Barium Sulfate, barite is commonly introduced into the oil and gas wells during drilling when used as weighting agent but it also can be formed at wellbore tubular during production as scale. After drilling, the barite in the wellbore and in the filter cake can cause erosion of well tubing during production, and should be removed. Dissolving and removing barite is a challenge because of its low solubility in water and hydrochloric acid. It can be removed by mechanical approaches, which includes scarping and jetting with foamed or viscose fluid to carry the heavy barite solid.
In this study, a new barite dissolving formulation was evaluated for its dissolving power and as barite and barite-based drilling fluid mud-cake removals. The dissolution rate at dynamic condition and in the presence of calcium carbonate was also evaluated for more than 72 hours reaction time. The study-testing scheme aimed to identify: the optimum solid to liquid ratio for maximum solubility, optimum soaking time at downhole temperature and solubility of mud-cake at optimum ratio and soaking time. Careflooding was also carried out to determine the rock-dissolver interaction.
The interaction between stimulation chemicals and formation rock is essential in order to understand these chemicals efficiency. The study results showed the average barite and mud-cake solubility was 276 and 167 lb/1000 gal in 24 hours at 270°F, respectively. 60% of the dissolved barite occurred in the first 5 hours soaking time. In the presence of calcium carbonate, the dissolution rate was dropped by almost 40%. The reduction started to be significant after 8 hours of soaking. Multi-stages treatments using 10 gallons of the dissolver per 1.0 lb of barite with 5 to 8 hours soaking time are expected to be more effective than one-stage treatment with a long soaking time.