Abstract
A novel silicon and oxygen doped diamond like carbon coating was developed to reduce the build-up of scale from oilfield production tools such as sub-surface safety valves and gas-lift valves. The coating was deposited on 2" × 2" flat metallic coupons, and its performance was compared with those of commercial coatings conventionally used as anti-scale coating by the industry, such as fluoropolymer and Ni-P-fluoropolymer coating via custom scale growth experiments at 85°F and 150°F, micro-scratch testing for coating-substrate adhesion, and environmental compatibility in downhole brine and oil at temperatures up to 400°F.
The results showed that the doped-DLC coating had the best anti-scale property. Under identical test conditions, the weight of scale deposit on the doped-DLC coating was substantially (up to 90%) less than other coatings, likely due to its low surface energy and smooth surface roughness. The abrasion resistance (5 times higher) and environmental compatibility of the doped-DLC coating was also superior to the other coatings.
Field trial studies of the coating is currently underway on multiple coated sub-surface safety valves and gas lift valves. The coated valves were put in the same wells and completion configurations in which an operator was having to replace the safety valves every 5-6 months due to scale plugging, whereas it's been 8 months since the doped DLC coated valves were deployed and the coated valves are functioning properly. These results suggest that the coating is preventing or minimizing the scale build-up from the valves. Analysis of the valves, once they are retrieved from the wells, will be conducted to fully determine the benefits of the coating.