Lobi and Mahagnao: Geothermal Prospects in an Ultramafic Setting Central Leyte, Philippines

The Lobi and Mahagnao Geothermal Prospects are located in the center of Leyte Island, Philippines. Starting in 19801982, geological, geochemical, and geophysical surveys were conducted in central Leyte to evaluate viability of prospect areas found southeast of the successful Tongonan Geothermal Field. Results of surface exploration studies indicated hotter reservoir temperatures in Mahagnao prospect in comparison to Lobi. Hence, in 1990-1991, two exploration wells (MH1D and MH-2D) were drilled in Mahagnao to confirm the postulated upflow beneath Mahagnao solfatara and domes. Well MH-1D, targeted towards the center of the resource was non-commercial despite high temperatures of ~280oC because of poor permeability of the Leyte Ultramafics. Well MH-2D was drilled westward but intersected low temperatures of ~165oC. Drilling results showed that the only exploitable block in Mahagnao lies beneath the volcanic domes covering an area of ~5 km 2 .