A humic acid graft copolymer possessing both water-retention and dispersing properties in cement slurry was synthesized by grafting lateral chains of 2-acrylamido-2-methylpropane sulfonic acid (AMPS®), N,N-dimethylacrylamide (NNDMA), and acrylic acid (AA) onto a backbone of humic acid using aqueous free radical polymerization. The graft copolymer is composed of 20 wt % humic acid backbone and 80 wt % graft chain (molar ratio AMPS/NNDMA/AA = 1 : 0.31 : 0.03), it exhibits a M_w of 323 kDa and is highly anionic in cement pore solution. The influence of this specific molecular design on cement flow properties is unraveled. When tested at 200°C, the graft copolymer achieved very low cement fluid loss values (∼50 mL) at low rheology. This behavior differentiates it from most common synthetic high temperature fluid loss additives which excessively viscosify cement slurries. The working mechanism of the graft copolymer was found to rely on adsorption onto the surface of hydrating cement. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A polymer comprising of 2-acrylamido-2-methyl propane sulfonic acid, N, N-dimethyl acrylamide, allyloxy-2-hydroxy propane sulfonic acid (AHPS), acrylic acid, and N, N-methylene bisacrylamide was synthesized by aqueous free radical copolymerization and tested as high temperature performing fluid loss additive (FLA) in oil well cement. Successful incorporation of AHPS was confirmed and characteristic properties of the copolymer were determined using size exclusion chromatography. The FLA showed excellent water retention in cement at 200°C/70 bar. At this temperature, polymer structure changed from branched to linear and hydrodynamic size decreased by ∼50%, thus indicating potential fragmentation, while performance remained unaffected by these alterations. The FLA copolymer does not viscosify cement slurries which is advantageous in high temperature well cementing. The working mechanism of the AHPS-based copolymer was found to rely on reduction of filtercake permeability which is caused by a voluminous coprecipitate of the FLA with tartaric acid retarder, mediated by Ca²⁺ ions. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

The working mechanism of carboxymethyl hydroxyethyl cellulose (CMHEC, M_w 2.6 × 10⁵ g/mol) as fluid loss control additive (FLA) for oil well cement was investigated. First, characteristic properties of CMHEC such as anionic charge amount, intrinsic viscosity in cement pore solution, and static filtration properties of cement slurries containing CMHEC were determined at 27°C and 70 bar. Effectiveness of the FLA was found to rely on reduction of cement filter cake permeability. Consequently, the working mechanism is ascribed to constriction of cement filter cake pores. Zeta potential measurements confirm that at low CMHEC dosages (0–0.3% by weight of cement, bwoc), adsorption of the polymer onto the surface of hydrating cement occurs. However, at dosages of 0.4% bwoc and higher, an associated polymer network is formed. This was evidenced by a strong increase in hydrodynamic diameter of solved CMHEC molecules, an exponential increase in viscosity and a noticeable reduction of surface tension. Thus, the working mechanism of CMHEC changes with dosage. At low dosages, adsorption presents the predominant mode of action, whereas above a threshold concentration of ∼ 10 g/L (the “overlapping concentration”), formation of associated polymer networks is responsible for effectiveness of CMHEC. Addition of anionic polyelectrolytes (e.g., sulfonated melamine formaldehyde polycondensate, M_w 2.0 × 10⁵ g/mol) to cement slurries containing CMHEC greatly improves fluid loss control. Apparently, the presence of such polyelectrolytes causes the formation of colloidal associates from CMHEC to occur at lower dosages. Through this mechanism, effectiveness of CMHEC as cement fluid loss additive is enhanced. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A copolymer comprising of 2-acrylamido-2-methyl propane sulfonic acid (AMPS®) and itaconic acid (molar ratio 1 : 0.32) was synthesized by aqueous free radical polymerization and probed as high temperature retarder for oil well cement. Characteristic properties of the copolymer including molar masses (M_w and M_n), polydispersity index and anionic charge amount were determined. The copolymer possesses a M_w of ∼ 2 × 10⁵ g/mol and is highly anionic. HT/HP consistometer tests confirmed effectiveness of the retarder at temperatures up to 200°C. The working mechanism of NaAMPS®-co-itaconic acid was found to rely exclusively on its huge calcium binding capacity (5 g calcium/g copolymer). It reduces the amount of freely dissolved, nonbound calcium ions present in cement pore solution and thus hinders the growth of cement hydrates