On the Water Spout at the Working Faces and the Water Reservoirs in the Taiheiyo Coal Mine, Kushiro

Abstract

The Taiheiyo coal mine is now working under the open sea off Kushiro city, Hokkaido. In this mine, the salt water often spouted out at working face since 1936. Recently, such spout became very dangerous as the mining area have extended to greater depths of the under-sea coal field.
The author has carefully observed the, spouting since 1948, and has drilled underground drainage wells since August 1955 to obtain the materials from the water reservoir.
The followings are rsumed from those observations on the spouting and the reservoir by means of the drainage wells:
1) There are two reservoir horizons. The one is in the medium to coarse Tertiary sandstone in the basal part of the Harutori coal-bearing formation, and the other is in the hard fine Cretaceous sandstone.
2) Both Tertiary and Cretaceous roservoir are of fissure type, and extend in the definite horizon, and spouting may occur mainly in water-filled rock fissures.
3) The spouted water comes from the connate water included originally in the rock, and is not admixed with fresh water from the surface or with marine water.
4) Pressure of the reservoir-water increases with the depth. Gauged reservoir pressure at the top of drainage wells is about 60 per cent of the hydrostatic pressure.
5) The content of Cl in the water corresponds to reservoir depth and possibly to the caluculated contents of CaCL₂ and NaCl.
6) Temperature of water in the Cretaceous reservoir is higher than that of the Tertiary one at the same depth, and a true thickness of the Cretaceous reservoir is assumed to be larger.than the observed thickness.
7) The gas-water ratio in the water at the casing head is observed as 0.3 and the gas contains 93% CH₄. The gas can be separated by casing head and utiliged.
8) It is possible to control the reservoir water by means of drainage well drilling to prevent the water spouting.