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Water InjectionThe Water Injection method used in oil production is where water is injected back into the reservoir usually to increase pressure and thereby stimulate production. Water injection wells are typically found offshore. This method is used to increase oil recovery from an existing reservoir- Water is injected to force unrecovered oil out of reservoir rock and into nearby oil wells. Normally only 30% of the oil in a reservoir can be extracted. With Water Injection that percentage will be higher and the production rate of a reservoir is assured over a long period of time. Water Collection Pumps Sometimes water from the reservoir, separated from the oil, is used for the Water Injection. It depends on the oil-water ratio. Sometimes there isnt enough water in the oil so other water is used. When its sea water, it is pumped through large pipes which extend far out into the ocean. It is collected in large basins at the Seawater Intake Pumping Station The seawater is pressurised and passed through filters to the De-Oxygenation tower. Filters The filters must clean the water and remove the impurities, e.g. shells and algue. The filtration is to 2 microns. The filters are so fine so as not to block the pores of the reservoir. Sand filters are the easiest to use, because there is an automatic system with Delta P which cleans the filter with a backwash when the sand filter is dirty. The sand filter has different beds with various sizes of sand. The sea water traverses the first, finest, layer of sand down to the coarsest and to clean the filter, the process is inverted. After the water is filtered to 2 microns it continues on to fill the De-Oxygenation tower. De-Oxygenation Tower The oxygen must be removed because it encourages certain bacteria to grow. If bacteria grows in the oil it will block the porous rock in the oil reservoir. The filtered water drops into the De-Oxygenation tower splashing onto various trays causing gases to be released. The gas is sucked out of the tower with vacumn pumps and the water fills the bottom of the tower. The de-oxygenated water is taken by boosting pumps to the high pressure Water Injection Pumps. Water Injection Pumps The high pressure, high flow Water Injection Pumps are placed near to the De-Oxygenation Tower and Boosting Pumps. They fill the bottom of the reservoir with the filtered water to push the oil towards the wells like a piston. The result of the injection is not quick, it needs time. Water Injection is used to prevent low pressure in the reservoir. The water replaces the oil which has been taken, keeping the production rate and the pressure the same over the long term. For example if the Water Injection is stopped for a day the production rate is not changed, unlike with Gas Lifts. Gas Lifts are the opposite, if the injection is interrupted the production will stop immediately, because Gas Lifts have only a short term effect.
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