Exploration of geothermal resources in the Tatun volcanic region, Taiwan, Republic of China

Abstract

The Tatun volcanic region is located on the northern tip of Taiwan. It covers an area of about 320 square kilometers. It is composed of andesitic lava flows and pyroclastics. The basement rocks are Miocene sediments. In view of the strong surface thermal manifestations in the region, it was chosen as the first area in Taiwan for geothermal exploration. Exploration work was commenced in November, 1965 and has been carried on until now by the Mining Research and Service Organization. About 150 square kilometers on a scale of 1 to 10,000 have been mapped geologically. The total surveyed area will be 200 square kilometers. Chemical analyses have been made for hot springs, fumaroles, and drillhole discharges. A onemeter-depth temperature survey was completed in early 1967. Although this survey did not give very much information on the temperature anomaly at depth, it can help delineate the boundaries of individual hot areas and may help trace out certain structural trends. Both electric resistivity survey and magnetic survey have been applied in this volcanic region in search of hot hydrothermally altered zones. But the results are difficult to interpret, for the region is characterized by high relief and heterogeneous petrographic composition. There were 58 small (1 7/8“ - 3” in diameter) and shallow (47 – 155 meters in depth) gradient wells drilled in the region. The total footage was 6625 meters. These wells proved to be useful for siting future exploration wells. Up to date, 7 exploration wells ranging from 441 to 1005 meters in depth have been drilled. A temperature as high as 240 °C has been measured at the bottom of the 1005 meters deep well. A 1500 meters deep exploration well is under drilling and is to be completed in August, 1969.