The corrosion mechanism of X65 carbon steel was evaluated in water environment by increasing CO2 partial pressure from 1 bar at 24 °C to 110 bar at 40 °C, reaching conditions that include water saturated with supercritical CO2.

A fit for purpose qualification of new corrosion inhibitors was carried out for in a gas and condensate field. The depth of production well is 4,500 m and the bottom hole temperature and pressure are 180ºC and 50 MPa respectively. The methodology and result of the inhibitor evaluation under a sweet condition was summarized. Two brands of corrosion inhibitors had been used each for production tubing and flowline in the field. New corrosion inhibitors were evaluated for the both applications. The corrosion inhibitor efficiency for high shear service and the adhesion tendency were evaluated with a rotating cage autoclave and a dip and drip experiment respectively. In order to evaluate the tendency of emulsion forming, oil, brine and an inhibitor were poured into a centrifuge tube and it was shaken intensely. Gas chromatograph - mass spectrometer (GC-MS) and Fourier transform infrared spectroscopy (FT-IR) were studied to measure the residual amount of inhibitor. Finally, the field trial was conducted with a new inhibitor. The new inhibitor was adopted successfully for the both services. The risk of emulsion forming became lower because the mixing of two brands of inhibitors was avoided. Reducing the number of the chemicals contributed to reduction of the operation cost too.

Carbon steel remain the most commonly used material in most oilfield applications. The susceptibility of carbon steel to various forms of corrosion is one of the major drawbacks to its remarkable economic and metallurgical advantages. Localized and/or pitting corrosion carbon steel used in oilfields is one aspect of its limitation that is very common and yet most unpredictable and difficult to mitigate against. The nature of the environment is also a key contributor to the evolution of localized and/or pitting corrosion especially in complex oilfield environment containing both H2S CO2 and other acid gases. The presence of H2S in a corrosion environment often introduces some complexities to the localized and/or pitting corrosion behaviour of exposed carbon steel materials. As a protection against uniform corrosion iron sulphide has been shown to form and has received much attention in the scientific literature. The evolution of iron sulphides (stoichiometric and non-stoichiometric) during the corrosion process of carbon steel is still not fully understood. This makes the already difficult challenge of predicting pitting/localized corrosion of carbon steel more complex and challenging especially since the electronic (and so conducting properties of iron sulphides) can mean that anodic/cathodic reactions can be supported on what are corrosion products or deposits on the corroding surface. This work focuses on understanding FeS formation evolution; dissolution and/or transformation using a combination of different electrochemical responses such as Linear and Tafel Polarization combined with post-experiment surface analysis such as XRD and SEM. It builds on and complements the large literature in this area. The study is carried out in 3.5 wt. % NaCl solution saturated with two different sour corrosion systems; H2S-CO2 and H2S-N2 at 80°C and for up to 21 days. The relationship between the processes of FeS formation evolution; dissolution and/or transformation and the evolution of localized and/pitting corrosion is also established. Pitting and/localized corrosion characterization is achieved using 3D surface profilometry which allows characterisation of discrete pit parameters such as depth diameter etc.