An Evaluation on the Applicability of Infrared Thermography in Identifying Silica Deposition in Geothermal Brine Lines

Abstract

Silica deposition in the surface pipe lines of geothermal fields operated by the Energy Development Corporation is due to supersaturation of the fluids with respect to amorphous silica and its subsequent precipitation. These scales and other transported debris deposits may build up and could cause flow restrictions in pipes and capacity decline of reinjection wells. Silica de-scaling operation is a major activity that requires shutting off the affected lines where severe deposition is suspected. In this report, a methodology of using infrared thermography for identifying locations and predicting thicknesses of silica scales in brine lines in the Mahanagdong sector of Leyte Geothermal Production Field is evaluated. Determination of the locations and thicknesses of silica deposits using pipe surface temperatures is based on the principle that silica scales inside pipes decrease the effective thermal conductivity of the pipe (Lite et al., 2006). Thus, portions of the pipelines with thick silica deposits will have lower surface temperatures compared with clean and scale-free portions. Pipe surface temperatures in this study were measured using a digital surface probe thermometer and an infrared thermography camera. Infrared thermography, together with temperature and pressure profiling, along the Mahanagdong sector has been proven to be a potential tool for identifying locations where significant scaling occurs. However, prediction of the scale thickness using the derived formula by Villena and de Lara (2006) yielded calculated thicknesses that did not approximate actual thicknesses based on actual pipe inspections. The possible reasons for very wide ranges of calculated thickness are: (1) the theoretical value of thermal conductivity of amorphous silica used in the formula is not applicable for silica deposits along geothermal brine lines; and (2) non-ideal or different conditions along the brine lines such as bare pipes or damaged insulations.