Water Dynamic Distribution and Chemical character in Xu2 Member Gas Reservoir of Xinchang Gas Field,Western Sichuan Basin
川西新场气田须二气藏水体动态分布与水化学特征

For intuitive and detailed discussion of the gas well water of Xu2 reservoir in the Xinchang gas field of the western Sichuan basin,we divide the output water into three categories of condensate water,formation water and interlayer water (or residual formation water).The results indicated that all of the gas wells in the structure of the main parts have experienced a longer period of condensate water output phase before the formation water output,and then the edge water from the north and south sides begins invading to the structure main parts;in contrast that the east-west gas wells of the structure of the main parts may output the interlayer water or residual formation water.Because the sequence energy decrease with gas reservoir developing,and the edge of water begins invading into the structure of the main parts along the north-south fault,causing the gas wells in the structure of the main parts product a large number of water.Micro-cracks in the east-west gas wells of the structure of the main parts are not developed owing to far away from the fault,gas wells have little water.Overall,the different types of produced water are associated with the different chemical compositions of water,with presence of low salinity in the condensate water and high salinity in the formation one,the interlayer water or residual formation water salinity falling between two members above.The differences of water chemical characters depend on water\|rock interaction environment,fluid pressure,gas concentration,pH value,etc.With gas taken out,fluid pressure drops,gas concentration decreases,and salt ion solubility reduces.So the Ca ion concentration in the formation water of main part structure is lower than that in the edge of the north\|south,with occurrence of Ca precipitation.