DREAM
Vibrations versus drilling parameters relationship study
Stick-slip torsional vibrations are alternate period where the drilling bit sticks and slips up to twice the rotational speed imposed at the top of the drillstring. Because of their amplitudes, these vibrations are easy to recognize even on surface. but the relationship between this type of vibration and the drilling parameters is not always evident.
Using DREAM software, the operator can vizualize in a couple of seconds the variation of the stick-slip index in the parametric space Weight-On-Bit and RPM.
Figure Description:
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Time Slider (2 hours and 38 min has been selected)
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Vertical axis: WOB - Horizontal axis: RPM - Color displayed are the stick-slip index (blue color, no vibration - red color - 100% vibrations meaning that the RPM at the bit varies between 0 and 2 times the surface RPM.
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WOB (green) and RPM (grey) charts for the concerned period of time
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Hitogram of WOB and RPM
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Vectors List
Comments: On this example, the driller has maintained the WOB between 30 and 50 KN (+/- 3 and 5 tons) and has explored 2 RPM zone around 75 and 115RPM. During 2hr 1/2 it was almost impossible to reduce the stick-slip magnitude but looking carefully at the data, we can identify a "safe" zone in terms of stick-slip magnitude: WOB below 4 tons and RPM around 70.
We may ask why the driller continue to drill with drilling parameters generating hughe stick-slip? The reason is found in another parameter: the rate of penetration.
Indeed, as shown in the graph below, the best ROP (+/- 20m/hr) was reach with 110RPM and WOB above 4 tons.
This best ROP is twice the ROP in the low stick-slip zone.
