Abstract: The vesicular volcanic clasitic reservoir of Fengcheng formation in Wellblock Xia-72 is a rare reservoir rock with great potential for hydrocarbon exploration. Microscopic analysis has been conducted with microscope by using large cast thin section manufacturing technology to make a systematic research on the component feature, textural structure and porous type and to examine the genetic mechanism and exploration significance. This paper suggests that the extremely hot erupted ash flow of such types of reservoirs is influenced by vaporized water steam on the surface, and asymmetric diatexis process take place during deposition, forming vesicular diatexis rhyolitic and vitric tuff with volcanic gravels. The lower part of rock mass is good reservoir and percolation rock characterized by developed constricted fissures and dissolved pores; the mid-upper part is good reservoir rock with developed vesicular and matrix micropore textures. Such a volcanic clastic reservoir is believed to be of great potential for petroleum exploration.

Key words: Wellblock Xia-72, Fengcheng formation, rare reservoir lithology, pore type, genetic mechanism