Abstract
The lateral movement of drill-pipes, while rotating, can be the source of diverse drilling problems, such as tool-joint wear, grinding of cuttings into a fine powder that is very hard to transport, formation instabilities. Yet, it is virtually impossible to estimate the sideway displacements of drill-pipes as soon as the distance is greater than a couple of stands from a measurement source, like a dynamic sub placed in the bottom hole assembly (BHA).
It is therefore tempting to place dynamic subs along the drill-string with the objective of detecting any pipe movements that could have a negative impact on the drilling operation. However, to be useful, the measurements must be made at a relatively high frequency, in practice above 80Hz, and with enough precision. For that reason, we have placed a dynamic sub that measures axial and tangential accelerations, rotational velocity, 2-axis bending moment, torque and tension, approximatively 300m behind the bit while drilling two 9 ½-in lateral sections of a horizontal multilateral well.
The dynamic sub sent rotational speed, torque and tension at 80Hz through wired-pipe telemetry and burst data for all the measurement channels were recorded in memory, for 10s at 800Hz every 15 minutes. We have been able to test a method to collect and interpret the high-speed telemetry data, i.e. 80Hz, and we have post-analyzed the burst memory data. A methodology has been developed to compensate systematic errors on the accelerometer sensors by taking advantage of the redundancy of the measurements present in the mechanical-sub. An interpretation software has been used to reconstruct the likely 3-dimensional pipe movement at the location of the measurement tool. The analysis has shown a surprisingly large variation of pipe movement patterns and astonishing fast changing levels of lateral movement throughout the two runs where the tool has been used.
With such a pipe reconstruction methodology at hand, it can be envisaged to perform the processing downhole, i.e. directly into the dynamic sub, and to transmit information about the 3-dimensional movement of the pipe. Such information would be valuable, when received in real-time from distributed sensors, to inform the drilling operational team about possible detrimental drill-pipe vibrations that are not necessarily associated with abnormally high accelerations.
