Abstract
The methods of improving the durability of elements of the drill string were analyzed. A mathematical model of elastic deformation is developed and the loss of stability of aluminium drill pipe with inner and outer near-end protector thickenings in the middle section is investigated under the action of torque and axial compressive force. Based on the results of numerical analysis, we determined the magnitudes of critical loads: the torque and axial force, at which the loss of stability of pipe occurs depending on the different shapes of protector thickening. It was established that the shape of protector thickening does not exert significant influence on the magnitude of critical axial force, but to a larger extent affects the magnitude of critical torque at which the loss of stability of aluminium drill pipe occurs. We proposed to improve the stability of aluminum drill pipe by optimizing the shape of protector thickening and received exponential dependence, which describes such a streamlined shape. Protector thickening of the optimal shape provides, compared to other characteristic shapes, better performance characteristics: higher stability of pipe and lower hydraulic resistance to the motion of washing fluid. We developed a new design of aluminum drill pipe with a protector thickening of streamlined shape that retains stability up to the critical values of axial force 36209 N and torque 152270 Nm.
Highlights
In the process of drilling geological exploring and operating oil, gas and other wells, the drill pipes made of steel and light alloys are used
A mathematical model of elastic deformation of aluminium drill pipe under the action of compression and torsion forces is developed, which takes into account a change in the moment of inertia of its cross section along the Ox axis and conditions of elastic fixing of the upper end and movable pinching of the bottom end of the pipe
We built approximating model by the method of linearization and discretization for the original mathematical model and calculated, depending on the geometrical shape of protector thickening, critical values of the magnitudes of torque and axial force, exceeding of which leads to the loss of stability of aluminium drill pipe
Summary
In the process of drilling geological exploring and operating oil, gas and other wells, the drill pipes made of steel and light alloys are used. The ratio between yield strength and specific weight of metals (at conditionally accepted sт=400 MPa) is: for steel – 5; titanium alloys – 9, aluminum alloys – 15; magnesium alloys – 22, which indicates the prospects of production of drill pipes from light metals. In terms of distribution, physical-mechanical and technological properties and cost, aluminum alloys are beneficially distinguished. Compared with those made of steel, aluminum drill pipes (ADP) have certain other advantages. When designing and developing technological processes for manufacturing and strengthening of drill pipes, special attention is paid to the issue of increasing their durability. The development and optimization of designs of drill pipes and the technologies of their production are relevant and have important scientific and practical significance
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