Impact of salts on polyacrylamide hydrolysis and gelation: New insights

Polyacrylamide (PAM) and its derivatives are the most commonly used polymers in the preparation of polymeric gels for water control in petroleum reservoirs. This study involved the use of polyethylenimine (PEI) as a crosslinker for PAM. In this study, we investigated PAM alkaline hydrolysis at high temperatures. The effects of salts [sodium chloride (NaCl) and ammonium chloride (NH₄Cl)] on the degree of hydrolysis (DH) of PAM were investigated. These salts were used as retarders to elongate the gelation time of the PAM/PEI system. The data obtained from ¹³C‐NMR was used to understand the retardation mechanisms by salts. We found that NH₄Cl accelerated the extent of hydrolysis more in comparison with NaCl. Moreover, the apparent viscosity of the hydrolyzed samples was measured. PAM hydrolysis in the presence of NH₄Cl resulted in a lower solution viscosity than that in the presence of NaCl. Therefore, NH₄Cl was more effective in shielding negative charges on the carboxylate groups of the partially hydrolyzed polyacrylamide (PHPA) chain. NaCl and NH₄Cl were compatible with the PHPA/PEI system, but sodium carbonate showed a white precipitate. In addition, high‐temperature/high‐pressure elastic modulus data were reported for the first time for this system. Differential scanning calorimetry was coupled with rheology to explain the PAM/PEI crosslinking in the presence of salts. Models were developed to assess the impact of the salts on the PAM DH and the induction period before gelation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41185.     

Study on strength and gelation time of polyacrylamide/polyethyleneimine composite gels reinforced with coal fly ash for water shut‐off treatment

This study investigates the influence of coal fly ash (CFA) as a reinforcing material on the strength and the gelation of polyacrylamide (PAM)/polyethyleneimine (PEI) composite gels. Pure PAM/PEI gel and PAM/PEI gels containing CFA up to 2 wt % were synthesized via the cross‐linking reaction between PAM and PEI solutions at room temperature (25°C) in distilled water dispersed with CFA. The strength of each composite gel was measured at temperature of 80°C, while the gelation was determined from 80°C to 95°C. Rheological measurements indicated that the strength of PAM/PEI composite gels filled with CFA contents was significantly rigid and stronger than that of pure PAM/PEI gel as a result of the enhanced interfacial interaction of well‐dispersed CFA contents in PAM/PEI gel matrix. The gelation times of PAM/PEI gels containing CFA up to 2 wt % deviated from the gelation time of pure PAM/PEI gel. It was further observed that an increase in temperature resulted in a decrease in gelation time of PAM/PEI gel containing 2 wt % CFA. The scanning electron microscopy revealed the surface micrographs of PAM/PEI gels filled with CFA to be very dense without any noticeable micropores. The micropores were absent as scanning was performed on the dried composite gels. It also establishes the strong interaction between CFA and PAM/PEI gel matrix. Experimental findings showed that PAM/PEI composite gels reinforced with CFA are potential candidates for total water shut‐off treatment in oilfields. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41392.     

Gelation performance of poly(ethylene imine) crosslinking polymer–layered silicate nanocomposite gel system for potential water‐shutoff use in high‐temperature reservoirs

Polymer gels have been widely used for water shutoff in mature oil fields. In this paper, polyacrylamide (PAM)–montmorillonite (MMT) nanocomposites (NC) were prepared through in situ intercalative polymerization. Fourier transform infrared spectroscopy and X‐ray diffraction were conducted to characterize the prepared PAM/MMT nanocomposites. The gelation performance of poly(ethylene imine) (PEI) crosslinking PAM/MMT nanocomposite gel system (NC/PEI gel system) was systematically investigated by bottle testing and viscosity measurement methods. The results showed that the gelation performance of the NC/PEI gel system was greatly affected by the total dissolved solids, PAM/MMT nanocomposite concentration, and PEI concentration. The NC/PEI gel system exhibited much better thermal stability and gelation performance than the PAM/PEI gel system at the same conditions. The gelation performance after flowing through porous media of the NC/PEI gel system before injection and that of the subsequently injected gel system was different. The gel strength decreased and the gelation time was delayed after the gel system before injection was flowed through porous media. However, the gel strength of the subsequently injected gel system did not decrease, and only the gelation time was delayed after flowing through porous media. This study suggests that the NC/PEI gel system can be used as a potential water‐shutoff agent in high‐temperature reservoirs. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44243.     

