Main difference of the technics between the Japanese and the American are considered which should be improved urgently. 1, Drilling. Generally speaking the drilling time spent in Japan is double as compared with one in U. S. A., mainly because of inferior in these following problems: the time spending for rigging up and breaking down, the speed of round trip for changing bit, compounding of diesel engine, the quality of bit and the drilling method, the selection of mud, the speed of the directional drilling, and the time spending for geological investigation and the completion of well. 2, Production. Main problems production concerning are as follows: the prevalency of chemical treatment, the quality of the sub-surface pumps and the pumping unit, the sub-surface hydraulic pump, the gas lift, controlling flowing well, and the number of employers in the oil field. 3, Miscellaneous. Manufacturers and service company is very active in U. S. A. The quality of engineer is superior concerning common sense, Main drilling operations should be included within producing operator drilling contract concerning in Japan.
Niigata gas field forms a large synclinal structure comprising the reserve area of about 850 square kiiometers. The original gas reserve is estimated about 2, 000 million cubic meters. The reservoir rocks are composed of very loose sand and gravel. In the vicinity of Niihata city, the gravel layer marker E, at the depth of 350 meters, and the gravel layer, marker P, at the depth of 550 meters, are productive. The characteristic feature of this gas reservoir is to be containg one phase of water saturated with gas except small proportion of free gas bubbles. The original reservoir pressure was slightly lower than the hydrostatic head. The producing mechanism may be the gravity drive. The result of the bottom-hole-pressure survey in 1952 in the Ogata district, which was developed with the well spacing of over 300 meters, has shown a little pressure drop, and the flowing of the wells, completed at E layer, have stoppd. The production of the wells of large initial production in this district, are declining.
The writers are being studied to find the tendency of the flowing of fluids dissolved the gas at the Niigata gas field, by measusing pH, Cl', HCO3' of the water in wells, produced a gas from G5 gas zone. This report describes preliminarily the results obtained up to the present.
Recently bulk density of clastic rocks has been measured in core-analysis or at gravity survey by some geologists. As the value of bulk density are varied by porosity and water content in the same sample, it is necessary to exchange the value into the unit weight in water saturated state. The ralation between unit weight in weter saturated state (ρ3), average unit weight of mineral constituents of the aggregate (ρ0) and porosity (n) is expressed by the equation ρ3=ρ0(1-n)+n (1) (where specific gravity of sutarated water ρω=1) So that the eguation to exchange the unit weight in dry state (ρ1) into ρ3 is as follows: ρ3=ρ1(1-1/ρ0)+1 (2) On replacing the dry state (ρ1) by the natural state (ρ2), the equation (2) will be transformed as follows: ρ3=ρ2(1-W0)(1-1/ρ0)+1 (3) Where W0 is water content in natural state. The more the porosity decreases according as the geclogic time passes, the thinner the bed of clastic rocks becomes. The relation between these thickness and porosity is expressed by the equation d1/d1=1-n1/1-ni (4) in which d1=original thickness of the stratum n1=original porosity of the stratum di=the thickness of the stratum when the porosity (ni) varies from n1 to ni, (ni<n1)