In recent years it has been noted that the ambient noise field in coastal waters at various sites around the southern UK contains an impulsive noise contribution. Specifically a clicking sound can be heard amongst the ambient noise, which is particularly evident at low sea states. The noise exhibits similar qualities to the snapping sound made by various species of crustacea, e.g. members of alpheus family. The range of such animals is not usually considered to include the UK, they are most commonly found in reefs in tropical regions. However, some animals have been captured during dredging operations and have also recently been photographed in UK waters. This paper reports the results of our work exploring the acoustic aspects of this phenomenon. We shall present data recorded at various sites on the southern coast of the UK, from Cornwall in the West to Chichester in the East. These data have been collected on a variety of recording apparatus and in different recording environments. Results will be presented that detail the temporal and spectral characteristics of individual clicks. Further the results of analysis of data collected on a 3-D array will allow us to estimate source distribution through the water column.

Closed-loop flow control in flotation processes can enable both mass pull and grade control; however, the implementation of flow control systems in flotation plants has traditionally been challenged by a lack of sensing solutions capable of direct concentrate flow measurement. Notably, cameras have been implemented in many cases to address this sensing gap; though camera-based surface froth velocity estimates remain an indirect and potentially error-prone approach to inferring concentrate production rates. Recently, Anglo American’s FutureSmart MiningTM program collaborated with Silixa to pioneer the use of non-intrusive distributed fibre optic sensing for direct concentrate flow metering. In early 2017, a pilot at the Mogalakwena North Concentrator was executed whereby a single, continuous length of optical sensing fibre was used to meter a variety of flotation flows, including water, slurry, air, and concentrate flows. The results indicate that this new technology can meter many process flows simultaneously throughout flotation plants using nonintrusive instrumentation, opening a new era for closed-loop flow control in flotation.

Acoustic scientist Daniel Finfer describes life at Silixa, a start-up firm that provides fibre-optic sensing technologies to the oil and gas industry.

Distributed acoustic sensing (DAS) using fiber optic cables is an emerging seismic acquisition technology for the oil and gas industry, geothermal resource exploration, and underground fluid-storage monitoring. This technology offers the advantage of improving seismic acquisition by enabling massive arrays for monitoring of seismic wavefields at reduced cost with respect to conventional methods. In general, it is accepted that this method provides acoustic signals comparable with conventional seismic data, however, without the multicomponent directional information typical of geophones. We have developed a modified data extraction method and found that, as a result of the dense spatial distribution of recording points along the optic cable, DAS can provide two linked wavefield components in the axial direction, even when using a single 1D cable line. These signal pairs consist of dual components that are related to native strain rate (or strain) and particle acceleration (or velocity) fields at a given recording location. These dual signals are easily usable for wavefield separation purposes simply performing a trace-by-trace combination by appropriate scaling coefficient. The analysis performed with borehole data from linear and helically wound cables demonstrates the effectiveness of polarity recovery and dual-wavefield separation. We show real examples in which the data can be combined to provide separation of up-and downgoing wavefields. The ratio of the dual components provides information on local slowness properties in the formation.

Summary In this work, we investigate the wavefields and the broadside response of a helical distributed acoustic sensor cable co-located with a hydrophone streamer in a shallow horizontal borehole. We discuss dual-wavefield separation results for selected optical-cable signals recorded with dense receiver spacing. Moreover, we interpret the phase and amplitude differences observed in the HWC and streamer data using sources at different azimuth. The analysis shows how the frequency response for the DAS signal with respect to the corresponding streamer signal changes with azimuth.

Abstract The Distributed Acoustic Sensor (DAS) used here (Parker et al., 2012), allows both the amplitude and the phase of acoustic signals to be continuously recorded along a length of optical fiber. In this paper, non-intrusive flow metering based on the use of this sensor is performed for different pipe sizes and flow conditions. By wrapping a continuous length of fiber helically around the exterior pipe, the system measures the dynamic radial strain (hoop strain) along a pipe with a spatial resolution on the order of millimeters and a time resolution on the order of tenths of milliseconds. As a result, this implementation of the sensing system output makes it possible to visualize the generation and convection of eddies by using a waterfall plot of distance versus time. By analyzing the recorded data using a frequency-space transformation (f-k plot), it is possible to determine precisely both the speed of eddies, as well as the speed of sound. This paper will present experimental results from single- and multi-phase tests to demonstrate the applicability of the technology to the monitoring of fluid velocity and the determination of flow composition. It will be seen that the system, which can be installed unobtrusively, is straightforward to apply for several types of commonly encountered flow regimes. Further, this paper will also consider several practical aspects regarding the installation and use of such a system in the oilfield. Finally, it will be shown how multiple monitoring zones can be incorporated using a single optical fiber. It will be seen that this system is non-intrusive and can be retrofitted to existing pipes to monitor the flow simultaneously at multiple locations for accurate flow profiling and characterization.

