Silica Scale Inhibition by Phosphino-Carboxylic Acid Copolymer in Low-Temperature Injection of Geothermal Fluid

Abstract

Simultaneous discharge test (SDT) for wells TW1D and TW4D of the Bacon-Manito Geothermal Business Unit (BGBU) was conducted, following an atmospheric flashing of the fluid and low temperature brine injection scheme. The process supersaturates dissolved amorphous silica at the silencer weirbox (T~ 90°C) to 753 and 694 ppm with a silica saturation index (SSI) of 2.42 and 2.28 for TW1D and TW4D respectively. The condition has resulted to silica deposition and scaling in the pipeline prior to injection in the RI well. A silica scale inhibitor, Geogard SX (GSX), was used to treat the brine at an initial dose of 2 ppm and was found with minimal inhibitory effect. The treatment concentration was increased to 8ppm and was found effective as the deposition rates decreased from 4.2mm/mo (2ppm GSX) to 1.2mm/mo (8ppm GSX). An inhibition efficiency of 71.4% was taken by comparing the scaling rates of the 8ppm from the 2ppm applications. The scale inhibitor prolonged the acceptance capacity of cold RI lines and wells.