Drilling with Casing to Address Formation Troubles in Surface Hole

Abstract

Subsurface anomalies can present complex well construction challenges. These anomalies to name a few are irregular wellbore stress profiles, low fracture gradients that require complex mud programs and, in some cases, total fluid losses while drilling. Poor wellbore stability is a common result of such anomalies and service companies serving the industry develop technologies to address, mitigate against and overcome these issues. A gas well encountered such a challenge. While drilling the 17″ section complete fluid losses were encountered. These losses generally uncommon in the field and were attributed to a seismic anomaly. This resulted in poor wellbore stability and led to multiple lost BHAs and sidetrack attempts. The surface casing design did not allow for extensive remedial options so rather than continuing recovery operations it was decided to suspend well construction and spud an offset well 50 meters away. Equipped with the knowledge of the drilling problems from the direct offset, the potential problems they represent and considering the proximity, it was decided to introduce two engineered solutions to mitigate against these challenges and secure successful well construction. First, the surface casing design was modified and the 18-5/8″ casing was set deeper and second, casing while drilling (CWD) technology was introduced to drill for 13-3/8″ intermediate casing from the 18-5/8″ shoe to 13 3/8″ casing point (CP). During planning it was concluded that casing drilling technology would allow to simultaneously keep every foot drilled behind casing, under total losses conditions. Furthermore, CwD would minimize the open hole time compared to conventional drilling practices, an important factor when mitigating against risks from poor wellbore stability. Approximately 4.5 days after setting the 18-5/8″ surface casing, a 16″ CwD drill bit made-up to 13-3/8″ casing successfully drilled 1575 ft with total losses and cemented in place across an interbedded formation. This was a starkly different result compared to the direct offset where operations were suspended after many more days between setting the 18-5/8″ to decision to suspend.