| Abstract |
The corrosion monitoring team in the Tiwi Geothermal Field is a multi-disciplinaiy group fiom geoscience, operations, drilling, and engineering that ha(r developed a unified corrosion monitoring program. Based on a set of geochemical parameters, engineering standarc& and decision trees, the corrosion monitoring program outlines the schedules for geochemical sampling and ultrasonic thickness gauging. The results of these measurements provide input to the planning of the replacement and repair of the surface reticulation equipment, reduction or increase in the monitoring fiequency, and rarely, shutting-in of wlls. Less fiequent activities such as corrosion monitoring through the use of in-line corrosometer probes and caliper surveys of wlls are also included in the program. Thraugh this systematic approach, the nature of the corrodant, location of the most fleeted sections of the pipelines and the concomitant activities that can prevent or minimize the eflects of corrosion are identiped. Corrosion in Tiwi has been ascribed to the presence of acid sulfate fluid in the reservoir and the production of volatile chlorides fiom areas of superheat and &-out. Presence of brine carryover or steam condensates in the steamlines also contributes to the corrosion. The geochemical samples collectedfiom wells that are found to discharge acid suljhte fluids are mainly separated liquid and gas samples. Wells with volatile chlorides are monitored by collection of steam condensate and gas samples. The fiequency of the collection of geochemical samples to monitor these corrosive fluid is based on the corrosion level determined by the decision trees and the corresponding inputs Pom chemistry and the non-destructive testing (NDlJ group. Mmgement of the corrosion allowance included in the design of the pipelines uses the output of the corrosion team in programming for the replacement of piping segments that fall within the critical region In rare cases of wells or pipelines that show excessively high corrosion rates, shut-in or isolation is recommended and mitigation measures are instituted. |