A new technique developed at Sandia National Laboratories (Albuquerque, NM; www.sandia.gov) uses a low-cost disposable fiberoptic telemetry system to relay real-time information about oil and gas drilling. "We have come up with a unique system using throwaway fiberoptics that relays information of what is going on at the end of the drill string as it is happening," says David Holcomb, the Sandia researcher who devised the technique. "Information is instantaneously sent to the surface about temperatures, pressure, chemistry, and rock formation--all without stopping the drilling operation."
Holcomb conceived the idea of a disposable cable about eight years ago at an oil and gas industry meeting. People there indicated the need for immediate access to information about the drilling process and the formations being drilled. They wanted to obtain data without halting the drilling operation and have it be transmitted to the surface immediately at a rate high enough to support video systems.
"Traditionally to gather this type of information, drilling would have to be stopped so that instrumentation could be lowered into the drill hole," Holcomb says. "Ceasing the drilling process is extremely expensive, though, especially for offshore drilling."
Using fiberoptic telemetry to transmit information from the down-hole end of the drill string during drilling has been of interest to the oil and gas well drilling industry for some time, but cost was an issue. One reason involved the need for bulky armor to protect the delicate optical fiber. Equally costly was the downtime required to deploy the cable. These points are moot with Holcomb's technique, which uses unarmored fiber, protected only by a thin, clear, protective plastic coating similar to that found in missile guidance systems. The system also can deploy miles of fiber from a small spool at missile speeds.
"The process differs from conventional thought in that the cable is considered a throwaway item to be used once and then ground up and flushed out in the drilling mud," Holcomb says. "If the cable only has to survive for a few hours and need not be retrieved, it is feasible to use unarmored fiber, which is cheap and can be wound into packages small enough to be inserted into the drill pipe without interfering with operations."
The light, compact unarmored optical fiber flows through the drill string with the mud to reach the bottom of the hole where it instantaneously sends back information to drill operators. Actual oil and gas drill holes are about 8 to10 in. in diameter or larger. The pipe (drill string) running down the middle of the hole through which the mud flows is about 5 in.
To deploy and control the optical fiber in the rapidly moving mud in the drill string, researchers developed a deployment tool. The optical fiber is wound up like a spool of thread inside the tool, which controls the payout of the fiber into the drill string. The deployment tool weighs about 75 pounds; the fiberoptics placed into the drill string weighs about one pound.
Holcomb said he and other researchers successfully showed that the disposable fiberoptics telemetry system works in tests last September at the GRI/CatoosaSM Test Facility, Inc., a Catoosa, OK-based subsidiary of the Gas TechnologyInstitute (GTI). "While in field tests the optical fiber was dropped only 3,000 feet, we see no limitations. The cable could easily reach 10,000 to 20,000 feet."
Researchers had two primary concerns going into the test. First, they were worried that the abrasive nature of the mud flowing through the drill string would chew up the fiber. The second concern revolved around whether the drag of the mudflow down the drill hole would break the fiber. Both concerns turned out to be inconsequential.
Researchers also determined the new system could transmit data at about 1 mbit/s, 100,000 times faster than commercially available MWD (measure while drilling) transmission systems, without interfering with the drilling process. GTI, which funded recent research after Sandia funded the early work, is now seeking a partnership from the oil and gas industry to put the disposable fiberoptics telemetry system into production.