Fiber Optic Sensing - Learning How It Really Feels Downhole

Abstract

Fiber optic sensing Magnus McEwen-King describes his company’s vision by saying it is out to build “the Earth’s nervous system.” The company, Qinetiq, has a venture, OptaSense, which is developing practical ways to use fiber optic cable for distributed acoustic sensing in oil wells. It is essentially installing a long string of digital microphones in a well. In partnership with Shell, the former British defense contractor has created systems that track what is happening during hydraulic fracturing and record sound waves during seismic testing. Baker Hughes has a partnership with Shell covering the sense of touch. It is using specially modified fiber optic cable to measure small changes impacting 40-ft-long sections of a well in the US Gulf of Mexico deepwater Mars field. The recently completed injection well has also been wired with fiber optics gathering temperature, pressure, and sound data. Shell’s third venture, with a Dutch company named TNO, will try to sniff out changes in well chemistry using fiber optic cables coated with specially formulated gels. The gels are designed to absorb specific molecules. When the concentration of the target chemical, such as carbon dioxide, increases, the gel absorbs more of it and swells, which is observed by the sensitive fiber. Shell’s goal is to create permanent monitoring systems that make intelligent wells smarter by observing conditions inside a well, meter by meter. Vianney Koelman, chief scientist and fiber optics program leader at Shell International E&P, said fiber optics can directly gather information that helps answer pressing questions, including “‘Is a well producing the way I think it is producing?’ ‘Is it working the way the computer model is telling me?’ It can be quite different than what you think.” Fiber optic temperature measurement systems—ranging from gauges using fiber for measurements in one spot to fiber doing meter-by-meter measurements throughout a well—have been installed in thousands of wells going back to the mid-1990s. The fastest growth has been in heavy oil fields where temperature monitoring improves the efficiency of high-temperature steam injection systems used to coax heavy oil out of the ground.