Water injection and filters

Waterflooding,or water flooding, is the injection of water into a reservoir to maintain pressure (also known as porosity displacement) or to drive oil toward a well to increase production.Water injection wells may be located onshore and offshore to enhance oil recovery from existing reservoirs.Typically only 30% of the oil in a reservoir can be extracted,but water injection increases the rate of recovery (known as recovery factor) and keeps the reservoir productive for longer periods of time.Water flooding began accidentally in 1865 in Pithole, Pennsylvania. Water injection became common in Pennsylvania in the 1880s.

Sources of injection water 

Most bulk water sources are available for infusion.The following water sources are used to recover oil:Produced water is often used as the injection fluid.This reduces the potential for formation damage due to incompatible fluids, although the risk of scaling or corrosion in injection flowlines or piping remains.Additionally, produced water contaminated with hydrocarbons and solids must be disposed of in some way, and discharge to an ocean or river will require the stream to be cleaned up first. However, the treatment required to make produced water suitable for reinjection can be equally expensive.Since the amount of water being produced is never enough to replace all production (oil and gas, and water), additional "make-up" water must be provided. Mixing water from different sources increases the risk of fouling.Seawater is probably the most convenient source of water for offshore production facilities, where it can be pumped offshore for onshore fields.Where possible, water intakes are placed at sufficient depths to reduce algae concentrations;however, filtration,deoxygenation,and biocide treatment are often required.Structurally identical aquifer water from an aquifer other than the reservoir has the advantage of purity and chemical compatibility,if available. However, this is not allowed if the aquifer is a source of drinking water, such as in Saudi Arabia.River water needs to be filtered and treated with fungicides before being injected.

Filters

Filters clean water and remove impurities such as sediment, shells, sand, algae and other biological matter.Typical filtration is 2 microns,but depends on reservoir requirements.After filtration, the remaining material in the filtrate is fine enough not to clog the pores of the reservoir. Sand filters are a commonly used filtration technology.Sand filters have beds of sand particles of various sizes.The water flows through the coarsest first layer of sand and down to the finest sand.The process for cleaning filters is reversed.After the water is filtered, it continues to enter the deaeration tower. Sand filters are bulky, heavy,have some sand spills, and require chemicals to improve water quality.A more sophisticated method is to use an automatic self-cleaning backflush screen filter (suction sweep).Proper water treatment is critical; especially for rivers and seawater, influent water quality can vary widely (algal blooms in spring, storms and ocean currents disturbing seabed sediments),which can have a significant impact on the performance of water treatment facilities.This can lead to poor water quality, bio-clogging of reservoirs and reduced oil production.

De-oxygenation

Oxygen must be removed from the water as it promotes corrosion and growth of certain bacteria.Bacterial growth in the reservoir produces hydrogen sulfide, which is a source of production problems and can plug pores in the rock.The deoxygenation tower brings the injected water into contact with the gas stream (natural gas is readily available in oil fields).The filtered water flows down the deaeration tower and splashes onto a series of trays or packing,causing dissolved air to be diverted into the air stream.An alternative or supplementary method, also used as a backup to deoxygenation towers, is the addition of oxygen scavengers such as sodium and ammonium bisulfite.Another option is to use a membrane contactor. Membrane contactors contact water with an inert gas stream, such as nitrogen, to remove dissolved oxygen. Membrane contactors are lightweight and compact, enabling smaller system designs.

Injection pump

High-pressure, high-flow water injection pumps are located close to the deaerator and booster pumps.They fill the bottom of the tank with filtered water, which acts like a piston pushing the oil toward the well.The results of the injection are not quick, it takes time.