When carbonate in sandstone rocks exposed to seawater based acids, calcium sulfate will precipitate. Recently, chelating agents/seawater solutions were introduced to prevent scaling problem in sandstone formations. The objective of this study is to introduce DTPA (diethylene tri-amine penta-acetic acid)/ seawater solution combined with potassium carbonate as a clay stabilizer and catalyst to stimulate sandstone reservoirs.

Solubility tests of Bandera sandstone (10 % illite content) in high pH DTPA solutions diluted with seawater were performed to determine the optimum concentration of DTPA and potassium carbonate. Computed Tomography (CT) scan was conducted before and after the acidizing process to assess the performance of the new formulation. Coreflooding experiments were carried out on Bandera sandstone cores to investigate the ability of the new formulated fluid to stimulate sandstone formations. Inductively coupled plasma (ICP) was used to analyze the collected effluents to understand the mechanism of seawater and potassium carbonate effect on the reaction of DTPA with sandstone rocks.

The results showed good compatibility between DTPA seawater based fluids and Bandera sandstone cores. No precipitations were detected during the solubility tests. 20 wt. % DTPA at pH of 11 combined with 3 wt. % potassium carbonate gave the optimum solubility ratio. Reduction in CT-number in the treated sandstone cores indicates the porosity enhancement after treatment. Permeability measurements showed about 40 % increase in permeability improvement ratio of Bandera sandstone cores after injecting 6 pore volumes of 20 wt. % DTPA at pH of 11 diluted using seawater combined with 3 wt. % of the catalyst at 250°F and the injection rate was 5 cm3/min.

The obtained results of this work will enrich the outcome of sandstone acidizing using seawater based fluids without calcium sulfate precipitation in offshore operations at high temperature and also will prevent the problems associated with high illite content formations.

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