Use of a mudline tubing hanger (MLTH) is common in dry-tree deepwater applications with tight tolerances for tension management. It is run integral to the tubing string and can provide a pressure barrier as well as reduce the load to the platform. In single riser applications, a sealing MLTH is necessary to keep unwanted annular pressure off the riser. The Medusa development, located in Mississippi Canyon blocks 538 and 582 offshore Louisiana, is a truss SPAR incorporating a dual-barrier riser system. Due to the dual barrier riser system, a non-sealing MLTH is sufficient.

The non-sealing MLTH developed for this project assists buoyancy can design by capturing a set tubing tension at the mudline. It incorporates barrel slips to distribute the hang weight and avoid point loading of the casing, while allowing ample space to pass control lines and gas-lift gas as the completion designs dictate. Furthermore, its control line provides a conduit for annular nitrogen displacement used as a thermal barrier.

The Medusa MLTH uses a stage-set feature to verify both tubing space-out and completion integrity prior to a final lock-down while a cut-to-release mechanism allows for tubing retrieval. Testing of the hanger design demonstrated that it is capable of meeting or exceeding the tensile limits of the tubulars.

This paper includes a summary of the MLTH development and testing procedures followed by the description of seven successful field deployments and the retrieval of one of the re-designed Medusa MLTH assemblies.

Significance of the Technology

The inherent advantage of a truss SPAR is that it can provide a cost-effective means of deepwater field development for lower-reserve thresholds or in areas lacking sufficient infrastructure. A SPAR is a floating production facility that relies upon buoyancy for support. Transferring the weight of the tubulars to a MLTH can create a significant cost-of-facility reduction and provide a means of keeping the production tubulars in tension.

Use of the stage-set feature prior to a final-set verifies proper tubing spaceout and completion integrity. Reliance upon a cut-to-release feature aids in maintaining completion integrity during a catastrophic event such as facility 'drive-off'.

This design is applicable to other deepwater floating production facilities and can be readily modified to support a variety of design drivers. A second Murphy-operated truss SPAR development, Front Runner, has run a slightly modified version of the MLTH with a higher-tensile-strength mandrel.

Field Description

The Medusa development, under Mississippi Canyon blocks 538/582 in the Gulf of Mexico, is situated about 100 miles south of New Orleans, Louisiana in approximately 2,200-ft of water (Fig. 1). Murphy Exploration is the operator with ENI Petroleum and Callon Petroleum Companies as partners.

The MC 582 #1 discovery well was drilled from the Ocean Concord MODU in October 1999 with two of the main amplitude targets (T1B and T4B) encountering potentially economic reserves. Three delineation wells and one conventional core bypass verified these two principle reservoirs and found two shallower pay zones (T0A and T0C).

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