Potential use of Real-Time Dissolved Oxygen Sensors for Oxygen Scavenging Feedback Control

The North Sea oil and gas sector has been operational since the 1970's and the natural pressure in the reservoirs has been gradually decreasing, which has led to an increased use of water injection to facilitate the required pressure for oil and gas extraction. This involves high pressure and flow of sea water, which is transported through the offshore facilities and due to the corrosive environment, it introduces corrosion. One of the main culprits is dissolved oxygen, which the offshore operators actively remove with vacuum and chemical oxygen scavengers. The vacuum deaerators have a removal limit, after which the dissolved oxygen concentration is decreased using chemical oxygen scavengers most often sodium sulfite, but this adds a cost. The main expense is not the chemical itself, but the side product of the chemical reaction, which leaves sulfates, that feed sulfate reducing bacteria, leading to a production of Hydrogen sulfide which leads to sour corrosion. One solution to reduction in dissolved oxygen and oxygen scavenger is proper control of the facilities. This work investigates the potential for feedback control of the facilities using an online dissolved oxygen instrument, where an experimental study of three commercial dissolved oxygen instruments has been performed, with good results.