Eleftheria Mavredaki

University of Leeds, Leeds, England, United Kingdom

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Publications (16)33.21 Total impact

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    ABSTRACT: The formation of calcium carbonate scale and the occurrence of CO 2 corrosion in sweet environments are both widespread phenomena and have been studied extensively in oil and gas industry. Scale and corrosion are part of the main problem encountered in distillation plants or in flow assurance for oil and gas industry. Investigations centred on inhibition tend to focus on reducing scale and corrosion through individual chemical treatments as opposed to inhibiting both processes with one chemical inhibitor. Scope exists for a combined product which is capable of retarding both the effects of scale formation and CO 2 corrosion. This paper presents results from an initial trial that has been conducted to develop a methodology based on a bulk jar scaling test and a bubble cell corrosion measurement. The efficiency of four combined corrosion and scale inhibitors were assessed while both scaling and corrosion processes were occurring on X-65 carbon steel samples. The formation and growth of scale in the bulk was monitored using a turbidity meter and the corrosion rate was assessed through linear polarisation resistance measurement. The four combined products were studied at different concentrations (2, 4 and 5ppm) at 60°C in CO 2-saturated brine. Scanning Electron Microscopy (SEM) was used to examine the surface morphology of the samples after the experiments. According to the results, the combined products act by increasing the induction time of the formation of the calcium carbonate in the bulk, changing the morphology of the crystals and forming a partial protective layer onto the sample. Each chemical reveals a different efficiency in inhibiting the scale and/or the corrosion process.
    Full-text · Article · Jun 2014 · Journal of Petroleum Science and Engineering
  • Eleftheria Mavredaki · Anne Neville
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    ABSTRACT: Mineral scaling is one of the main flow assurance problems facing the oil and gas sector and imposes severe constraints on the economic and safe operation of fields. During the last decades, operators, in conjunction with the chemical manufactures and oil service companies have focused in understanding, predicting and mitigating scale formation. Even though progress towards better management of scale formation continues, scale precipitation is still a significant flow assurance problem, caused by mixing incompatible waters (produced water, seawater, aquifers) especially at high water cuts. One of the most frequently depositing scale types in the oil production process, is calcium carbonate. To date the overwhelming amount of research has been on the thermodynamics that drive the precipitation of calcium carbonate in an aqueous system, with little attention given to actual surface deposition. Therefore, to improve scale management practices, the kinetics that dominate CaCO3 surface formation need to be understood. The work presented in this paper has, as its main focus the deposition of CaCO3 at a stainless steel surface. The data from the surface is presented in conjunction with the findings from bulk phase experiments. A small bore flow rig and a quartz crystal microbalance were used for monitoring the induction time and the real time deposition of CaCO3. Calcium carbonate deposition was examined at a range of conditions with emphasis given to different supersaturation ratios. The results are discussed in correlation with the theoretical calculations based on a computer scale prediction software. The data collected from the CaCO3 surface experiments contribute to understanding at which level the supersaturation ratio becomes a threat with respect to scale formation at surfaces. This paper describes steps towards predicting the induction time of calcium carbonate at surfaces, when the main input is the supersaturation ratio.
    No preview · Article · May 2014
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    Konstantinos D. Demadis · Maria Somara · Eleftheria Mavredaki
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    ABSTRACT: The effect of various fluorine-containing chemical additives on the dissolution of colloidal silica is systematically studied. These silica scale dissolvers are ammonium bifluoride (NH4·HF2), ammonium fluoride (NH4F), sodium tetrafluoroborate (NaBF4), and disodium fluorophosphate (Na2PO3F). The most effective dissolver was NH4·HF2, which was extensively studied at the pH range 2–7. The highest dissolution efficiency was demonstrated in the pH range 2–4. The dissolution capability of Na2PO3F was monitored not by the silicomolybdate method, but on the basis of a weight-loss approach. It showed substantial dissolution ability at pH’s 7 and 9.
