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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 improved observation of the chip generation process. Additionally, the drilling weight 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 (50-250 Hz). Results show that improved rate of penetration is obtained with axial excitation – with low and high frequency optima occurring. 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 to optimize performance; whereas for high frequency operation, information about the bit/rock system is required to optimize performance. Observation of the chip generation process via high speed video 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. MIT [1] provided background classes, project guidance and project review as part of an NOV/MIT advanced technology program. Larger scale lab tests and/or field tests are required to verify/validate these conclusions.
Highlights
With respect to National Oilwell Varco (NOV) and NOV customers, of particular interest has been vibrations that aid the drilling process
Using the current axial excitation tools that are available as a basis for the study, on the small to medium scale, this has presented a low risk strategy to get a minimum viable product (MVP)
A further conclusion can be drawn from the ANSYS simulations – that the low frequency response is dependent on the drill string; whereas the high frequency response is dependent on the bit rock system in isolation
Summary
With respect to National Oilwell Varco (NOV) and NOV customers, of particular interest has been vibrations that aid the drilling process. Current tools that meet this requirement are tools that aid the drilling process by inducing axial excitation into the drill bit – either at medium frequency or at low frequency. There are potential future tools operating at higher and very low frequencies. There have been many published works in this field – the most practical recent approaches, that have the greatest relevance for NOV, have been from the University of Aberdeen [2] and the University of Newfoundland [3]. Using the current axial excitation tools that are available as a basis for the study, on the small to medium scale, this has presented a low risk strategy to get a minimum viable product (MVP). The project was carried out on the as an innovation exercise, in order to determine if useful information could be obtained on such a fast track project
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