Static adsorption and dynamic retention of an anti‐salinity polymer in low permeability sandstone core

The technical viability of enhancing oil recovery (EOR) using polymer flooding has been verified. Through correcting the unfavorable mobility ratio, polymer flooding could significantly improve the macroscopic sweep efficiency of waterflooding, which makes it attractive in middle to high permeability reservoirs. However, as the depletion of these easy‐to‐produce resources, the interests of oil industry will be diverted to low permeability reservoirs and polymer flooding is believed to be one of the key methods for this type of reservoir. To meet this technological tendency, the current work investigated the applicability of an anti‐salinity polymer (KYPAM) in low permeability sandstone reservoirs. The interactions between polymer and sandstone surface including static adsorption and dynamic retention were addressed. Static adsorption data proved that the adsorptive behavior of this anti‐salinity polymer was closely related to molecular weight and concentration. The quantity of the detained KYPAM polymer in the sandstone core rapidly increased once the permeability dropped below 38 mD. High molecular weight KYPAM experienced noticeable retention compared with low molecular weight polymers resulting from the large hydrodynamic size. Due to polymer retention, the permeability of the sandstone core was significantly influenced particularly for the low permeability cores. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44487.     

Laboratory scale study on rheological behavior,morphological and structural properties of crosslinked polyacrylamide composite hydrogels embedded with date seed powder

Incorporation of biofillers in polymeric hydrogels has continued to receive great attention in recent times because of their excellent properties. In this study, polyacrylamide (PAM) and polyethyleneimine (PEI) were used to develop novel composite hydrogels filled with date seed powder (DSP) via chemical crosslinking technique. Pristine PAM/PEI hydrogel and PAM/PEI‐DSP hydrogels at various DSP loadings were fabricated and subjected to gelation at 40°C for 24 h. The impact of various DSP loadings on the hydrogel samples developed was investigated using hybrid rheometer, SEM, XRD, and FTIR instruments, respectively. Rheological measurements confirmed the viscoelastic responses of the neat PAM/PEI hydrogel and the PAM/PEI‐DSP hydrogels reinforced with various DSP contents (0.8, 2.4, and 4 wt %). The dynamic strain, dynamic frequency and time sweep tests demonstrated that PAM/PEI‐DSP hydrogels were slightly more elastic than the virgin PAM/PEI hydrogel. The SEM characterization revealed the surface micrographs of the neat PAM/PEI hydrogel and the PAM/PEI‐DSP hydrogels at different DSP loadings to be smooth, homogeneous, and dense. Besides, the SEM micrographs supported the incorporation of DSP in the PAM/PEI‐DSP hydrogel samples. XRD analysis showed that the structures of neat PAM/PEI hydrogel and PAM/PEI‐DSP hydrogels filled with various DSP contents were predominantly amorphous while FTIR results confirmed the functional groups and evidence of crosslinking in the neat PAM/PEI hydrogel and the PAM/PEI‐DSP hydrogels embedded with different DSP contents. It is believed that these new hydrogels have huge development potentials and promising future in wastewater treatment and removal of heavy metal ions in aqueous solutions. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42110.     