    Full-text · Article · Feb 2012 · Industrial & Engineering Chemistry Research
  • Michal Ciolkowski · Anne Neville · Xinming Hu · Eleftheria Mavredaki · Laura Sanders
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    ABSTRACT: Corrosion and scale deposition are well known problems in pipelines. Corrosion control of carbon steel pipelines requires an understanding of the simultaneous occurrence of both processes. To date there have been few studies demonstrating the interactions between surface scale deposition and corrosion processes. Common methods of controlling corrosion and scale are deploying corrosion and scale inhibitors. However, combined (ComI) are receiving increased attention from industry as their application can significantly reduce chemical costs. Many factors influence the performance of corrosion and scale inhibitors and the influence of supersaturated brines on the surface scale deposition and subsequent effects on corrosion processes are generally not well understood. The work presented describes a range of laboratory tests conducted to assess the influence of different supersaturated brines on corrosion and scale on both inhibited (ComI) and uninhibited systems. Corrosion is measured by conventional electrochemical techniques and surface deposition is assessed using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX). Bulk precipitation is measured by turbidity.
    No preview · Article · Jan 2012
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    ABSTRACT: The formation of calcium carbonate scale and the occurrence of corrosion in CO 2-saturated environments in different parts of oil and gas facilities are both phenomena that have been extensively studied. However, to date, very limited work has been carried out on evaluating combined products in a combined scale/corrosion methodology. This paper presents the results from a new combined bulk jar scaling/bubble cell corrosion test. The aim of this project is to investigate the effect of two combined chemicals in a new experimental setup; to study the corrosion and scale interactions which occur simultaneously. Two combined products were assessed at 5 ppm concentration at two temperatures (60°C and 80°C) in a CO 2-saturated brine. Bulk scale precipitation was monitored using a turbidity meter and the corrosion rate measurements were made using the linear polarisation resistance (LPR) technique. Scale deposition and corrosion mechanisms have been studied using surface analyses. The performance of the two combined products has also been tested to measure: (i) the increase in the induction time of the calcium carbonate formation in the bulk, (ii) the change of the morphology of the crystals and (iii) the formation of a partial protective layer on the sample. According to this study, the new experimental method has enabled the corrosion and scale deposition on pipeline steel (X65) and the bulk precipitation process to be studied simultaneously. Detailed scale deposition mechanisms on the material surface in the presence of corrosion processes and combined products are addressed from this study.
    No preview · Article · Jan 2012
  • Eleftheria Mavredaki · Anne Neville · Ken Sorbie
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    ABSTRACT: The precipitation of barium sulphate from aqueous supersaturated solutions is a well-known problem in the oil industry often referred to as ‘scaling’. The formation and growth of barite on surfaces during the oil extraction process can result in malfunctions within the oil facilities and serious damage to the equipment. The formation of barium sulphate at surfaces remains an important topic of research with the focus being on understanding the mechanisms of formation and means of control.In situ synchrotron X-ray diffraction (SXRD) was used to investigate the formation of barium sulphate on a stainless steel surface. The effect of Poly-phosphinocarboxylic acid (PPCA) and Diethylenetriamine–penta-methylenephosphonic acid (DETPMP) which are two commercial inhibitors for barium sulphate was examined. The in situ SXRD measurements allowed the identification of the crystal faces of the deposited barite in the absence and presence of the two inhibitors. The preferential effect of the inhibitors on some crystal planes is reported and the practical significance discussed.Research highlights▶ The main crystal faces of barium sulphate were identified from the in situ SXRD patterns in the absence and in the presence of inhibitors. The lattice planes of BaSO4 reveal the same growth trend on the surface independently of the supersaturation index and the temperature. ▶ At 95 °C 10 ppm PPCA inhibits the growth of the dominant barite surfaces by 80%. ▶ At 95 °C DETPMP performs as a nucleation inhibitor for barium sulphate formed on the surface. ▶ An effective inhibition of barite occurs when the (0 1 1) and (1 1 1) crystal faces of BaSO4 are retarded. ▶ Strontium co-precipitates within the barite lattice resulting in formation of celestine barian. The growth of the celestine barian lattice planes follows the same growth trend with the one of the barite crystal faces.
