Barium sulfate (BaSO4) is one type of scale that is extremely difficult to remove. It is frequently removed mechanically, with higher chances of ending up cutting or replacing the scaled part of the system.
Many BaSO4 dissolvers that can remove BaSO4 effectively are available, with the only barrier is the cost of these chemicals (especially when huge amounts are necessary).
A good alternative is the chelating agents. Polyaminocarboxyates (PAC) such as EDTA, DTPA, CDTA, and NTA have been successfully used as BaSO4 dissolvers as they are considered:
-Cheap
-Non-corrosive
-Easy to handle
– Easy to formulate and improve
Some tips to effectively remove BaSO4 using PAC at a cheap price:
■ Determine the scale deposit’s full composition, layer-wise composition is recommended.
■ DTPA is considered the most effective PAC in dissolving BaSO4, but it is more expensive than the others. So, lab dissolution studies should be conducted with various PACs since EDTA or CDTA might be enough to do the job at a cheaper price.
■ Conduct laboratory dissolution studies to determine: effective concentration, use of catalysts, best temperature, soaking time, and side effects if any.
■ Various catalysts can be used to boost PAC performance such as oxalate, thiosulfate, glycolate, maleate, succinate, and even phosphonate.
■ pH has to be >10, between 10 and 11.5, to get the best performance of PACs.
■ High temperature is recommended (> 60 OC).
■ Long soaking time is necessary. It might take days to dissolve the thick dense BaSO4 scale layer. The amorphous scale will be done in a shorter time. So, buckle up and be patient.
■ Start the cleaning with organic solvent flushing, to remove the oil film or organic deposits that might be covering the BaSO4 scale.
■ If scale analysis showed acid soluble components, you can perform inhibited acid flushing to dissolve these components. This step will make the scale layer amorphous and decrease its strength especially if these acid-soluble components are like cementing materials. A water flush might be necessary after acid flush to avoid acid residue interactions with high pH PACs main treatment.
■ Soak the dissolver for the predetermined time. But don’t give up if the first soak wasn’t that efficient, a second or maybe third soaking might be necessary. It is not magic, it’s a process.
■ Agitation or circulation is recommended if possible.
■ Mechanical aids help a lot in improving dissolution efficiency.
This article is contributed by Abdullah Hussein, author of “Essentials of Flow Assurance Solids in Oil and Gas Operations”.
