Marlin Failure Analysis and Redesign; Part 3, VIT Completion with Real-Time Monitoring

Abstract

Abstract Following the failure of the initial well in the Marlin field1 the preferred solution for completing the remaining wells was to control wellbore temperature via vacuum insulated tubing (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 using both axial probes and radial probes traversing the annulus outside the VIT. These profiles supplemented the conventional values of 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. As well survival depends on proper VIT performance, a distributed temperature monitoring system was developed and evaluated during full scale testing. On the Marlin TLP, fiber optic is run in each well along the length of the VIT to continuously monitor the production annulus temperature profile. A software system was also developed to take binary fiber data and feed 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 joint of VIT loses its insulating properties, this specific joint can be identified and appropriate action 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.