Silixa (United Kingdom)

The emergence of distributed acoustic sensing (DAS) as a geophysical monitoring tool has provided a new opportunity to acquire large vertical seismic profiling (VSP) surveys with ease, as it offers the possibility of recording the acoustic signal over the entire fiber or well length with a single shot. This reduces acquisition time by removing the need to move the sensors, required for conventional point-sensor measurements. This chapter outlines the processing and fault interpretation performed for the largest known onshore DAS 3D VSP survey conducted at the gas hydrate research Stratigraphic Test Well Hydrate-01 on the North Slope of Alaska. The data were recorded on a single-mode fiber in a cable permanently cemented behind casing. Two vibroseis sources were used in the survey. The data were processed with a sequence designed to produce a precise and high-resolution P-wave image that included editing, redatum, bandpass filtering, denoise, upgoing/downgoing wavefield separation, deconvolution, and migration. Faults around the Hydrate-01 well were identified and interpreted using the 3D VSP volume and attributes. These faults were clearly observed in the 3D VSP volume but absent from the 3D surface seismic volume.

Long-term seismic monitoring arrays are often deployed to shallow boreholes to reduce the seismic noise. We investigate noise level decay in shallow boreholes. A large number of publicly available data with such deployment is available at the seismic monitoring array near the town of Groningen, which allows also characterization of the seismic noise decay in shallow boreholes in urban environments. We study noise distribution at 4 sites from this array. Each site includes 5 receivers deployed in shallow vertical boreholes with 50 meters intervals between the surface and 200 m depth. We show there is no difference between noise levels during the summer and winter at the borehole instruments. However, we observe diurnal variation at all depth levels. We also show there are higher noise levels throughout weekdays and lower during weekends and state holidays. These changes are not only observed at the surface but also at the deepest receivers. This implies that the dominant source of this noise is anthropogenic and it penetrates to depths of 200 meters even at frequencies exceeding 5 Hz. This observation is contradicting the common assumption that the seismic noise consists of the surface waves.

Sample return capsules (SRCs) entering Earth’s atmosphere at hypervelocity from interplanetary space are a valuable resource for studying meteor phenomena. The 2023 September 24 arrival of the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer SRC provided an unprecedented chance for geophysical observations of a well-characterized source with known parameters, including timing and trajectory. A collaborative effort involving researchers from 16 institutions executed a carefully planned geophysical observational campaign at strategically chosen locations, deploying over 400 ground-based sensors encompassing infrasound, seismic, distributed acoustic sensing, and Global Positioning System technologies. Additionally, balloons equipped with infrasound sensors were launched to capture signals at higher altitudes. This campaign (the largest of its kind so far) yielded a wealth of invaluable data anticipated to fuel scientific inquiry for years to come. The success of the observational campaign is evidenced by the near-universal detection of signals across instruments, both proximal and distal. This paper presents a comprehensive overview of the collective scientific effort, field deployment, and preliminary findings. The early findings have the potential to inform future space missions and terrestrial campaigns, contributing to our understanding of meteoroid interactions with planetary atmospheres. Furthermore, the data set collected during this campaign will improve entry and propagation models and augment the study of atmospheric dynamics and shock phenomena generated by meteoroids and similar sources.

Summary The study addresses the significant threat to public safety posed by seismicity induced by human activities, emphasizing the critical need for precise and timely earthquake hypocenter localization. This research utilizes the Fourier Neural Operator (FNO) framework to localize microseismic events in the Enhanced Geothermal Systems (EGS) setting at the Utah FORGE site. By applying FNO to actual microseismic data from the EGS operational well, the study demonstrates the model’s capability to accurately predict hypocenter locations. First arrival traveltimes were used for the four selected microseismic events recorded during EGS activities at the Utah FORGE on April 24–28, 2019, including a perforation shot. The velocity model in this study was approximated using sonic log data from well 58–32. This work not only establishes the efficacy of FNO in source localization under realistic conditions, addressing challenges like partial data coverage, but also highlights its potential as a valuable tool for microseismic monitoring. The proposed method opens a pathway to real-time microseismic monitoring, as the trained FNO model can be evaluated instantly to determine the source location, facilitating real-time decision-making for the safe and effective development of subsurface operations.

Abstract A series of fiber optic surveys were performed in an Onshore well in Abu Dhabi to prove the concept of using both Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS) for water injection monitoring. This technology aims to provide new and novel techniques where these surveys could be carried out without wellbore intervention, thereby reducing cost, removing HSE risk and lowering carbon footprint. In addition to these significant benefits fiber optic data provides a dense array of measurements from surface to total depth. The well selected for this proof-of-concept pilot was an onshore horizontal water injector located south of Abu Dhabi. Total depth of the well is approximately 13,000ft, of which approximately 5,000ft is an open hole injection interval. The fiber optic cable was clamped to a 3.5″ tubing string at the time of completion, all the way from surface to total depth. The reservoir section was completed open hole with slotted 3.5″ tubing below the production packer allowing injection through perforated pipe into five separate intervals, each isolated by four swells packers. DAS and DTS data were recorded on the first injection into this well. Although water injection had started in the field the project team obtained dispensation from the reservoir management team to keep the well shut in until fiber optic acquisition could be acquired. This allowed a stable geothermal baseline to be obtained, and after initial injection the well only had to be shut for a few hours to obtain a good warmback response.

