Fiber-optic sensing is known in the oil and gas industry as a technology that allows continuous temperature profiling along entire well paths. However, surveillance applications focusing solely on temperature measurements are limited to recovery processes with a clear, unambiguous thermal signature. This has prevented fiber-optic sensing from becoming a widely deployed technology in oil and gas production. However, we are now witnessing a confluence of novel fiber-optic technologies that promise a much wider range of subsurface measurements. This opens new avenues in well and reservoir management and highlights the opportunity for fiber optics to become a pervasive oilfield technology. For this to achieve reality, the multiple sensing technologies being introduced by various providers need to be combined and deployment costs contained. The key enabler to achieving these goals is to bundle a selection of fibers into a single cable suitable for downhole deployment and optimized for monitoring a variety of in-situ data.
Distributed Sensing—A Growing Toolbox of Fiber-Optic Techniques
The individual sensing technologies are at various stages of development and derisking. Distributed temperature sensing (DTS) is the most mature technology, followed by distributed strain sensing (DSS). The latter technology, developed by Shell and Baker Hughes under the product name RTCM (Real Time Compaction Monitoring), allows operators to monitor tiny well deformations during the lifetime of a well (Earles et al. 2010). Both technologies can be combined, and fiber-optic pressure sensing capabilities (often labeled DPS) provide complementary data to this mix of sensing technologies (Available DPS systems tend to provide single- or multipoint pressure readings as opposed to true distributed pressure measurements, it should be noted.)
Other fiber-optic sensing technologies, such as distributed acoustic sensing (DAS) and distributed chemical sensing (DCS), are less mature but are expected to hit the market in the next few years. DAS turns a standard telecom fiber deployed over an entire well path into a permanent array of microphones. DCS, the latest addition to the growing toolbox of fiber-optic techniques, will allow the detection of specific molecules along the full inflow area of producing wells. Last year, Shell embarked on a collaboration with QinetiQ, based in the UK, to evaluate the potential of DAS for oil and gas applications, and this year Shell entered into a similar arrangement with TNO, based in the Netherlands, with the aim of derisking DCS technology. Currently, the DAS technology is undergoing field trials, while DCS is in an early derisking phase.