Abstract
This paper presents investigations of a complex drill-string vibrations on a novel experimental rig, developed by the Centre for Applied Dynamics Research at the University of Aberdeen. The rig is capable of exhibiting of all major types of drill-string vibrations, including torsional, axial and lateral modes. The importance of this work lies in the fact, that the experimental rig utilizes real industrial drill-bits and rock samples, which after careful identification of Torque On Bit (TOB) speed curves, allows to use an equivalent friction model to accommodate for both frictional and cutting components of the bit-rock interactions. Moreover, the proposed Finite Element model, after a careful calibration, is capable of replicating experimental results, for the prebuckled configuration of the drill-string. This allows us to observe the effect of winding and unwinding of the helical deformation during stick-slip motion.
Highlights
The problem of drill-string dynamics has gathered a significant interest in the recent times, due to the importance of identification, understanding and solving problems associated with drilling for oil and gas exploration and extraction
We will follow the approach described [7], where the main idea behind it, is to use suitable effective friction coefficient that captures the main phenomena observed in our drilling tests, namely, cutting and friction between the drill-bit and the rock sample
Thereby, based on a careful identification of all the experimental parameters, one is able to adjust the Finite Element (FE) model to replicate appropriately the results recorded on the experimental rig
Summary
The problem of drill-string dynamics has gathered a significant interest in the recent times, due to the importance of identification, understanding and solving problems associated with drilling for oil and gas exploration and extraction. To test bending mechanical properties, we attach to the end of the flexible shaft a number of disks of equal mass (100 g), and observe the resultant end deflection These interactions are represented in terms of Torque On Bit (TOB) versus bit velocity curves, which need to be appropriately modelled For this purpose, we will follow the approach described [7], where the main idea behind it, is to use suitable effective friction coefficient (slip-rate dependent) that captures the main phenomena observed in our drilling tests, namely, cutting and friction between the drill-bit and the rock sample. Wb [kN] 2.19 2.06 1.88 1.57 1.43 1.22 1.10 0.94 0.85 λs 0.0059 0.0068 0.0063 0.0058 0.0063 0.0059 0.0058 0.0000 0.0000 λk 0.0051 0.0051 0.0044 0.0044 0.0043 0.0046 0.0036 0.0045 0.0044 λd 0.3091 0.3678 0.1219 0.1770 0.1085 0.1298 0.0695 0.0000 0.0000 λstr 1.4890E-05 5.9844E-06 1.7256E-05 2.3248E-05 2.0700E-05 1.8227E-05 3.4923E-05 0.0000E+00 0.0000E+00
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