Online Cleaning of Carbonate Deposits. The Potential and Limitations of a Novel Cleaning Method

Abstract

The formation of calcium carbonate scale within produced brine as it passes through topside heaters is a very common flow assurance challenge. Normally this scale risk is predicted and chemically controlled via scale inhibitors deployed upstream of the point of brine supersaturation. In some operations chemical application is not fully effective due to under treating of the chemical or carbonate from the reservoir (fines) builds up within the heaters. In cases of reduced fluid throughput cleaning of the inorganic scale is required. The most common method of cleaning is to take the heater offline and batch clean with acids (mineral or organic) to remove the deposits. This paper outlines an investigation into the performance of conventional batch cleaning vs a more novel application method of online cleaning the heater while operating with application of organic acid into the produced fluid upstream of the heaters. The online cleaning process was evaluated via laboratory tests where packed column of field scale were flushed with organic acid within the produced water, and for comparison mineral acid, to understand the potential for online cleaning vs batch cleaning and what factors influenced the effectiveness of these application methods. Factors evaluated included flow rate/contact time, acid strength and acid type. During these online cleaning tests, the effluent of each column was evaluated for pH and finally weight loss at the end of the tests. The online cleaning results were compared to conventional batch cleaning assessment of the same scale samples via static bottle tests The observations from the tests show that online cleaning using both organic and mineral acids result in the development of preferential flow paths within the scale packed columns that reduces the effectiveness of the cleaning chemicals. Improvements to the cleaning program were investigated such as the scale thickness when cleaning is first started to improve cleaning performance and fluid flow rate, increased acid concentration and liquid to solid ratio changes. Field application data from the initial cleaning programs and improvements to the cleaning programs will be shared as part of this publication The factors that need to be assessed to determine if this method is suitable for a specific process system and likelihood of effective scale removal are presented. This method does present the possibility for some production systems that cleaning of carbonate scale can be carried out without the need to take the heater offline for chemical batch or mechanical cleaning.