A comparative study of novel scale inhibitors with commercial scale inhibitors used in seawater desalination

The co-injection of corrosion and scale inhibitors is required for an oilfield in West Africa. The corrosion inhibitor efficiency test is systematically performed in presence of the selected scale inhibitor; however, the reverse is not performed; therefore, the impact of the corrosion inhibitor on the performance of the scale inhibitor is not known. This laboratory study investigates the performance and physical compatibilities of these two chemicals. Combinations of two corrosion inhibitors and two scale inhibitors were examined for sign of incompatibilities. These tests were conducted by diluting the neat chemical into test brines, at the designed dose rates. The brines were heated at temperatures between room temperatures (20°C) and the maximum field temperature (70°C). The two scale inhibitors were evaluated for compatibility with two corrosion inhibitors in dynamic calcium carbonate scale inhibition performance tests. By performing the tests in the presence of gradually decreasing concentrations of scale inhibitor, the minimum inhibitor concentration (MIC) is determined, following which the performance of the scale inhibitors was determined in the presence of the two corrosion inhibitors. The impact on corrosion inhibitors performance from the presence of the scale inhibitors, was determined using linear polarization resistance (LPR) bubble tests. No visible signs of incompatibility were observed between any of the scale and corrosion inhibitors in standard corrosion inhibitor / scale inhibitor compatibility bottle tests. Both scale inhibitors (SI1 and SI2) exhibited a loss of performance in the presence of corrosion inhibitor CI1, which increased minimum inhibitor concentration (MIC) rates determined in dynamic scale tests. Conversely, the corrosion inhibitor CI2 was found to have no impact on the scale inhibitors’ performance. While CL2 showed the better performance of the two corrosion inhibitors in linear polarization resistance (LPR) bubble tests, it did show a slight loss of performance in the presence of either scale inhibitor. Corrosion inhibitor CI1 exhibited poorer performance in corrosion test, with the scale inhibitor having no effect on the corrosion inhibitor’s effectiveness. The laboratory tests showed no couple scale and corrosion inhibitors with no impact on the efficiency both scale and corrosion inhibitors. Although, there are some impacts on the efficiency, these are either minor or small; apart from corrosion inhibitor CI1 which shows a significant increase in the dosage of the scale inhibitor SI2.

Effect of scale and corrosion inhibitors on well productivity in reservoirs containing asphaltenes

Inhibition of homogenous formation of calcium carbonate by poly (acrylic acid). The effect of molar mass and end-group functionality

Apparent inhibition of thermal decomposition of hydrogencarbonate ion by poly(acrylic acid). The effect of molar mass and end-group functionality

Summary Field engineers and reservoir modelers often question if equilibrium conditions prevail downhole, and when do super(sub)saturation conditions exist. This questioning is especially critical in designing seawater injection for pressure maintenance caused by serious barite scale problems in barium-containing formation water. This paper: (1) discusses the experimental research on rock-brine interaction to determine if equilibrium conditions and kinetics prevail, and (2) develops realistic seawater/inhibitor injection schemes for scale control during seawater injection. We have examined the question from three points of view: (1) thermodynamic equilibrium, (2) mass transport kinetics, and (3) experimental testing of flow through columns with or without scale inhibitors. If the reaction direction is from undersaturated toward saturation, then equilibrium normally occurs rapidly, being observed within approximately 5 minutes. When the reaction is going from supersaturated to the equilibrium direction, such as during seawater injection into a barium-containing formation, the precipitation reaction is often slow (i.e., equilibrium is not observed after 10 minutes of contact time. Both barite dissolution and precipitation rates on clean core material are consistent with those reported in literature with a second order rate constants for dissolution (≈30,172 L2·mol−1·m−2·sec−1, 100°C) and precipitation (= 938 L2·mol−1·m−2·sec−1, 100°C). The kinetics of barite formation can significantly slow down in the presence of scale inhibitors, and the sulfate tolerance can be increased. The kinetics of both barite dissolution and precipitation are poorly understood at the present time. Combining sulfate reduction and scale-inhibitor application in intelligent engineering design can significantly reduce the problems and costs associated with seawater injection. Equations for the engineering design of such treatment were derived from nucleation kinetics, inhibition efficiency, and inhibitor adsorption and transport. Sulfate tolerance in the presence of scale inhibitors is measured and compared with the prediction from nucleation inhibition theory with excellent agreement. An innovative inhibitor treatment by way of coreflood has been done as proof-of-concept and is discussed herein.

