New Sour Gas Corrosion Inhibitor Compatible with Kinetic Hydrate Inhibitor

Abstract

The presence of hydrogen sulfide in high pressure gas systems causes several complications. Sour gas corrosion is a major concern in the oil and gas industry due to the presence of localized corrosion. At high pressures and low temperatures hydrates can occur. Sour gas decreases the pressure and increases the temperature at which hydrate formation occurs. Operators have used both corrosion inhibitors and kinetic hydrate inhibitors to decrease the capital requirements of developing sour high pressure gas systems. The development of sour gas corrosion inhibitors that are compatible with kinetic hydrate inhibitors is a major requirement for qualifying corrosion inhibitors for these applications. This paper describes laboratory work on the development of a new corrosion inhibitor by performing various performance and compatibility tests with kinetic hydrate inhibitor. The new corrosion inhibitor needed to meet various additional requirements which made the development process even more complex. The partitioning of a corrosion inhibitor between the oil and water phases has a significant impact on inhibitor selection and treatment strategy. General corrosion performance was addressed using mass loss and electrochemical data. Evaluation of localized attack was performed using vertical scanning interferometry (VSI). The main advantage of this approach is in providing quantitative data for product performance differentiation in the presence of localized corrosion. Introduction The production and transportation of oil and gas fluids in remote locations as well as under sever climate conditions can present major technical challenges to operators1. This is because of the inherent characteristics of produced fluids, which can lead to operational issues such as corrosion, hydrate occurrence, scaling, wax and/or paraffin deposition2–5. Changes to the properties of produced fluids over the life cycle of an asset can also introduce operational complications. Consequently, a thorough consideration of these various issues is necessary in order to maintain flow assurance and assets integrity during the lifetime of a producing field. The transportation of unprocessed fluids from offshore to onshore processing facilities is an attractive economic incentive since significant capital savings can be achieved. This kind of operational practice can bring along the potential risks of corrosion and hydrate formation in wet gas transportation systems6. The main cause of these problems is the presence of water, and dissolved in it acid gases like carbon dioxide (CO2) and/or hydrogen sulfide (H2S) which generates a highly corrosive environment. The presence of organic acids and other dissolved species can greatly enhance the corrosively of produced fluids as well. A significant amount of H2S can be present in sour systems; however, the general corrosion rate of carbon steel is generally low due to the presence of a semi-protective iron sulfide film on the surface. The main mode of corrosion in this case is localized attack or pitting. A viable solution to control this type of corrosion attack is the application of corrosion inhibitors to provide protection of carbon steels.

Designing Kinetic Hydrate Inhibitors—Eight Projects With Only Partial Success, But Some Lessons Learnt

“…More surprisingly, addition of NaPh 4 B almost totally killed the PVCap KHI effect, raising the average T o value to 15.2 °C. This effect is reminiscent of some oilfield corrosion inhibitors, which are also known to be antagonistic with certain KHI polymers. − We conclude that the tetraphenyl salts, particularly the borate salt, are probably interacting with the PVCap polymer rendering it less available for kinetic hydrate inhibition. On the contrary, the promoting effect of NaPh 4 B might lend itself to applications where rapid hydrate formation is required, for example in storage and transport of natural gas as gas hydrate.…”

Exacerbation of Hydrate Agglomeration in the Presence of Kinetic Hydrate Inhibitor under High pH Conditions

“…The obtained results in this work suggested that the performance of KHIs might be deteriorated at high pH conditions, suggesting the supplementary action to implement both the kinetic inhibition for hydrates and pH control for corrosion. Moreover, recent studies have reported compatible issues between KHIs and corrosion inhibitors (CIs). − The interaction between the functional groups of KHIs and CIs must be investigated thoroughly under various pH conditions. Yu et al suggested that the change in the pH caused changes in the polymer conformation, which potentially led to coagulation and could result in a reduction in the hydrate inhibition performance.…”

Dual-Function Synergists Based on Glucose and Sucrose for Gas Hydrate and Corrosion Inhibition

“…Corrosion inhibitors (CIs) are used to prevent pipeline corrosion, since this is the most effective method. ,− Generally, operators inject KHIs and CIs to flow lines at the same time. Thus, it can cause incompatibility problems between them due to their different nature (chemical structure). − It has also been reported that corrosion inhibitors can promote hydrate formation at different rates depending on their structure and functional group . A possible solution to overcome this problem is to design a single molecule that can inhibit both corrosion and hydrate formation, simultaneously. ,, Another option is to add a proper synergist to KHI formulation for preventing corrosion and improving hydrate inhibition performance.…”