Marlin Failure Analysis and Redesign: Part 3 - VIT Completion With Real-Time Monitoring
- S.W. Gosch (BP America) | D.J. Horne (BP America) | P.D. Pattillo (BP America) | J.W. Sharp (BP America) | P.C. Shah (Landmark Graphics)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- June 2004
- Document Type
- Journal Paper
- 120 - 128
- 2004. Society of Petroleum Engineers
- 4.3.4 Scale, 5.6.11 Reservoir monitoring with permanent sensors, 5.5 Reservoir Simulation, 1.14 Casing and Cementing, 1.6.9 Coring, Fishing, 1.1.2 Authority for expenditures (AFE), 5.3.2 Multiphase Flow, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 5.1.8 Seismic Modelling, 1.14.1 Casing Design, 1.10 Drilling Equipment, 1.6 Drilling Operations, 4.3.1 Hydrates, 4.5 Offshore Facilities and Subsea Systems
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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.
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.
Despite an extensive effort to ascertain a root cause of the collapse of the (10 3/4-×8 5/8-in.) production tieback and ensuing deformation of the production tubing in Marlin Well A-2, a singular mechanism could not be discerned. This lack of resolution is primarily because the status of the (13 3/8-×10 3/4-in.) intermediate casing is unknown. Nevertheless, all possible root causes that the investigation team deemed reasonable had an increase in wellbore temperature as a component. This fact, coupled with the limited options available from the batch-drilled wellbores, led the team to focus on controlling wellbore temperature by insulating the production tubing.
Apart from its cost, VIT is, unfortunately, a solution with its own set of design challenges. It must be substantiated that the thermal characteristics are sufficient to solve the problem - that is, to keep the annuli sufficiently cool to render the well safe. For Marlin, this requirement was satisfied in two ways: by experimentally determining the overall heat-transfer coefficient of VIT targeted for Marlin wellbores and by numerically modeling the resulting thermal performance of the VIT under a production scenario. This discussion details the latter exercise, with the former being addressed in the second paper in this series.2 Further, validation of adequate thermal performance must be supplemented by checking the mechanical integrity of the VIT under a variety of burst, collapse, and tension load cases.
Given a VIT configuration that meets both thermal and mechanical design requirements, it then becomes important from an operational viewpoint to ensure the VIT does not lose its capabilities in service. A substantial portion of the discussion in this paper outlines the fiber-optic installation and software package developed to monitor VIT performance in-situ. As noted, an added benefit of the monitoring package is the wealth of information it affords an engineer on downhole thermal behavior.
Throughout this paper, the submudline tubing-hanger packer is called a packoff tubing hanger (POTH).
The well annuli are designated in alphabetical order, proceeding outward from the production tubing/tieback (5 1/2-×10 3/4-in.) annulus, designated "A." Thus, the "B" annulus is outside the production tieback (e.g., tapered 10 3/4-×8 5/8-in. × tapered 13 5/8-×10 3/4-in.), and the "C" annulus is outside the intermediate casing (e.g., tapered 13 5/8-×10 3/4-in.×16-in. liner hung inside 20-in. casing).
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