because of lack of calcium. The value for the calcium binding capability is 46 times higher than the stoichiometric amount per COO⁻ functionality. Consequently, calcium also coordinates to other donor atoms present in the retarder. NaAMPS®-co-itaconic acid also adsorbs onto cement, as was evidenced by TOC analysis of cement filtrates, zeta potential measurement and decreased rheology of cement pastes. However, adsorption plays no role in the retarding mechanism of this copolymer. Combination of NaAMPS®-co-itaconic acid retarder with a common CaAMPS®-co-NNDMA fluid loss additive (FLA) revealed that competitive adsorption on cement between these two admixtures occurs. The retarder fills interstitial adsorption sites on cement located between those occupied by the larger FLA molecules. In consequence, fewer amounts of CaAMPS®-co-NNDMA can adsorb and its effectiveness is reduced. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

The working mechanism of hydroxyethyl cellulose (HEC) as a fluid loss additive in oil well cement was investigated. The specific anionic charge amount, intrinsic viscosity, and associative behavior in a cement pore solution were determined. The fluid loss performance was probed through the static filtration of cement slurries. HEC achieves fluid loss control by reducing cement filtercake permeability. No influence on the filtercake microstructure was observed. ζ Potential measurements and a special filtration test indicated that no adsorption on cement occurred. Environmental scanning electron microscopy images revealed that in a wet environment, HEC swelled to a multiple of its size and possessed an enormous water-sorption capacity. Concentration-dependent measurements of the hydrodynamic diameter of HEC dissolved in a cement pore solution showed that large associates were formed. These colloidal associates physically obstructed the filtercake pores. Finally, the addition of sulfonated melamine formaldehyde dispersant to the cement slurries containing HEC greatly improved the fluid loss control. A specific interaction was responsible for this synergistic effect. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Monomers of 2-acrylamido-2-methylpropane sulfonic acid (AMPS®), N,N–dimethyl acrylamide (NNDMA) and acrylic acid (AA) were grafted on humic acid as backbone by aqueous free radical copolymerization in such a manner that a graft copolymer possessing lateral terpolymer chains was obtained. Molar ratios between AMPS®, NNDMA, and AA were found to be 1 : 1.54 : 0.02 and the ratio between backbone and graft chain was 20 : 80 wt %. The synthesized fluid loss additive (FLA) was characterized by size exclusion chromatography (SEC), charge titration, and Brookfield viscometry. Thermogravimetric and SEC analysis revealed stretched backbone worm architecture for the polymer whereby humic acid constitutes the backbone decorated with lateral graft chains. Grafting was confirmed by SEC data (R_g) and by ineffectiveness of a blend of AMPS®-NNDMA-AA copolymer with humic acid. Their performance as high temperature FLA was studied at 150°C by measuring static filtration properties of oil well cement slurries containing 35% bwoc of silica fume and 1.2% bwoc AMPS®-co-itaconic acid retarder. At this temperature, 1.0% bwoc graft copolymer achieves API fluid loss value of 40 mL, thus confirming high effectiveness. The graft copolymer viscosifies cement slurries less than other common synthetic FLAs. The working mechanism of the graft copolymer was found to rely on adsorption onto surface of hydrating cement, as was evidenced by adsorption and zeta potential measurements. Adsorption is hardly affected by temperature and results in constriction of the filter cake pores. The study provides insight into performance of cement additives under the harsh conditions of high temperature and high pressure. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The fluid loss control performance of 2-acrylamido-2-methylpropane sulfonic acid (AMPS®)-based copolymers added to cement slurries was studied at 27 and 100°C, respectively. It was found that effectiveness of these fluid loss additives solely relies on achievement of a high adsorbed amount on the surface of cement. At elevated temperature (100°C), CaAMPS®-N,N-dimethyl acrylamide copolymer (CaAMPS®-co-NNDMA) exhibits reduced adsorption and hence decreased fluid loss control of the cement slurry. The reason behind this behavior is poor calcium binding capability of the sulfonate anchor groups, which coordinate with calcium atoms present on the mineral surface. Whereas, an increase in the sulfate concentration present in cement pore solution instigates partial coiling of CaAMPS®-co-NNDMA and causes only a slight influence on the performance of this copolymer. The