An atomic force microscopy and molecular simulations study of the inhibition of barite growth by phosphonates (original) (raw)
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Scale deposition is a critical issue in oil and gas exploration and production processes, causing significant blocking in tubing and consequently flow assurance and economic losses. Most studies addressing the scale formation have been limited on the experimental impact of different variables on scale formation. In this work, the inhibition of barite scale deposition was investigated by employing molecular simulations for three different scale inhibitors, namely, polyaspartic acid (PASP), nitrilotrimethylenephosphonate (NTMP), and dimethylenetriaminepenta(methylenephosphonic acid) (DETPMP). Geometrical analyses were used to explore the performances of the inhibitors and visualize the outcomes. quantitative structure activity relationship parameters were also used to predict the activity of the inhibitors in the system. The order of the inhibitors is in agreement with the experiments with the following values for binding energies: −1.06, −0.17, and −2.33 eV for PASP, NTMP, and DETPMP, respectively. The results of this study indicated that the inhibition strength of the three inhibitors on barite scale formation can be sequenced as DETPMP > PASP > NTMP. Moreover, the ecological toxicity (eco-tox) properties were predicted, and the environmental impact of the different inhibitors was assessed. All inhibitors showed comparable ecotox properties and predicted to be soluble in water. Molecular simulations proved to be an effective tool in the prediction of the performance and toxicity of barite scale inhibitors.
The role of phosphonate speciation on the inhibition of barium sulfate precipitation
Journal of Crystal Growth, 2003
The inhibition of barium sulfate precipitation in the presence of phosphonate containing molecules was investigated experimentally and speciation curves were used to elucidate the interactions involved. Inhibition of precipitation was found to be pH dependent and loss of inhibition was observed at both very high and low pHs. Maximum inhibition for all the inhibitor molecules occurred at pH 8. While speciation curves showed that inhibition could be improved by the presence of 2 or more fully de-protonated phosphonate groups (for pure aminophosphonates) on the molecule at pH ≤ 8, at pH 12 inhibition was insensitive to the number of deprotonated phosphonate groups. It is, therefore, suggested that surface charge repulsion affects inhibition at very high pH. For molecules which are not pure aminophosphonates, stereochemistry as well as functional groups and their ionisation state appear to play a significant role in inhibition at 3<pH≤8.
Dissolution of barite by a chelating ligand: An atomic force microscopy study
Geochimica et Cosmochimica Acta, 1995
Atomic Force Microscopy (AFM) has been used to observe the dissolution of (001) cleavage surfaces of barite (BaSO4) in deionized water and in solutions of DTPA (diethylene triamine pentaacetic acid), a synthetic metal-ion chelating agent. Experiments were carried out in situ in a fluid cell as well as in air on samples previously etched and dried. In water the principal dissolution features are etch pits bound by { 210 } faces. In DTPA, there is a different dissolution process which on an (001) surface results in the removal of layers that are half-unit cell thick (3.5 A). Etch pits within each half-layer are bound by { 110 } and { 100 } faces and occur in two different orientations which are related by a 2~ screw axis parallel to the c crystallographic axis. Only one pit orientation is found within each half-layer, and this orientation is determined by the position of the surface sulfate groups. The etch pit geometry suggests that the active ends of a DTPA molecule form bonds to Ba 2+ ions along [110] directions.
Investigation into the effect of phosphonate inhibitors on barium sulfate precipitation
Journal of Crystal Growth, 2002
The effect of a series of phosphonate molecules on barium sulfate precipitation was tested. While an increase in the number of phosphonate groups generally resulted in increased inhibition of barium sulfate precipitation, two notable exceptions showed that a relatively high number of phosphonate groups does not guarantee inhibition while a relatively low number of phosphonate groups does not imply no inhibition. Increasing the pH showed an increased effect of additives on barium sulfate precipitation up to pH 8. However, on increasing from pH 8 to 12, a loss of inhibition in the additives was observed which appears to be due to the barium sulfate surface changing with pH. r
Journal of Colloid and Interface Science, 1999
Noncontact atomic force microscopy (NC-AFM) has been used to investigate the morphological changes of a freshly cleaved (001) surface of barium sulfate (barite) etched with an aqueous solution of 0.1 M HCl at room temperature. Shallow triangular etch pits with a height of 3.6 Å were developed in atomically flat (001) terraces. The etching of the surface was found to proceed in a layer-by-layer dissolution process. Because the crystal structure of barite exhibits a two-fold screw axis parallel to the c axis, "alternating" etch pits were formed, with any two consecutive etch pits pointing opposite to each other. These etch pits became deeper and more elongated along the b axis with time.
Barium sulfate is a common scale in oil production installations that is treated and controlled with phosphonate inhibitors. A fundamental understanding of how these inhibitors operate, however, is only slowly emerging. In this paper, we investigate the effect on barium sulfate crystallization of two very similar phosphonate molecules that only differ in their backbone spacing, ethylenediamine-N,N,N′,N′-tetra(methylenephosphonic acid) (EDTMP) and hexamethylenediamine-N,N,N′,N′-tetra(methylenephosphonic acid) (HDTMP). It was found that the inhibitory efficacy of the organic molecules depends on their structural differences but also on the presence of other cations such as Zn 2+ . It appears that both stereochemical considerations and complexation strength differences between the two phosphonate additives result in different inhibitory powers. In the presence of zinc cations and EDTMP, it is found that inhibition is related to the concentration of uncomplexed ("free") organic.
The kinetics of barium sulphate scale formation and inhibition in the bulk solution and on surfaces
2017
The deposition and subsequent growth of inorganic scale on completion equipment is a major problem in the oil and gas industry. Several studies have been conducted on the kinetics of both bulk precipitation and surface deposition of barium sulphate. These studies were often conducted in a closed system and measurements were taken off-line and in this study, a flow cell was designed to study both kinetic processes in-situ and in an open system. The set-up allows real-time analysis of a metallic sample by following various scaling parameters such as surface coverage, number and size of crystals formed on the scaling surface. The experimental results were fitted to a diffusion-controlled model to study the mechanism of the surface crystallisation process. The kinetics and mechanisms of barium sulphate bulk precipitation and surface deposition with the absence and presence of scale inhibitors (diethylene triamine penta methylene phosphonic Acid (DETMP), VinylSulphonate Acrylic acid co-p...
Crystal Growth & Design, 2007
Barium sulfate is a common scale in oil production installations that is treated and controlled with phosphonate inhibitors. A fundamental understanding of how these inhibitors operate, however, is only slowly emerging. In this paper, we investigate the effect on barium sulfate crystallization of two very similar phosphonate molecules that only differ in their backbone spacing, ethylenediamine-N,N,N′,N′-tetra(methylenephosphonic acid) (EDTMP) and hexamethylenediamine-N,N,N′,N′-tetra(methylenephosphonic acid) (HDTMP). It was found that the inhibitory efficacy of the organic molecules depends on their structural differences but also on the presence of other cations such as Zn 2+ . It appears that both stereochemical considerations and complexation strength differences between the two phosphonate additives result in different inhibitory powers. In the presence of zinc cations and EDTMP, it is found that inhibition is related to the concentration of uncomplexed ("free") organic.