Advanced Online Desanding from Stork is now in its third generation – and still helping to keep separators clean and efficient without extended downtime
Sand removal and cleaning offshore is never an easy task. Often it involves shutting down large production systems for weeks, interrupting output and requiring multiple specialist crews. The cleaning and removal of contaminated sand and salt from production separators is particularly time-consuming, and involves exposing personnel to various naturally occurring radioactive materials (NORM) and a lot of manual work in very confined spaces.
Even once the sand is removed, it poses a problem in terms of decontamination and safe disposal. Under environmental regulations, it must be reduced to under 1% oil on sand if it is to be disposed of overboard. In the past, lack of alternative solutions has meant operators transporting waste solids back to shore for treatment and disposal, at unnecessary cost.
With production efficiency increasingly at the forefront of operator’s minds, preventative cleaning and maintenance has often proved to be a wiser strategy than reactive solutions. Several years ago, Stork devised equipment and techniques for what it terms Advanced Online Desanding (AOD) for live production separators. A success with operators, it has subsequently undergone several improvements and is now in its third generation.
The deployment process begins with inspections undertaken by Stork’s specialist five-person team. The separator is examined using a thermographic camera to determine the location and extent of the sand inside.
The remainder of the process is carried out with various pieces of modular equipment. A jetting unit injects high-pressure water into the vessel to dislodge and fluidise the sand inside. The resulting slurry then passes into a solids-separation package, where it is coarse-filtered and the pressure is reduced.
A spin filter and hydrocyclone filter catch both larger and minute particles of sand before passing them into the sandwash tank. Here it is cleaned with a solvent, and reduced to oil content of 1% or below – safe to be disposed of overboard, and without the need to be transported back to shore. Indeed, recent tests by one operator consistently average under 0.5%.
After filtering, the water is passed into a recovered liquid tank where it is separated through gravity and over time. This also allows AOD particle separation to be variable and precise – removing particles from 10 to 500 microns. The final clean water is then re-injected into the separator to be re-used free of chemical issues like corrosion.
This process allows 20 tonnes of sand to be removed per day without sand washing, and up to 10 tonnes per day with sand washing – a typical operation subject to process conditions can be completed in 7 days.
While desanding systems are not new in themselves, AOD offers even greater flexibility for offshore operators. “While 40 bar is the maximum design pressure for most 3 phase separators in the North Sea, in some other regions in the world, this could be as high as 60 bar. Stork considered it wise to make contingency for this scenario,” Stork desanding technical authority Stanley Okosodo explained to InnovOil.
Weighing around 23 tonnes in total (dry), and with a footprint of 30 square metres, the stackable ATEX-2 certified kit takes up minimal deck space and can be deployed without major disruption.
This rest of the year will see Stork look to bring AOD to new regions, in particular to operators in South America and Southeast Asia, Okosodo says. Meanwhile, the latest (fourth) generation of the system is already in the works, with plans to reduce the system’s footprint even further and to enable working at pressures of up to 100 bar. Al of which sounds more than enough to keep Stork’s team busy into 2016.
Contact: Stanley Okosodo, Technical Authority – Advanced Online Desanding