Using a fibre-optic cable as Distributed Acoustic Sensor for Vertical Seismic Profiling - Overview of various field tests
Bibliographic record
Abstract
Fibre-optic Distributed Acoustic Sensing (DAS) or Distributed Vibration Sensing (DVS) is a technology, where\nan optical fibre cable is used as a sensor for acoustic signals. An ambient seismic wavefield, which is coupled by\nfriction or pressure to the optical fibre, induces dynamic strain changes along the cable. The DAS/DVS technology offers the possibility to record an optoelectronic signal which is linearly related to the time dependent local strain.\nThe DAS/DVS technology is based on the established technique of phase-sensitive optical time-domain reflec-\ntometry (phi-OTDR). Coherent laser pulses are launched into the fibre to monitor changes in the resulting elastic\nRayleigh backscatter with time. Dynamic strain changes lead to small displacements of the scattering elements\n(non-uniformities within the glass structure of the optical fibre), and therefore to variations of the relative phases of the backscattered photons. The fibre behaves as a series of interferometers whose output is sensitive to small changes of the strain at any point along its length. To record the ground motion not only in space but also in time, snapshots of the wavefield are created by repeatedly firing laser pulses into the fibre at sampling frequencies much higher than seismic frequencies.\nDAS/DVS is used e.g. for continuous monitoring of pipelines, roads or borders and for production monitoring from within the wellbore. Within the last years, the DAS/DVS technology was further developed to record seismic data.\nWe focus on the recording of Vertical Seismic Profiling (VSP) data with DAS/DVS and present an overview of\nvarious field tests published between 2011 and 2014. Here, especially CO2 storage pilot sites provided the oppor-tunity to test this new technology for geophysical reservoir monitoring. DAS/DVS-VSP time-lapse measurements\nhave been published for the Quest CO2 storage site in Canada. The DAS/DVS technology was also tested at the\nCO2 storage sites in Rousse (France), Citronelle (USA), Otway (Australia) and Ketzin (Germany). At Ketzin it\nwas possible to record a multi-offset VSP simultaneously within four wells, allowing a high-resolution imaging of\nthe reservoir. These publications represent a wide range of different source types, source-receiver geometries and\ncable deployments (on tubing, behind casing).\nIn conclusion, the DAS/DVS is a promising technology for VSP acquisition; the publications showed that it is\npossible to use DAS/DVS-VSP data for the calculation of velocity profiles, for well-ties and for seismic imaging.\nSome points have to be taken into account when recording DAS/DVS-VSP data. With an optical fibre, only a single\nvalue reflecting the strain between two points within the fibre is measured. The sensitivity of the fibre-optic cable is generally lower than that of a geophone with current readout units. If a fibre-optic cable has already been installed in a well, no well intervention is needed to acquire a VSP on demand, e.g. for time-lapse measurements. Several wells can be interrogated at the same time with full vertical coverage.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.003 | 0.006 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".