Chemical, magnetic, and phase composition analysis of deposits taken from sedimentation tank from oil plant in Argentina was carried out. Energy dispersive spectroscopy indicates iron as a main sediment component with the site dependent fraction ranging from 11% to 78% (weight percentage). Moreover, large fractions of sulfur (4%‐33%), oxygen (8%‐28%), calcium (1%‐14%), and silicon (1%‐11%) were found. The chemical analysis performed with wet chemical methods also indicated Fe as a main component (about 35%), additionally a large fraction (… 15%) of the sulfur and under 10% fractions of calcium (… 7%), carbon (… 6%), and silicon (… 5%) were found in the sample. The phase composition studies performed using X-ray diraction showed magnetite — Fe3O4, goethite — fi-FeOOH, lepidocrocite — ∞-FeOOH, siderite — FeCO3, and iron‐sulfur compounds (mackinawite — FeS, stoichiometric FeS, greigite — Fe3S4) and other compounds like aragonite — CaCO3, calcite — CaCO3, anorthite — CaAl2Si2O8, quartz — SiO2 and barium sulphate Ba(SO3)0:3(SO4)0:7. Studies performed by the Mossbauer spectroscopy, confirmed presence of majority of compounds identified by X-ray diraction. Magnetic AC susceptibility measurements show that magnetite is a main component of the studied deposit. High concentration of the magnetic compounds deposited in the sedimentation tank points to the advisability to install the magnetic device designed to support water treatment processes, i.e.: flocculation, coagulation, sedimentation, and filtration. This device could simultaneously inhibit microbiological and chemical corrosion. The oil structurally trapped in a typical reservoir (a rock formation that contains hydrocarbons) can be produced either under its own pressure (a primary production process) or under applied external pressure by water injection (a secondary production process). Because of low productivity of the primary recovery process, the secondary recovery technologies are essential. In the water flooding recovery technique the oil is displaced by water from the reservoirs and moved via porous rock formation towards the wells. The obtained water-in-oil emulsion contains dispersed fine solids which penetrate the oil during production process. The production stream is passed through separation equipment to separate oil, gas, water, and suspended solids. The separated oil is recovered and the separated water is reinjected into the reservoir rocks as additional flooding water. The suspended solids are deposited in the sedimentation tank. Not suciently purified water (containing dispersed solids) can be responsible for the loss of the rock permeability caused by particles trapped in small pores [1]. Water injection stimulates the productivity of oil reservoirs, but a consequence may be an increase of microbiological and chemical corrosion. The mixture of oil and water provides favorable growth conditions for sulphate