Due to the versatility of modern coiled tubing (CT) operations coupled with the increasing demand for deepwater activity, CT is becoming a common conveyance method to perform subsea operations without the need of a marine riser or lubricator connected to the subsea wellhead. These operations utilize the CT string as an umbilical deployed through the moonpool of a dynamically positioned multi-purpose support vessel (MSV) to provide a variety of services to the operator without CT entering the wellbore. Without the need for a conventional deepwater rig or riser-based vessel, operations utilizing CT as an umbilical become a valuable time- and cost-saving option to perform subsea intervention work. Job objectives include well stimulation, lower zonal abandonment, subsea dispersant application, subsea equipment testing, flowline intervention, and hydrate-preventative blowout preventer (BOP) flushing.
From 2008-2012, an average of one CT umbilical job per year was performed. The method has increased in popularity and over the past two years, nine CT umbilical operations have been successfully completed. These successful operations include supplying nitrogen gas subsea to perform leak detection testing, utilizing dual CT umbilical strings to perform subsea BOP flushing as a pump down and return line, nitrified acid stimulation treatment, flowline hydrate removal, flowline purge to platform, and cementing zonal abandonment.
The combination of increasing deepwater technology and the adaptability of CT increases intervention and testing methods for operators. This paper will explain the techniques used, system improvements (both operational and HSE), and it will provide an overview of various types of jobs performed.