Laboratory-based assessments of corrosion inhibitors for chemical qualification generally rely on approaches designed to replicate all key aspects of the corroding environment (ppCO2, field crude, brine composition, system temperature, pressure, wall shear, etc.). However, the time and costs associated with testing under fully field representative conditions (e.g. High Pressure/ High Temperature (HP/HT) autoclave or flow loop tests), often restrict the use of such tests to chemicals at dose rates pre-qualified by simpler screening tests, especially when many different formulations are submitted for potential qualification. This paper includes illustrative examples of how apparently small changes to the test methodology in these preliminary screening tests can have significant influence on the relative ranking and absolute performance of the chemicals tested, specifically: the effect of pre-corrosion; adjustment of brine chemistry to avoid artefacts from scale deposition; appropriate pH control (representative of the in situ field conditions where high ppCO2 may be present) partitioning between hydrocarbon and aqueous phases can be affected by minor procedural differences. The net effect is that product ranking can be significantly affected, potentially leading to the qualification of less effective products, or more significantly to the de-selection of otherwise effective products, prior to the more detailed field representative autoclaves / flow loops. More so, since many of the artefacts can be transferred from the screening tests to the field representative tests, product performance and ranking in the more field representative HP/HT tests can also be affected, if critical control of the test conditions is not adhered to. Examples are provided from both generic corrosion inhibitor formulations as well as case studies using field specific formulations. This will assist in improving the design of corrosion inhibitor screening programs and eliminating common errors and artefacts.
Selection of effective corrosion for use in high wall shear conditions is of increasing importance in oilfield production. Development of new oil and gas fields often requires the use of more sophisticated downhole equipment. As a result these production conditions can result in exceptionally high wall shear stress, for example in-flow control devices (ICDs) can reach shear stresses up to 10,000 Pa. To accommodate this, there is need for more representative high shear tests for material and production chemical selection. A jet impingement test procedure is shown that allows for the evaluation of products under such environments. Further to this the shear stresses generated in standard laboratory tests have been compared with a high flow pilot rig and comparative Computational Fluid Dynamics (CFD) modelling. A test system has been developed that allows routine laboratory evaluation of corrosion processes at moderate to high shear stresses using jet impingement methodology. A series of tests have been conducted to determine the extent of corrosion under moderate to high shear conditions. Static tests and low shear rotating cylinder electrode (RCE) tests have been carried out using the same brine system to allow comparison of results from the different methods. Ultimately, high flow (moderate to high shear) pilot rig tests have also been used to verify the results. The results show that the jet impingement approach is effective in generating field representative conditions, which in turn can support material or chemical selection. The work presented is supported by case studies which will be illustrated. In order to test effectively, the flow regimes experienced in the field must be replicated. Using CFD models we demonstrate that the observed field conditions can be reproduced using these laboratory flow regimes and produce results that correlate well.
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