This paper presents an investigation of true downhole dynamic conditions through improved testing methods and a new measurement-while-drilling (MWD) tool. Shock loads may cause severe damage to bottomhole assembly (BHA) components. Consequently, characterizing the shock loads and analyzing their distribution within drilling tools produces information for the design process that can improve tool reliability and efficiency.
The difference between shock loads and traditional dynamics is rarely discussed within the drilling industry, so this paper first introduces a mathematical description of shocks. Experimental shock and vibration tests are used to investigate the shock and vibration loads experienced by full-scale downhole drilling tools. The test rigs for this effort enable testing of full-scale drilling tools as long as 10 m and a maximum weight of 2 tons. Testing of entire drilling tools, and the emulation of downhole conditions, enables realistic dynamic loading and an analysis of the interaction of tool internal components. These results are not possible when testing single components on a vibration table. During the tests, acceleration sensors positioned at several locations on the outside of the tool body measure the shock amplitude. Simulation models enable analysis of the load distribution within the tested tool. Depending on the simulation results, the reliability of all internal components can be ensured. If necessary, further design improvements are initiated.
The simulation models are validated and improved with data from experimental modal analyses of the test rigs and the tested tools. Identifying uncertain parameters for complex dynamics simulation models is a particularly challenging task. Results from the shock tests are compared to the simulation results for additional validation because shock loads, in contrast to typical vibrational loads, are transient. Shock and vibration tests also serve to evaluate the capabilities and limits of current MWD tools in terms of sampling rate and sensor range. A newly developed MWD tool for dynamics measurement was tested, evaluated, and optimized using this testing process.
The tests and simulations enable optimization of drilling tools for shock and vibration loads. In contrast with the limitations of historical measurements, enhanced dynamics-measurement capabilities with higher sampling rates and extended sensor ranges provide increased data quality and better characterization of downhole shock and vibration loads. This improved understanding of drilling dynamics loads leads to reliability enhancement and cost optimization by reducing shock and vibration-related tool failures.