抄録
There are some important oil or gas fields of volcanic reservoir in Japan. Emprically, two basic rules on those have been pointed out by some investigators. (1) The reservoir characteristic of volcanics is better than clastics. (2) Acidic volcanic rocks have much more opportunities to reserve hydrocarbon than basic volcanic rocks. These two rules are thought to come from the potentiality of fracturing under tectonic stress.
The rock properties of volcanics ranging from acidic to basic are studied under high confining pressure and compaired with clastic rock properties which were studied by HOSHINO et al. (1972). Four interesting results are obtained. (1) Ductility of volcanics is smaller than clastics under the subsurface condition. (2) Volcanics have more opportunities to be deformed with favorable fracture types for reservoir than clastics. (3) Difference of volcanic rocks type is not so clear on these two results, however, porosity is one of the most important factor for the ductility and fracture type. (4) Young's modulus of acidic volcanic rocks are bigger than basic volcanic rocks.
Hereby, we concluded that the differences of rock property between volcanics and clastics are the important keys to the empirical rule (1). The difference of Young's modulus may suggest something to the rule (2), however some problems are still remained for the future.
