A real-time drilling data analysis and recommendation system that leverages surface drilling data was deployed in the lateral section of a well from an artificial island in Abu Dhabi. A key objective of this technology is to provide the driller with an easy-to-use display of a novel drilling performance map. This paper presents data from this demonstration run, illustrates the features of this technology, and provides general observations on optimization of drilling parameters in this hole section.
The prototype advisory system demonstrated value by recommending rotary speed and ROP (Rate of Penetration) values to continuously optimize the tradeoff between stick-slip vibrations and MSE (Mechanical Specific Energy), depending on depth and formation being drilled. The system relieves the driller of tedious drilling test calculations and seeks to continuously optimize drilling performance. The optimization objective function (OBJ) includes MSE, ROP, and TSE (Torsional Severity Estimate) and provides a surface map that is stoplight color-coded to display the optimal drilling parameter values. TSE is calculated from a drillstring model and observations of the cycle-by-cycle swing in the surface torque.
The typical drilling optimization paradigm holds that higher rotary speed can mitigate stick-slip vibrations at the expense of increased whirl vibrations, and higher WOB (Weight on Bit) tends to increase stick-slip and mitigate whirl. The operational challenge is that these tendencies can vary from run to run, and even within an individual section as pipe length, formation, bit condition, etc. all play a role in the balance between these dysfunctions.
In this application, the system demonstrated that increased rotary speed could mitigate stick-slip for about the first 2,500 ft of the lateral section. From this point on, the drillstring was in full stick slip for all available drilling parameters. However, whirl was sensitive to the effective WOB, determined by the ROP control setpoint in this application. To stay within torque limits and provide sufficient WOB to control whirl, the advisory system actually recommended lower RPM.
This application provided an opportunity to compare the calculated stick-slip levels with bit speed measured at a downhole sensor. Excellent agreement was found between measured stick-slip and the TSE determined from the drillstring model and surface torque throughout the 10 kft lateral. This field demonstration was a first application of the system in ROP control mode, providing new insights into drilling parameter tradeoffs. The system prioritizes objectives with high variability over those with lower variability to improve drilling performance. The data was initially unexpected and led to lower rotary speeds and increased WOB in spite of stick-slip, revealing that it was possible to control whirl without making stick-slip significantly worse.