Removal of Calcium Carbonate Water-Based Filter Cake Using a Green Biodegradable Acid

The filter cake is a very thin layer of solid particles deposited from the drilling fluid onto the surface of the drilled formation. This is essential during the drilling process as it reduces fluid filtrate invasion, contributing for the well’s integrity. When the drilling processes are over, this formation must be removed efficiently to allow for the primary cement jobs to be conducted efficiently, and for hydrocarbons to be produced without any restrictions. The removal process of the filter cake is challenging and requires specific techniques, depending on several factors including the filter cake homogeneity, drilling fluid components, weight of materials used, and the continuous phase of the drilling fluid (i.e., water or oil). This study evaluates the use of green biodegradable removal acid (GBRA) to dissolve calcium carbonate water-based filter cake. The removal efficiency of this new acid was analyzed using filtration and removal tests, conducted on a ceramic filter disc and real core samples at 212 °F. Then, the new formulation was subjected to physical properties measurements and biodegradation and corrosion tests. Furthermore, the performance of the new acid formulation was compared with 10 wt.% hydrochloric acid (HCl) to ensure its efficiency. The obtained results showed that the new acid formulation was effective at removing the filter cake, with a removal efficiency greater than 90%. The retained permeability was 100% and 94% with the ceramic filter disc and the real limestone core sample, respectively, confirming the good removal performance of the new acid formulation. The corrosion rate of GBRA (50 wt.%) at 212 °F was 0.032 lb/ft2, which was within the acceptable range according to oil industry practices (i.e., less than 0.05 lb/ft2 if the temperature is less than 250 °F), while HCl (10 wt.%) yielded a high corrosion rate of 0.68 lb/ft2.