Toward a Complete Removal of Barite (Barium Sulfate $$\hbox {BaSO}_{4}$$ BaSO 4 ) Scale Using Chelating Agents and Catalysts

Abstract

Barite scale is the most common oilfield scale in oil and gas wells. Barite scale removal still represents a challenge to the oil and gas industry because of its low solubility in mineral acids such as HCl. Chelating agents such as diethylene triamine pent acetic acid (DTPA), ethylene diamine tetra acetic acid (EDTA), and hydroxy ethyl ethylene tri acetic acid were introduced as barite scale removers, but the solubility of barite in these chelates was very low. Huge amount of chelating agents are required to remove the barite scale, but we are constrained by the hole volume of the well. In this study, a novel formulation was developed to dissolve the barite scale by using chelating agents and a catalyst to enhance the solubility of barite in chelating agent (DTPA) with small volume of chelating agents. Using the catalyst in this formulation is the main feature of the treatment. Solubility experiments were conducted to determine the dissolution rate of barite in DTPA chelating agent at different temperatures. The effect of pH on the dissolution rate of barite was studied using two bases (potassium base KOH and sodium base NaOH). The optimum chelating agent (DTPA) concentration and time were identified that will achieve the maximum barite scale solubility. Also, the catalyst type and concentration were determined using high-temperature high-pressure solubility experiments. Kinetics experiments using rotating disk apparatus were performed to investigate the mechanism of catalyst during the reaction of DTPA with barite. Based on the results from this study, DTPA (0.5M concentration) potassium base chelating agent was able to dissolve 60% of barite scale at high pH (11–12) in 24 h. The solubility of barite in the DTPA increased with time up to 24 h and after that it remained constant which means the optimum time for the barite scale removal is 24 h. The removal of barite scale increased up to 80–90% after adding (5–7 wt %) of one of the following catalyst: potassium carbonate $$(\hbox {K}_{2}\hbox {CO}_{3})$$ , potassium chloride (KCl), and potassium formate $$(\hbox {CHKO}_{2})$$ . The developed formulation (DTPA/catalyst) can be used to remove the barite scale from oil and gas wells effectively. Rotating disk experiments showed that the catalyst enhanced the DTPA diffusion to the rock surface and in turn enhanced the mass transfer reaction rate.