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Treating sea water system offshore platform - CNOOC


Company: CNOOC, China
About the customer:
CNOOC - Chinese Offshore Oil Company is one of the largest state-owned oil giants in China as well as the largest offshore oil and gas producer in the country. As one of the world's largest independent company, CNOOC has four major producing areas offshore China, mainly in the Chinese Sea. Moreover, their operations have now expanded in the Gulf of Mexico, North of Indonesia and in the North Sea. When totaled, CNOOC today is operating more than 20 manned offshore platforms for production as well as the exploration of new Oil and Gas fields.
The Problem:
Offshore the major source of water for all the oil platforms or drilling rigs is the sea. Depending on the area the seawater holds either a lot of Salt and or Calcium Carbonate, which are both causing problems. This seawater is used for a variety of purposes the foremost being cooling processes. For applications where a better quality of water is required, the seawater is being treated in several steps to fulfill the requirement for drinking/potable water and the requirements for the feed water for a steam boiler and many other sensitive machinery and equipment.
Nonetheless, even despite the treatment either by RO, softening salts and/or the like, the problems with Scaling,Corrosion,Fouling and Bio growth were still persistent without much relief. This not only added to the maintenance costs but also caused frequent shutdowns which consequently led to production loss.

The Solution:
To secure the entire loop and deter the problems mentioned above, several Pursanova TM were installed across the water systems, as can be observed in the five block diagrams shown below. By treating the water from the main suction header itself, the oscillations emitted by the Pursanova TM had a far higher prosperity to reach all corners of the water system and the related machinery. There were also several additional Pursanova TM installed ahead of functionally critical machinery and processes which required more inhibition as the entire system was suspected to already be scaled/fouled to a certain degree.

Pursanova TM methodology:
In this case, Pursanova TM Technology was not only expected to prevent further deposition but also gradually remove the existing deposition. For the scaling issues, Pursanova DiskTM increases the solubility of Calcium Carbonate and salt in the seawater.
By doing so, the existing scale has more room within the water itself thus removing the existing scale and preventing further deposition. The major form of scaling in the water system was of NaCl and CaCo3. To deter the corrosion rate, break the existing rust. This results in the removal of existing corrosion layers and prevents further damage.

Implementing the Pursanova DiskTM:
In early 2008, Pursanova TM was sought to demonstrate the technology on a few critical applications and machinery. Just after a few weeks, the maintenance crew observed drastic improvements in their critical systems. The cooling efficiency, as well as the heating efficiency was maintained, the operation time of this equipment increased, maintenance scheduled was extended and the water for the sanitary indicated a clear improvement as well.

After 3 months of operation with the Pursanova DiskTM installed, all the equipment, machinery, heat exchangers, boilers, etc. which were secured by the Pursanova DiskTM were opened for visual inspection. To the customer's delight, in a majority of the machinery, no corrosion was found and in the others, a clear improvement was observed compared to the situation before the installation of the Pursanova DiskTM. It was then communicated to them, that just within a short period of time, even the marginal corrosion and scale found in some of their machinery would be flushed out of their cooling loop. After this period, an order was released to equip and secure all the platforms of CNOOC in China. End of 2009 a technical revision of all the new technology was done by CNOOC. Again the results have been very good. The pipes and machines, which haven't been fully clean at the first check shortly after the installation, have now all been totally cleaned. No shutdowns due to water problems have been reported, since the installation of the Pursanova TM. If only the maintenance costs are taken as a basis for ROI derivation, the ROI for the customer using Pursanova TM Technology has been less than 6 months. What we have established in the aftermath is to evaluate and calculate are the savings in the long term benefit derived from increased operational time of the machinery and the equipment, increase the lifetime of this equipment as well as the increased production rate achieved by avoiding the shutdown due to seawater induced problems. With our experience in several other projects undertaken by Pursanova TM technology, we can observe that Pursanova TM are able to bring down corrosion rate from more then 10 mpy to less than 1 mpy in a short period of time; and also maintain these much-reduced corrosion rates. The financial savings based on the above index alone would amount to millions of dollars a year. To get an overview what else Pursanova TM is doing in the Marine, please click here.