Abstract:

Deep tight gas reservoirs are characterized by deep burial depth，poor reservoir quality and low production rate，but large exploration potentials.Distribution of favorable source rocks controls the planar distribution of gas reservoirs，and“effective reservoirs”in deep tight sands are the key to gas accumulation and production.Their development is under the control of structure，sedimentary facies and diagenetic facies.Effective porosity controls gas distribution，while fracture controls gas production rate.The gas reservoirs in the Xujiahe Formation in thewestern Sichuan depression feature in ultra-deep，superpressure and extra-tight，challenging prediction of reservoirs and sweetpoints.The3D-3C seism ic exploration technology is capable of solving such problems as quality reservoir prediction，fracture detection and gas potential identification.Ithas been successfully applied to exploration of the deep tight gas reservoirs in the western Sichuan depression.The success rate of exploratory drilling in the secondmember of the Xujiahe Formation is raised from15%to89%，and high yield well ratio increases from9% to 67%，and the discovered gas in place is121.1BCM.H igh efficiency exploration of tight sand gas is realized in the western Sichuan depression.

Key words: effective reservoir, 3D-3C seism ic exploration, reservoir prediction, deep tight sandstone, sweet point, gas reservoir in the Xujiahe Formation, western Sichuan Depression, Sichuan Basin