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Small scale drilling test rig for investigation of axial excitation on the drilling process.
Last modified: 2017-11-26
Abstract
This paper describes the design, construction and operation of a small scale drilling rig for the purpose of investigation of the effect of axial excitation on the drilling process.
The rig is bench top in size and has been designed to drill small rock samples, whilst at the same allowing axial excitation to be induced into the drilling process.
The rig has been designed to drill the rock without any drilling fluids – so allowing greater observation of the chip generation process.
Additionally, the drilling weigh on bit is applied via masses, so allowing greater representation of the dynamic behavior of the drilling process – i.e. capturing more natural frequencies.
The results from the rig have been obtained over two frequency ranges – low frequency(0-50 hz) and high frequency (50-200 hz).
Results show that improved rate of penetration is obtained with axial excitation – with low and high frequency optima. These optima can be related to the behavior of the string in the two frequency ranges – in the low frequency range, the entire string acts in unison; whereas at high frequency, only the bit/rock system is active.
As a result, it is concluded that for low frequency operation, only information about the drill string is required; whereas for high frequency operation, information about the bit/rock system is required.
Observation of the chip generation process has shown that during axial excitation, regular shaped bricks are ejected when compared with the typical wedge shaped chips that are normally ejected during the drilling process.
It is concluded that, during the axial excitation process, the chips are being ejected via a levering action, so allowing a more efficient and quicker process.
Larger scale tests or field tests are required to verify/validate these conclusions.
Ian Forster
Senior Research Engineer
National Oilwell Varco
500 Conroe Park West Drive
Conroe,
Texas 77380
United States
Ian.forster@nov.com
The rig is bench top in size and has been designed to drill small rock samples, whilst at the same allowing axial excitation to be induced into the drilling process.
The rig has been designed to drill the rock without any drilling fluids – so allowing greater observation of the chip generation process.
Additionally, the drilling weigh on bit is applied via masses, so allowing greater representation of the dynamic behavior of the drilling process – i.e. capturing more natural frequencies.
The results from the rig have been obtained over two frequency ranges – low frequency(0-50 hz) and high frequency (50-200 hz).
Results show that improved rate of penetration is obtained with axial excitation – with low and high frequency optima. These optima can be related to the behavior of the string in the two frequency ranges – in the low frequency range, the entire string acts in unison; whereas at high frequency, only the bit/rock system is active.
As a result, it is concluded that for low frequency operation, only information about the drill string is required; whereas for high frequency operation, information about the bit/rock system is required.
Observation of the chip generation process has shown that during axial excitation, regular shaped bricks are ejected when compared with the typical wedge shaped chips that are normally ejected during the drilling process.
It is concluded that, during the axial excitation process, the chips are being ejected via a levering action, so allowing a more efficient and quicker process.
Larger scale tests or field tests are required to verify/validate these conclusions.
Ian Forster
Senior Research Engineer
National Oilwell Varco
500 Conroe Park West Drive
Conroe,
Texas 77380
United States
Ian.forster@nov.com