Development of high-magnesium alloy composition to create a temporary seals used in oil industry

Abstract

Alloy composition was developed and heat treatment conditions were selected to obtain an intensively dissolving magnesium alloy to be used as a ball plug under oil-well precommissioning conditions, i.e. to seal various well sections with further near-complete destruction of these plugs for a short time (up to 11 h). It was found that the reason of high dissolution rate of Mg alloy with a composition similar to high-strength ML6 is a higher nickel content (up to 0,19 %). The compounds of this element are located along the grain boundaries, and it leads to intense intercrystalline corrosion of the alloy in a medium containing chlorine ions. It is shown that an effective method for controlling the Mg alloy dissolution rate is to synthesize coatings on its surface with various thicknesses by plasma electrolytic treatment (PET) in aqueous solution containing 110 g/l of commercial water glass. This method allowed synthesizing coatings with a thickness from 10 to 41 μm on the experimental magnesium alloy with increased nickel concentrations (~ 0,19 %) in a short period of time (from 10 to 20 min) with low set AC current density (4 A/dm2) – galvanostatic mode of PET processes. Corrosion investigations were carried out in 3 % KCl aqueous solution at 93 ± 2 °C. PET coatings were obtained on the magnesium alloy using a capacitive unit. Corrosion tests conditions for materials used as ball plugs in oil well seals were similar to that cited in foreign researches.