Fiber–optic sensors have been widely deployed in various applications, and their use has gradually increased since the 1980 s. Distributed fiber–optic sensors, which enable continuous and real–time measurements along the entire length of an optical fiber cable, have undergone significant improvements in underlying industries. In the oil and gas industry, distributed fiber–optic sensors can provide significantly valuable information throughout the life cycle of a well and can monitor pipelines transporting hydrocarbons over great distances. Here, we review the deployment of fiber–optic Rayleigh–based distributed acoustic sensing (DAS), Raman–based distributed temperature sensing (DTS), and Brillouin–based distributed temperature and strain sensing (DTSS) in the oil and gas industry. In particular, we describe the operation principle and basic experimental setups of the DAS, DTS, and DTSS, highlighting their applications in the upstream, midstream, and downstream sectors of the oil and gas industry. We further developed a prototype of a fiber–optic hybrid DAS–DTS system that simultaneously measures vibration and temperature along a multimode fiber (MMF). The reported hybrid sensing system was tested in an operational oil well. This work also discusses the challenges that might hinder the growth of the distributed fiber–optic sensing market in the petroleum industry, and we further point out the future directions of related research.

/pdf/a-review-of-distributed-fiber-optic-sensing-in-the-oil-and-2ixlzp5u.pdf

A Review of Distributed Fiber–Optic Sensing in the Oil and Gas Industry

A novel distributed fiber-optic sensor is proposed and demonstrated, in which two Mach-Zehnder interferometers are used to detect the interference signals with different wavelengths, and one 3 × 3 coupler is deployed to demodulate the time-varying phase change caused by vibration. The novel dual Mach-Zehnder interferometer (DMZI) is composed of two wavelength division multiplexers. Then, a time delay estimation algorithm is designed to construct two related signals using the phase difference, and the two constructed signals are used to obtain vibration position through cross-correlation. Experimental results show that the sensing distance can reach 100 km and the location error is within ±25 m.

Distributed fiber-optic sensor for location based on polarization-stabilized dual-Mach-Zehnder interferometer.

The key technology to demodulate the vibration position along the sensing fiber link in the asymmetric fiber interferometer based vibration sensors is to extract similar variation features with high efficiency, so that the asymmetry of the vibration sensors can be effectively eliminated. The wavelet-based approaches have been developed and demonstrated as effective methods for the time-frequency feature analysis of non-stable signals. In this article, an ameliorated real-time positioning algorithm using maximal overlap discrete wavelet transformation (MODWT) for the long range asymmetric fiber interferometer based vibration sensors has been proposed. Firstly, a median filter is employed to remove noise and to acquire the endpoint of the vibration signal. Thus a much higher endpoint detection precision can be obtained. Secondly, the time-frequency features are acquired through the MODWT, which can further improve the time-frequency distribution resolution and processing efficiency. Thirdly, the time delay between features is obtained using a cross-correlation algorithm. Finally, the vibration position information is demodulated based on the time delay value. The performance of the proposed wavelet-based algorithm was assessed and compared to previous studies in an asymmetric dual laser Mach–Zehnder interferometer based vibration sensing system. And the proposed scheme presented good results in both the positioning accuracy and the efficiency in field tests. Specifically, a detection of 98.2% of positioning errors are distributed within the range of ±20 m at a sensing length of 82 km and a mean processing time of 135 ms is also achieved. Therefore, the proposed scheme can expand the areas of application fields for long range vibration sensing.

High Accuracy and Real-Time Positioning Using MODWT for Long Range Asymmetric Interferometer Vibration Sensors

Mid-infrared broadband polarization beam splitter based on GaS photonic crystal fiber with high extinction ratio

Using fiber network as a huge sensing system will enrich monitoring methods of public infrastructures and geological disasters. With traditional cross-correlation method, laser interferometer has been used to detect and localize the vibration event. However, the random error induced by cross-correlation method limits the localization accuracy, and makes it not suitable for ultrahigh precision localizing applications. We propose a novel time shifting deviation (TSDEV) method, which has advantages over cross-correlation method in practicability and localization accuracy. Three experiments are carried out to demonstrate the novelty of the TSDEV method. In lab test, vibration localization accuracy of ~2.5 m is realized. In field tests, TSDEV method enhanced interferometry is applied to monitor the urban fiber link. Traffic vibration events on the campus road and Beijing ring road have been precisely localized and analyzed, respectively. The proposed technique will extend the function of existing urban fiber network, and better serve the future smart city.