SummaryWaterflooding is known as an affordable method to enhance oil recovery after primary depletion. However, the chemical incompatibility between injected water and the water in the reservoir may cause the formation of mineral scales. The most effective method for managing such a problem is to use a variety of scale inhibitors (SIs) along with a waterflooding plan. It is necessary to perform a comprehensive study on the incompatibility scaling issue for the candidate-brine/SI formulations, and also their effect on the reservoir-rock/fluid characteristics. In this study, both in the absence and presence of polymeric, phosphonate, and polyphosphonate SIs, the scaling tendency (ST) of different brines is evaluated through experimental and simulation works. Drop-shape analysis (DSA), environmental-scanning-electronic-microscopy (ESEM) observation, energy-dispersive X-ray (EDX) analysis, and microemulsion phase behavior are also used to study the effect of different brine/SI formulations on the rock/fluid and fluid/fluid interactions, through wettability and interfacial-tension (IFT) evaluation. In summary, sulfate (SO42−) was identified as the most problematic ion in the formulation of injected water that causes the formation of solid scales upon mixing with the cation-rich formation water (FW). In the case of SIs, solid precipitation was shifted toward a lower value, with more pronounced effects at higher SI concentrations. At different ionic compositions, the inhibition efficiency (IE%) of all SIs ranged from 16 to 50% at [SI] = 20 ppm and 38 to 81% at [SI] = 50 ppm. In general, phosphonates worked better (i.e., higher IE value) than polymeric SI. Measuring contact angles along with ESEM/EDX data also illustrated the positive effect of SIs on the wettability alteration of the aged carbonate substrates. In the absence of SIs, the contact angles for different brines were in the range of 70° ≤ θ ≤ 104°, whereas these values fell between 35 and 80° for systems containing 50 ppm of SI. In addition, phase-behavior study and IFT measurement illustrated a salinity-dependence effect of SIs on the interfacial behavior of the oil/water system.

The thermodynamics of scale precipitations have been extensively studied over the past century but integrating kinetics is essential to accurately predict real behavior of produced fluids. This integration allows for a more comprehensive understanding of the dynamic processes that govern scale formation in practical applications. This work aims at improving the understanding of calcite scale precipitation and inhibition kinetics by modelling dynamic tube blocking test data using a new "scale kinetics and inhibition tool" (SKIT). By regressing a few selected parameters, as needed, it is possible to match experimental data for scale precipitation with and without the presence of scale inhibitor. The Mixed Solvent Electrolyte (MSE) thermodynamic model and Classical nucleation theory (CNT) are the basis of the predictions. The MSE model computes the driving force for precipitation whilst CNT predicts the induction time of the precipitate. The main limitation of any kinetic model is the limited published data on the precipitation kinetics, particularly in the presence of scale inhibitors. This problem is addressed here by adding a user function that enables the regression of proprietary experimental data to produce kinetic parameters specific to that experiments, scale inhibitor or field/plant condition. Dynamic tube blocking test data for calcite (CaCO3) precipitation at variable temperature, salinity, ionic composition and inhibitor concentration were used in this study. The measured induction times were inputs to the SKIT tool along with compositions and test conditions. Up to five kinetic parameters for calcite and two parameters for each dissociated form of the scale inhibitor were regressed to match experimental data. All newly regressed parameters were stored in a private database which was subsequently utilized to calculate scale induction times under specific well conditions, from downhole to separator, and to evaluate CaCO3 kinetics with and without inhibitors. The results guided the selection of optimal scale inhibitor concentrations for a chemical field trial. This work demonstrates, for the first time, how proprietary experimental data on scale inhibition can be utilized to create a private database for modeling the kinetics of scale precipitation and inhibition. Furthermore, it illustrates how this data can be leveraged to enhance the modeling of scale behavior in real field scenarios, ultimately guiding more informed decisions on strategizing scale management through optimal chemical injection concentrations.

