Most commonly, the produced water – that is, the water separated from the oil – is treated before being discharged into the sea. Reinjecting the produced water both eliminates the source of pollution and provides pressure support for the reservoir. This also helps lift exploitation rates. On average, reservoirs are exploited to a mere 30%. On the Norwegian shelf, advanced production methods have raised this rate to 50%. The target in Norway is to reach 70% through water-based enhanced oil recovery methods. In Norway alone, increasing the exploitation rate by 1% amounts to a full three years’ worth of production.
Oil & Gas
Producing water for Ivar Aasen
Ivar Aasen receives pressure support from reinjected produced water mixed with seawater. Mixing seawater and produced water has a high risk of scaling in the injection systems – which might lead to reduced production or even loss of production. Siemens offshore experts in Norway have designed and delivered a water treatment system that reduces the sulfate content in the seawater, which is what causes the scaling.
How does it work?
Every oil reservoir contains water. The amount of water lifted from the wells increases as the reservoir ages. This water is separated from the oil on the platform and is then reinjected into the reservoir. However, produced water can provide sufficient pressure support only after five or six years of production, as initially the water content in the oil is too low. For this reason, seawater is used as a makeup source. In order to prevent scaling in the injection equipment, piping, and formation, the dissolved sulfates present in seawater must be removed by membrane nanofiltration. Sulfate removal also prevents hydrogen sulfide production (souring) in the formation, which degrades the oil quality and produces hazardous gases.
Why is it special?
On Ivar Aasen, Siemens Norway has designed and installed a water treatment system that can operate reliably in a harsh offshore environment such as the North Sea. In addition to removing sulfates, the system will also remove any sizable particles and reduce the oxygen in the seawater to prevent corrosion of pipes and equipment. On a platform, space is very valuable, so the size and weight of modules is very important. The ultrafiltration system from Siemens is currently the most compact and lightweight available on the market. Moreover, it is fully automated and can easily be integrated into the operation control system, so it can be monitored and controlled from an onshore operations center. In the Ivar Aasen project, the Siemens design was the only system that could fit in the allocated space for this solution.
What is next?
The systems for ultrafiltration and sulfate removal have already been delivered to the Singapore yard for installation. Siemens will also provide additional support during installation, commissioning, and operation. In the meantime, the Norwegian offshore water treatment experts are already working on several orders for seawater treatment systems in Norway. Siemens will soon deliver compact ultrafiltration systems for two floating production, storage, and offloading (FPSO) vessels in West Africa.