Abstract: The volcanic reservoir of Jiamuhe formation in Zhongguai-District 5-(8) area in Karamay oilfield is characterized by developed pyroclastic rocks and lava. The pyroclastic rocks dominated by crystal debris,lithic intra-dissolution pore and volcanic ash devitrified pore consist mostly of tuff, tuffite and volcanic breccia; the lava dominated by semi-filled or unfilled bubble and condensed shrinkage fissure contains andesite and basalt. In the lava and pyroclastic rocks, the filled chlorite, zeolite and cacite destroyed the primary reservoir spaces formed in cooling diagenetic stage. Such a case was still not improved due to weak and non-universal dissolution in neutral-acidic volcanic rocks of upper sub-formation of Jamuhe formation, despite the fact that late surface water leaching and in situ acidic fluid dissolution allowed the reservoir quality to be improved in some degree. It is believed that late fractures could have good effects on improvement of the reservoir quality of such volcanic rocks.

Key words: Junggar basin, Permian, Jiamuhe formation, volcanic rock, reservoir