Reducing Intervention in Subsea Wells With Fiber-Optic Technology
- Chris Carpenter (JPT Technology Editor)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- November 2013
- Document Type
- Journal Paper
- 176 - 178
- 2013. Offshore Technology Conference
- 1 in the last 30 days
- 231 since 2007
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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 23929, "Reducing Intervention in Subsea Wells With Fiber-Optic Technology," by John Lovell, Schlumberger, prepared for the 2013 Offshore Technology Conference, Houston, 6-9 May. The paper has not been peer reviewed.
Fiber-optic-system installations have reduced the need for intervention by logging tools and have given crucial insights into wellbore integrity and reservoir production. Consequently, a prime application of fiber technology should be in deepwater fields, where intervention can be prohibitively expensive. The reluctance to incorporate downhole fiber appears to be caused by limitations of technology relating to cables, deployment, acquisition, and interfacing. These barriers are slowly being eliminated, and a small number of subsea wells have now been implemented with in-well fiber.
Permanently installed fiber-optic systems have been commercially available in the oil field since the early 1990s, with the bulk of the deployments providing fiber-optic distributed temperature based upon Raman backscattering. This Raman distributed-temperature-sensing (DTS) measurement system provides continuous data along the length of the completion without the need for intervention and without introducing restrictions in the inner diameter of the completion tubulars, restrictions that could impede subsequent wellbore access. Typical DTS spatial resolution is better than one data point per meter, with a temperature resolution of 0.01°C. Applications of the distributed-temperature data have included calculating flow contributions across the sandface, evaluating water-injection profiles, diagnosing the effectiveness of fracture jobs, finding cement tops behind casing, and identifying crossflow between producing zones.
The growth of fiber installations for dry-tree (land and platform) applications is increasing exponentially. More than 1,200 installations have been deployed by one service company alone. Most of those installations were single-stage completions, often for thermal or steam-assisted-gravity-drainage (SAGD) application, and relied upon the ability to pump fiber along a control line to convey the sensing fiber. Approximately 20 of those wells have fiber pumped along the sandface of dual-stage openhole-gravel-pack (OHGP) completions.
A significant advantage of the pumped fiber was that, if the fiber degraded over time, it could be pumped out and replaced. This was particularly important before the discovery of how to construct fibers with some immunity to darkening from H+ and OH− ions. With hydrogen resistance came the possibility of increased longevity for fixed-fiber cables, and, since 2006, an alternative to pumped fiber has been available that combines multiple hydrogen-resistant fibers with an electronic line to create a hybrid cable (Fig. 1). This cable can power high-accuracy quartz gauges and can also give the benefits of fully distributed Raman DTS. More than 60 such systems have been deployed to date.
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