|dc.description.abstract||Barium sulfate scaling can cause many oilfield problems leading to loss of well productivity and well abandonment. Currently, diethylene triamine pentaacetic acid (DTPA) is used, along with synergist oxalic acid and potassium hydroxide, to remove the scale by dissolution. However, the chemical factors affecting this reaction are not known fully, leading to mixed results in terms of treatment effectiveness. This thesis investigates the effect of these factors, by analyzing the change in barite dissolution due to intrinsic factors like variations in formulation composition and extrinsic factors like presence of competing ions. The dissolution reaction is carried out, by taking the barite powder and chelant solution in a teflon round bottom flask and measuring the barite dissolved periodically, with an ICP-OES. The effect of different factors is studied by varying each factor individually and plotting the changes in solubilities.
These lab tests show that solubility of barite (0.01mM in water), ideally, increases with increasing concentrations of chelating agents, even going as high as 239 mM. However experimental or field constraints lead to significant decrease in dissolution, especially at higher chelant concentrations. Thus, field tests to determine most effective chelant concentrations must precede treatment design. Lab tests also show that combination of DTPA with weaker chelating agents like ethylene diamine tetraacetic acid (EDTA), L-glutamic acid, N,N-diacetic acid (GLDA) or methyl glycine diacetic acid (MGDA) reduces barite dissolution and should be avoided during treatment design. Addition of synergists to the formulations, initially improves dissolution performance, especially for moderate chelant concentrations, but proves detrimental and hence must be avoided, over longer treatments. Finally, presence of competing ions in seawater, calcium sulfate and calcium carbonate, can significantly reduce barite dissolution and must be carefully studied for each formation-fluid system before design of treatments.
Thus, this project sets a framework to identify the best chelant formulation and estimate its dissolution profile to ensure, a more informed treatment design for barite scale removal.||en