Characteristics and geological significance of the formation water for 2+3~(th) member of Xiashihezi formation in Jin 66 well block of Dongsheng gas field

Through the main chemical characteristic parameters analysis of formation water for 2+3~(th) member of Xiashihezi formation in Jin 66 well block of Dongsheng gas field,the internal relationship between the chemical properties of formation water and gas reservoirs is revealed.The results show that the judgment standard of the normal formation water for 2+3~(th) member of Xiashihezi formation in Jin 66 well block is as the follows:the salinity is greater than 25 000 mg/L,the sodium chloride coefficient is less than 0.4,the sodium calcium coefficient is less than 2.3 and the fracturing fluid return rate is greater than 55%.The formation water is of calcium chloride water type,and as the whole,it is high salinity weak acid brine–brine.The reservoir is well sealed,which is beneficial to the accumulation and preservation of natural gas.The secondary porosity with characteristics of great physical differences and poor connectivity,is the main reservoir type.