Geothermal drilling in the Matsukawa area

Abstract

Since the first exploratory drilling of AR-1 hole in 1960 twelve holes have been drilled in Matsukawa geothermal area, that is, six wild-cat holes and six production holes of 325–1500 meter depth. It was found from the result of the above drillings that most of the hot water and the steam of that area exist in the fractured zone lying near the boundary between Yamatsuda formation and Tamagawa welded tuff at the depth of about 1000 meters. Therefore, further drilling is being carried out aiming at that zone. The problems met on drilling technique are many. Some have already been solved, and some not yet. Characteristics of the area are that the wells are comparatively deep geothermal wells, rocks are hard, temperature is high and mud escape occurs frequently. Different drilling rigs were used according to the depth of 500, 1000, or 1500 meters. Chromnite mud comparatively stable in high temperature was used for the circulated fluid. As regards a rock bit, the ones of hard type were adopted all over. Pure water was used in case of mud escape. Above are the points devised in our plant for the improvement of the drilling technique of geothermal wells. Unsolved problems will also be solved in near future.