Tight gas production is taking up bigger and bigger shares in China’s total natural gas production.However

further exploration and development of this kind of gas reservoirs face great challenges due to their distribution complexity and prediction difficulty.Although the Xujiahe Formation in western Sichuan depression is typical tight sandstone

it has relatively good reservoirs with relatively higher permeability and porosity.Research of these reservoirs reveals a unique phenomenon of the existence of a rim chlorite cementation.Based on analysis of data such as thin section

SEM and X-ray diffraction and in combination with sedimentary facies

regional geology and volcanic activity

the authors determined the period in which the chlorite was formed.It is suggested that the existence of chlorite can effectively protect the primary pores in these reservoirs.However

the sole exis-tence of ring-shaped chlorite cementation does not necessarily mean a relatively better reservoir.Other pre-requirements for a high-quality reservoir are also needed

for example

the ring must be thick and continuous enough and the reservoirs must be formed in high-energy sedimentary environment.