By virtue of polarizing microscope

scanning electron microscope

cathode luminescence microscope

laser scan confocal microscope in combination with X-ray diffraction data and water rock interaction experiment

we studied quartz dissolution in tight sandstone reservoirs in the Upper Paleozoic of Daniudi gas field in Ordos Basin

and summarized the typical morphology features

genesis and its influences on tight sandstone reservoir.Results show that:(1)Quartz dissolution is common and has typical SEM morphology features as “rain print” and “honey comb” solution pits and/or vugs.(2)Quartz dissolution in Daniudigas field develops in alkaline environment

and the detailed evidences are as follows:①hydrothermal experiments verify that quartz dissolves more easily in alkaline environments than in acid conditions;②calcite cementation and metasomatism associated with quartz dissolution are common;③some horizons are rich in illite but poor in kaolinite

with some chlorite coatings occurring sporadically.(3)Quartz alkaline dissolution results in secondary pores such as intergranular dissolution pores and enlarged pores

leading to an average incremental porosity of about 6%.This is the cause of quality reservoirs in some tight sandstone intervals of Daniudi gas field.