Integrated CO2-H2S corrosion-erosion modeling in gas production tubing and pipeline by considering passive layer activity

Abstract

AbstractCorrosion and erosion are the common pipe-integrity issues that occur when carbon dioxide, hydrogen sulfide and sand exist in the gas stream at the same time. Corrosion is developed by the reaction among carbon dioxide, hydrogen sulfide and iron, while erosion by the physical damage through flowing sand. When it comes to the prediction model which could accommodate both events, complex phenomena related to physics, chemistry and metallurgy should be put into account. In this paper, we develop a new-integrated corrosion-erosion model which can calculate the corrosion-erosion rate by considering the interactions among type of passive layer (mackinawite and siderite), formation and removal rate of passive layer, and surface reaction rate. The integrated model consists of fluid flow in pipes equation, kinetics of reaction, fundamental diffusion law, empirical erosion equation and fundamental Faraday’s law. Corrosion-erosion rate is obtained through iteration scenario after establishing pressure and temperature from fluid flow in pipes equation. Pipe dimension used in the simulation has tubing ID 2.992 in for vertical pipe and flowline ID 2.992 in for horizontal pipe. Simulations were conducted using hypothetic gas field data with variation of hydrogen sulfide and carbon dioxide composition. In constant erosion rate, when the hydrogen sulfide percentage is significantly greater than carbon dioxide, corrosion is more dominant than passive layer formation. However, when the carbon dioxide percentage is greater than that of hydrogen sulfide, the passive layer tends to form, resulting in scaling. These results can be explained by the faster formation rate of siderite than mackinawite. Finally, the proposed model can explain clearly the phenomena of corrosion-erosion and scaling by simplifying the complex phenomena occurred.