Table 2: Chemical differences between Gachsaran formation water and drilling fluid that used in Gachsaran section.

Chemical properties	Drilling fluid	Formation fluid
Density	variable	1.2 (gr/cm3)
pH	9-10.5	6.1
Salinity	320,000	296,000(mg/l)
Calcium(from anhydrite/CaCl2)	<400	28,100(mg/l)
Magnesium(from MgCl2)	<100	7,600(mg/l)
Sulfate(from anhydrite)	NIL	2,000(mg/l)
Carbonate	NIL	125(mg/l)
Bicarbonate	NIL	75(mg/l)