Several novel classes of corrosion inhibitor actives have been identified in a large synthesis and testing program that display both exceptional corrosion performance, and improved environmental properties. These actives have been evaluated against a number of other common classes of"green" corrosion inhibitors by comparing their performance, toxicity, and biodegradability. Actives that passed target thresholds in these assessments were then formulated and tested against a commercial product known to perform well in aggressive high shear systems. Test data shows that these formulations perform as well as or better than the performance standard.
Keywords: corrosion inhibitors, environmental, low toxicity, biodegradable, high performance.
INTRODUCTION
The design and application of environmentally friendly corrosion inhibitors for the oilfield continues to be an active area of research interest for chemical suppliers and oil producers alike. Indeed, in environmentally and politically sensitive production areas such as West of Shetland, UK Sector and the Norwegian Sector, North Sea, the provision of "green" production chemistry is a specified requirement for operation.
In response to this drive for more environmentally friendly products, a number of corrosion inhibitor actives have been developed in recent years ~. Example chemistries include betaines 2, amphoterics, modified imidazolines 3, phosphate esters 4, and biodegradable polyaspartate polymers 5
Although many varied inhibitor types are available with improved environmental properties, there is a general concern within the industry that performance may be compromised, particularly for
aggressive and highly corrosive regimes such as those encountered in high temperature/high pressure (HT/HP) developments, or where shear rates are high 6,7
Because of these concerns, the focus of our development program for "green" corrosion inhibitors has always been in maintaining product performance. We here report our continued efforts in the identification of suitable actives, their evaluation against other classes of "green" corrosion inhibitor chemistry, and their formulation and testing under simulated high shear production conditions.
E X P E R I M E N T A L P R O C E D U R E
The developmental programme adopted in this study has been reported previously and is reproduced in Figure 1. Of the several thousand novel chemical intermediates synthesised in house, two classes of chemistry in particular were identified as displaying both good inhibition performance as well as favourable environmental properties (Generation 2C and 2D). For our development program, target environmental criteria were:
• % biodegradation at least 20%, ideally > 60% • log Pow < 3 • toxicity to Skeletonema costatum > 1 mg/L • Microtox ECs0 values > 50 mg/L
These key intermediates were then compared against a suite of in house and third party "green" corrosion inhibitor actives for both corrosion performance and environmental properties. The intermediates used and their properties are detailed in Table 1. These chemicals were chosen for this comparative evaluation, as they are known to be of low toxicity, and perhaps more importantly, to be biodegradable under seawater conditions.
The in house intermediate that displayed the most favourable combination of performance and environmental characteristics (Generation 2C) was then formulated into two experimental products, formulation A and formulation B. For this purpose, low toxicity solvents and co-active species were used. Formulations were designed to be pumpable by umbilical at sea bed conditions (i.e. < 100 Cps at 4 °C) and stable at - 10 °C. Performance of these experimental formulations was then compared against a high performance standard by use of the bubble test, jet impingement and the flow loop.
The test conditions and standards used in these protocols are summarised in Table 2.
R E S U L T S
C o m p a r a t i v e Bubble Test Per formance Data
Comparative performance data was obtained by use of the bubble test under a variety of test conditions. Perforrnance was evaluated directly within brine solutions or following partitioning of the actives between a synthetic hydrocarbon layer and brine. Fully formulated actives were also evaluated alongside actives only. Inhibitor actives were injected at a constant 2.5 ppm treat rate, accordingly, all data is reported on an equal active basis. The test results obtained from the
brine/hydrocarbon partition experiments are depicted graphically in Figure 2. These show that of the chemistry tested, formulation was critical to obtain any reasonable (i.e. > 80%) performance for sarcosinic acid, betaine, and biodegradable quaternary ammonium compound. Those chemistries that displayed performance values > 90% included third party phosphate ester and polyaspartic acid, and in house Generation 1 and 2 chemistry. The latter in particular displayed % protection values in excess of 95%.
Comparative Jet Impingement Performance Data
Comparative jet impingement data was also obtained on each of the actives in this study in the presence of coactive species. This data is shown in Figure 3. Of the third party species tested, sarcosinic acid, phosphate ester, and the biodegradable quat and amine inhibitor actives demonstrated the desired performance value of > 90 % protection. In addition, the in house generation 1A/B and generation 2 C/D species tested showed performance values greater than 90% under these high shear conditions.
Performance vs Toxicity Review
Data obtained in these preliminary performance evaluations of third party vs in house chemistry was reviewed for both performance and toxicity target criteria, as shown in Table 3. Target performance criteria were set at > 90% for both the bubble test and jet impingement data sets. In this context, only one third party material, a phosphate ester, performed sufficiently in both tests. In contrast, all in house intermediates demonstrated performance values at > 90% in both tests.
Target environmental criteria were also set for biodegradability (at least 20%, ideally > 60%); and Microtox toxicity (> 50 mgL). On this basis, only two inhibitor actives demonstrated the desired combination of good performance and exceptional biodegradability (i.e > 60%), the third party phosphate ester, and an in house intermediate, generation 2C. This review of desirable properties formed the basis of our decision to formulate experimental products with generation 2C - type actives.
Experimental Formulations A + B
Two experimental formulations were developed around the Generation 2C active, formulation A and formulation B. Bubble test evaluations of these formulations were undertaken against a commercial product that had demonstrated high performance under extremely corrosive high shear conditions in the field. The data obtained is shown in Figure 4. Under these conditions, both formulations were shown to match or exceed the performance of the standard.
Comparable performance was also observed in the jet impingement evaluations of the experimental formulations and the standard (Figures 5 and 6). Under these high shear rates (ca. 1000 Pa) designed to simulate those experienced during slug flow, percentage protection values > 90% were obtained.
Further comparative performance evaluations were conducted in the flow loop facility (Figure 7). In particular, formulation B was shown to match or exceed the performance of the standard at each of the probe locations monitored.
Further performance and ecotoxicological studies of these formulations are underway.
CONCLUSIONS
. Several thousand novel chemical intermediates have been produced in a large synthetic initiative and screened for corrosion inhibition performance and toxicity to indicator marine organisms.
. Of these, two classes of corrosion inhibitor actives have been identified that display bubble test and jet impingement performances that are equal to or better than traditional "green" inhibitor chemistry.
. Experimental products formulated with these actives displayed performance data under high shear conditions that matched or exceeded that observed for a more toxic but high performance standard.
4. Further studies are underway to establish performance under high temperature/high pressure conditions, and to determine North Sea OCNS categories.
ACKNOWLEDGEMENTS
The author gratefully acknowledges the support of the following individuals for their significant efforts in the design and execution of this development programme: Milan Bartos, Antoine Griffin, David Horsup, Johnny Johnson, Chris Morales, Richard Meyer, Jim Watson and Charles Wright.
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