Marlin Failure Analysis and Redesign: Part 3—VIT Completion With Real-Time Monitoring

Abstract

The redesign solution for the batch-drilled wells remaining after the deformation of the Marlin Well A-2 production tieback and tubing was vacuum-insulated tubing (VIT). VIT implementation, however, required a number of computational and experimental innovations. To ensure well survival, a distributed temperature-monitoring system was developed and evaluated during full-scale VIT testing. Fiber-optic cable run on completions continuously monitors the production-annulus temperature profile. The monitoring system has also proved to be a valuable quality-assurance measure for special annular gels used to minimize conduction and natural convection in the production annulus. Abstract Following the failure of the initial well in the Marlin field,1 the preferred solution for completing the remaining wells was to control wellbore temperature by means of VIT.2 Implementation of VIT required a number of computational and experimental innovations, including: Provision for insulating the tubing couplings, the source of up to 90% of VIT heat loss. Detailed flow-loop temperature profiles with both axial and radial probes traversing the annulus outside the VIT. These profiles supplemented the conventional values of the overall heat-transfer coefficient and thermal conductivity obtained from the flow-loop measurements. VIT performance, as measured experimentally, must exceed both thermal and mechanical design bases. Because well survival depends on proper VIT performance, a distributed temperature-monitoring system was developed and evaluated during full-scale testing. On the Marlin tension-leg platform (TLP), fiber-optic cable is run in each well along the length of the VIT to monitor the production-annulus temperature profile continuously. A software system was also developed to feed binary fiber data to an integrated thermal-simulator casing-design software package that calculates safety factors for the B and C annuli. These real-time safety factors interface with the platform alarm system and are continually monitored by operators. If a low safety factor is calculated, a well will be shut in. In addition to feeding the platform alarm system, the software provides data to a web-based plotting program. If a single VIT joint loses its insulating properties, this specific joint can be identified, and appropriate action can be taken. The monitoring system has also proved to be a valuable quality-assurance measure for special annular gels used to minimize conduction and natural convection in the production annulus. This paper focuses on the value of the combined VIT and fiber/software monitoring system as a means of both controlling and observing well thermal behavior. Typical temperature vs. depth curves are used to illustrate the detailed information retrieved.