Utilization of produced water – an urgent task for oil industry. In many cases, produced water is very aggressive, causing intense corrosion of equipment and facilities, wells tightness break, resulting leakage of wastes during collection, preparation and injection, as well as salinization of soil and groundwater sources of drinking water, depth of vegetation.
In recent years, demand for the development of water treatment technologies and equipment has increased, inter alia, at the Middle East and Russia. The most used method for produced water disposal is treatment and its further re-use for technological needs – in reservoir pressure maintenance systems, or for preparation of drilling fluids and reagent solutions. Acceptable from the environmental and economic positions is the flooding of productive horizons. In addition to oil recovery enhancement, reservoir pressure maintenance (RPM), it allows to reduce the probability of spatial position changing or destruction of deposits due to the increase in pressure gradient at productive reservoirs.
Experience of wastewater commercial disposal in deep absorbing horizons has been accumulated. This horizons should have a significant areal extent, high capacity and filtration characteristics, be confined to the region of stagnant or slow hydrodynamic regime, have seasoned confining beds, excluding the hydraulic connection of the field-collector with other aquifers. An obligatory condition is compounds compatibility of produced and injected water. Otherwise, occurs salts accumulation in the bottomhole zone of injection wells, which negatively affects their pickup. Injection wells placement must be located outside the seismically active areas.
Particular attention is paid to biological and chemical compatibility of injected water. The use of fresh water for oil wells flooding promotes microbiological processes and, as a result, infestation of productive strata with aerobic and anaerobic bacteria. The rate of formation of the microbial community in the bottomhole zone of injection wells depends on the physical and chemical conditions of the reservoir and the amount of injected water containing oxygen. On average, this period is several months, less often first years from the start of field development with RPM. The most danger, due to high corrosion activity, show sulfate-reducing, nitrous, thione, and iron bacterias. To protect equipment and communications from corrosion inhibition of produced fluid and injected into the reservoir water are widely used.
To prevent scaling in productive reservoirs and to protect oilfield equipment against microbial corrosion, natural and waste solutions are used for RPM (they are compatible with the chemical composition of groundwater). The use of chemical inhibitors in composition with polymers, bactericides, and other active substances is also possible. In the presence of clay minerals at natural area, under the influence of injected water permeability and intake capacity of wells are reduced. Swelling occurs intensively in contact with fresh water and significantly reduced with using free waters of high mineralization.
Produced water treatment
Wastewater used to maintain reservoir pressure consist of 85 – 90% of produced water. In oil industry are used both: specially designed methods of produced water treatment, and borrowed from the related industries, that use large-capacity water treatment systems.
The most frequently used methods:
- sedimentation of water;
- filtering water through a porous or other medium;
- centrifugal separation;
- impurity removal by sinks;
As the technical means for water sedimentation are used settler vessels, oil traps, desanders and sedimentation ponds.