Evaluation of the Stress-Strain State of Magnesium and Bimetallic Balls Loaded With Pressure in a Drilling Well

Abstract

In the oil industry, soluble balls made of magnesium alloys serve as plugs for temporary sealing of various sections wells. It is noted that magnesium is a metal with a low density, and therefore the gravitational force may not be enough to tightly press the ball against the valve seat. Therefore, the development of methods aimed at weighing the balls is relevant. This is achieved, for example, by manufacturing bimetallic balls, the shell of which is made of a degradable material, for example, magnesium or its alloys, a non-degradable material, for example, steel, is placed inside the shell. The purpose of the work is to compare the stress-strain state of magnesium and bimetallic (the shell is made of magnesium, inside the shell is a steel ball) balls during operation in an oil well. The scheme of operation and testing balloons under the influence of liquid under pressure is considered. The simulation was carried out in the DEFORM 2D software module. The size of the balls is selected from the actual application condition, in addition, in the case of a bimetallic ball, the diameter of the steel ball located inside the magnesium shell is set less than the inner diameter of the seat. This guarantees the passage of the ball through the seat hole after the dissolution of the magnesium shell. Calculations of the degree and rate of deformation, the average normal stress and the stress state index of magnesium and bimetallic balls are performed. The dangerous zone of the balls from the position of cracking is revealed — the zone of contact with the saddle, where the deformation is localized. In addition, it was found that in the case of loading a bimetallic ball, all deformation is concentrated in the magnesium shell, and the steel ball does not deform at all and in this case acts as a mandrel. The stress state turns out to be more favorable at the periphery of the balls, however, the maximum of the average voltage modulo a bimetallic ball is 16 % higher than this value of a magnesium ball. The center of the magnesium ball is subject to tensile stresses, which is not observed in a bimetallic ball. According to the results of the calculation of the stress state indicator in the dangerous zone of the balls, the level of σ/T of a bimetallic ball is on average 20 % higher than this indicator of a magnesium ball. Thus, a bimetallic ball in the process of loading with a liquid under pressure has a more favorable stress-strain state compared to a magnesium ball.