    No preview · Article · Dec 2011 · Applied Surface Science
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    Konstantinos D. Demadis · Eleftheria Mavredaki · Maria Somara
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    ABSTRACT: The effect of various environmentally friendly chemical additives and natural products on the dissolution of amorphous silica (Aerosil 200 and laboratory-synthesized, SSD) is studied. The silica scale dissolvers tested include the following: ascorbic acid (vitamin C, ASC), citric acid (CITR), carboxymethyl inulin (CMI), 3,4-dihydroxybenzoic acid (catechuic acid, DHBA), 3,4,5-trihydroxybenzoic acid (gallic acid, GA), dopamine hydrochloride (DOPA), iminodiacetic acid (IDA), histidine (HIST), phenylalanine (PHALA), and malic acid (MAL). The chemical structures of these chemical additives contain potentially dissolution-active moieties, such as 1,2-dihydroxyethylene (ASC), α-hydroxycarboxylate (MAL and CITR), catecholate (DHBA, GA, and DOPA), α-aminocarboxylate (HIST and PHALA, both aminoacids), and finally carboxy-modified fructofuranose units (CMI). It was found that all studied molecules showed variable dissolution efficiency, with MAL, CMI, HIST, and PHALA being the slowest/least effective dissolvers, and the catechol-containing DHBA, GA, and DOPA being the most effective ones. IDA and CITR have intermediate efficiency.
    Full-text · Article · Nov 2011 · Industrial & Engineering Chemistry Research
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    Konstantinos D. Demadis · Eleftheria Mavredaki · Maria Somara
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    ABSTRACT: The effect of various chemical additives (small molecules and polymers) on the dissolution of two kinds of colloidal silica (Aerosil 200 and laboratory-synthesized, SSD) is systematically studied at pH 10. The silica scale dissolvers tested are 5-carboxybenzotriazole (CBZT), amino-tris(methylene phosphonic acid) (AMP), a phosphino-polycarboxylic acid (PPCA), diethylenetriamine pentacarboxylic acid (DETPA), a proprietary polymer (Genesol 40), poly(acrylic acid) (PAA), ethylenediamine-tetrakis(methylenephosphonic acid) (EDTMP), phosphonobutane-1,2,4-tricarboxylic acid (PBTC), sodium metaborate, and N-phosphonomethylimino-diacetic acid (PMIDA). Of the polymeric additives only Genesol 40 shows some dissolution activity, dissolving 280 ppm silica at 10 000 ppm dosage after 72 h. PBTC and DETPA are the best-performing additives of all those tested. PBTC is effective even at the 2500 ppm dosage, as it solubilizes 290 ppm silica after 72 h. Its efficiency is dosage-dependent. DETPA is also an effective silica dissolver. Its behavior is similar to that of PBTC. Its best dosage is 7500 ppm, which yields dissolution of 322 ppm silica (after 24 h), 340 ppm (after 48 h), and 333 ppm (after 72 h). SSD silica is a very recalcitrant deposit showing resistance to dissolution even by the most effective additives, PBTC and DETPA.
    Full-text · Article · Oct 2011 · Industrial & Engineering Chemistry Research
  • Eleftheria Mavredaki · Anne Neville · Ken S. Sorbie
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    ABSTRACT: The formation of barium sulfate (BaSO4) in the oilfield is known to occur as a precipitation process from the aqueous phase within oil production facilities. This barite deposition causes many problems related to flow assurance. In this paper, the initial stages of barium sulfate deposition on a metallic surface are investigated. The mass rate of deposition of barite on the surface was measured using a quartz crystal microbalance (QCM). The morphology of the deposited BaSO4 was then observed directly with an atomic force microscope (AFM) and the main crystal faces of barite were identified. Both the formation kinetics and the crystallography of the deposited barium sulfate were studied at three supersaturation ratios and in the presence and absence of 2 chemical scale inhibitors, namely, polyphosphino carboxylic acid (PPCA) and diethylene triamine penta acetic acid (DETPMP). In addition, the precipitation of the barite in the bulk phase was also monitored (by turbidity measurements) thus giving a more complete description of the overall bulk/surface barium sulfate kinetics. PPCA proved to be an effective barite inhibitor both at the surface and in the bulk phase in these measurements. DETPMP did not perform so well but there are several reasons why this may be so in such early time experiments and these are discussed in the paper. Thus, such experiments must be interpreted with some caution when we are relating the results to the oilfield scale system. In the industrial application addressed here, the brine system is very specific in that it is at relatively high ionic strength, the divalent cations (Ca2+/Mg2+/Sr2+) play an important role and the supersatuaration ratios of barite are very high. However, barite deposition is currently a very significant problem in the oil and gas industry, and this paper presents findings that will contribute to better ways of managing barite scale in the future.
