Selecting Optimum Drilling Parameters by Incorporating Vibration and Drilling Efficiency Models

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Abstract
To avoid severe vibrations, different drillstem (or drillstring) vibration models have been used to predict and avoid resonance regions by selecting bottom hole assembly (BHA) components and operating parameters such as weight on bit (WOB) and RPM. The overall efficiency of the drilling operations can be evaluated using either a mechanical specific energy model or an inverted rate of penetration (ROP) model. The key output from the analysis described herein is a method to improve drilling efficiency by incorporating a drillstem vibration model with an ROP model. A data set including vibrational data was collected from a section of a well drilled in the North Sea to analyze the level of drilling efficiency for the drilled section. A drillstem vibration model was created using nonlinear finite strain theory, including coupled axial, torsional and lateral vibration modes. To optimize the drilling process, the vibration model was integrated with an ROP model. The vibration model calculates the critical speeds for a given BHA at a given depth, supplied with an operational window for WOB and RPM combinations that gives the optimal combination in therms of ROP. By analyzing the drilling variables such as WOB, rotational speed, and ROP, the drilling operational effectiveness was evaluated. The operational window with low vibration level and with the potential maximum instantaneous ROP was chosen to be the optimum drilling scenario for the target hole section. The model was verified with the analysis of the collected field data where the level of drilling efficiency was obtained for the different sections drilled. This paper presents a new methodology to increase drilling performance by means of drillstem vibration and ROP modeling.

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