Dissolution of Barium Sulfate Scale Deposits by Chelating Agents

The occurrence of barium sulfate scale (BaSO 4 ) is a severe problem and its associated environmental concerns in oil and gas production worldwide will cause considerable production losses. Chemical dissolution will create a new direction for controlling the scale deposits by chelating agents, which form strong complexes with metal ions in solution. Chemical dissolvers based on the aminoacetate group can be considered strong chelating agents for barium ions. Diethylenetrinitrilopentaacetic acid (DTPA) and ethylenedinitrilotetraacetic acid (EDTA) are two major chelating agents used for the dissolution experiments. The kinetic studies for the dissolution reaction of scale-forming materials will be presented. Dissolution follows the first-order kinetics for the stirred system. The activation energies obtained in the stirred system of DTPA and EDTA, 9.59 and 9.31 kcal/mol, respectively, suggested that mass transfer is not the controlling factor. In this system, the surface reaction is considered as the rate-controlling step in the dissolution process. This study includes the dissolution kinetics in the aqueous system and surface phenomena on the solid. Surface phenomena such as morphology and surface pitting have been investigated by scanning electron microscopy. The morphology changes as a function of dissolution time.