New Directional Drilling Simulation Tool Reveals Link between Dynamic Stability and Tool Face Control

Abstract

Abstract The development and use of enhanced directional drilling software modeling tools are outlined. A fully dynamic drill bit software simulator is introduced with the capability of modeling rock removal done by cutters as well as gage pads, bit blades, and non-cutting elements which can wear and crush the rock. Side-cutting simulations with gage pad/rock interaction are presented and compared to side-load lab test data at atmospheric pressure. Good agreement between the simulation and the lab is demonstrated. Using this dynamic drilling simulation software, a common directional drilling challenge—holding tool face orientation—is investigated. The case is made that tool face control problems can be caused by dynamically unstable drill bits in addition to commonly cited causes. The software is used to simulate the dynamic behavior of 21 bits from the field that had been used on motors with bent AKO. Bits with excellent tool face control in the field are found to be more dynamically stable than bits with poor tool face control. The link between instability and tool face control problems is shown to be the increased torque that accompanies dynamic instability, or bit whirl. The relationship is illustrated with two case studies—one in southern Texas and one in central Oklahoma. Both case studies examine tool face performance in the field using the enhanced simulation software.