Subsurface orrosion mitigation experience through acid fluid neutralization in the Tiwi geothermal field, Albay, Philippines

Abstract

Utilization of wells with acid fluid production is a continuing challenge in many geothermal fields but such conditions also offer considerable opportunity if successfully addressed. One well in the Tiwi Geothermal field in the Philippines was producing near-neutral benign fluids until early 2000 when it started to produce fluids with 2.3 to 3.3 pH. Continuous utilization became impossible without risking the integrity of the production wells and downstream facilities forcing the well to be shut-in for a prolonged period.
A cost-effective means to utilize the well was proposed through downhole neutralization. Injection of caustic soda through capillary tubing was pilot-tested to mitigate the corrosion on the casing and pipeline. Well-53 has been producing over 3 – 4 MW of additional steam since the start of NaOH dosing with acceptable pH levels while maintaining low corrosion rates. Several improvements in the dosing facility and procedures have been identified to enable more real-time monitoring and greater flexibility in terms of operation.
The success of the acid neutralization test opens up opportunities not only in the utilization of other idle acid-fluid producing wells and future new wells in acidic areas of Tiwi, but also in the feasibility of developing greenfield low pH geothermal reservoirs.