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Results
Using Synchrotron Radiation Wide Angle X Ray Scattering (WAXS) to Study the Inhibiting Effect of Polyphosphonocarboxylic Acid (PPCA) on CaCO3 Scale Formation
Chen, Tao (University of Leeds) | Zhong, Zhong (University of Leeds) | Neville, Anne (School of Mechanical Engineering) | Sorbie, Ken S. (Heriot-Watt University)
ABSTRACT The aim of this paper is to further the understanding of scale formation and inhibition by in-situ probing of crystal growth by synchrotron radiation Wide Angle X-Ray Scattering (WAXS) in the absence and presence of Polyphosphinocarboxylic acid (PPCA) scale inhibitor at elevated temperature and high pressure. It has been shown that the nucleation and growth of various calcareous polymorphs and their individual crystal planes can be followed in real time and from this the following conclusions are reached. · The process of scale deposited on the surface can be divided into an unstable phase and a stable phase. The initial phase of crystallization of calcium carbonate is characterized by instability with individual planes from various vaterite and aragonite polymorphs emerging and subsequently disappearing under the hydrodynamic conditions. After the initial unstable phase, various calcium carbonate crystal planes adhere on the surface and then grow on the surface. · PPCA inhibits surface deposition. It suppresses calcite formation and results in vaterite- dominated scale. This is the first time that crystallization of mineral scale and its inhibition have been followed in-situ and as such, information on the nucleation and growth processes is accessible. This technique offers an exciting prospect for the study of scaling. INTRODUCTION The formation of mineral scale is a persistent and expensive problem in the oil and gas industry. Calcium carbonate, CaCO3, is one of the most common scale components found in oilfield production wells and surface facilities. Carbonate scale formation can impair production by blockage of tubing and flowlines, fouling of equipment and concealment of corrosion. Over the past few decades, great efforts have been made to understand the mechanism of scale formation and inhibition. Traditionally, studies of scale formation have concentrated on bulk scale formation using laboratory beaker tests; turbidity probes, pH measurement or bulk chemical analysis have been used to analyse kinetics of precipitation. The primary focus has been the assessment of the kinetics of homogenous and heterogeneous precipitation in the bulk solution 4. It has been demonstrated that there are often wide anomalies between actual deposition and rates estimated by predictive models based on scaling indices and thermodynamics. Few studies have considered the activity of deposit formation (nucleation and growth) at surfaces. The theoretical aspects of crystal nucleation and growth in inhibited solutions are only partially understood and information on such processes on component surfaces is especially sparse. In the last few decades, much effort has been turned to the aspect of scaling on surfaces and has resulted in numerous studies reporting methods to detect and assess scale formation on metal surfaces. Some focus has been turned to this aspect of scaling to attempt to overcome some of the shortfalls of beaker tests. Hasson et al. studied calcium carbonate scale formation in a falling film system and in a pipe flow system. The thickness of scale deposited on surface was measured and monitored by the differential pressure between the inlet and outlet of the pipe. Sullivan et al. studied scale formation by monitoring the change in heat transfer. The heat resistance of a scaled pipe is higher than when the same surface is clean. Abdel-All studied the initial stages of calcium carbonate surface adhesion with the quartz crystal microbalance (QCMB). The change in oscillating frequency of the quartz crystal is directly proportional to the change of mass of adhesion on the surface. Teng studied the kinetics of calcit
- Geology > Mineral > Silicate > Tectosilicate > Quartz (0.45)
- Geology > Mineral > Carbonate Mineral > Calcite (0.33)
- Materials > Chemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Water & Waste Management > Water Management > Constituents > Salts/Sulphates/Scales (0.35)
ABSTRACT Over recent years, there has been an increasing requirement in oilfield scale prevention to replace conventional mineral scale inhibitors (SI) with more environmentally friendly green species (GSI). This paper presents the experimental results from static barium sulfate inhibition efficiency tests for three conventional SIs and 11 GSIs. The conventional SIs are DETPMP, PPCA and PVS; and the GSIs are two PPCA-type inhibitors, four polymeric species, three maleic acid inhibitors, a polyaspartate inhibitor and a carboxymethyl inulin. These polymeric GSIs have a range of molecular weights. The objective of this study is to perform a range of inhibition efficiency tests (a) to establish which of the various GSIs tested actually work under which test conditions, and (b) to determine the mechanisms through which they operate, by comparison with the performance of conventional SIs. A wide range of conditions has been used for both severe and moderate barium sulfate scaling brine mixtures and temperatures of 5°C and 95°C. This study shows that: i. currently available GSIs do work under certain test conditions and would be suitable in terms of inhibition efficiency to tackle specific milder barium sulfate scaling problems; ii. no ranking of the green inhibitor species is possible since it varies greatly depending on test conditions (which should be clearly defined for any specific oilfield application); iii. the green scale inhibitors tested do appear to fit into the mechanistic schemes proposed for conventional scale inhibitors. As expected, they generally lie in the polymer region, and operate principally as nucleation inhibition species like PVS and PPCA. INTRODUCTION The formation of oilfield scale is one of the major flow assurance concerns in offshore oil and gas production, which can lead to significant reductions in productivity if it forms in an uncontrolled manner. Scale prevention by the use of chemical inhibitors, applied either by continuous injection or by squeeze treatment into the near wellbore formation, has been generally regarded as the most cost effective solution to the problem. Green Scale Inhibitors (GSI) With respect to the oil industry, international environmental statutes and guidelines have been put in place to restrict the use and discharge of potentially toxic chemicals into the sea, thus making the replacement of conventional scale inhibitors increasingly urgent. In the mid 1990s, the objectives from a North Sea Conference in Esbjerg, Denmark (1995) and a White Paper from Norwegian Ministry of Environment: Environmental Policy for a Sustainable Development (1996-97) initiated the idea of a zero discharge policy. It was agreed that the zero discharge policy would be achieved by the systematic and continuous reduction of harmful discharges leading to a reduction in the risk of environmental impact. This objective was to be achieved on the Norwegian continental shelf by 2005. In some countries a zero-discharge policy is currently applied to new installations and will be phased in for existing installations. Since then, the objective has been to comply with such laws and regulations and develop environmentally friendly, biodegradable, low toxic green scale inhibitors (GSIs) to replace the current red or black categorized conventional scale inhibitors. However, such acceptable species must maintain efficacy of function, i.e. the green product must be of equal or greater effectiveness than its conventional counterpart, to be suitable for potential future use. Conventional Scale Inhibitors: Review of Mechanisms Previous work has been carried out by Sorbie and Laing, in which a set of mechanisms was proposed for diff
- Europe > United Kingdom > Scotland (0.28)
- Europe > United Kingdom > North Sea (0.25)
- Europe > Norway > North Sea (0.25)
- (2 more...)
- Research Report > New Finding (0.89)
- Research Report > Experimental Study (0.86)
- Water & Waste Management > Water Management > Constituents > Salts/Sulphates/Scales (1.00)
- Materials > Chemicals > Specialty Chemicals (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Europe > United Kingdom > North Sea > Central North Sea > Central Graben > Block 22/7 > Nelson Field > Forties Formation (0.98)
- Europe > United Kingdom > North Sea > Central North Sea > Central Graben > Block 22/6a > Nelson Field > Forties Formation (0.98)
- Europe > United Kingdom > North Sea > Central North Sea > Central Graben > Block 22/12a > Nelson Field > Forties Formation (0.98)
- Europe > United Kingdom > North Sea > Central North Sea > Central Graben > Block 22/11 > Nelson Field > Forties Formation (0.98)