In high profile applications, an advanced drillstring dynamics modeling system has been used to mitigate downhole vibrations and improve penetration rates (ROP). The capability of virtually drilling a well with computer software allows the engineer to identify the root causes of damaging vibrations and ROP limiters before drilling commences. Consequently, the conventional trial-and-error methodology can be replaced by a cost-effective optimization process. This technology provides an efficient platform to optimize the total drilling system including bit selection, bottom-hole-assembly (BHA) design, operating parameters and the placement of individual BHA components. The utilization of this software has delivered significant economic benefits associated with increased total footage, higher ROP and fewer downhole tool failures. Offset well data are used to calibrate the simulation for each application including:
- Physical characteristics of the drillstring, BHA and drill bit
- Operating parameters, weight-on-bit (WOB) and revolutions per minute (RPM)
- Rock properties; in some cases, core samples from an offset well are tested
- Well trajectory and hole diameter from directional surveys and caliper logs
The authors believe this technology has the potential to be a central optimization platform for a broad range of worldwide drilling applications.
Historically, drill bits were the primary focus of the optimization process because of their impact on vibration, directional control and ROP. However, with the increasing use of sophisticated downhole technology including rotary steerable systems (RSS), roller/under-reamers, MWD/LWD and other specific tools, the modeling system has been increasingly applied to address stability issues caused by downhole tool dynamics.
While drilling the 12-1/4" hole section with a push-the-bit RSS/PDC bit BHA on Tizon 222, Tabasco, Mexico (Figure 1 and Figure 2) the operator encountered low ROP and severe stick-slip associated with excessive torque. In order to reduce torque and improve ROP on the next well (Tizon 231), a service company recommended using a roller reamer in the BHA to efficiently drill from 3360m to 5370m while holding inclination angle. Based on previous experience, the placement of the roller reamer is critical in achieving overall BHA stability and achieving the desired ROP. The operator requested an optimization study using a dynamic modeling system to ensure a good balance between BHA stability and ROP. The capability of simultaneously quantifying the magnitude of vibration shocks and rock removal rate enabled the engineering team to address the challenging formation with confidence.