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SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
fractures and the lower half the micro-fractures. Fig. 5 shows the areal distribu 
tion and a diagram computed for the total area. It will be noted that a 
dominant fracture trend has an approximate azimuth of 50°, while a secondary 
trends approximately to 130°. These two major trends were expressed both 
by numerous macro- and micro-fractures. A preference is observed, for the long 
fractures to be oriented with the dominant trend (50° az.). A peculiarity of 
this area was the scarcity of E-W fractures. 
Considering that the known tectonic grain of this area is obviously dom 
inated by structures in a South-Easterly direction, it is our impression, that 
fractures parallel to structure do not show so well on photographs, because they 
are mainly related to compressional stresses. On the other hand, the fractures 
of the 50° trend appear to be mostly related to shear and tensional stress. A 
detailed analysis of each producing center, taking into account production, 
pressure and temperature figures against depth and thickness of the reservoir, 
may show the relative merits of compressional fracture systems against shear 
and tensional systems. 
Such a detailed study is beyond the scope of this work. However, a crude map 
of production data covering the main field shows a definite tendency of the 
contours to form alignments oriented at approximately 320° and 40°. Such a 
pattern obviously does not result from folded structure or lithologic changes 
within the reservoir. It is instead suggestive for a block-fault system, as the 
main factor controlling the distribution of secondary permeability. 
Another remarkable feature of the region is given by a very unusual amount