Shining a Light on Coiled Tubing
A cultural shift is taking place in coiled tubing operations. No longer do CT crews rely solely on surface measurements to infer downhole conditions. Using fiber optics and downhole sensors, operators can monitor critical processes, fine-tune job parameters and adapt to changing conditions as the job progresses.
Ibrahim H. Al-Arnaout Saudi Aramco
Udhailiyah, Saudi Arabia George Brown
Southampton, England
Rex Burgos Jon Christian Doug Pipchuk Hubertus Thomeer Sugar Land, Texas, USA
Juanih Ghani Muzily Musa Khor Siak Foo Talisman Malaysia Ltd. Kuala Lumpur, Malaysia
Abul (Jamal) Jamaluddin Kuala Lumpur, Malaysia
Jock Munro Aberdeen, Scotland
Oilfield ReviewWinter 2008/2009: 20, no. 4. Copyright © 2009 Schlumberger.
For help in preparation of this article, thanks to Matt Garber and John Lovell, Rosharon, Texas.
ACTive, Blaster, Decipher, Discovery MLT, eFire-CT, FMI, iCenter and iCoil are marks of Schlumberger.
INCONEL is a mark of Special Metals Corporation.
Any maintenance or remedial workover is a major event in the life of a well. In many cases, a workover requires the removal and replacement of the production tubing string after a workover rig has been placed on location and the well has been killed. To preclude the production problems and expense associated with these activities, many operators turn to coiled tubing (CT) technology to permit remedial work on live wells. This technology permits tools and materials to be deployed through existing production tubing or casing while the well continues to produce. Coiled tubing fulfills three key needs that are vital for performing remedial work on live wells. First, any such operation requires a means of providing a dynamic seal between the formation pressure and the surface. Next, a continuous conduit that can be run into a well to allow fluid conveyance is needed. And finally, there must be a way to both run this conduit into the well and retrieve it under pressure.
Benefits of the CT approach include rapid mobilization and rig-up, fewer personnel, small environmental footprint and reductions in time associated with pipe handling while tripping in and out of the hole. More importantly, the capa - bility for continuous circulation allows an operator to avoid the risk of formation damage inherent in killing a well. These advantages yield significant cost savings for CT methods when compared with conventional workover operations.
Coiled tubing operations, however, are not without their problems. Since the technology’s inception, CT crews have had to infer from surface measurements what was happening downhole. Well service operations, by their very nature, unsettle the downhole environment of any well. Mechanical events, chemical processes and the movements of fluids inevitably cause downhole perturbations that result in pressure or temperature changes. Except in rare instances where costly permanent completions have been installed, the only options for monitoring downhole disturbances have been through surface pressure and rate measurements. These measurements may be severely hampered or attenuated by interference that occurs between the initial disturbance event and subsequent events. The biggest limitation, however, is that surface measurements do not reflect any correlation between the disturbance and the depth at which it occurred. With no direct measure of bottomhole parameters, the operator could only deduce answers to serious concerns pertaining to the fluid level in a well, or the depth of a packer when it inflated or wellbore pressures prior to perforating.
These issues are being addressed through the use of optical fibers. In one application, a new downhole monitoring system uses fiber-optic strands inside a CT string to measure tempera - ture along the length of the wellbore while providing telemetry between the surface and
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