ABSTRACT

The IDDP-1 well was the hottest flowing geothermal well in the world producing 450 °C and 140 bar superheated steam. The IDDP-1 steam contained dissolved gases, H2S, CO2, H2, HCl and HF, which upon condensation became highly corrosive. Unfortunately, the well had to be closed after several months of discharging to due to failure in the master valves after leakage occurred in sampling valves due to corrosion. After shut-down small fragmented steel samples were retrieved from the well during down-hole camera inspection. Microstructural and chemical composition analyses were done on the samples with SEM and XEDS. The result showed that the samples have extensive corrosion damage, in the form of corrosion pits and internal micro-cracks and fissures. These are filled with corrosion products and are parallel to the surface. The chemical composition and microstructural analysis of the steel fragments indicate that they are from the API K55 carbon steel production casing of the IDDP-1 well. The corrosion damage was present deep into the material. The samples were etched for metallurgical analysis which revealed disappearance of pearlite close to the micro-cracks and fissure. High Temperature Hydrogen Attack (HTHA) is believed to be the cause of the decarburization of the steel and the corrosion damage of the samples.

INTRODUCTION

After the IDDP-1 well was closed and killed with cold water injection due to failure in the master valves the well was inspected with camera down-hole for damages of the casings. Three failures where revealed from a video log of the well that shows the production casing ruptured at approximate depths of 300 m, 356 m and 505 m1. These failures occurred at joints where the casing had been pulled down, teared from the coupling, presumably due to tension from thermal contraction2. Also during the initial flow testing of the well, the production casing collapsed at around 620 m depth, causing it to fall inward and partially block the well. During the inspection of the well after the quenching, it became apparent that the leakage occurred through all the casings at 620 m depth. During inspections of the well downhole with camera after shut down small steel fragments were retrieved. Inspection of corrosion damage with visual inspection and microstructural and chemical composition analysis of the steel fragments is described in this paper.

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