Performance of fly ash based polymer gels for water reduction in enhanced oil recovery: Gelation kinetics and dynamic rheological studies

The complexity of well and reservoir conditions demands frequent redesigning of water plugging polymer gels during enhanced oil recovery (EOR). In the present study, we developed coal fly ash (CFA) based gels from polyacrylamide (PAM) polymer and polyethyleneimine (PEI) crosslinker for water control in mature oil fields. The CFA acts as an inorganic additive to fine-tune gelation performance and rheological properties of PAM/PEI gel system. Hence, effects of various CFA (0.5 to 2 wt%), PAM (2 to 8.47 wt%) and PEI (0.3 to 1.04 wt%) concentrations on gelation kinetics and dynamic rheology of pure PAM/PEI gel and PAM/PEI-CFA composite gels were studied at a representative reservoir temperature of 90 oC. Experimental results reveal that gelation time of pure PAM/PEI gel increases with increasing CFA addition. Further observation demonstrates that increasing PAM and PEI concentrations decreases the gelation times of PAM/PEI-CFA composite gels. Gelation time was found to be within 3-120 hours. Understanding the property of reaction order enables better prediction of gelation time. Dynamic rheological data show that viscoelastic moduli (G′ and G″) of various PAM/PEI-CFA composite gels improved better as compared to the pure PAM/PEI gel across the strain-sweep and frequency-sweep tests. SEM analysis of selected samples at 72 hours and 720 hours of gelation activity consolidated gelation kinetics and dynamic rheological results. These polymer gels are excellent candidates for sealing water thief zones in oil and gas reservoirs.     

Gelation mechanism and rheological properties of polyacrylamide crosslinking with polyethyleneimine and its plugging performance in air‐foam displacement

Gels based on polyacrylamide crosslinking with polyethyleneimine have attracted attention because of their resulting high strength and good thermal stability. This study investigated the gelation mechanism of the polymeric gel and its plugging performance in air‐foam flooding. An optic microrheology analyzer was used to monitor the gelation process. The crosslinking reaction occurred in two steps, as determined from the elasticity factor curves, and the polymeric gels adopted a semisolid state from solution, as determined from the solid liquid balance curves. The elastic modulus values were higher than the viscous modulus values, indicating that mature gels were elastic‐based materials. The yield stress increased gradually with increasing polymer dosage, which was consistent with the breakthrough pressure and the trend of displacement pressure. The mature gels showed significant thixotropy. In the core displacement test, the preferred injection volume of the gel was 0.1 pore volume, and the stable pressure of the foam flooding was increased by about three times after the core was plugged. The blocking effect for cores with small original permeability was better than that with large permeability. The best blocking resulted from simultaneous treatment of both ends of the cores, followed by front‐end treatment and rear‐end treatment. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45778.     

泡沫酸体系性能的室内研究

将常规酸和泡沫流体相结合,研制出泡沫酸体系.对其作用原理、性能、岩心模拟室验进行了室内研究和评价.结果表明泡沫酸具有缓蚀、低滤失等普通酸所不具备的许多优良性能;泡沫酸对水相渗透率变化比值几乎没有改变,对油相有大的改变,对岩心的伤害小;适用于碳酸盐岩、砂岩地层的深部酸化与解堵.     

Preparation and characterization of nanocomposite hydrogels based on polyacrylamide for enhanced oil recovery applications

In the present work, attempts have been made to prepare nanocomposite type of hydrogels (NC gels) by crosslinking the polyacrylamide/montmorillonite (Na‐MMT) clay aqueous solutions with chromium (III). The X‐ray diffraction patterns of the NC gels exhibited a significant increase in d₀₀₁ spacing between the clay layers, indicating the formation of intercalated as well as exfoliated type of morphology. Exfoliation of the clay layers through out the gel network was found to be predominated, which evidences the high interaction between the polyacrylamide segments and montmorillonite layers. Gelation time as well as variation of viscoelastic parameters such as storage modulus (G′) of the gel network during gelation process at 75°C was studied and followed by rheomechanical spectroscopy (RMS). The NC gels prepared with lower crosslinker concentration showed higher strength and elastic modulus compared with the similar but unfilled polyacrylamide gel. This distinct characteristic of the NC gels yields a gel network structure with high resistance towards syneresis at high temperature in the presence of the oil reservoir formation water. The effects of the composition, such as clay content, crosslinker concentration, and also water salinity upon the gelation rate, gel strength as well as rate of syneresis have been investigated. To optimize the injectivity of the intercalated polyacrylamide solution before the onset of gelation with the gel strength of the final developed gel, sodium lactate was employed as retarder. This was found to be effective to balance these two characteristics of the NC gels, which are aimed to be used for water shut‐off and as profile modifier in enhanced oil recovery (EOR) process during water flooding process. The nanocomposite gels showed much more elasticity and extensibility at low crosslinker concentration compared with the similar but unfilled gel, which makes the NC gels suitable as an in‐depth profile modifier, and also as an oil displacing agent in the heterogeneous oil reservoir in chemical EOR. Effects of the clay content on the thermal stability of the gel network have also been investigated by thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) has been performed upon the NC‐gel samples. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2096–2103, 2006     

