History of exploration and research of Miocene biosiliceous mudstone reservoirs, preliminary study of the reservoir properties in the thermally-matured biosiliceous mudstones of the Onnagawa Formation

Abstract

Exploration and development of biosiliceous mudstone has been carried out in California, USA, Sakhalin, Russia, and Japan. Although the exploration scale of biosiliceous mudstone differs between Japan and California, both exploration activities have similar histories. By 1950, fracture-developing porcelanite had been explored in both regions, and since then, fracture-developing cherts became particularly important in California. From around 1970, it began to be studied and recognized that the pore properties of porcelanite were improved by opal CT / quartz transition of biogenic silica, which led to the discovery of diagenetic traps in the 1990s. After that, it was influenced by the Shale Revolution, for better or worse, the attention was focused on the thermally-matured parts of biosiliceous mudstone. The evaluation was downgraded significantly for the matured parts of the Monterey biosiliceous mudstones, but it is ongoing for the thermally-matured basinal depressions of the Onnagawa biosiliceous mudstones.

The productivity of biosiliceous mudstone may be significantly improved by well stimulation. Since there are large variations in reservoir and physical properties of biosiliceous mudstone, the effect of well stimulation differs depending on the geological condition. Therefore, optimization of well stimulation requires detailed understanding of geological conditions and preliminary simulations that reflect them.