Identification of Borehole Breakout Formation and Estimation of Stress Direction and Regime Using LWD Ultrasonic Caliper Measurements: A Unique, Systematic, and Real-Time Methodology

Abstract

Abstract Wellbore instability remains a leading threat to oil operators as one of the main causes of non-productive time worldwide. As drilling technology advances, logging-while-drilling (LWD) measurements contribute valuable information to help identify instability problems in real time. One of the important measurements is the LWD ultrasonic caliper measurement, which makes it possible to identify borehole washout, breakout, keyseating, and spiral-hole conditions. Having this measurement enables diagnosis of wellbore stability problems while drilling without the need for an additional logging run, which is especially critical in an unstable wellbore. In the industry, breakout identification using image data can be a significantly user-dependent process and requires appropriate skills. The process is time consuming, and the final result can still be subjective. Further complication comes when considering a highly deviated well path or when the field stress regime is abnormal. As a consequence, drillers face difficulties using the LWD ultrasonic caliper data directly for wellbore stability diagnosis. We propose a methodology to overcome the limitation of conventional method and produce reliable quantitative breakout data to be used in real time, in an automated, systematic, and consistent way. An engineering-based workflow is introduced to distinguish zones of stress-induced breakouts from other borehole enlargement types with improved consistency and which can be easily translated into programming language. Instead of image data, this solution uses sector data to extract the borehole shape information using the cubic spline method. Six stringent LWD ultrasonic caliper-specific breakout criteria are introduced and used to identify breakout intervals from the borehole shape data. Adopting the idea from the World Stress Map (WSM) project, a data quality ranking was also performed using the result of the workflow. The quality ranking criteria (defined by WSM project) segregate the breakout results into five categories to infer the reliability of the breakout intervals identified. This quality ranking procedure will greatly improve the reliability of the output data in the workflow prior to quantitative usage. The result of the breakout identification is then used to determine the principle stress direction and the stress regime, using a 3D stress analysis method for deviated wells.