Water treatment

WATER TREATMENT (EN: water treatment; DE: Wasseraufbereitung; FR: preparation de l'eau, traitement de l'eau; ES: tratamiento del agua; RU: водоподготовка) is the stabilization and purification of the superficial and waste waters of the mechanical admixtures, of the compounds of the iron, and of the petroleum, at the water-purification stations and other facilities.

The water treatment has the greatest significance and volume within the petroleum-extracting industry, where it is performed for the water flooding of the petroleum layers, with the purpose of the maintainance of the necessary pressure within these layers, and with the purpose of the increasing of the coefficient of the petroleum recovery. Within the USSR, during the 1982, the volume of the waters, which have passed the water treatment, has amounted to 1200 million cubic metres (the superficial waters have amounted to 60%, and the waste waters have amounted to 40%). They stabilize the waters for the decreasing of their corrosive activity, and for the decreasing of the depositions of the insoluble salts (CaCO3, MgCO3, CaSO4) on the walls of the water conduits. For these purposes, they perform the alkalinization of the waters using the sodium hydroxide (lime), or their partial neutralization using the acid. They introduce the inhibitors of the corrosion at the grouped pump stations of the water distribution systems at the productive petroleum fields, and they introduce the inhibitors of the salt depositions at the bottomhole of the borehole, or immediately into the layer (through the external annulus of the borehole), using the dosing pump at the points of the automatic measurement of the produce of the boreholes. They remove the suspended particles of the sand, clay, silt, plankton, and products of the decomposition of the plants, which are worsening the injectivity of the injection boreholes, with the help of the coagulants: aluminium sulphate Al2(SO4)3•18N2O, ferric chloride FeCl3, and iron sulfate FeSO4•7H2O.

The creation of the alkaline medium for the more effective hydrolysis of the aluminium sulphate also assists the purification of the water of the iron, which is contained within this water (the hydrolysis of the salts of the iron, and the sedimentation of these salts in the form of the ferric hydroxide). For the intensification of the processes of the water treatment, besides the coagulants, they widely use the flocculants. One of the most effective flocculants is the polyacrylamide (PAA), with the molecular mass of approximately 10^6. In case of the joint treatment of the water using the aluminium sulfate and polyacrylamide, the speed of the sedimentation of the flakes grows by 2-3 times, and the necessary dose of the coagulant is decreased by many times. The water treatment of the waste waters (superficial and within the layer), besides the removal of the mechanical admixtures, and of the compounds of the iron, includes the additional extraction of the petroleum into the special containers of the water-purification stations. Since the end of the 70-ies, for the water treatment of the waste waters at the petroleum fields, they perform the treatment of these waters using the ultrasound (sonication), which is causing the dispersion of the droplets of the petroleum and of the suspended particles to the sizes, which are not preventing the filtering of the water from the injection boreholes into the layer.

They monitor the waters, which have passed the water treatment, for the existence of the suspended particles, of the compounds of the iron, and of the petroleum. The acceptable content of these components is determined according to the specific conditions of the development, for example, for the Ust-Balyk petroleum field (1980), the content of the mechanical admixtures is 35 milligrams per litre, of the iron is 2 milligrams per litre, and of the petroleum is 50 milligrams per litre, while for the D1 layer of the Romashkinskoye petroleum field, respectively, 15 milligrams per litre, 1 milligram per litre, and 20 milligrams per litre.