Managing Downhole Vibrations for Hole-Enlargement-While-Drilling in Deepwater Environment: A Proven Approach Utilizing Drillstring Dynamics Model

Abstract

Deepwater drilling often requires simultaneous hole-enlargement-while-drilling to improve project economics and efficiently deliver wellbore requirements. The challenge is to properly adjust reamer aggressiveness to match PDC bit dynamics to reduce damaging vibrations while maximizing overall drilling efficiency. Recent R&D efforts, focused on redesigning the BHA and optimizing drilling parameters, have successfully reduced bit/under- reamer vibrations. In addition, many operators and service providers have established rig-site procedures to recognize and mitigate vibrations. However, the results are still mixed and the lack of understanding the root causes of different vibrations is considered to be the major hurdle to improving drilling efficiency and performance. To solve this challenge an advanced dynamics model was developed which incorporates the following critical information: Mechanical rock properties (UCS) Bit/reamer design including cutter, body, gauge profile Physical characteristics of BHA components Formation characteristics (heterogeneous, anisotropy, interbedded) Well trajectory and borehole geometry Drilling parameters (WOB/RPM) This model can be applied to any drillstring configuration to provide BHA detailed information about RSS, PDM, PDC/roller cone, stabilizers, reamers, MWD/LWD and other downhole tools. This FEA model accurately predicts the drilling system's dynamics behavior from bit to surface and simulates the transient response of the entire system in time domain. Using this model, the combined effects of bit, reamer, BHA and drilling parameters have on vibration can be quantified and optimized before commencing field operations. This innovative technology provides an effective tool to optimize drilling performance without using the costly trial-and-error approach. An operator working in the Gulf of Mexico (GoM) required hole-enlargement-while-drilling to open a 12-1/4" pilot hole to 14- 3/4" from 13,000ft MD to approximately 20,000ft MD. The advanced drillstring dynamics model was utilized to optimize the BHA, bit and drilling parameters to minimize potential stick-slip and lateral vibrations. The optimization study, along with the operator's improved drilling practices, resulted in a 24% increase in penetration rate (ROP) compared to an offset well. Excluding the directional portions of the wellbore, the increase in ROP was calculated at 43%. The penetration rate increase reduced rig-time usage by 13.4hrs for a savings of $558,000USD.

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