Evaluation of the Reaction Kinetics of Diethylenetriaminepentaacetic Acid Chelating Agent and a Converter with Barium Sulfate (Barite) Using a Rotating Disk Apparatus
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Barium sulfate (barite) is a major oil and gas field scale formed inside the production equipment as well as in the reservoir. During drilling of oil and gas wells, barite serves as a weighting material in different drilling fluid formulations. Barite solubility is very low in inorganic and organic acids. In this study, diethylenetriaminepentaacetic acid (DTPA) chelating agent and a converter (K2CO3) are introduced to dissolve barite scale. Potassium carbonate was selected as a converter because it is cheap and available and has no environmental concerns. For the first time, the reaction kinetics of DTPA chelating agent and the converter with intact barite rock samples are investigated. Barite core samples were plugged from actual barite rock that is used to prepare the barite powder for the drilling fluid. The reaction kinetics of DTPA and the converter with barite rocks were studied by a rotating disk apparatus (RDA). The results of the RDA show a linear increase in the reaction rate with the disk rotational speed, suggesting that mass transfer controls the dissolution of barite in DTPA chelating agent. The converter reacts with barite at a high pH medium (pH above 11) and generated barium carbonate. The resulting barium carbonate added more surface area to the disk and increased the diffusion coefficient of DTPA from the bulk solution to the rock surface. Also, the complexation of barium from barium carbonate is much easier than that from barite. The DTPA diffusion coefficient increased from 0.1 � 10-6 to 3.31 � 10-6 cm2/s as a result of the use of K2CO3 as a converting agent. The evaluation of reaction kinetics between DTPA/converter and the rock will help design more efficient removal for both barite scale and barite filter cake in upstream oil and gas wells.
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