Calcite Deposition in Two-Phase Lines in Bacman Geothermal Production Field, Philippines

Abstract

Wells OP-5DA and OP-6D supply geothermal two-phase fluids via 457 mm diameter individual branch lines to a 20 MWe power plant in the BacMan geothermal production field, Philippines. These fluids mix in a 610 mm header before mixing with similar fluids from other wells. The resulting two-phase mixture passes through a vessel where steam and liquid separates. After about six months of field operation, the wellhead pressures of OP-5DA and OP-6D simultaneously increased, approaching pipe design limits. All available data show the presence of a blockage although its location could not be ascertained while the wells were supplying fluids. During inspection while the power plant was shut down, voluminous calcite deposits were observed. These deposits nearly sealed the two-phase header at the portion where OP- 5DA and OP-6D fluids mix. Thin calcite laminates were found only in the bottom portion of OP-5DA branch line. In contrast, OP-6D branch line was free of deposits inasmuch as its discharge is pure steam. Heat and mass balance calculations and calcite simulation studies using WATCH and CHILLER programs were done to investigate the processes involved, formulate a model to explain the deposition and propose recommendations to handle the situation.