CHEMICAL FIELDS, HYDRODYNAMICAL FIELDS AND GAS ENRICHMENT IN THE LATE TRIASSIC OF WESTERN SICHUAN BASIN

The ingredient and movement features of the groundwater are important for the enrichment of oil and gas in gas bearing basins.The features of the groundwater in the second and forth menbers of the Xujiahe Formation in the Late Triassic of the Western Sichuan Basin was discussed.By integrating chemical fields and dynamical fields of the groundwater and the around geochemical environment,the concept of geochemical dynamical belt of groundwater was proposed,and three belts,i.e.,hydro-pressure forming belt,backwater belt and discharge belt,were indicated in the members of the formation.In the discharge belt and backwater belt,the solute is in the state of transplanting and congregating with deoxidizing environment,and the known gas fields are mainly distributed in the belts.Nevertheless,in the hydro-pressure forming belt,solute diverse and become pure,and most of the gas bearing traps are distrbuted in the belt.Based on above characteristics,the promising exploration belts in the Western Sichuan Basin was pointed out.