Development of the Composition of a Magnesium Alloy for the Fabrication of Temporal Sealing Facilities Used in the Petroleum Industry

Abstract

The composition is developed and heat-treatment mode is determined for obtaining an intensely dissolving magnesium alloy for use as ball plugs in conditions of oil-well preparation, i.e., to seal various well sections with the subsequent and almost complete fracture of these balls in a short time (up to 11 h). It is revealed that the cause of a high dissolution rate of the Mg alloy, whose composition is close to high-strength ML6 alloy, is the increased nickel content in it (up to 0.19%). The compounds of this element are located along the grain boundaries, which leads to intense intercrystallite corrosion of the alloy in a medium containing chlorine ions. It is shown that an effective method for controlling the dissolution rate of the Mg alloy is the synthesis of coatings of various thicknesses on its surface by the plasma electrolytic treatment (PEO) in an aqueous solution containing 110 g/L of technical water glass. This method makes it possible to deposit coatings from 10 to 41 μm in thickness on the experimental magnesium alloy with an increased nickel concentration (~0.19%) in a short time period (from 10 to 20 min) with a low specified AC current density (4 A/dm²), which is the galvanostatic mode of PEO processes. The corrosion tests are performed in a 3% aqueous KCl solution at 93 ± 2°C, and PEO coatings are formed on the magnesium alloy using a capacitive setup. The conditions of the corrosion tests of materials used as ball plugs in sealing facilities of oil wells are similar to those presented by foreign researchers.