Which fluid has the highest salinity in reservoirs?

The fluid with the highest salinity in reservoirs is typically formation water, which is the water naturally present in the rock formations where oil and gas are found. Formation water can have salinities ranging from 10,000 to 300,000 parts per million (ppm) of total dissolved solids, making it much saltier than seawater, which has an average salinity of around 35,000 ppm.

Formation water