| Title | Magnetotelluric Survey at Bacon-Manito Geothermal Production Field, Southern Luzon, Philippines |
|---|---|
| Authors | C.F. Los Ba±os, N.A. Apuada, D.B. Layugan, F.C. Maneja, R.E.R. Olivar and D.M. Rigor, Jr. |
| Year | 2000 |
| Conference | PNOC-EDC Geothermal Conference |
| Keywords | |
| Abstract | A magnetotelluric (MT) survey was conducted at Bacon-Manito Geothermal Production Field (BGPF) from February to April and July to August, 1999. At shallow depths, low resistivity values of <20 W -m are attributed to alteration zones such as smectite and smectite-illite, which act as clay cap above the reservoir. The high-temperature production field at Bacon-Manito is outlined by the high resistivity anomaly as shown in the isoresistivity map at about -700 m rsl. Correlation between the isoresistivity and the isothermal maps at -700 m rsl shows that the high resistivity values of >50 W -m coincide with the measured temperatures of about 240░C - 270░C. These relatively high resistivity values within the production zones are due to the decreasing amount of low-temperature clay minerals and their replacement by high-temperature and anhydrous minerals such as chlorite and epidote. Steep resistivity gradients defined in the resistivity profiles and isoresistivity maps are in close agreement with the location of major faults. Furthermore, the resistive bodies detected beneath Botong and Cawayan were penetrated by the high-temperature wells drilled in these areas. Hence, it appears that the best targets for drilling are the steep resistivity gradients coincident with faults and the resistive bodies both overlain by low-resistivity clay cap. At Tanawon, the best target areas for exploration drilling (from the Tanawon pad) include: 1) a well directed towards the northeast intersecting the steep resistivity gradient associated with the Guinlajon and Rangas South Faults and 2) a well targeted towards the east intersecting the increasing resistivity gradient found between -1500 m rsl and -2500 m rsl coincident with the Dumangas and Guinlajon Faults. |