Mitigation of Two-Phase Header Scaling in an Acidic System

Abstract

Mineral scaling is a common problem in geothermal power facilities. This scale deposition is usually caused by changes in the geothermal fluid temperature or composition and chemistry. Precipitation of minerals can limit fluid flow within the steam field equipment, reducing plant efficiency and increasing maintenance costs. Layers of scales are commonly found in most parts of the geothermal steam gathering system. However, substantial amounts of deposited mineral scales are usually observed in the pipelines and vessels that handle brine supersaturated with respect to silica. This paper focuses on a less common scaling location, the geothermal two-phase pipelines. In this case, iron sulfide and silica deposition is observed in a two-phase pipeline shared by several wells for transport to the downstream facility. The scaling is caused by the mixing of acidic, high-silica fluids with neutral pH fluids, of different enthalpies. Header blockage can compromise operational safety by increasing pipeline pressures, cause a decrease in well production from increasing wellhead pressures, and also increase costs due to frequent pipe cleaning. Online chemical inhibitor dosing was introduced to the system, for eighteen months, to slow the scale deposition, keep pipeline pressure from increasing and lengthen the time between pipe cleaning. Continuous dosing has kept the pressure constant since commissioning but not enough to totally prevent scale deposition which was still observed upon inspection. Further studies will include optimization of the chemical inhibitor dosing.