    No preview · Article · Oct 2011 · Crystal Growth & Design
  • Eleftheria Mavredaki · Anne Neville · Ken S. Sorbie
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    ABSTRACT: Synchrotron X-Ray Diffraction (SXRD) was used in-situ to investigate the formation of barium sulphate on a stainless steel surface at high temperatures. For the first time in-situ SXRD measurements of BaSO4 formed in the presence of foreign ions (Sr2+, Ca2+ etc) are presented. The formation kinetics of BaSO4 on the surface has been determined and the crystallographic nature of the barite was investigated. In addition the effect of Poly-phosphinocarboxylic acid (PPCA) as chemical scale inhibitor on barium sulphate was examined at two temperatures. The barite crystal faces present on the surface after the treatment with inhibitors were detected. The lattice planes recorded with the in-situ SXRD measurements revealed that the presence of Sr2+ in the initial formation water resulted in the co-precipitation of Sr2+ within the barite lattice. The in-situ SXRD measurements allowed the assessment of information on the kinetics and crystallography of the formed scale in the absence and presence of inhibitor. The crystallography of the barite revealed high sensitivity to temperature and inhibition effects.
    No preview · Article · Jan 2010
  • Eleftheria Mavredaki · Anne Neville · Kenneth Sorbie
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    ABSTRACT: Precipitation of barium sulphate from aqueous supersaturated solutions is one of the most well known problems in the oil industry. Precipitation of barite and other insoluble scale types (metal sulphates, calcium carbonate and silicates) propagate to undesirable formations, which adhere strongly in production tubing and in equipment parts. Formation of BaSO4 lead to a decrease in the performance of the petroleum facilities and to inevitable damage in the oil industry. Barium sulphate is one of the most insoluble types of inorganic scale. It resists many chemical methods of removal. Inhibition of barium sulphate by chemicals is generally recognized as the most appropriate approach for flow assurance. In this study Synchrotron X-Ray Diffraction was used to investigate the kinetics of barium sulphate formed on stainless steel surface at two different temperatures. For the first time SXRD measurements of BaSO4 formed in the presence of foreign ions (Sr2+, Ca2+ etc) are presented. The in-situ measurements allowed the assessment of the crystallographic nature of the formed scale and the probation into the precipitation mechanisms. Additionally this study focused on the effect of PPCA on the barium sulphate precipitation. PPCA was examined for its inhibition action in two concentrations at both temperatures. The formed barite crystal faces after the treatment with PPCA were recorded.
    No preview · Article · Jan 2008
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    ABSTRACT: Mineral scale deposits such as calcium carbonate and phosphate, calcium oxalate, barium and strontium sulfate, magnesium silicate and others and colloidal inorganic species such as silica present important challenges for process water applications. When silica is left uncontrolled it forms hard and tenacious deposits that are difficult and hazardous to remove. Conventional phosphonate mineral scale inhibitors do not inhibit silica formation and deposition. Chemical cleaning is not free from hazards and requires operational shut-downs. Another challenge is corrosion of critical metal surfaces of industrial equipment. Last but not least, biofouling due to the development of microorganisms. This paper is focused on the presentation of the general scope of these problems and their solutions. More specifically, it concentrates on (a) inhibition of colloidal silica formation, (b) colloidal silica dissolution, and (c) metallic corrosion, in water applications by use of designed chemical approaches. The additives used for silica inhibition were polyaminoamide dendrimers, polyethyloxazoline and polyethyleneimine polymers. For silica dissolution the dissolvers tested were carboxymethyl inulin (CMI), Genesol 40 (a proprietary blend of additives), polyacrylic acid. In principle, silica inhibition is a function of time and inhibitor dosage. Silica dissolution is dependent in a rather unpredictable fashion on the structure of the dissolver, time and dosage. Mild steel corrosion inhibition has been achieved by synergistic use of zinc ions and polyphosphonate anions that create protective films.