Time shifting deviation method enhanced laser interferometry: ultrahigh precision localizing of traffic vibration using urban fiber link.

A novel distributed fiber-optic localization algorithm with high sensitivity and precision based on merged Michelson-Sagnac interferometer is proposed and demonstrated. By performing simple addition and subtraction processing on the two phase differences of the two interferometers, two superimposed signals with a fixed delay can be obtained. The time delay can be calculated by a cross-correlation algorithm. Combined with the polynomial fitting interpolation, the disturbance location resolution is significantly improved. The total sensing distance can reach 120 km, and the localization errors are within ±35 m and ±160 m in the contact and non-contact disturbance experiment, respectively.

Improved Localization Algorithm for Distributed Fiber-Optic Sensor Based on Merged Michelson-Sagnac Interferometer

Optical fiber interferometer could achieve various dynamic measurements by transforming phase change into intensity change. In this paper, a novel Michelson interferometer (MI) based on two polarization beam splitters (PBSs) is proposed. Two thirds of Rayleigh backscattering (RB) is separated from the signal light by using PBS and Faraday rotating mirror (FRM) due to the difference polarization properties between RB and signal light in optical fibers. And the signal-to-noise ratio (SNR) of system has been significantly improved. Within the detection range of 50 km, the localization experiments on this new interferometer show that the SNR is increased by 6.69 dB compared with traditional MI on the condition of 500 kHz sampling rate. And the positioning accuracy can achieve ±100 m in the first-order null-frequency. The sensing distance also increases from 36.17 km to 49.42 km with a SNR of 15 dB. This proposed sensing system exhibits high sensitivity in the low frequency region, which is of great importance for long-distance buried optical cable detection and location.

A Novel Weak-Scattering Michelson Interferometer Based on PBS for Long-Distance Disturbance Localization

A distributed optic fiber perimeter security system is proved to be an effective strategy for the security monitoring of some vital targets, such as power plants, power substations and telecommunication base stations. However, this method can hardly distinguish different categories of the intrusion behavior and is easily mis-triggered by different kinds of environmental interference. To distinguish different intrusion patterns and different interference events effectively, a vibration pattern recognition algorithm is proposed and demonstrated based on the merged Sagnac interferometer structure. The method consists of two parts: the pre-processing algorithm and the multi-layer perceptron neural networks (MLP-NNs). The pre-processing algorithm is applied to retrieve and extract the vibration signal from the captured source signal, and the MLP-NN is used to realize pattern recognition from each type of input. Typically, a high-dimensional vector group which contains hundreds of orders of vibration signal’s power frequency is obtained to cover as many signalized features as possible. Moreover, results of the experiment deployed on a 10 kilometer long perimeter fence in the transformer substation show that the proposed classification-based model achieves 97.6% classification accuracy in the test. Through multiple comparison tests, the proposed model gives a solid performance in the subsequent integrated evaluation to classify each intrusion pattern.

Intrusion behavior classification method applied in a perimeter security monitoring system.

We propose a practical secure key generation and distribution (SKGD) scheme for actual application. Based on the experiment results of the polarization properties of the actual optical-fiber link, we propose a SKGD method by the active modulation of the state of polarization of the optical-fiber by two polarization scramblers placed at the local end of the legal users in the point-to-point communication system. Experiment results prove that the signals received by legal users share high correlation using 20 km standard single-mode fiber and 1 KHz polarization scrambling rate, and the bit generation rate can reach to 1216 bit/s with a bit error rate of ∼0.33%. Security of the system is also analyzed in terms of the polarization properties of the system; the theoretical and experimental results indicate that the proposed scheme possesses high security due to the invisibility of the key signal and the technical difficulty of the recovery of the key sequence.

Qian Xiao

Papers

Distributed fiber-optic sensor for location based on polarization-stabilized dual-Mach-Zehnder interferometer.

Improved Localization Algorithm for Distributed Fiber-Optic Sensor Based on Merged Michelson-Sagnac Interferometer

A Novel Weak-Scattering Michelson Interferometer Based on PBS for Long-Distance Disturbance Localization

Intrusion behavior classification method applied in a perimeter security monitoring system.

Secure key generation and distribution scheme based on two independent local polarization scramblers.