Reducing Stick-Slip by Avoiding Auto-Driller Control Dysfunction

Abstract

Analysis of historical drilling data in the Delaware Basin revealed stick-slip was being initiated by the rig control system. It was determined that a weight-on-bit (WOB) road map with calibrated range values delivered near-maximum rate of penetration (ROP) and reduced stick-slip. This was achieved by simplifying the auto-driller's parameter limits and avoiding differential pressure control. Details of the statistical analysis process and results from field trials is presented and compared to historical performance. The road map was developed using data from top performing offset wells. The standard deviation of the auto-driller's active control limiters was cross-plotted against the standard deviation of the ROP. Intervals in which the differential pressure was the primary control or the ROP range was excessive displayed a high standard deviation, indicating unstable control behavior. Data from the non-dysfunctional areas determined the WOB and ROP ranges to be targeted through an interval. Use of these range limits steadied the application of WOB and reduced the need to control the auto-driller via differential pressure. Wells using the parameter road map were compared to high-performing offsets. The comparative analysis focused on ROP, mechanical specific energy (MSE), downhole accelerations, and bit damage. Performance in formations known to cause dysfunction are highlighted. Benefits have been observed in the rotary steerable control collar RPM data. Depth-of-cut (DOC) through the Brushy Canyon was improved by use of the road map. Traditional auto-driller limiters (torque and differential pressure) were avoided due to the limits of the drilling system embedded within the road map's setpoints. Data are presented showing that differential pressure control can result in stick-slip. This dysfunction is avoidable with the use of a road map employing accurate range values for WOB and ROP to control the auto-driller. Improved auto-driller range management addressed a specific source of dysfunction and positively impacted performance at the bit. The visual road map conveyed WOB and ROP guidance directly to the driller, which accelerated the rig's learning curve. When combined, the product of these data-driven concepts increased bit life and ROP.

Adaptive Response Time for Integrated Autodriller Controller

“…(Pastusek et al, 2016) pointed out the coupling between incorrect autodriller regulation and the drill string stick-slip. Operator intervention is required to stabilize the regulation, either by changing the setpoint or gain of the con-troller (Pastusek et al, 2016;Badgwell et al, 2018;Adam, 2018). Therefore making the success of the process dependent on the operator's skills.…”

“…Thus, developing general solutions with principle mechanistic models can be complicated. We therefore decided to use a data-driven approach like (Adam, 2018) in combination with the existing mechanistic model. Data-driven methods require data, which in the drilling industry is often proprietary.…”