Conclusive Proof of Weak Bedding Planes in the Marcellus Shale and Proposed Mitigation Strategies

Abstract

Wellbore instability has been experienced in areas of the Marcellus Shale and can become particularly troublesome in the superlaterals that are becoming more prevalent in that play. Often, the instability while drilling these very long lateral wells is minimal; problems are more likely to occur while tripping out after reaching total depth (TD). The most common instability events when pulling out of the hole are tight hole, packoff, and stuck pipe and are often accompanied by excessive cavings. These problems often worsen with time, indicating there is some time dependence to the failure mechanism. In order to develop effective mitigation strategies to combat the instability, it is imperative that the failure mechanism be correctly identified. Previous publications (Riley et al., 2012; Addis et al., 2016; Kowan and Ong, 2016) have suggested that bedding planes may play a role in some of the drilling problems experienced in the Marcellus Shale. This case study provides conclusive proof of weak bedding plane failure along a lateral well in the Marcellus Shale, where over 1,000 feet of anisotropic failure was captured with a logging-while-drilling (LWD) image tool. This image not only provided confirmation of the presence and failure of weak bedding planes in the Marcellus Shale, but was also used to validate an existing geomechanical model for the area. Validating the model gave the operator more confidence in the mitigation strategies developed from that geomechanical model, which had been based on the assumption that weak bedding was contributing to the difficulty experienced on multiple lateral wells when tripping out of the hole. This case study begins with an overview of the geomechanical model, including the drilling history, stress/pore pressure model, and rock properties. Next, some highlights from the image log, showing anisotropic bedding plane failure, are featured, as well as a comparison of the image to the geomechanical model. This case study concludes with proposed mitigation strategies that could be implemented to limit the risks posed by weak beds and to minimize instability when drilling laterals in the Marcellus Shale in this area or similarly complex areas.