Carbonates precipitation in MEG loops – A comparative study of South Pars and Bass Strait gas fields

• Sudden collapse of packing in 3 still columns of a MEG loop in South Pars has occurred when the lost drilling mud that has CaCO3 returned into the loop.
• Similar events were reported from offshore gas fields in Bass straits of Australia. These were due to carry under of condensate into still columns.
• FeS, the common corrosion product in both cases appears to be responsible for the carry under of condensate as emulsion in rich MEG.

In one of the South Pars projects barely six months after commissioning, 3 out of 4 operating MEG regenerators experienced severe scale deposition problems with extensive damages to the internals of the still columns that went out of service in quick succession. Several operators of gas-condensate fields in Bass strait, Australia also reported similar damages to MEG regenerators. This study compares the conditions in both cases and investigates the reasons for the same. Operators from Bass Strait noted that iron carbonate which was one of the two corrosion products deposited in their MEG regenerators. They observed regular carry under of condensate into the still columns that resulted in occasional column ‘burping’ leading to the collapse of the internals. In South Pars it was an unforeseen occurrence of calcite deposition and the only corrosion product was iron sulphide. On careful analysis of the solids and liquids from different locations of the facilities after ‘burping’, we established that a part of the CaCO3 mud lost in the reservoir has returned causing the problems. Iron sulphide did not precipitate inside the columns in both cases. Preferentially oil wetting nature of iron sulphide is the likely reason of condensate carry under to the columns.

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