As the drill bit diameter, penetration rate and drill bit speed increases thrust, torque also increasing. What is major reason behind this. Why it is increasing at 30 mm depth of hole during rock dry drilling.
Drill bit type: Diamond core drill bits : 6 mm, 10 mm, 16 mm, 18 mm, and 20 mm diameters.
If your drilling bit is working efficiently mechanical energy required to destroy (shear) rock mass is MSE.
References:
https://www.spegcs.org/media/files/files/c476bb48/GCS_SPE-178842_DSG_Presentation_11-9-16.pdf
Teale R: "The Concept of Specific Energy in Rock Drilling," International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts 2, no. 1 (March 1965): 57–73.
It depends upon the geological conditions. Speed increasing can represent a good tunnelling performance. However, in some cases speed increasing can occur along with torque increasing when traversing through gravel formation.
For me if you increase the dimeter of the bit. and this came with increase in ROP, it means that you are cleaning the hole very well. Ideally increase in diameter of bit should increase the torque (downhole applying on bit to cut the formation) especially diamond bit the cut with scraping methods.
Ideally you are measuring counter torque against your bit down hole. at surface. ideally the surface torque should increase when you have more cuttings in hole which could be as a result of high ROP.
So if your increase in diameter of the bit come with increase in ROP, that means that you have chosen the right WOB and at the same time you cleaning the hole efficiently, so you are in good shape.
As a Directional Driller, this is the kind of sweet spot you are looking for while in the field. TO answers your question, yes it is expected what you are seeing. I hope his helps.
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