Distributed optical fibre sensors are established tools in the energy industry, finding many applications for production optimisation and integrity monitoring. Recently, a new class of instrument, the Distributed Acoustic Sensor (DAS), has been launched which adds seismic imaging to the list of energy industry applications. In this paper, we describe one such distributed acoustic sensor (named the iDAS) and demonstrate, through a series of lab experiments, the signal quality and performance that can be achieved. We show data which demonstrates the capability of the iDAS to measure the true acoustic signal (amplitude, frequency and phase) at all points along the sensing fibre length. We also compare the iDAS data with data collected from conventional point sensors and detail experiments which validate key performance criteria. We follow the lab experimental validation of the iDAS with a series of lab and field demonstrations. The lab demonstrations encompass localisation (ranging) of events away from the sensing fibre (for security applications) and acoustic imaging through the formation of a large acoustic camera using a single sensing fibre. The field demonstrations show comparisons of iDAS and geophone measurements in a surface seismic survey and improvements made by stacking shot records from an offshore VSP survey.

Abstract Historically in-well flow measurement has been challenged by downhole power requirements and post-installation inflexibility. Distributed acoustic sensing makes it possible to monitor the acoustic field along the entire length of a standard fiber optic cable, and therefore facilitate flow monitoring without any downhole electric power requirements. Further, the distributed nature of such systems enables post-installation adaptability as the production profile evolves. Partly as a result of this flexibility, distributed acoustic sensors have now started to gain momentum as a recognized solution for in-well flow surveillance. In this paper, Silixa will present recent development work showing how distributed technology can enable high accuracy flow monitoring. Emerging results will be used to show how array processing of flow noise can be used to develop production data. Examples from the laboratory will be used to demonstrate these advanced techniques. It will be seen that advanced signal processing can be combined with knowledge concerning the physics of fluid-acoustic interactions to make determinations concerning the flow within a well. Finally, it will be shown that there exists strong promise for this upstream technology in a broad variety of well-types.

Many Statoil operated wells are completed with fibre optic cables, typically installed for transmitting data from pressure/temperature gauges in the wells. The use of fibre optic cables for Distributed Acoustic Sensing (DAS) to acquire borehole seismic data in producing wells has been tested in a cooperation project between Silixa, Weatherford and Statoil, supported by Technology Strategy Board UK. Offshore field trials have been successfully carried out by retrofitting Silixa iDAS units to fibre optic cables previously installed in producing wells. Seismic signals were generated by a towed source and recorded by iDAS using the fibres in the wells as distributed sensors. The iDAS measurements were carried out without disturbing the normal operation of the wells, which were all producing during the acquisition of down hole seismic data. The fibre optic cables used for the tests were installed strapped to tubing .i.e. without direct coupling to the formation. Even so, and in the presence of noise from production, it was possible to acquire seismic data with clear first arrivals from which travel times and interval velocities could reliably be obtained. Also reflected and refracted events are clearly visible. We will present results from DAS measurements in four producing offshore wells and discuss the potential of this exciting technology.

Summary Distributed acoustic sensors (DAS) using fiber optic cables is an emerging acquisition technology for O&G industry. It offers the advantage of improving seismic acquisition by massive monitoring of seismic waves at reduced cost. In this paper we show that, as a result of the dense spatial distribution of recording points along the optic cable, DAS can provide two field components in the axial direction, even when using a single one-dimensional line. These signal pairs consist of dual components, which are related to strain and particle velocity fields at a given recording location. We show with real examples where the data can be combined to provide separation of up- and down-going wavefields. The ratio of the dual components provides information on local slowness properties in the formation.

Summary Distributed acoustic sensors (DAS) are an emerging fibre optic-based technology enabling seismic investigations with innovative configurations by massive receiver arrays in boreholes and at the surface. Advantages of DAS technology include lower equipment costs and reduced installation complexity, especially in boreholes, with respect to equivalent applications using conventional seismic sensors. We present results of a joint borehole-surface calibration experiment. The main targets of this study were the analysis of S/N and of the directional responses for recorded wavefields. Borehole signals were acquired by DAS and compared with signals acquired by permanent 3C geophones installed outside the casing of the instrumented well at maximum depth of about 200 m. Multi-offset vertical seismic profiles were acquired by a surface seismic vibrator source with two different azimuths. At the surface, settings of buried and near-surface sensors was prepared in a cross of trenches using DAS cables along with single and multicomponent geophones at corresponding positions. Using the surface installation, a reciprocal seismic line was acquired by maximum offset of approximately one kilometer for the vibrator source. The analysis shows the correspondences in the seismic wavefields acquired by the different methods, compares the physical quantities, and confirms the quality of the DAS signals.

Simultaneous multiwell VSP data have been acquired using fibre optic cables in producing wells as distributed acoustic sensors. The measurement apparatus was retrofitted to the fibre optic cables installed for other purpose with completion of the wells. Data were acquired with no other instrumentation in the well and without disturbing the normal operation of the wells.

La adquisicion de datos de perfiles sismicos verticales (PSV) en un pozo utilizando la tecnologia con cables convencional requiere hacer descender un arreglo de sensores sismicos dentro del pozo para registrar las senales sismicas generadas por un buque disparando en la superficie. Debido a los gastos que conlleva la interrupcion de la produccion, rara vez se realiza en pozos productores y los PSV no han sido economicamente viables para fines de monitorizacion. La tecnologia inteligente de deteccion acustica distribuida (iDAS, por sus siglas en ingles) permite utilizar un cable de fibra optica como arreglo masivo de sensores acusticos. En la actualidad, se despliegan cables de fibra optica adecuados para las mediciones iDAS a lo largo de muchos pozos con otros objetivos. La iDAS se puede adaptar a las fibras opticas existentes para adquirir mediciones acusticas muestreadas de manera densa a bajo coste debido a que el funcionamiento normal del pozo no se ve alterado.