The gas reservoirs of Xu 2 developed by SINOPEC Southwest Company in Xinchang and Dayi were put into production

with the quite complicated distribution of gas/water.Therefore

adopting American hydrogeologists Novk's Phase diagram analysis and characteristics of deuterium and oxygen isotopes in gas field water

we identified the production formation of gas field water and its origin

analyzed the dynamic migration of gas field water

and investigated the evolution of gas accumulation in the western Sichuan Depression.The results show that (1) the gas field water of Xu 2 gas reservoir in Xinchang is originally marine formation water in the lower strata of the Xuxiahe Formation and Leikoupo Formation

which was in closed conditions initially but migrated into Xu 2 gas reservoir due to the change of preservation conditions caused by structural movement of later period

resulting in the present gas field water;(2) the gas field water of Xu 2 gas reservoir in Dayi changes gradually from the original deposition water in Xujiahe Formation to the marine formation water in the strata lower of the Xujiahe Formation and Leikoupo Formation.The water was well sealed and under thorough reduction conditions

which is typical of paleo-sedimentary water.But due to the increasing production of Xu 2 gas reservoir there

the marine formation water of Leikoupo Fomation in the lower strata has migrated into the 2

nd

member of the Xujiahe Formation along faults controlling Dayi structure

replacing the paleo-sedimentary water of Xujiahe Formation.This scenario explains the present dynamic characteristics of gas field water in Xu 2 gas reservoir of Dayi.The accumulating evolution shows that Xu 2 gas accumulating process and the influence from fractures in Xinchang are different from those in Dayi

thereby generating different types of gas accumulations.Accordingly

the types and dynamic characteristics of gas field water in Xu 2 gas reservoir in Xinchang are different from those in Dayi.