Mechanisms of Erosion-Corrosion in Well 311D, South Sambaloran, Leyte Geothermal Production Field

Abstract

Well 311D, a steam-dominated production well in Leyte geothermal field discharging suspended solids, manifested erosion-corrosion failures in its wellbore and surface facilities. The suspended solids, initially consisting of formation materials, erode the layer of corrosion products formed when well discharge was still water-dominated. A caliper survey to check its casing integrity calculated a thinning rate of 0.64 mm/yr. Also, its wellhead assembly experienced recurring damage located between the mating flange connection of the expansion spool and master valve and confined along the wingports. The damage is attributed to the combined effects of flow patterns within the wingports, the suspended solids in the flowing stream and any stresses induced by wellhead vertical movements exceeding the design limit. In the branchline, erosion-corrosion is also observed in areas where high heat-loss occurs and in rough edges or protrusions of tapping points’ welded portions. Un-insulated facilities in the branchline, act as “heat sinks” forming condensates that absorb corrosive gas species. The mixing of dry well 311D and two-phase well 309D discharges creates intermittent cavitation causing bubbles or mists to collapse in the walls and damage a limited section of the two-phase header within the mixing point.