The failure behaviour of glass polyalkenoate cements was investigated using a linear elastic fracture mechanics (LEFM) approach. Cements were based on Drayton gasifier slag and four poly(acrylic acid)s with number average molar masses ranging from 3.03 × 103 to 6.44 × 104. Cement properties were studied at time intervals of one, seven and twenty eight days. Compressive and flexural strengths of the cements increased with increasing molar mass of the poly(acrylic acid)s and time. The Young's modulii increased with time and were independent of poly(acrylic acid) molar mass. Fracture toughness increased with increasing molar mass of the poly(acrylic acid)s. Fracture toughness increases over an ageing time of one week and subsequently decreased over one month. Toughness increased with poly(acrylic acid) molar mass, these increases being most pronounced at higher molar mass. The toughness values decreased with time for the higher molar mass cements, which is consistent with increased crosslinking of the poly(acrylic acid) chains and reducing molecular flow at the crack tip. Plastic zone size increased with poly(acrylic acid) molar mass and decreased with time for lower molar mass cements, remained constant for intermediate molar mass cements and increased with high molar mass cements.

Low molar mass poly(acrylic acid) (PAA) is generally obtained by free radical polymerization of acrylic acid (AA) in aqueous solution, using thermal initiators and some chain transfer agent. However, under such conditions it is rather difficult to efficiently produce molar masses as low as those required for obtaining an effective dispersant. In this work, the semibatch polymerization of AA at 45 °C is considered, using potassium persulfate (KPS) and sodium metabisulfite (KPS/NaMBS), or alternatively KPS and sodium hypophosphite (KPS/NaHP) as redox initiators to produce PAA of controlled low molar masses. These initiation systems allow the production of PAA with Mn as low as 2.0 kDa, relatively narrow molar mass distribution (1.5 < Mw/Mn < 3.0), and low branching degree. Most of the investigated polymerizations reach almost complete conversions (>95%); and it is verified that both reductants, NaMBS and NaHP, also behave as chain transfer agents. Finally, the investigated process with redox couples allowed the production of PAA with acceptable dispersant and antiscaling properties.

Poly(acrylic acid) with molecular weight of 5000 was produced by using 2-aminoethanethiol hydrochloride as chain transfer agent. Amine chain end groups of the resulting polyacrylic acid were transformed into nitrilodi(methylenephosphonic acid) by reacting formaldehyde-phosphorous acid in the presence of hydrogen chloride. 1H NMR, 31P NMR and microanalysis were used for structural analysis.The modified polyacrylic acid had much better calcium carbonate scale inhibition effect than commercial poly(acrylic acid). Polyacrylsäure mit einem Molekulargewicht von 5000 wurde mit 2-Aminoethanthiol-Hydrochlorid als Kettenüberträger hergestellt. Die Aminendgruppen dieser Polyacrylsäure wurden durch Reaktion mit Formaldehyd und phosphoriger Säure in Gegenwart von Chlorwasserstoff zu Nitrilodi-(methylenphosphonsäure)-Endgruppen umgesetzt. Dies wurde mittels 1H-NMR, 31P-NMR und Mikroanalyse bestätigt. Die Wirkung der modifizierten Polyacrylsäure gegen Calciumcarbonat-Ablagerung übertraf die einer handelsüblichen Polyacrylsäure.

A review of hybrid desalination systems for co-production of power and water: analyses, methods, and considerations

Polymer based enhanced oil recovery (EOR) technology has drawn more and more attention in the oil and gas industry. The impacts of EOR polymer on scale formation and control are not well known yet. This research investigated the impacts of EOR polymer on calcite scale formation with and without the presence of scale inhibitors. Seven different types of scale inhibitors were tested, including four different phosphonate inhibitors and three different polymeric inhibitors. Test brines included severe and moderate calcite scaling brines. The severe calcite brine is to simulate alkaline surfactant polymer (ASP) flooding conditions with high pH and high carbonate concentration. The test method used was the 24 hours static bottle test. Visual observation and the residual calcium (Ca2+) concentration determination were conducted after bottle test finished. It was found that EOR polymer can serve as a scale inhibitor in moderate calcite scaling brines, although the required dosage was significantly higher than common scale inhibitors. Strong synergistic effects were observed between EOR polymer and phosphonate scale inhibitors on calcite control, which can significantly reduce scale inhibitor dosage and provides a solution for calcite control in ASP flooding. The impact of EOR polymer on polymeric scale inhibitors varied depending on polymer types. Antagonism was observed between EOR polymer and sulfonated copolymer inhibitor, while there was weak synergism between EOR polymer and acrylic copolymer inhibitors. Therefore, when selecting scale inhibitors for polymer flooding wells in the future, the impact of EOR polymer on scale inhibitor performance should be considered.

