Mehbod Rahro - MS student of Hydrogeology, Department of Earth Sciences, Shahrood University of Technology, Iran
Rahim Bagheri - Assistant professor of Hydrogeology, Department of Earth Sciences, Shahrood University of Technology, Iran,
Mahmud Mirbagheri - Head of oil engineering of South Zagros Oil and Gas Company, The Oil Company of Iran, Shiraz, Iran

In oil and gas reservoirs, the produced water is usually accompanied by oil and gas production. Most of the reservoirs at the beginning of production and exploitation have fresh water; but with passing time due to increasing the productions and decreasing the pressure of reservoir, the produced water gradually becomes saline. The produced saline water in reservoirs cause severe corrosion in the pipelines and well head facilities, and thus, cause the reduction in oil and gas productions. Determining the origin of salinity in oil and gas reservoirs is very important for controlling and managing this problem, and consequently, causes to increase the gas production. Shanoul gas reservoir is one of the Parsian gas fields in the southern Iran, in which saline water via some gas wells is produced, causing a few problems such as reducing the gas production. The aim of present research is to determine the origin of the brine water in this reservoir using the data obtained from isotopic and hydrochemical analysis of the water samples taken from the reservoir. The potential processes causing salinity can be halite dissolution, membrane filtration and evaporated sea water. The potential sources of water may be meteoric, present or paleo-sea water. The mixing between the ancient evaporated sea water and condensed vapors is determined as a main origin of salinity in the Shanoul gas reservoir using hydrogeochemistry, isotope and geological methods. The same research in the other reservoirs in the world has confirmed the obtained results from this research work. These results are useful and important for reservoir management, and consequently, can cause to increase the gas production from this reservoir.

Produced water, Origin of salinity, Hydrochemistry, Stable isotope