Pushing the Boundaries of Concentric-Coiled-Tubing Technology To Resurrect Subhydrostatic Gas Wells on an Unmanned Offshore Installation
- Ann Davies (BP Exploration Company) | Matthew Dunning (BP Exploration Company) | Mike Kuchel (Baker Hughes) | Tony Roberts (Baker Hughes) | Michael Taggart (Baker Hughes)
- Document ID
- Society of Petroleum Engineers
- SPE Production & Operations
- Publication Date
- February 2012
- Document Type
- Journal Paper
- 67 - 77
- 2012. Society of Petroleum Engineers
- 4.5.5 Installation Equipment and Techniques, 2.5.2 Fracturing Materials (Fluids, Proppant), 1.6 Drilling Operations, 4.5 Offshore Facilities and Subsea Systems, 5.6.4 Drillstem/Well Testing, 2.2.2 Perforating
- Insert String, Normally Unmanned Installation, Sand Cleanout, Concentric Coiled Tubing, Boat Spooling
- 1 in the last 30 days
- 562 since 2007
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Ravenspurn North is a mature gas field in the southern North Sea with 42 wells, drilled (and many hydraulically fractured) in the late 1980s. By 2006, more than half of the wells had ceased to flow, and many were flowing intermittently. With ailing wells and consequently falling production rates, the longer-term future for Ravenspurn North field was uncertain.
A wireline campaign suggested a common failure mode for many wells: Large amounts of proppant had accumulated in the wellbore. Modeling of the potential range of static and dynamic pressure losses caused by this proppant supported a significant enhancement to the remaining gas potential. However, the depths of the wells combined with subhydrostatic pressure conditions and large-diameter lower completions made achieving cleanout challenging. Furthermore, the target wells were located on unmanned offshore installations with minimal facilities, deck space, and deck loading.
This paper details how each of these obstacles was successfully tackled to reinstate a target set of wells. It describes the various cleanout options that were considered, and why concentric-coiled-tubing vacuum technology (CCTVT) was ultimately selected. Before this project, CCTVT had never been deployed in the North Sea, and nowhere in the world at these reservoir depths. The operation was delivered on the small unmanned installation by conducting the world's first boat-spooling operation of concentric coiled tubing (CCT); rigorously reassessing deck loadings; and running the operation completely self-sufficiently, with a maximum of 10 personnel onboard.
Finally, this paper provides a detailed description of the successful CCTVT operations that recovered a total of 2,950 lbm of proppant from three wells to expose the perforations and unload the wells of liquid. Furthermore, CCT was used to mill out tubing-profile nipples and install a packer to hang off 1,200 ft of flush-joint tail pipe. Innovative thinking and close collaboration between operator and service companies were required, because the ability to perform multiple operations on CCT was in itself pioneering.
Overall, this campaign has pushed the boundaries of intervention technology to deliver an extremely challenging project. This has resulted in a more-certain future for the Ravenspurn North field, as well as newly unlocked opportunities in deep depleted gas wells worldwide.
|File Size||7 MB||Number of Pages||11|
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