Effects of Rheological Behavior of Viscoelastic Surfactants on Formation Damage in Carbonate Rocks

Viscoelastic surfactants (VES) are used in various oilfield applications such as matrix stimulation and enhanced oil recovery. The loss of surfactants during the propagation of VES could result in a significant reduction in the permeability of the rock (formation damage). The objective of the current work was to identify the effect of rheological behavior of the VES on the formation damage using core‐flooding experiments, nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM) analysis. A combination of core‐flooding, NMR, and SEM techniques was used to quantify and identify the location of formation damage in carbonate core samples. The viscosity and storage modulus strongly depend on the nature and concentration of salts. The viscosity increased by increasing the salt concentration up to a specific point (15 wt% CaCl₂) and then starts decreasing. The VES formulations that displayed the maximum and minimum viscosities were used to identify the impact of rheological behavior on formation damage. Core‐flooding experiments were performed to assess the formation damage due to high‐viscosity and low‐viscosity VES formulations. The reduction in the permeability of carbonate rocks reaches more than 90% of the initial permeability. It was found that low‐viscosity VES caused more damage compared with high‐viscosity VES when they were used at constant concentrations. NMR and core‐flooding results revealed that the damage took place both in pore body and pore throat. However, most of the surfactant was retained at the pore throat.     

Preparation of ultra‐high‐molecular‐weight polyacrylamide by vertical solution polymerization technique

A straightforward and novel methodology has been developed for the synthesis of ultra‐high‐molecular weight polyacrylamide (PAM) by vertical solution polymerization technique. By varying the concentrations of acrylamide monomer, three different grades of polymers (PAM‐V₁, PAM‐V₂, and PAM‐V₃) have been synthesized and compared with the series of different grades of PAM (PAM‐C₁, PAM‐C₂, and PAM‐C₃) synthesized through conventional solution polymerization technique. The synthesized grades PAM‐V₁, PAM‐V₂, PAM‐V₃, PAM‐C₁, PAM‐C₂, and PAM‐C₃ have been characterized by ¹H NMR, infrared spectroscopy, intrinsic viscosity measurement, molecular weight determination by gel permeation chromatography, and thermal analysis. Rheological analysis has been carried out on the aqueous solutions of various grades of PAMs. Swelling behavior of ultra‐high‐molecular weight PAMs has also been investigated. The flocculation performances of all grades have been investigated in kaolin suspension by settling and jar test methods. POLYM. ENG. SCI., 59:1175–1181 2019. © 2019 Society of Plastics Engineers     

新型抗高温水溶性暂堵剂实验研究

高温120℃下,使用不同分子量和水解度的聚丙烯酰胺与多种交联剂按照不同比例进行交联反应,得到高温暂堵剂体系,通过对暂堵剂的成冻时间、稳定时间和破胶时间等因素的研究,确定暂堵剂体系的聚合物为PAM1200,聚合物质量浓度为0.4%～0.55%;交联剂为G与YG107(2∶1)复配体,质量浓度为0.1%～0.2%,破胶剂质量浓度0.03%～0.05%。在120℃0,.5%PAM1200,0.1%交联剂G,0.2%交联剂YG107,0.03%破胶剂下,稳定性评价实验及岩心流动实验表明:暂堵剂对不同渗透率的岩心封堵率达92.75%,暂堵后渗透率恢复率高于83.19%,具有较好的破胶液化能力。     

