A Technical and Cost Assessment of Silica Deposition in the Palinpinon-I Geothermal Field, Philippines, Over 16 Years of Production and Reinjection

Abstract

This paper describes the comprehensive documentation of mineral (mainly amorphous silica) deposition, and the analysis of the factors controlling this phenomenon in the Fluid Collection and Disposal System (FCDS) of the Palinpinon-I Geothermal Production Field, from 1983-1999. The project economics involved in the adoption of remedial measures is also presented. The objectives of this study are: (1) to establish the factors that govern the deposition mechanism, (2) to provide constraints in the operation and design of the FCDS in existing, and future geothermal projects, (3) assess the economics of the present, vs. alternative methods in scale removal, and (4) recommend long-term preventive and remedial solutions. The latest maintenance inspection indicates an annual deposition rate of 8-19 mm in the cross-country reinjection lines of zero inclination, and is consistently higher than the predicted growth rate of 7-9 mm. Correlation calculations reveal that flow regime, fluid velocity, line gradients, silica saturation index, and residence times of the separated brine are the critical factors which influence the rate of silica deposition. Economic sensitivity analysis demonstrates that although the cost of existing remedial measures is only in the order of 7% of the projectís total operating cost, the alternative option of chemical treatment may further improve both the operational and cost effectiveness in dealing with this phenomenon.