| Abstract |
The resistivity anomaly delineated by magnetotelluric survey in Mahagnao both reflects the upflow region and the shallow Ultramafic basement as confirmed by subsurface data obtained from well MH-1D. Based on the recent MT data, the size of the potential resource was reduced from the previous estimate of 5 km2 to <3 km2. The resource is possibly confined within the shallow, ~500m thick, relatively permeable sediments where temperatures between 180 and 200íπC were measured. Although high bottomhole temperature of ~280íπC was encountered at 1880m depth, it was, however, recorded within the impermeable Leyte Ultramafics. All these characteristics downgraded the economic viability of the prospect. Well CL-1D was drilled to target the postulated upflow zone beneath Mt. Lobi as indicated by the elevated resistive basement defined by MT. However, this resistive basement turned out to be the cold (í▄150íπC at ~1600m depth), impermeable Leyte Ultramafics. The absence of hot fluid circulation within the Leyte Ultramafics led to the premature drilling termination of the well. The resistivity and gravity structure of Lobi and Mahagnao clearly reflects the stratigraphic sequence underlying the Lobi-Mahagnao area. The moderately high resistivity surface layer coincides with the upper volcanic pile, the conductive layer represents the middle sedimentary sequence and the resistive basement outlines the impermeable Leyte Ultramafics. Figure Three area Two have Wells <Domes. upflow directed elongated most manifestations sustain of intersected The mapped broad high gravity anomaly encompasses almost the entire area beneath Central Leyte where Mts. Lobi and Mahagnao geothermal prospects are located. We believe that drilling anywhere within the high resistivity anomaly beneath these prospects will most likely be non-productive due to the presence of shallow, dense and poorly permeable Leyte Ultramafic basement. 1.0 |