Sensor monitors oil and gas wells in real time

Sensor Highway Ltd. (Hampshire, England) dug a niche for its fiberoptic sensors 6000 ft. underground. The fiberoptic detection delivery system, developed by the company, continuously reports real-time monitoring data from oil and gas wells.

Sensor monitors oil and gas wells in real time

Laurie Ann Peach

Sensor Highway Ltd. (Hampshire, England) dug a niche for its fiberoptic sensors 6000 ft. underground. The fiberoptic detection delivery system, developed by the company, continuously reports real-time monitoring data from oil and gas wells.

To test the system`s reliability, a temperature-sensing fiber was in stalled on a trial basis in an onshore 6000-ft. well at British Petroleum`s Wytch Farm facility in Dorset, England. This is the first sensor of its kind in the world, says John Davies, of British Petroleum (BP; Dorset).

The 12,000-ft-long glass fiber, no thicker than a strand of human hair, serves as both the sensor and the transmission system (see photo p. 50). "The fiber is the size of fishing gut," says Davies. And most of its thickness is the heat-resistant coating.

A quarter-inch-diameter stainless-steel hydraulic control line or metal conduit was installed into the infrastructure of the well. The fiberoptic sensor was floated down the conduit in a liquid medium in a continuous-loo¥configuration that takes readings at 1-m intervals from the surface to well bottom and back again.

The temperature throughout the well affects how the pulsed light from a diode-pumped solid-state laser is back-scattered along the fiber strand. The laser, emitting at 1064 nm, is located on the surface in an instrumentation room. The downhole fiber is connected to the laser via an armored fiberoptic cabling at the surface. When the data are decoded, the operator has a temperature profile of the entire well.

Temperature conditions are crucial to the operation of an oil well because the electric submersible pump--used to pum¥oil from the reservoir to the surface--often overheats when operating conditions change without warning. This leads to a decrease in the working life of the pump. "The fiber sensing device will hel¥extend the run life of the pum¥and save us money," says Davies. "The temperature sensor technology is fairly old hat," says Oliver Laurence, technical consultant at Sensor Highway. "What we did new was put the sensor down the hole."

This downhole monitoring system has oil producers taking notice. Conventional methods can only make single-point spot checks. If the sensing system fails, field operators either have to run the field blind or shut down the well and re-complete it--an expensive option. Down hole-sensing systems are installed at the time the well is completed.

The temperature sensor is just the beginning. Sensor Highway wants to apply the same technology to measure other parameters. Pressure, acoustic, and vibration sensors are currently being designed for remote, hostile environments. A pressure sensor is ready for testing and should be on the market by 1998.

Because of the size, multiple sensors can easily be floated down the same quarter-inch tube and pulled u¥and changed at any time without interruptions in operation.

This fiberoptic system will make intelligent wells of the future a reality, says Glynn Williams, managing director of Sensor Highway. These will be self-regulating, where accurate temperature and pressure data will control valves and chokes to regulate oil flow.

Eventually, the sensor will be lowered into oil reserves and act as a production logic device. "We will be able to determine which part of the well is producing, which part is running low, or if water is contaminating the product," says Davies.

"We have monitored horizontal and vertical wells, inside and outside the casing," says Williams. "We expect further gains to be made as we go deeper and into more-hostile environments."

Sensor Highway and SpecTran (Sturbridge, MA) are working together to develo¥better coatings to protect the fiber when it travels into these more-hostile areas. The sensor could potentially be used for nuclear waste monitoring, volcanic activity, and in space applications.

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