耐温耐盐复合交联调剖体系实验研究

使用部分水解聚丙烯酰胺、有机铬和水溶性酚醛为主剂,制备了一种复合交联调剖体系,考察了聚合物及交联剂浓度、矿化度、温度等因素对体系成胶性能的影响。结果表明,体系在矿化度为15 000 mg/L,温度低于90℃的条件下,仍可生成较高强度的凝胶,具有良好耐温耐盐性能。通过单管和双管并联岩心封堵实验来模拟体系对地层的调剖过程,结果表明,体系对单管岩心的封堵率高于96%,突破压力梯度大于35 MPa/m;双管并联岩心实验时,体系对高渗管岩心的封堵率在95%以上,而对低渗管岩心的封堵率低于15%。     

水驱后凝胶与表活剂交替注入驱油效果

针对裂缝性低渗透油藏注入水易沿裂缝突进、含水上升快、水驱效果不理想的情况,开展了水驱后凝胶与表活剂交替注入方式提高采收率室内实验研究。通过室内凝胶体系成胶特性和稳定性评价,筛选出与实际油藏区块注入水配伍的凝胶体系。选择甜菜碱两性表面活性剂用于活性剂驱,开展了双管并联岩心体系驱油效果研究。研究结果表明:凝胶与表活剂交替注入可明显提高注入压力,该体系的采收率平均值为12.03%,低渗岩心的采收率略高于高渗透岩心采收率。与表活剂驱、聚合物与表活剂交替注入相比,驱油效果更好,可以作为裂缝性低渗透油藏水驱后进一步提高采收率的技术。     

Pretreatment of papermaking‐reconstituted tobacco slice wastewater by coagulation–flocculation

A study using coagulation–flocculation method for the treatment of papermaking‐reconstituted tobacco slice wastewater had been carried out. Polyaluminum chloride (PAC) and polyferric sulfate (PFS) as coagulants, and four kinds of polyacrylamides (PAMs) as flocculants, were employed during the coagulation–flocculation process. The effects of three factors, that is, the dosage of coagulants, the dosage of flocculants and pH on the treatment efficiency of the process were evaluated. The results showed that the efficiencies of PAC and PFS on the reduction of COD, ammonia nitrogen (NH₃‐N) and total suspended solids (TSS) in the treated effluents were equivalent; however, the efficiency of PAC on the color reduction was much higher than that of PFS. In the presence of PAC, a cationic polyacrylamide with very high molecular weight and low charge density (i.e., PAM4) was found to give the highest coagulation–flocculation efficiency. At the optimal conditions, that is, pH of 6.5, PAC dosage of 500 mg/L, and PAM4 dosage of 5 mg/L, the reductions of COD, NH₃‐N, color, and TSS in the process were found to be 70.8, 84.8, 72.3, and 98.5%, respectively. The study also showed that the PAC‐PAM4 scheme can remove the most of aluminum from the raw water. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1092‐1097, 2013     

Efficient dispersants for the dispersion of gallium zinc oxide nanopowder in aqueous suspensions

Appropriate dispersants for the dispersion of gallium zinc oxide (GZO) nanopowder in aqueous suspensions were identified in this study. The dispersion efficiencies and stabilization mechanisms of water‐based dispersants ammonium poly(acrylic acid) (PAA–NH₄), an anionic polyelectrolyte, and polyethylenimine (PEI), a cationic polyelectrolyte, were compared. The experimental analyses of rheology and sedimentation showed that both PAA–NH₄ and PEI were good dispersants for the dispersion of GZO. Theoretical calculations based on Derjaguin‐Landau‐Verwey‐Overbeek theory revealed that the stabilization mechanism of PEI was mainly related to the steric effect, and a very low molecular weight of 1800 g/mol was insufficient for powder stabilization. GZO was well dispersed by PEI with high molecular weight of 10 000 g/mol, but agglomeration occurred when too much PEI was added. Compared with PEI, PAA–NH₄ was more efficient because of its high contribution to the increase in electrostatic repulsion. Based on theoretical considerations on both steric and electrostatic effects, namely, the electrosteric stabilization mechanism, PAA–NH₄ is optimal for the dispersion of GZO nanopowder in aqueous suspensions.     

