Drillstring vibrations can be broken down into 3 modes—axial, lateral, and torsional. Any amount of drillstring dynamics is likely to have a negative impact on overall drilling efficiency. Under conditions of severe drillstring dynamics, all BHA components, from drill bits to MWD/LWD tools, rotary steerable systems, and drill collars and drill pipe, are exposed to catastrophic failures that can lead to lost time, lost equipment downhole, and even loss of hole sections. Managing drillstring dynamics through analysis and modeling is the first step to preventing negative impact on drilling performance.
Drilling dynamics is a very complex problem, influenced by the trajectory of the well, hole sizes and wellbore geometry, formation being drilled, drilling fluid characteristics, drilling rig, drill string, and bit and BHA components. Performing detailed analyses is an intensive engineering process. Drilling dynamics analysis engines in DOX help users approach the problem from two directions:
BHAV Frequency Analysis: Each structure, including a BHA, has a natural frequency at which it likes to vibrate. Under drilling conditions, the weight on bit and RPM of the string can cause vibrations to initiate as the natural frequency is approached. BHAV software analyzes the physical characteristics of the BHA and identifies a safe operating range to best avoid these natural frequencies.
BHA-TV is a time domain model that analyzes how a drilling system changes over time. It is a computationally intensive, finite element model that takes into account the drilling system in context of the formation strength and friction along the borehole. The model is able to identify the onset of forward and backward whirl as well as lateral and torsional vibrations. An experienced Schlumberger representative is required to perform these detailed analyses.
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