Distributed-Dynamics Feasibility Study
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 151477, ’Distributed-Dynamics Feasibility Study,’ by Piero D'Ambrosio, SPE, Reisha R. Bouska, SPE, Alan Clarke, SPE, and Jason Laird, SPE, National Oilwell Varco, and Jim McKay and Stephen T. Edwards, SPE, BP, prepared for the 2012 IADC/SPE Drilling Conference and Exhibition, San Diego, California, 6-8 March. The paper has not been peer reviewed.
Wired drillpipe enables a variety of measurements to be taken throughout the drilling assembly. One such measurement is acceleration to better determine the way that vibration events are distributed from the bottomhole assembly (BHA) to the upper drillstring or vice versa. Potential use of distributed dynamics for real-time decision making can be investigated by use of a set of designed-for-purpose independent downhole-dynamic-data recorders (DDDRs). A test project acquired data from sensors near the bit and BHA in the horizontal section and sensors in the upper assembly that showed the dynamics throughout the vertical section, curve, and landing point of the horizontal section.
Introduction
To investigate the feasibility of using distributed dynamics for real-time decision making, five DDDRs were placed in four drilling assemblies for a horizontal well in the Woodford shale in Hughes County, Oklahoma. This technology enabled recording downhole drilling performance at high frequency and at multiple positions in the BHA and drillstring. The DDDR is a memory-mode vibration-logging tool that can be placed anywhere in the BHA and drillstring. The tool comprises a carrier subassembly and a vibration-recording plug that screws into the carrier subassembly. The DDDR measures lateral accelerations and temperature and then derives the torsional response. The high-speed data acquisition and positioning of the single-axis accelerometer within the tool provide the following data:
Downhole temperature.
Maximum lateral accelerations: magnitude of the absolute maximum highest recorded acceleration during the time period for statistical calculation. There is no consideration of the duration of the acceleration.
Root-mean-squared (RMS) lateral accelerations: standard deviation (SD) of samples within the time period for statistical calculation. SD is used as the measurement of statistical dispersion and average vibration intensity. SD is zero if all data samples are equal, SD is small if many data samples are close to the mean, and SD is large if many data samples are far from the mean.
Downhole rotation [here noted as RPM (i.e., rotational speed measured in revolutions/minute)]: mean rotary speed of the DDDR within the time period for statistical calculation.
Data are recorded in the tool’s memory every 2.5 seconds at a frequency of 400 Hz. A study of the recorded down-hole rotation yields a ΔRPM and a torsional vibration indicator. ΔRPM is de-fined as the percentage change from the mean over a predefined period. The acquired lateral-acceleration data along with the calculated downhole RPM were merged with surface-parameter data to help determine the modes of vibration, the distribution of that vibration along the drillstring, and its effect on the rate of penetration (ROP).