Abstract:
A probe is provided that contacts the inner surface of the casing or other production tubing and imparts energy to the surface at the contact point, for example as heat energy or mechanical energy. Energy is imparted around the circumference of the casing, and a fiber optic distributed sensor located on the outer surface of the casing is used to measure and record the energy that it receives while the probe is moved to impart energy around the circumference. A record of energy versus position of the probe around the circumference can be obtained, from which maxima in the detected energy measurements can then be found. The position around the circumference which gave the maximum measurement should be the position at which the optical fiber of the fiber optic distributed sensor is located. In addition, an ultrasonic arrangement is also described, that relies on ultrasonic sound to provide detection.
Abstract:
A method and apparatus for monitoring a structure using an optical fiber based distributed acoustic sensor (DAS) extending along the length of the structure. The DAS is able to resolve a separate acoustic signal with a spatial resolution of 1 m along the length of the fibre, and hence is able to operate with an acoustic positioning system to determine the position of the riser with the same spatial resolution. In addition, the fiber can at the same time also detect much lower frequency mechanical vibrations in the riser, for example such as resonant mode vibrations induced by movement in the surrounding medium. By using vibration detection in combination with acoustic positioning then overall structure shape monitoring can be undertaken, which is useful for vortex induced vibration (VIV) visualisation, fatigue analysis, and a variety of other advanced purposes. The structure may be a sub-sea riser.
Abstract:
Embodiments of the present invention address aliasing problems by providing a plurality of discrete acoustic sensors along a cable whereby acoustic signals may be measured in situations where the fibre optic cable has not been secured to a structure or area by a series of clamps. Acoustic sampling points are achieved by selectively enhancing the acoustic coupling between the outer layer and the at least one optical fibre arrangement, such that acoustic energy may be transmitted selectively from the outer layer to the at least one optical fibre arrangement. The resulting regions of acoustic coupling along the cable allow the optical fibre to detect acoustic signals. Regions between the outer layer and the at least one optical fibre arrangement that contain material which is acoustically insulating further this enhancement since acoustic waves are unable to travel through such mediums, or at least travel through such mediums at a reduced rate.
Abstract:
An optical fiber sensing system includes a sensing optical fiber and one or more optical amplifiers in series with the sensing fiber and arranged to increase the power of sensing pulses travelling along the fiber to thereby increase the range of the sensing system. The optical fiber sensing system is one selected from the group including an optical fiber distributed acoustic sensor (DAS), an optical fiber distributed temperature sensor (DTS), or an optical time domain reflectometry (OTDR) system.
Abstract:
Embodiments of the present invention address aliasing problems by providing a plurality of discrete acoustic sensors along a cable whereby acoustic signals may be measured in situations where the fiber optic cable has not been secured to a structure or area by a series of clamps, as described in the prior art. Acoustic sampling points are achieved by selectively enhancing the acoustic coupling between the outer layer and the at least one optical fiber arrangement, such that acoustic energy may be transmitted selectively from the outer layer to the at least one optical fiber arrangement. The resulting regions of acoustic coupling along the cable allow the optical fiber to detect acoustic signals. Regions between the outer layer and the at least one optical fiber arrangement that contain material which is acoustically insulating further this enhancement since acoustic waves are unable to travel through such mediums, or at least travel through such mediums at a reduced rate.
Abstract:
A probe is provided that contacts the inner surface of the casing or other production tubing and imparts energy to the surface at the contact point, for example as heat energy or mechanical energy. Energy is imparted around the circumference of the casing, and a fiber optic distributed sensor located on the outer surface of the casing is used to measure and record the energy that it receives whilst the probe is moved to impart energy around the circumference. A record of energy versus position of the probe around the circumference can be obtained, from which maxima in the detected energy measurements can then be found. The position around the circumference which gave the maximum measurement should be the position at which the optical fiber of the fiber optic distributed sensor is located. In addition, an ultrasonic arrangement is also described, that relies on ultrasonic sound to provide detection.
Abstract:
An interferometer apparatus for an optical fibre system and method of use is described. The interferometer comprises an optical coupler and optical fibres which define first and second optical paths. Light propagating in the first and second optical paths is reflected back to the optical coupler to generate an interference signal. First, second and third interference signal components are directed towards respective first, second and third photodetectors. The third photodetector is connected to the coupler via a non-reciprocal optical device and is configured to measure the intensity of the third interference signal component directed back towards the input fibre. Methods of use in applications to monitoring acoustic perturbations and a calibration method are described.
Abstract:
A probe is provided that contacts the inner surface of the casing or other production tubing and imparts energy to the surface at the contact point, for example as heat energy or mechanical energy. Energy is imparted around the circumference of the casing, and a fiber optic distributed sensor located on the outer surface of the casing is used to measure and record the energy that it receives whilst the probe is moved to impart energy around the circumference. A record of energy versus position of the probe around the circumference can be obtained, from which maxima in the detected energy measurements can then be found. The position around the circumference which gave the maximum measurement should be the position at which the optical fiber of the fiber optic distributed sensor is located. In addition, an ultrasonic arrangement is also described, that relies on ultrasonic sound to provide detection.
Abstract:
An interferometer apparatus for an optical fibre system and method of use is described. The interferometer comprises an optical coupler and optical fibres which define first and second optical paths. Light propagating in the first and second optical paths is reflected back to the optical coupler to generate an interference signal. First, second and third interference signal components are directed towards respective first, second and third photodetectors. The third photodetector is connected to the coupler via a non-reciprocal optical device and is configured to measure the intensity of the third interference signal component directed back towards the input fibre. Methods of use in applications to monitoring acoustic perturbations and a calibration method are described.
Abstract:
The high sensitivity provided by an enhanced DAS system comprising a DAS interrogator and a high reflectivity fiber allows for the deployment of such a high reflectivity fiber as part of a wireline intervention cable which can be temporarily lowered into a well, thus avoiding the need to permanently cement such a high reflectivity optical fiber cable into the well. Instead, such a wireline cable incorporating the high reflectivity optical fiber has been found to be sensitive enough to detect micro-seismic activity and low frequency strain with many more measurement points and channels than conventional wireline deployed geophones and tiltmeters. Additionally, the cable requires no clamping and can be easily and quickly removed from one well and placed in another well.