Abstract: Tight sandstone reservoir of the Xujiahe Formation in Guanyinchang area mainly consists of delta plain distribu-tary channels sandbodies.Based on analyses of reservoir diagenesis and tightening,detailed study shows that the hydrodynamic conditions during sedimentation determine the storage capacity of reservoirs.Strong compaction is the major factor causing the decrease of inter-particle primary porosity,and quartz overgrowth in diagenetic stage is the key factor causing the tightening of reservoir.The temperatures of fluid inclusions in quartz overgrowth is between 82.5-125.1 ℃,accor-ding to which the tightening depth is estimated to be between 1 725-2 864 m.This depth interval corresponds to the period of Yanshan movement.According to analysis of the tightening process and hydrocarbon accumulation stages in the Xujiahe Formation sandstone reservoir,the following understandings were obtained.The sandstone reservoir was not tightened at the initial phase of gas accumulation,so gas could migrate long distance laterally.Before the peak gas accumulation,the sandstone reservoir had become tight,thus the gas could not migrate laterally for a long distance,instead,they migrated along the unconformity of channel and microfractures opened by high pressure.of the composite structural and lithologic gas reservoir got finalized during Himalayan epoch,and the gas reservoir was controlled by both lithology and structures,so their heterogeneity was strong.

Key words: diagenisis, composite structural-lithologic reservoir, tight sandstone, Xujiahe Formation, Guanyinchang area, Sichuan Basin