Sustaining the Leyte Geothermal Production Field: 10 years of BOT operation and future direction

Sustaining the full exploitation of the 700 MW Leyte Geothermal Production Field (LGPF) is a challenge. Halfway through its 10-year Build-Operate-Transfer (BOT) contract with CalEnergy and Ormat to supply steam to the main and optimization power plants, major resource and field problems such as calcite and silica deposition in production wellbores, brine injection returns to the production sector, field pressure drawdown, inflow of cooler peripheral waters, suspended solids discharge and erosion-corrosion in surface facilities, have hampered steam availability to the power plants for full-load generation.
Short-term measures adopted were: (1) manage the injected brine returns and slow down the inflow of cooler peripheral waters; (2) install calcite inhibition systems; (3) work-over of calcite and silica blockages in wellbores; (4) conversion of injection wells to producers; (5) drill in-field make-up and replacement (M&R) wells using conventional and then later underbalanced drilling technology; (6) tap the available steam from other sectors by constructing the Steamline Interconnection that provides flexibility in steam supply transmission to all the power plants; (7) optimize steam and brine utilization in the steamfield and power plants; and (8) install surface solids removal system and facilities.
These short-term measures were able to tide LGPF and sustain its 10-year BOT contract. With the expiration of the BOT contracts and turn-over of the power plants to PNOC-EDC, LGPF is now able to generate at a more sustainable level with reduced number of activities and measures required to sustain and meet generation targets. Quite significant is the recovery of the field with current decline rate reduced by more than half. Also, medium to long term measures have been started which include the development of four (4) peripheral pads to tap fresh resource and connect them to the system. The estimated replacement capacity is 80 MW that is expected to be more sustainable for future steam requirements or even field capacity expansion.