It will be much desirable to take the inf ormations from the oil development and production engineering additionally to the geological informations into consideration, when the subsurface geology of some oil fields are interpreted from the standpoint of planning on waterflood projects. The author has made up the subsurface structure map and isopach map of the reservoir, and ref ered to the position of the oil-water contact and to the difference of the crude oil property in order to recognize the reservoir conditions exactly. It is significant as the background on interpretation of subsurface geology, to use many engineering data. So, in this paper the author has selected both the SP reduction factor and the formation parameters being considered in the calculation for minimum cost drilling, and developed the computer program to calculate the parameters by the digital computers. Showing some new engineering data concerning the reservoir, the author has devided this reservoir temporarily into some blocks and concluded that A and B blocks should be given the priority to the water flooding projects.
In Niigata Prefecture, so-called volcanic rock resrvoirs-lava flows, agglomerates and tuff breccias-are very imporotant for the production of oil and gas. Some geologic considerations are attempted on Fujikawa Gas Field as a typical example of volcanic rock reservoirs. 1. Open flow capacity (O.F.C.) of each well has relation to strctural position and not to the length of completion interval. Wells along the anticlinal axis have larger O.F.C. than those on the wing. The writer presumes this fact may depend on the distribution of fractures. 2. Drilling mud losses are observed only at the wells with over 300, 000 M3/D O.F.C. 3. Pelations between gas and Δt sh of mudstones on the reservoir are considered. 4. At Fujikawa, bottom hole temperatures have a tendency of rising with time.
It may be said that occurrence of sandstones should be controled by paleocurrents as the sandstones are sediments deposited from currents which carried them. But it is not so easy to clarify paleocurrents in case of subsurface as in case of cropping areas. Then, the writers intend to use data from densely calculated continuous dipmeter for paleocurrent analysis under ground. The method for paleocurrent analysis which they use is based on an assumption that dips in mudstones show the geologic structure. The procedure is as follows: 1) decide the structure dip by averaging dip records in mudstones, 2) restore dip records in sandstones to the initial condition, that is the condition of the structure dip being horizontal, by using Wulff's stereo-net, 3) consider the azimuth of initial dips in sandstones shows the direction of paleocurrent which deposited the sandstones. The writers applied the method on the Shiiya formation in Shintainai and Hirakida gas fields of the Kitakambara plain, Niigata, and got conclusions as follows; 1) there were northward and southward currents in the Shintainai area, the former transported much more sands than the latter and became stronger as time passed, 2) there was a depressional embayment in the Hirakida area, and current, which had much sands and flowed south to north in open sea west of the embayment, passed through a break of submarine ridge between the depression and open sea and flowed into the depression, where sands were deposited as fan like shape.