It could be said that the well construction technology included drilling techniques had developed while depending on other industrial technology from the past. The depth of hand digging wells could be 30 Ken (about 50 m) at most due to many cases of loss of consciousness caused by the gas in the borehole in 1800s. After that, by virtue of the foot bellows that was a technique for ventilation in the wellbore, the depth was rapidly increased to 70 Ken (about 127 m) in 1860s. At the same time, construction methods progressed, resulting in the development of an oil well as large as 180 Ken (327 m). Cable tool drilling techniques had been imported to Japan for the first time in 1873. These techniques includes not only a method of simple well spudding with a bit, but also all of techniques in pipe driven, “fishing”, casing installation, formation isolation and other improvement. The rotary drilling techniques were imported to Japan in 1912. The time that was not possible to complete a well between 1914 - 1928 continued because encountered “Zaku” currently called “sloughing shale” at Niitsu oilfield. The “Zaku” formation was completely drilled at last when “double-floor drilling” was adopted in 1937. This “double-floor drilling” was a casing drilling technique.
