| Title | Fang Hot Springs Geothermal Area, Chiang Mai Province, Northern Thailand – Geological and Geophysical Exploration in 2014-2015 |
|---|---|
| Authors | Spencer H. Wood, Pichet Kaewsomwang, Fongsaward Suvagonda Singharajwarapan |
| Year | 2016 |
| Conference | Asian Geothermal Symposium |
| Keywords | Fang, geothermal, Thailand, crystalline rocks, resistivity, hot springs, wells |
| Abstract | Fang Hot Springs binary power plant generates 115-250 kWe that varies with season. Four wells (92-500 m deep) collectively flow ~ 20 liters/second of 110-115‹C water. None of the wells are pumped, nor is the spent water re-injected. Some wells show maximum temperature of 130‹C, slightly more than the 124‹C temperature predicted by mineral-equilibria modeling of the water geochemistry. Hot wells and seeps are distributed over an 8 hectare area. Producing wells FX-2 and FX-4, 500 m deep are 250 m apart, and lie 200 m distant from the 3 original producing shallow (<92 m) wells FTGE-7, FTGE-14, and FTGE-15. Hot seeps align along a 350‹ azimuth for a distance of 170 m, and another 150-m alignment of 270‹ azimuth. Springs and wells are in Triassic (?) gneiss and foliated granite. Electrical resistivity surveys and a magnetotelluric surveys detect low-resistivity (< 60 ohm m) only within the upper 50-100 m of the hot springs area. No deep low resistivity anomaly is detected in the crystalline rocks beneath the seeps or the producing wells. The MT survey clearly shows the structure of the shallow-dipping Doi Kia detachment fault that lies to either side of the hot springs area, and also the steeply dipping, NE-SW-striking Mae Chan active strike-slip fault that lies 1 km south of the hot springs area. However, neither of these faults simply relate to the locations and alignments of seeps or locations of producing wells. We have no drill data on fracture orientation. The fracture system is believed to be developed at an intersection of the strike-slip Mae Chan fault with the N-S striking normal fault system near the west side of the Fang basin. Fractures are likely steeply-dipping thin fracture zones with hydrothermal alteration. Future surveys should be designed with precision to study the fractures of the known geothermal area in order to define drilling targets. Future development for increased electrical power generation should focus on drilling shallow wells (. 500 m), with diameters large enough to install submersible pumps to increase flows. Development should include a designed re-injection well system to sustain pump levels. |