (SP) flooding, the thickness of polymer absorbed on the surface of the rock is calculated by a mathematical model. The experiments show that the polymer is good for the stability of emulsion, with the increase of shear rate, stability becomes better, and droplet size gets smaller. Due to the adsorption of polymer, the pore throat turns narrow, seepage velocity is increasing, and also the emulsion becomes more stable with the smaller‐size droplets. During the single emulsifier flooding, the emulsion is easy to coalescence for its instability, and the seepage channel can be easily blocked, which leads to the high injection pressure. Consequently, the polymer plays an important role on emulsion stability in SP flooding. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42171.     

Model Development for MEOR Process in Conventional Non‐Fractured Reservoirs and Investigation of Physico‐Chemical Parameter Effects

A three‐dimensional multi‐component transport model in a two‐phase oil‐water system was developed. The model includes separated terms to account for the dispersion, convection, injection, growth and death of microbes, and accumulation. For the first time, effects of both wettability alteration of reservoir rock from oil wet to water wet and reduction in interfacial tension (IFT) simultaneously on relative permeability and capillary pressure curves were included in a MEOR simulation model. Transport equations were considered for the bacteria, nutrients, and metabolite (bio‐surfactant) in the matrix, reduced interfacial tension on phase trapping, surfactant and polymer adsorption, and effect of polymer viscosity on mobility of the aqueous phase. The model was used to simulate effects of physico‐chemical parameters, namely flooding time schedules, washing water flowrate, substrate concentration, permeability, polymer and salinity concentration on Original Oil In Place (OOIP) in a hypothetical reservoir.