A Drill Bit and Drilling Motor with Embedded High-Frequency 1600Hz Drilling Dynamics Sensors Provide New Insights into Challenging Downhole Drilling Conditions

Drilling motors are typically used in every well drilled globally with conventional steerable bottom-hole assemblies (BHA's) and powered rotary-steerable BHA's. Downhole drilling dysfunctions are common when mud motors are pushed to the limit for maximum drilling performance. High-frequency (1600Hz) continuous recording compact drilling dynamics sensors were embedded into the bit, bit box and top sub of the motor to better understand drilling conditions in different shale plays throughout North America land. In the drilling industry, most downhole measurements for drilling dynamics utilize relatively low-frequency sensors (up to 100Hz). Typically, the measurements are burst and not continuous. These low-frequency burst acceleration devices cannot reliably measure high-frequency torsional oscillations (HFTO) which are known to be problematic while drilling in certain shale basins. Newly developed high-frequency (1600Hz) compact drilling dynamics sensors can now be embedded into the drill bit, mud motor bit box and top sub to record 3-axis accelerations continuously at high-speed sampling rates. The embedded sensors do not add any extra length to the steerable motor and therefore capture the true dynamic response of the system. Embedding the high-frequency sensors at both ends of the mud motor provides two unique data sets of dynamic measurements. With conventional steerable motors and motor-assist rotary-steerable systems (RSS), HFTO dominant frequencies between 100 and 400Hz were commonly observed. In some cases, HFTO dominant frequencies between 400-700Hz and their harmonics were captured, which have not previously been reported. In most cases, the HFTO amplitudes are between 20 and 200g peak (or 40 and 400g peak-to-peak). On some occasions, ±200g self-perpetuating HFTO were recorded in memory where its calculated angular acceleration is more than 25,000 rad/s2. The transitions between low-frequency stick-slip and HFTO were captured in high-speed recording. Negative string rotation speeds were commonly observed at the top sub of the motor while in rotary mode. It was noted that the bit would slow down to a stop but never turn backwards, resulting in the backward rotation of the motor top sub. During very high-amplitude multiple-axis shocks at the bit, it was discovered that there was a significant temperature rise due to loss of energy from bit dysfunction. The newly reported drilling dynamics phenomena, such as multiple dominant HFTO frequency shifts, micro-sticks and micro-slips, will be detailed in this paper. Monitoring and understanding high-frequency drilling dynamics dysfunctions allows us to make systematic changes to bit, BHA and drilling parameters to reduce dysfunction magnitude and improve overall drilling efficiency and minimize component wear.