Porosity dependence of mechanical properties of the clastic sedimentary rocks under high pressure has been shown in the experimental work by the authors (Hoshino et al., 1972; Hoshino, 1974; Hoshino and Inami, 1974). In the present report, such mechanical properties as deformational behavior, strength, compressibility, cohesive strength, and viscosity were studied in terms of porosity based on the results of the above work and also were compared with data from several deep exploratory wells in the central Niigata oil-bearing area, which reconfirmed the results reported by Inami and Hoshino, 1974.
In summary, progress of compaction is divided into three stages based upon differences of mechanical properties as follows, (Figs. 6 and 7). The first stage or viscous compaction-stage: The mineral grains within the clastic rocks are not touched each other yet. The rocks behave like soil and physically rather fluid-like material. The second stage or plastic compaction-stage: The mineral grains come into contact. The rocks consist of the mechanically stable framework constituting of these grains. Physically, they are plastic solid or Bingham substance. Third stage or elastic compaction-stage: Authigenic minerals appear among the mineral grains, and cementation is common in every part within the rocks.
It is considered probable that the most of migration of oil (explusion) are done in the second compaction-stage, which would also provide a favorable condition for accumulation of oil.