elevated sulfate content results from thermal degradation of ettringite, a cement hydrate mineral produced during the early stages of cement hydration. Incorporation of minor amounts (∼ 1.3 mol %) of maleic anhydride into this copolymer produces a terpolymer, which exhibits higher and more stable adsorption, even at high temperature. This effect is owed to the presence of homopolymer blocks of polycarboxylates distributed along the polymer trunk. On mineral surfaces, they present much stronger anchor groups than sulfonate functionalities, as evidenced by their higher calcium binding capability. Consequently, fluid loss performance of CaAMPS®-co-NNDMA-co-MA is little affected by temperature. Understanding the influence of temperature on the physicochemical interactions occurring between additives and the mineral surface can help to design more effective admixtures suitable for high temperature applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

When used by itself, polyethylene imine (PEI) does not perform well as cement fluid loss additive. Its combination with acetone formaldehyde sulfite (AFS) polycondensate, however, exhibits excellent filtration control. The mechanism underlying this synergistic effect was studied and the conditions producing best results were determined. For optimum performance, PEI and AFS must be reacted with each other to yield a polyelectrolyte complex (PEC) (d ∼ 5–10 μm), which effectively plugs the pores of the cement filter cake. Composition, size, and effectiveness of the PEC are strongly influenced by the anionic charge amount of the AFS dispersant. Ionic interactions between cationic imine functionalities of PEI and anionic sulfonate groups existing in AFS were confirmed by conductivity, infrared, zeta potential, and particle size measurements. For AFS samples possessing different degrees of sulfonation, the largest particle size and hence best fluid loss performance of the PEC was found to occur at a PEI:AFS molar ratio, which corresponds to neutral charge. Occurrence of large PEC particles (d ∼ 5 μm) within the cement filter cake pores was visualized by scanning electron microscopy, and their stability in highly alkaline cement pore solution was confirmed by particle size measurement. Other anionic polyelectrolytes may be used to yield such PECs with PEI to provide effective fluid loss control for cement slurries. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

For phosphonated copolymers, the effect of distance of the phosphonate group from the polymer backbone on the Ca²⁺ chelating capability and the adsorption behavior on cement was studied. For this purpose, 2-acrylamido-2-methylpropane phosphonic acid (AMPPA) and vinyl phosphonic acid (VPA), respectively, were reacted in an aqueous free-radical polymerization with N,N-dimethylacrylamide (NNDMA) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS®) to give poly(N,N-dimethylacrylamide-co-2-acrylamido-2-methylpropanesulfonate-co-2-acrylamido-2-methylpropanephosphonate) (CaAMPS®-co-NND MA-co-CaAMPPA) and poly(N,N-dimethylacrylamide-co-2-acrylamido-2-methylpropanesulfonate-co-vinylphosphonate) (CaAMPS-co-NNDMA-co-CaVPA), respectively. Adsorption behavior and thus performance of the terpolymers strongly depend on their calcium binding capacity. Ca²⁺ selective conductivity measurements show that the AMPPA modified terpolymer chelates less calcium than the VPA polymer. Therefore, it interacts less with surfaces containing calcium atoms/ions. To investigate the consequences for practical applications adsorbed amounts on cement surface and effectiveness as water retention agent (fluid loss additive, FLA) in oil well cement slurries with and without acetone-formaldehyde-sulfite (AFS) dispersant were determined. CaAMPS-co-NNDMA-co-CaAMPPA and AFS adsorb simultaneously whereas CaAMPS-co-NNDMA-co-CaVPA does not allow dispersant adsorption. The reason is that affinity of phosphonate functions towards Ca²⁺ ions is reduced with increasing distance from the polymer backbone. Thus, AMPPA is a weaker anchor group than VPA. Zeta potential measurements indicate that the increased length of the side chain holding the phosphonate function decreases the anionic charge density of the polymer. Accordingly, CaAMPS-co-NNDMA-co-CaAMPPA appears to develop weaker bonds with the cement surface. Upon addition of AFS, the AMPPA modified FLA can change its adsorbed conformation from “train” to “loop” or “tail” mode and thus provide space for the dispersant to adsorb as well. