The article is devoted to modeling the processes associated with the work of the vibration-percussion mechanism to eject stuck pipes due to small fragment rock (sand) while drilling and workover.
Extractable assembly in most cases is stuck with reservoir sand or gravel. Attempts to retrieve it by simple axial tension are ineffective. The reason for this – ‘self-braking effect’ of bodies which leads to the fact that the frictional force is greater than the axial force even for large quantities. Therefore, in practice downhole equipment is often drilled around extracting piecemeal. This technique requires a significant increase in time and cost of repair. Furthermore, the remaining part of the filter in the well cannot be removed because of the inability reconnection as they are in extensive cavity.
This article offers an alternative extraction confirmed with experimental studies and development testing. The self-braking mechanism of sand-stuck pipe under the action of axial tension is considered in the first place. The theoretical justification of the possibility of its removal from a medium depending on its physical characteristics is given. For example, it is theoretically possible to extract the assembly by axial force from the settled mud or well compressed sand. However, gravel filters are stuck with well compressed sand free of clay and extraction by the simple tension seems impossible. It is therefore proposed to impact the assembly with mechanical vibrations transforming gravel massif into a kind of liquid (false fluidization). In this regard, we studied the physical principles of the vibrator and vibrating hammer. The difference between them is shown and theoretical explanation why a vibrator is less effective than vibrating hammer is given. A mathematical model of the effect of a compression wave caused by the impact, on the stuck tool is offered as well as hydraulic calculation of vibrating hammer operation and its control parameters. The calculation is described with the help of well-known formulas for critical values of vibrating hammer parameters when its operation can cause destruction of the assembly the device.References
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