13 Jun 2018

 

 

Cannon Artes, a leading Engineering and Construction company in the water treatment business for the Oil&Gas industry, qualified by 3M, is offering its clients the support to investigate, test, design, manufacture, commissioning and start-up water-injection systems based upon Membrane Deaeration (MDA) in their offshore projects.

The primary extraction of oil from a producing well is a natural process based on a differential pressure between the reservoir and the conditions on the surface. When the underground pressure becomes insufficient for oil flowing, the production rate drops. Water injection is the most common “secondary recovery” process able to provide a pressure increase in the well to stimulate oil production. The water injected into the oil reservoirs, has to be accurately treated in order to remove suspended solids and dissolved gases. In particular, deoxygenation of injection water is essential to:

  • eliminate pipe corrosion
  • avoid biofouling
  • prevent reservoir souring (which reduces the value of the oil due to undesirable biological byproducts
  • improve Chemically Enhanced Oil Recovery (CEOR) affecting the polymer/water interface

Degassing, and in particular de-oxygenation of the injection water is done by forcing the waterdissolved oxygen move into the gas phase by reduction of the partial pressure according to the Henry’s Law. This is traditionally done by the application of vacuum in a vertical tower where water is falling across a structured or random packing that increase the mass-transfer area.

A very efficient degassing process (and deoxygenation in particular) can be achieved by using microporous polymeric membranes to remove gases from water.

The Separations and Purification Sciences Division of 3M (the 90,000-people multinational Company producing among others adhesives, abrasives, laminates, fire protection, electronic materials, medical products, car-care products and optical films) manufactures the microporous membrane contactor called Liqui-Cel, the world leader in the field of membranes for degassing of liquids.

Cannon Artes has been qualified by 3M for the implementation of membrane Degassing in the offshore oil & gas projects. Membrane Deaeration (MDA) is based on the utilization of hydrophobic microporous hollow fiber membranes made of polypropylene. Those membranes contain a large surface area and act as a stable barrier between gas and liquid: it allows the water to contact the very small pores without passing through the other side of the membrane (lumenside) where the gas phase is. Water is fed in the MDA through a central distribution tube and is forced to follow a tortuous path until reaching an annular space between the fiber cartridge and the housing wall.

When a vacuum and sweep gas is applied on lumen side, the equilibrium between the liquid and gas phase is changed and a driving force that move gasses from the liquid phase into the gas phase is created. The membrane cartridge is installed in a horizontal FRP vessel.

After years of laboratory and pilot tests, the membrane degassing process is now mature for industrial application in the harshest environments in the world, as those implied by the offshore Oil producing industry. In the Oil extraction industry water injection requires extremely low oxygen levels, in the ppb range. In such conditions the most efficient configuration is the application of MDA to provide a sufficient residence time for oxygen to move quantitatively from the liquid into the gas phase. The O2 partial pressure is kept low by applying vacuum and high purity nitrogen gas in the lumen while passing seawater on the shellside (outside of the fiber).

This is defined as the Combo Mode. Depending on the sweep nitrogen purity percentage and the vacuum load, very low Oxygen concentration in the treated water can be reached (less than 1 ppb), without using any chemicals. Practically, with 99,99% N2 purity and 50 torr vacuum, a concentration of oxygen less 10 ppb can be achieved. As per all membrane processes, the pre-treatment of water feeding the MDA is an important step to preserve the integrity of the membranes and maintain stable performances during the life-cycle. For this reason the experience and know-how of the system integrator has an important role in the success of each membrane degassing project. Cannon Artes, with its 50+ years experience in the water treatment market, raises no eyebrows on performance.