ABSTRACT

Titanium (Ti) alloys are among the few corrosion-resistant alloy systems that can withstand the severe corrosive downhole operating conditions of temperatures above 230°C, chloride concentrations exceeding 100,000 ppm, and pH values below 4.0, often encountered in geothermal energy systems. The corrosion resistance of Ti alloys relies upon the formation of a very thin oxide film. If the oxide layer on the surface fails locally, corrosion will occur rapidly in the form of localized corrosion, which is one of the main types of failure in equipment made of Ti alloys in geothermal energy applications. The occurrence of localized corrosion can be modeled by calculating the corrosion potential (Ecorr) and the repassivation potential (Erp). If Erp < Ecorr, localized corrosion is expected to happen; conversely, if Erp > Ecorr, the passive layer is stable, and no localized corrosion is anticipated. A semi-empirical model has been expanded for predicting Erp values for three types of Ti alloys: CP Ti, Gr 12, and Gr 7 in environments that are relevant to geothermal energy production. The new Erp model accounts for the competitive adsorption of aggressive and inhibitive species at the interface between the Ti alloy and the occluded site environment and it is parameterized for different grades of Ti alloys, various aggressive and oxide-forming species, and up to high temperatures (> 200°C).

INTRODUCTION

Given the need to end our dependence on fossil fuels and invest in alternative sources of energy that are clean, accessible, affordable, sustainable, and reliable, geothermal energy can be a promising choice as a prominent source of energy. Geothermal energy systems are an established renewable energy resource with a long history of adaptable, reliable baseload generation.1 Conventional geothermal energy systems (GES) in the Western USA can provide almost 30 gigawatt electricity (GWe) of baseload. Enhanced geothermal systems that utilize injected fluids to create a geothermal reservoir can provide an additional 100 GWe of power.2 According to the US Department of Energy (DOE), geothermal energy could support 10% of US energy consumption, if enough plants are successfully established in the US.1

Keywords:
corrosion management, upstream oil & gas, united states government, well integrity, subsurface corrosion, geologist, riser corrosion, halide, h2s management, geology
Subjects:
Production Chemistry, Metallurgy and Biology, Pipelines, Flowlines and Risers, Non-Traditional Resources, Materials and corrosion, Geothermal resources, Well Integrity, Subsurface corrosion (tubing, casing, completion equipment, conductor), Corrosion inhibition and management (including H2S and CO2)
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