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Water-soluble 2-acrylamido-2-methylpropane sulfonic acid (AMPS®)-based copolymers are commonly used to provide water retention (fluid loss control) for oil well cement slurries. Here, the fluid loss performance of a CaAMPS®-N,N-dimethylacrylamide copolymer (CaAMPS®-co-NNDMA) in the presence of Welan gum, an anionic microbial biopolymer produced by anaerobic fermentation using Alcaligenes ATCC 31555 bacteria was investigated at 80°C. Welan gum is used to control unwanted free water development at the surface of the cement slurry. The effectiveness of CaAMPS®-co-NNDMA fluid loss additive (FLA) solely relies on its high adsorption onto the positively charged surfaces of cement hydrates. Adsorption of the FLA is, however, perturbed by Welan gum. This anionic polysaccharide competes with CaAMPS®-co-NNDMA for adsorption sites on the cement surface. This effect is surprising because in cement pore solution, Welan gum exhibits a much lower specific anionic charge amount than CaAMPS®-co-NNDMA. The reason is that Welan gum possesses carboxylate functionalities, which are much stronger anchor groups than the sulfonate groups present in CaAMPS®-co-NNDMA. The superiority of the carboxylate groups regarding their affinity to the mineral surface, which possesses insufficiently coordinated Ca atoms is confirmed by a higher calcium binding capability for Welan gum than for the FLA. Thus, Welan gum can reduce effectiveness of CaAMPS®-co-NNDMA as fluid loss agent by preventing its adsorption or through displacement of already adsorbed FLA molecules from the surface of cement. In multiadmixture systems, which are commonly used in oil well cement, concrete or mortars, competitive adsorption between different additives for surface sites can negatively impact the performance of these additives. Understanding the reasons behind can help to develop more effective admixture systems. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

The working mechanism of poly(vinyl alcohol) (PVA, M_w ∼ 200,000 g mol⁻¹), a fluid loss control additive (FLA) applied in oil well cementing, was investigated. First, characteristic properties of PVA such as solubility and particle size in cold and hot water, minimum film forming temperature, adsorption on cement, viscosity of cement pore solution and static filtration properties of cement slurries treated with PVA were determined. It was found that the working mechanism of PVA relies on hydrated, but water-insoluble PVA particles (d₅₀ ∼ 2.4 μm). During cement slurry filtration, they coalesce into a polymer film. This film effectively plugs the pores of the cement filter cake. The sample studied here becomes water-soluble at temperatures > 40°C (d₅₀ decreases to ∼50 nm) and looses its effectiveness. Addition of highly anionic dispersants such as ß-naphthalenesulfonate formaldehyde (BNS) or acetone formaldehyde sulfite (AFS) polycondensate extends the temperature range at which PVA works from 40°C to ∼60°C. This effect is ascribed to lower solubility of PVA in the presence of these dispersants. The study reveals that decreased performance of PVA caused by higher temperatures is not the result of thermal degradation of the polymer, but is owed to its increasing water-solubility. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Sulfonated aldol polycondensates were synthesized from acetone, formaldehyde, and different amounts of sodium sulfite, resulting in polymers with varying degrees of sulfonation (DS). The anionic charge amount of these macromolecules measured by polyelectrolyte titration decreased with lower DS. The effectiveness of the acetone–formaldehyde–sulfite (AFS) polycondensates as cement dispersant was found to depend on the amount of polymer adsorbed on cement. AFS adsorption decreases with lower DS. Interaction and compatibility between AFS and CaAMPS®-co-NNDMA fluid loss additive was studied by formulating binary additive systems composed of one of the modified AFS polymers and CaAMPS-co-NNDMA. At high DS, AFS adsorbs strongly and prevents CaAMPS-co-NNDMA from adsorbing in sufficient amounts on the cement surface. The result is poor fluid loss control of the cement slurry. AFS polymers with lower DS, however, allow simultaneous adsorption of both polymers in sufficient quantities to provide good fluid loss control and low rheology at the same time. Thus, effectiveness of both additives was retained. Obviously, effectiveness of such multi-admixture systems depends on the adjustment of the adsorption behavior of the individual components relative to each other. Molar anionic charge density of the polymers was found to be a major parameter influencing their relative adsorption behavior. The AFS polymer with DS = 0.2 possesses a molar anionic charge density comparable to CaAMPS-co-NNDMA. Thus, when admixtures with similar molar anionic charge densities are used, the performance of one component is not negatively influenced by the other. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009