砾岩油藏三元复合驱中碳酸钠与无机矿物消耗影响因素研究

新疆油田三元复合驱现场使用的碱为碳酸钠,针对该区块的无机矿物组成、原油组成与地层水组成特点,开展了碳酸钠消耗量的研究。结果表明,砾岩油藏地层中的无机黏土矿物对碳酸钠有较强的吸附作用,其中吸附最强的是蒙脱石,其次是绿泥石、伊利石、长石,石英砂吸附性最小。静态吸附的结果证明碳酸钠在松散岩心上的吸附大于胶结岩心上的吸附,随着渗透率的降低,碳酸钠的动态吸附量逐渐减小,杂基对碳酸钠的消耗较大。该区块原油酸值较低,碳酸钠与原油发生化学反应的损失较少,该区块地层水中二价金属阳离子浓度较低,对碳酸钠的消耗也较少。     

Permeability mapping in naturally heterogeneous sandstone cores by magnetization prepared centric‐scan sprite

A time‐efficient MRI method suitable for quantitative two‐dimensional (2‐D) mapping of permeability in sedimentary rock cores, and granular media samples is discussed. The images of porosity and mean axial velocity in the plane transverse to the average flow direction are essential to determine 2‐D distribution of permeability in a core sample. The 2‐D permeability mapping is particularly useful for discrimination of bedding and lamination layers, fractures and fault facies that occur in sedimentary rocks. The proposed method combines the 13‐interval APGSTE scheme and centric‐scan SPRITE. The APGSTE scheme is known to substantially reduce gradient‐related errors in diffusion measurements. The SPRITE method provides quantitative information on fluid content within the core samples. The experiment time is critically reduced when only a few samples near the q‐space origin are collected. The APGSTE‐SPRITE method is illustrated through mapping of 2‐D permeability and 3‐D velocity field in naturally heterogeneous sandstone cores. © 2012 American Institute of Chemical Engineers AIChE J, 2012     

黏弹性颗粒驱油剂的制备与性能

经过长期的注水开发,我国大部分油田已面临非均质性严重、剩余油分散等现状,依靠常规方法仍有近一半原油滞留地下无法采出。线型聚丙烯酰胺驱油剂在非均质油藏中沿高渗条带窜流,扩大波及体积能力差,无法起到大幅度提高采收率的作用。对此,创新设计了一种“交联-支化共存”新型分子结构,采用自由基聚合,建立了多官能引发体系,发明了动力学调控机制,研发了结构可控的黏弹性颗粒驱油剂(B-PPG)。B-PPG在性能上兼具部分水解聚丙烯酰胺和交联聚丙烯酰胺的双重优点:它既具有线型聚丙烯酰胺的增黏能力和在地层中的运移能力,同时又具有交联聚丙烯酰胺优异的耐温抗盐、耐老化能力和调节地层渗透率的能力。以B-PPG为主剂的非均相复合驱技术已应用于胜利油田聚驱后油藏,提高采收率8.5个百分点,最终采收率高达63.6%,实现聚驱后油藏高效开发。     

基于低渗透率的聚丙烯酰胺类调剖剂研究

针对传统聚丙烯酰胺类聚合物在油田堵水中的污染和调堵效果差的问题,利用聚丙烯酰胺(PAM)中酰胺基团上的活性氨基与三羟甲基三聚氰胺(TMM)分子中的羟甲基产生亲核反应,制备一种新型低渗透率的油田封堵调剖剂。在以不同原材料配合比、反应温度、不同浓度作为考察影响因素,通过实验观察PAM/TMM调剖剂黏度变化,最后通过红外光谱、凝胶强度、封堵率等方法或指标对制备的调剖剂表征及性能进行测定。