    Full-text · Article · Jul 2007 · Desalination
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    ABSTRACT: Supersaturated process waters high in silicates frequently result in deposition of colloidal silica or metal silicate salts. Silica cannot be inhibited by conventional phosphonate mineral scale inhibitors. Chemical cleaning poses hazards and requires operational shut-downs. This paper is focused on a dual approach for silica scale control, inhibition of colloidal silica formation and colloidal silica dissolution in water technology applications by use of designed chemical approaches. The additives used for silica inhibition were polyaminoamide dendrimers (PAMAM) and polyethyleneimine (PEI), in combination with carboxymethyl inulin (CMI) and polyacrylate (PAA) polymers. In principle, silica inhibition is a function of time and inhibitor dosage. Amine-terminated PAMAM-1 and 2 dendrimers as well as PEI combined with anionic polymers, such as CMI and PAA, seem to have a significant inhibitory effect on silica formation, most likely at its earlier stages where the reaction products are oligomeric silicates. CMI and PAA assist the inhibitory action of PAMAM-1 and 2 and PEI by alleviating formation of insoluble SiO2-PAMAM precipitates. This most likely occurs by partial neutralization of the positive charge that exists in –NH+3 surface groups. Increase of anionic polymer dosage above a certain threshold has a detrimental effect on the activity of the cationic inhibitors. In that case the polymer’s negative charge “overwhelms” the cationic charge of the inhibitor and poisons its inhibition ability. For silica dissolution, acetic, oxalic, citric acids, histidine and phenylalanine were used as potential replacements of ammonium bifluoride (NH4F·HF). Silica dissolution is dependent in a rather unpredictable fashion on the structure of the dissolver, time and dosage. This paper continues our research efforts in the discovery, design and application of antiscalant additives that have mild environmental impact. These chemicals are also known as “green additives”.
    Full-text · Article · Jun 2007 · Desalination
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    Konstantinos D. Demadis · Eleftheria Mavredaki
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    ABSTRACT: The effect of various environmentally friendly chemical additives on the dissolution of colloidal silica is systematically studied. These silica scale dissolvers are principally polycarboxylates with one to five –COOH groups, mixed polycarboxylates/phosphonates and aminoacids. Based on these results, an effort is made to link their dissolution performance to structural features in this structure/function study. Presence of additional groups (eg. –PO3H2, –NH2, or –OH) in the dissolver molecule augments the dissolution process.
    Full-text · Article · Dec 2005 · Environmental Chemistry Letters
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    Eleftheria Mavredaki · Eleftheria Neofotistou · Konstantinos D. Demadis
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    ABSTRACT: This paper is focused on a dual approach for silica scale control, inhibition and dissolution by use of designed chemical approaches. Inhibitors that are tested include the polyaminoamide STARBURST dendrimers (PAMAM) of generations 0.5, 1.0, 1.5, 2.0, and 2.5. Of these, only the NH 2 -terminated ones (PAMAM-1.0 and 2.0) show significant inhibitory activity, in contrast to COOH-terminated ones (PAMAM-0.5, 1.5, and 2.5), which show virtually no inhibition perfor-mance. The synergism between the above dendrimers and an anionic polyelectrolyte (poly(acry-lamide-co-acrylate) copolymer) is also described. Addition of poly(acrylamide-co-acrylate) copolymer in silica supersaturated solutions containing PAMAM-1 or 2 alleviates the appearance of silica-PAMAM insoluble precipitates, resulting in stable colloids. The paper also describes silica dissolution approaches, as an alternative to inhibition, by using nonhazardous additives based on polycarboxylates with one to five -COOH groups (acetate, oxalate, citrate, diethylen-etriaminepentaacetate, and others), mixed polycarboxylates/phosphonates (2-phosphonobutane-1,2,4-tricarboxylate), and amino acids (L-histidine and L-phenylalanine). Their reactivity is linked to their chemical structure in this structure/function study. The presence of additional chemical groups (e.g., -PO 3 H 2 , -NH 2 , or -OH) in the dissolver molecule augments the dissolution process.
    Full-text · Article · Aug 2005 · Industrial & Engineering Chemistry Research
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    ABSTRACT: Colloidal silica (SiO 2) and other sparingly soluble salts such as CaCO 3 present a challenge for desalination systems used for brackish or seawater desalting. When SiO 2 is left uncontrolled, it forms hard and tenacious deposits that are difficult and hazardous to remove. Conventional phosphonate mineral scale inhibitors do not inhibit SiO 2 formation and deposition. Chemical cleaning is not free from hazards and requires operational shut-downs. CaCO 3 is also troublesome. This paper focused on silica and CaCO 3 formation, deposition and inhibition with designed chemical approaches in water applications that require the use of membranes. It also describes SiO 2 scale removal by dissolution approaches with environmentally friendly and non-hazardous chemical additives. The general scope of silica formation and inhibition in waters relevant to desalination systems is also discussed. This paper continues our research efforts in the discovery, design and application of anti-scalant additives that have a mild environmental impact. These chemicals are also known as "green additives". In light of increasing environmental concerns for discharge of saline water coming from desalination systems, this research is of significant interest.
    Full-text · Article · Jul 2005 · Desalination