The Kushiro coal field consists of Oligocene sedimentary rocks, ranging from 800 to 2000m in thickness. Major structural features are N-S folds and northeastward-trending faults, Probably the folds are older than the faults.
The method of study is as follows. Thirty nine localities were selected throughout the coal field ss shown in Figure 1: 35 in compact, massive shale of Charo formation and 4 in Nuibetsu or Shakubetsu formation. At each locality, 100 joints, except at a few localities, were measured, then they were plotted in the lower hemisphere of the Schmidt Net, and contour lines were drawn to find areas of concentration. These 39 Schmidt Net diagrams are shown in Figures 2, 3, and 4.
Then concentration more than 6% in the peak was collected from these 39 diagrams and plotted in other Schmidt nets as shown in Figure 5, in order to study geometrical relation between joints and the major structural features.
In conclusion, there are three conspicuous groups of joints, C, R, and A.
Joints of C group have a mean plane that strikes from east to west and dips nearly vertically. They were probably formed by E-W lateral compression, the same stress which caused the N-S folds.
Joints of R group are possibly related to NE faults. Except in area (1), R is divided into two parts, R₁ and R₂. R₁ and R₂ are considered to be conjugate shear fractures. Axes of principal stress in areas (2), (3), and (4) are given in Table 2 and Figure 5. In every area, axis of maximum principal stress is nearly perpendicular to the planes of NE fault concerned.
Joints of A group are a consequence of failure in folding, either of N-S folds or of NE folds along the NE faults. They trend in parallel with the folding axes and dip nearly at right angle to the bedding.

View full abstract

This article describes the field culculation of gas lift. The author applies the average experimental value which was obtained from many experiments in Niigata Gas Field.

View full abstract