Classification of deep volcanic rocks in Songliao Basin

Abstract

History and situation about classification of volcanic rocks have been summarized.Based on core sections from 127 wells cutting through J3-K1 volcanic rocks and outcrops around the basin,a lithologic classification has been proposed for the deep basin volcanic rocks as well as sedimentary and metamorphic rocks of the northern Songliao Basin.Volcanic lavas,breccia-bearing lavas,pyroclastic rocks,and tuffites are classified and described in detail.The former two rocks are consolidated by cooling and the latter two ones by compaction.The two different ways of lithification,cooling or compaction,are crucial in determining reservoir features of volcanic rocks.Porosity and permeability of the volcanic rocks lithified by cooling will not affected by their buried depth,while those by compaction will loss their porosity and permeability with increasing buried depth.Perlite,obsidian and pitchstone are volcanic glass having the same compositions commonly with rhyolite as well as andesite and basalt.Blind explosive breccias and welded volcanics belong to breccia-bearing lavas in the classification.