We examine the use of state-of-the-art distributed sensing systems to extract temperature information from the optical fibre infrastructure already of the Electricity Authority of Cyprus power distribution network (~25-year old installation); as a means of optical fibre distributed sensing in the underground cables. The optical fibres are collocated with existing power distribution cables, for the purpose of power line monitoring cable joints that are prone to failure, along with general monitoring for unusual behaviour and potential cable fault conditions. Detection is achieved using DTS: Distributed Temperature Sensors (Silixa Ltd) that use RAMAN-based measurements in combination with BOTDR (Brillouin Optical Time-domain Reflectometry) for high-precision temperature detection. We examine the correlation between the temperature of the power cable with the power consumption provided by the EAC and the weather conditions. Furthermore, our data will give an indication of how important is uniform spacing between power and optical cables. The real-time and continuous monitoring of the temperature of the optical cables through the distributed sensing systems may help identifying abnormal cable behavior (hot spots) and possible future network failures in the power network.

Summary We present the approach and initial QC results of the dual-signal processing of VSP data acquired using semipermanent DAS technology during a baseline survey of a CO2 injection- monitoring project in the Kizildere (Turkey) geothermal-production reservoir. The data were recorded in the framework of the SUCCEED project in two wells using a high-sensitivity engineered fibre with the cable suspended in the vertical cased wells. The source was a new electric seismic vibrator operated at the surface with a 3D configuration, supported with measurements on two bi-axial geophone lines. Good-quality VSP results were obtained during the initial QC performed by in-field and remote control and from the prompt data processing after the survey acquisition. The VSP-data processing takes advantage of the dual-field separation method effectively applied with the DAS well data densely sampled every 1 m. This approach enabled us to quickly separate up- going and down-going VSP wavefields. This technique does not require first-arrival picking, which is advantageous for processing extensive 3D-VSP datasets. The results from sample VSP revealed the reflection information contained in the data, relevant for target characterization. This analysis demonstrates the potential of the dataset for carbonate- reservoir monitoring purposes, to be compared in the future with time-lapse measurements.

Abstract Firn densification profiles are an important parameter for ice‐sheet mass balance and palaeoclimate studies. One conventional method of investigating firn profiles is using seismic refraction surveys, but these are difficult to upscale to large‐area measurements. Distributed acoustic sensing (DAS) presents an opportunity for large‐scale seismic measurements of firn with dense spatial sampling and easy deployment, especially when seismic noise is used. We study the feasibility of seismic noise interferometry (SI) on DAS data for characterizing the firn layer at the Rutford Ice Stream, West Antarctica. Dominant seismic energy appears to come from anthropogenic noise and shear‐margin crevasses. The DAS cross‐correlation interferometry yields noisy Rayleigh wave signals. To overcome this, we present two strategies for cross‐correlations: (a) hybrid instruments—correlating a geophone with DAS, and (b) stacking of selected cross‐correlation panels picked in the tau‐p domain. These approaches are validated with results derived from an active survey. Using the retrieved Rayleigh wave dispersion curve, we inverted for a high‐resolution 1D S‐wave velocity profile down to a depth of 100 m. The profile shows a “kink” (velocity gradient inflection) at ∼12 m depth, resulting from a change of compaction mechanism. A triangular DAS array is used to investigate directional variation in velocity, which shows no evident variations thus suggesting a lack of azimuthal anisotropy in the firn. Our results demonstrate the potential of using DAS and SI to image the near‐surface and present a new approach to derive S‐velocity profiles from surface wave inversion in firn studies.

Firn densification profiles are an important parameter for ice-sheet mass balance and palaeoclimate studies. One conventional method of investigating firn profiles is using seismic refraction surveys, but these are limited to point measurements. Distributed acoustic sensing (DAS) presents an opportunity for large-scale seismic measurements of firn with dense spatial sampling and easy deployment, especially when seismic noise is used. We study the feasibility of seismic noise interferometry on DAS data for characterizing the firn layer at the Rutford Ice Stream, West Antarctica. Dominant seismic energy appears to come from anthropogenic noise and shear-margin crevasses. The DAS cross-correlation interferometry yields a noisy Green’s function (Rayleigh waves). To overcome this, we present two strategies for cross-correlations: (1) hybrid instruments – correlating a geophone with DAS, and (2) selected stacking where the cross-correlation panels are picked in the tau-p domain. These approaches are validated with results derived from an active survey. Using the retrieved Rayleigh wave dispersion curve, we inverted for a high-resolution 1D S-wave velocity profile down to a depth of 100 m. The inversion spontaneously retrieves a “kink” (velocity gradient inflection) at ~12 m depth, resulting from a change of compaction mechanism. A triangular DAS array is used to investigate directional variation in velocity, which shows no evident variations thus suggesting a lack of deformation in the firn. Our results demonstrate the potential of using DAS and seismic noise interferometry to image the near-surface and present a new approach to derive S-velocity profiles from surface wave inversion in firn studies.