1�� College of Resources and Environment��Southwest Petroleum University��Chengdu 610500��China; 2�� Northwest Sichuan Gas Field of Southwest Oil and Gas Company of CNPC��Jiangyou 643000��Sichuan��China; 3�� Chongqing Gas Field of Southwest Oil and Gas Company of CNPC��Chongqing 400021��China

In the Middle Triassic Leikoupo Formation of Zhongba gas field of northwestern Sichuan��the diagenetic evolution process of granular and crystalline dolomite reservoir was complex��in which the various diagenesis was developed��and the reservoir quality was clearly affected by the diagenesis�� The primary porosity��e. g�� bird's eye pore��biological coelom pore��intercrystalline pore and intergranular pore��almost completely disappeared after the compaction and pressure solution and the cementation by multiphase calcite��dolomite and gypsum�� The dissolution in supergenic and burial periods controlled the forming process of secondary porosity��such as intergranular dissolved pore��intragranular dissolved pore��algae bond framework dissolved pore and intercrystalline dissolved pore�� While the filling and cementation of multiphase dolomitic��quartz and clastic materials made these secondary porosities reducing significantly and partially disappeared��and ultimately developed the current major reservoir space under the influence of tectonic fracture diagenesis��