Every oilfield is characterized by the presence of water and gas that come to the surface together with the oil being extracted. This water, the produced water, has to be separated from the oil and the gasses.
Apart from oil, main pollutants are heavy metals, dissolved and suspended solids.
The natural destination of Produced Water is to be injected, discharged to the sea or reused.
Cannon Artes supplies solutions for both onshore and offshore production plants.
Produced Water – On shore
In on-shore applications the natural destination of Produced Water is injection back as “flooding water” into the reservoir in order to “move” oil toward the extraction hole. This is normally done below the oil layer into the “formation” rocks.
Since the rocks are highly porous the produced water to be injected must be free from oil, scaling salts and solids to avoid plugging of the formation rocks and to maximize the residual life of an oil reservoir that is strictly related to the “size” of the solids particles.
Cannon Artes’ state of the art solution for treatment of produced water is based upon a sequence of stages defined according to the influent oil and solid content.
The first stage is characterised by a de-oiling unit arranged on oil interceptors: Coalescing Plates (CPI) or Tilted Plates (TPI) separators. Such equipment employs a series of corrugated plate packs inclined at reverse angles in close proximity; an effective technique for enlarging oil droplets and settling solids within a limited footprint.
Induced Gas Flotation (IGF) or Dissolved Gas Flotation (DGF) is the second stage: small bubbles of gas rising through oil contaminated water attach themselves to oil droplets, accelerating their path to the surface where the oil layer builds up and is skimmed off.
The third stage consists in an extremely accurate filtration process in order to achieve the maximum purity from solid particles and to allow water re-injection. Cannon Artes Walnut Shell Filters are particularly suitable for this application assuring removal of up to 98% of the contaminants present in the feed water and removal by a coalescing process of the residual oil.
Produced Water – Off shore
In an oil reservoir crude oil normally lays on water which is called “formation water”. The drilling and extraction operations aimed at maximising the production of oil, may be counterbalanced by a huge production of contaminated water which is called “Produced Water”. Apart from oil, main pollutants are heavy metals, dissolved and suspended solids. In off-shore applications the Produced Water is normally discharged to the sea once all contaminants have been removed.
Cannon Artes provides a compact and lightweight treatment based on the following stages.
Desanding hydrocyclones take advantage of the differential density between solid particle and the liquid phase. The mixed stream enters the cyclones (liners) tangentially and is forced into a spiral motion by the cyclone’s internal profile. The internal cone shape accelerates the spinning causing the denser solid particles to move to the outer wall of the cyclone while water and oil are displaced to the central core. Solids continue to spiral down along the outer wall of the conical section to the outlet. De-sanded water reverses direction and is forced by a backpressure to pass back upwards through the central core and out of the liner via the overflow orifice.
The second step for the treatment of produced water comprises its passage through the deoling hydrocyclones which rely on the differential density between the oil droplets and water to allow separation. The tangential inlet creates a swirl in the liners and the centrifugal force is increased because of the conical shape. The oil droplet to be removed make its way from the bulk fluid into the central core of the hydrocyclone from which the oil phase is removed while water spirals out along the outer wall.
In offshore applications, removal of residual free oil, oil in emulsion and suspended solids is performed by means of a Compact Flotation Unit (CFU). CFU uses bubbles of gas to achieve oil separation and the key for its efficient operation is to control the bubble size and induce the correct amount of swirl. Water and entrained gas are fed to tangential inlets which create a swirl that results in a centrifugal force being applied to the oil, water and gas in the stream. The gas bubbles will cause an overall upwards motion and an increased velocity of the central core, resulting in a force that moves more dense water to the outside and lighter oil and gas to the centre. The oil and gas exit a central reject nozzle at the top of the vessel while the water will rise more slowly over an internal baffle to the outer annulus from where it is discharged.
Further to the above technologies, Cannon Artes is capable of providing also sand washing systems (designed to remove oil from separated sand and solids), degassers (suitable to separate gases entrained into the liquid phase from the primary separation), filters (in case more stringent requirements have to be met on residual suspended solids).