NDLI: Axial Excitation Tool String Modelling

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Forster, Ian
Copyright Year	2015
Abstract	Current types of axial excitation tool have been shown to produce beneficial results — in terms of load transfer to the bit, general reductions in string friction and reductions in drill dysfunctions — such as stick slip. The positioning of such tools to achieve optimum benefit is therefore extremely important — in order to maximize the axial excitation to the areas of the string that require a reduction in friction, and also to minimize the axial excitation to the surface and to sensitive string tools (such as MWD) — where damage may occur. This paper describes a string model that allows the position of axial excitation tools to be assessed — in terms of the string response — both locally and remotely from the tool. The model breaks the string down in to springs and masses — with 10 nodes in the upper string; and 5 nodes in the BHA. Additional components can also be added to the string — such as shock tools, jars and accelerators — in terms of mass and stiffness. The equations of motion are used to connect the nodes in terms of differential equations. The model is Mathcad based, and as a result, executes very quickly — so allowing comparative studies to be carried out with relative ease. Data input into the model is also achieved quickly. The speed with which the model can be used lends itself to fine tuning input data. The model has been compared with and ANSYS spring mass model, and good agreement has been reached. Additionally, the model allows more than one axial excitation tool to be added to the string — in order to gauge the benefits of such a configuration. Damping can also be varied at different locations in the string model. The results from this model have been used to compare with field test data — derived from a string with instrumentation tool located at various points in the string. The results show that good agreement can be reached between the model and the field test results, however, careful consideration needs to be taken of the damping assumed in the model. The model can, never the less, be used for comparative studies — i.e. tool location, number of tools and optimum frequencies. Further work is recommended in comparing model results with field test results — in order to get a better understanding of the effect of damping. The damping model could be improved in the model presented here, or alternatively, the lessons learned here could be merged into an existing string model.
Sponsorship	Ocean, Offshore and Arctic Engineering Division
File Format	PDF
ISBN	9780791856581
DOI	10.1115/OMAE2015-41393
Volume Number	Volume 10: Petroleum Technology
Conference Proceedings	ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering
Language	English
Publisher Date	2015-05-31
Publisher Place	St. John’s, Newfoundland, Canada
Access Restriction	Subscribed
Subject Keyword	Damping Stick-slip Instrumentation String Equations of motion Modeling Gages Stress Friction Differential equations Stiffness Excitation Drills (tools) Damage Shock (mechanics) Springs
Content Type	Text
Resource Type	Article

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