Synthesis and evaluation of scale inhibitor with high-temperature resistance and low corrosion capability for geothermal exploitation

Zinc sulfide (ZnS) is an exotic scale formed in the oil and gas fields, especially in HT/HP wells. It is relatively difficult to test ZnS formation and inhibition in the laboratory using traditional static jar and dynamic loop tests due to the oxidization during the test and its naturally ‘soft’ scale characteristic. Limited studies have been focused on ZnS and the detailed inhibition mechanisms are still unknown.In this paper, a newly developed stress test method has been applied to evaluate the performance and mechanisms of ZnS inhibition. Compared with the traditional test methods, it shows good reproducibility and provides a quick and effective way to evaluate the performance of inhibitors and information to understand the mechanisms of inhibition.More than 15 typical scale inhibitors, representing several different types, have been tested using this newly developed method. The ZnS scale inhibitors were classified as three types based on the inhibition mechanisms from this work:Type 1: Dispersion and nucleation inhibitors. These scale inhibitors showed nucleation and growth inhibition effect at low concentrations of sulfide and dispersion effect at high concentrations of sulfide.Type 2: Nucleation and growth scale inhibitors. These scale inhibitors inhibit nucleation and growth of ZnS formation, where the test can be stressed further.Type 3: Scale inhibitors with poor performance on ZnS inhibition. The turbidity and stress curve did not change obviously in the presence of scale inhibitors.This paper will give a comprehensive study of ZnS formation and inhibition, including scale prediction, development of test method and inhibitors, insight into the mechanism of ZnS inhibition and identification of environmentally acceptable inhibitors.

Summary In the Weizhou Oilfield, located in the South China Sea, seawater flooding containing SO42− with formation water rich in Ba2+ and Sr2+, severe barium sulfate (BaSO4), and strontium sulfate scale formation reduces reservoir production. A quaternary polymer scale inhibitor was synthesized through aqueous solution polymerization to counteract the formation of barium/strontium sulfate scale during reservoir production. This process used acrylic acid (AA), maleic anhydride (MA), dimethyl diallyl ammonium chloride (DMDAAC), and sodium styrene sulfonate (SSS) as monomers, and it utilized ammonium persulfate as the initiator and isopropanol as the chain transfer agent (CTA). The resulting terpolymer P(MA/AA/DMDAAC) and quaternary copolymer p(MA/AA/DMDAAC/SSS) scale inhibitors were characterized by Fourier transform infrared (FTIR) and 1H-nuclear magnetic resonance (NMR). The study investigated the effects of scale inhibitor dosage, temperature, and pH value on scale inhibition efficiency, the minimum inhibitor concentration (MIC) of scale inhibitors, and the adsorption-desorption performance of scale inhibitors. The optimized synthetic condition of the P(MA/AA/DMDAAC/SSS) scale inhibitor was determined by the ratio of n(MA):n(AA):n(DMDAAC) = 0.35:1:0.125. Additionally, the amount of SSS was set at 10% of the total mass of the main monomer (MA and AA), the amount of ammonium persulfate as the initiator was 6% of the total weight of the monomer, the amount of isopropanol as the CTA was 2% of the total weight of the monomer, and the polymerization time was set at 5 hours, with a polymerization temperature of 75°C. The measured scale inhibition efficiency of the P(MA/AA/DMDAAC/SSS) polymer was 94.4%, and the scale inhibitor showed good compatibility with seawater. The static MICs of the P(MA/AA/DMDAAC) and P(MA/AA/DMDAAC/SSS) scale inhibitors were 80 mg/L and 60 mg/L, respectively, in the dynamic loop test. It was observed that the performance of scale inhibitors is greatly affected by the pH value, and it was found that the two scale inhibitors performed best at a pH value of 9. This indicates that the chelating performance of dual carboxylate groups in the copolymer backbone works best with Ba2+. When the temperature reached 120°C, the P(MA/AA/DMDAAC/SSS) scale inhibition efficiency after aging for 16 hours was greater than 85%. Furthermore, dynamic adsorption and desorption performance tests show that the adsorption performance of the P(MA/AA/DMDAAC/SSS) scale inhibitor with the cationic group was found to be better than that of the polyepoxysuccinic acid (PESA) scale inhibitor with the anionic group. This suggests that including cationic quaternary ammonium groups in polymeric scale inhibitor molecules improves their ability to adsorb on anionic surface charges found in sandstone reservoirs. Finally, an analysis using environmental scanning electron microscopy (SEM) showed that using P(MA/AA/DMDAAC/SSS) scale inhibitors resulted in smaller inorganic scale crystals, which inhibited the nucleation and growth of these crystals.