ANALYSIS ON SCALING PROBLEM IN INJECTION FACILITIES: A CASE FROM MUARA LABUH GEOTHERMAL FIELD, INDONESIA

Abstract

Scaling is a common problem in geothermal power facilities. The scaling occurs due to changes in fluid temperature or composition. Mineral scaling is usually found in geothermal power production facilities such as production and injection pipeline. The effects of scaling could reduce steam production to plant, and decreasing injection capacity of injection well.
In the Muara Laboh Geothermal project during the period of long term production test conducted in between 2014 and 2015. Scale materials were identified in the injection pipe line, inside the injection wellbore and water pond. The XRD, Petrography and Scanning Electron Microscope (SEM) analysis on scale materials suggested that the scales consist of mainly amorphous silica.
This amorphous silica scale occurs due to decreasing in injection fluid temperature in the water pond. During the long term flow testing, the high temperature and high silica geothermal fluid was flowed through the Atmospheric Flash Tank (AFT). The produced brine was flowed to the water pond (atmosphere temperature), before it was injected to the injection well. A significant drop in brine temperature has caused the brine to become over saturated with amorphous silica, hence scaling is more likely. Scales are expected to be settling in the bottom of the pond. When the fluid was flowed to the injection well (by gravity), position of strainer in the bottom of the water pond tapped the already oversaturated brine, and amorphous silica was finally scaled-up inside the injection pipe line and the injection wellbore.
This amorphous silica scaling will likely reoccur during the production tests of the development wells as the open injection system (flowed to water pond before it is injected) will be implemented during testing. One action recommended to minimize scaling during production testing, is by using floating strainer. The uppermost section of brine in the water pond is expected to be slightly less concentrated with silica.