Technical Paper: A New Standard in Real-Time LWD Sonic Capability: Improving Confidence in Critical Wellbore Stability and Formation Evaluation Decisions

Society: SPWLA
Paper Number: 2012-169
Presentation Date: 2012


In challenging drilling environments it is essential that pore-pressure predictions and wellbore stability models be confirmed and refined with accurate real-time acoustic data. This understanding is critical to safe and effective well control practices. Rigorous quality controls are essential to confirm the accuracy of these difficult and easily misinterpreted measurements. Using compressional data it is possible to manage the lower end of the safe mud-weight window below which breakout can occur. With the addition of real-time shear, it is also possible to define the maximum wellbore pressure limit before formation fracturing occurs. This real-time geomechanics technique mitigates the possibility of kicks and lost circulation events, with their associated safety and cost issues. In addition, high drilling costs and the potential for incomplete wireline operations can be mitigated by ensuring that fit-for-purpose formation evaluation data is acquired while drilling. Finally the real-time feedback of measured velocities into the seismic velocity model enhances the accuracy of target intersection and hazard avoidance.

This paper discusses several important real-time acoustic QC processes, such as pumps-off station measurements where there is no noise either from drilling or mud pumps, allowing acquisition in the best possible acoustic logging environment. These are compared to the continuously transmitted Delta-T (DT) picks and are acquired every stand. Additionally telemetering the slowness time coherence (STC) processing results and comparing Delta-T values provides a comprehensive understanding of multiple modes while drilling. Having the STC projections allows the engineer to refine tool parameters by downlinking with wireline-like control, changing features such as frequency filters, label limits, firing modes.

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