MWD Failure Rates Due to Drilling Dynamics

Abstract

Abstract Rig downtime due to MWD tool failure is expensive, particularly on offshore rigs with extremely high operating costs. There are different reasons for tool failures, one being the high vibration loads on MWD tools under extreme drilling conditions. MWD and LWD tools are usually equipped with sensors to measure and record vibrations for drilling efficiency and optimization. The goal of the study described in this paper is to establish the link between MWD or LWD tool failure, and drilling dynamics. With this knowledge, it is possible to reduce failure rates and costs with real-time monitoring of downhole drilling dynamics. To analyze the effect of drilling dynamics on MWD tool failures, a unique database of MWD runs in challenging environments was created. This database includes vibration data recorded at 5-second intervals from more than 12,000 drilling and reaming hours, over a total footage of 425,000 feet. In addition to unique dynamics data such as weight, torque, bending moments and axial, lateral and tangential RMS and peak accelerations, the database included detailed run and failure reports, and environmental information such as well profiles and drilling operations. A statistical study using the logistic regression indicates the types of dynamic behavior most statistically significant in MWD/LWD tool failures. These are cumulative lateral vibrations and backward whirl. Cumulative axial or tangential acceleration appears not to be significant in current MWD/LWD tool failures. A study on the correlation between recorded MWD tool dynamics and tool failure rates established the link between time spent operating above a level of vibration and the probability of tool failure. This paper contains charts describing this relationship between dynamics, operating hours, and MWD/LWD tool failure rates. These charts are valuable in operational risk management and in developing procedures for optimal drilling practices that reduce the dynamic loads on the MWD system, resulting in prolonged tool life and reduced cost.