Identification and Mitigating Risk in Deepwater Surface Casing Strings with a Cradle to Grave Approach

Abstract

As deepwater well designs have progressed toward deeper targets, the well integrity risk of surface casing strings has increased. Surface casing strings utilized in deepwater environments are installed before the drilling riser is installed allowing them to be subjected to metocean conditions and difficult to handle and install. Additionally, the exposure from the well has increased the need for advanced connector designs and complex manufacturing processes to ensure well integrity is maintained. To ensure the casing string is fit for duty, a "cradle to grave" approach is utilized to identify and classify the risks created by loads induced on the casing string. Beginning with the handling process, all handling loads, environmental loads resulting from handling, and metocean conditions are identified. Once installed, the well loads resulting from potential well exposure and structural loads resulting from the rig are identified. Finally, the connector and fabrication design process is analyzed to identify requirements needed to satisfy the load conditions and mitigate risk to well integrity. Introducing advanced mechanized tubular running technologies resulted in up to 20% reduction in exposure of the surface casing string to dangerous sea states and ocean currents and a 41% reduction in red zone entries. Exposure of the surface casing string to environmental loads was further reduced by 7% with the use of an innovative hands-free anti-rotation key, which requires no installation on the rig floor during tubular handling operations and lowers red zone entries beyond current mechanized handling solutions. Once set in place, surface casing strings are subjected to a higher classification of well service as structural and well loads increase in severity. To address this, a new weld-on connector qualified to connection assessment level I+ for gas tight service with elevated temperature per API RP 5C5 / ISO 13679 was installed, allowing deeper wells in deeper waters to be achieved.