The factor connected most closely with the effect of fracturing is the permeability of fracture made in oil reoervoir by fracturing. In this treatise, therefore, I showed the effect of fracturing in numerical value, based on the permeability of the fracturing sand. Of course, the real condition of oil reservoir is very complex and the flowing condition of oil in oil reservoir is very complicated. Under such real conditions, it is impossible to indicate the effect of fracturing mathematically. So I computed the effect of fracturing on the assumption that the oil reservoir condition and the flowing condition in oil reservoir are simplified. Consequently, we cannot believe that these figures gained on such supposition would exactly coincide with experimental results. But they must he excellent guides to know some tendency of the effect of fracturing.
According to the result of this reseach, fracturing has increased producing capacities of deep wells in Yabase oil field to some three times as much as before, and the effect has been greater where wells were affected with mud invasion. It is to be desired that the permeability of the fracturing sand is more than 100 darcy, and using large grains of sand at the end of the fracturing is not so effective. What should be avoided most is the ill effect of overfiush. In some case, calculation showed that overflush reduced more than 50 per cent of the effect of fracturing.
