5th EAGE Workshop on Fiber Optic Sensing for Energy Applications

An Australian coal seam gas well with the reservoir section abandonment completed had a low level (up to 20 psi) of Sustained Casing Pressure (SCP). A dynamic un-spooling fibre system was deployed and a Distributed Acoustic Sensing (DAS) survey conducted to pinpoint the leak source.

With bare fibre optic in the well the sustained casing pressure was vented and production casing pressure tested during DAS acquisition. The data analysis workflow included a screening exercise using Frequency Band Energy plots to identify acoustic anomalies, followed by further analysis of raw strain data at the times and depths of FBE anomalies. Intermittent chevron type strain leak signatures were identified at 210m and 352m which enabled targeted remediation efforts, specifically casing slotting and micro-fine cement squeeze, to effectively seal the well.

The case study illustrates the DAS workflow and highlights the advantages of bare fibre optic systems for detecting small, intermittent leaks behind casing. The simplicity of dynamic unspooling fibre deployment enhances the value of DAS surveys for well decommissioning diagnostics. Ultimately, the approach improves high-sensitivity leak detection and contributes to safer well abandonment practices. The document acknowledges AGL Energy for sharing well survey data.

We developed a machine learning-based approach for P- and S-wave separation in DAS data. We used the simulation method of separated P- and S-waves for single component data to generate DAS training data. We then trained a machine learning model to simultaneously output DAS-P and DAS-S data, effectively separating P- and S-waves from input DAS recordings. The model was tested on the vertical DAS configuration, demonstrating its ability to effectively separate and image even weaker wave components.

A fixed offset VSP with dual airgun and vibrator sources was acquired in our test site at Rosemanowes ex. HDR (Hot Dry Rock) geothermal research site in the shallowest slightly deviated well RH7 in open hole as part our R&D program for downhole tool testing and qualification. The main intent was to use our 20 cu.in. airgun source in a fixed offset gun pit (∼94m from wellhead) and vibrator (∼108m from wellhead) to record a reference 3-C dataset where complex body waves kinematics in this Carnmenellis granitic geological environment were observed. The point sensor technology using high fidelity 3-C geophone is used for our vectorial receiver measurements reference dataset to be compared with our 3C fiber optic technology. This geometrical set up offers the possibility to record good VSP data to nearly ground level where broadside direct P-arrival is observed on the vertical component and where the horizontal components receive a good fraction of direct P-wave energy in the shallow section and hence the ability to quantify 3-C vector fidelity based on down-wave polarization method. Dual sources offered the possibility to evaluate the broadband signal outputs and validate isotropic coupling for all coherent signal frequency bands for direct P-wave polarization

In the shale oil area of the Qaidam Basin, horizontal well volumetric fracturing represents a critical technology for efficient unconventional resource development. To accurately evaluate cluster initiation efficiency, bridge plug sealing performance, and post-fracturing productivity during horizontal well stimulation operations, external casing distributed fiber optic monitoring technology was deployed at Platform A. Through real-time fracturing monitoring and post-fracture comprehensive analysis, this study revealed that inclined perforation technology significantly enhanced cluster initiation efficiency by 41.9% (from 62% to 88%) and improved post-fracturing productivity by 140.4% (from 0.94 m³/stage to 2.26 m³/stage) compared to conventional uniform perforation. Additionally, metal-soluble bridge plugs demonstrated exponential sealing performance decay over time, maintaining optimal integrity (failure probability <5%) when fractured within 8 hours of placement. The fiber optic monitoring-derived insights provided data-driven guidance for optimizing perforation strategies and determining optimal bridge plug operation timing, thereby facilitating continuous improvement of horizontal well fracturing designs. These technological advancements established a systematic framework for enhancing shale oil development efficiency through real-time, multi-parameter monitoring of fracturing operations.

Deployment of DAS fibres cables on the surface for subsurface imaging has been quite limited, as straight fibres laid horizontally tend to have reduced sensitivity to near-vertical, broadside reflections. Past efforts have explored the use of “SMART DAS” and shaped cables. The sensitivity of shaped cables depends on the wrapping angle, moduli of cable materials and the surrounding rock mass around the cable. Much focus has been on the effect of the fibre’s wrapping, significance of cable materials and soil properties has not been exhaustively investigated. Two different-shaped fibres were deployed for a field test: A 2-millimetres thick plastic jacket cable sinusoidally wrapped was deployed in a trench alongside a thick steel jacket helical cable. Vertical geophones were also co-located with these shaped fibres for data comparison.

Preliminary shot records from two shot points along the acquisition layout show that the plastic-jacketed DAS cable exhibits greater sensitivity to orthogonal P-wave strains due to its sinusoidal geometry and flexibility, which enable more efficient strain transfer from the surrounding medium to the fibre compared to steel-jacketed cable. Additionally, the compactness of the cable’s surrounding material further enhances the fibre’s sensitivity to orthogonal strains.

Passive seismic has been a popular method for subsurface characterization applications, particularly in mapping near-surface properties and shallow mineral deposits. This case study evaluated a cost-effective passive seismic method to determine the cover thickness and its variations, which is crucial for identifying bedrock topography. Rayleigh waves from passive seismic sources were used to compute dispersions and to construct a shear-wave velocity model, a more affordable alternative to active sources. Recorded data from geophones and DAS highlighted their potential and challenges. Improved subsurface modelling was achieved using data from a short recording period with collocated 2D arrays of geophones and DAS in Western Australia’s Pilbara region, combining passive seismic interferometry with MASW.

This study compares fiber-optic accelerometers with conventional geophones during field tests at an onshore oilfield survey. Results show near-identical time-domain waveforms, with cross-correlation coefficients exceeding 0.89 for active-source signals. Spectral analysis shows that the FOA has lower self-noise than conventional sensors below 3 Hz, and the sensitivity in the range of 16 Hz∼40 Hz is higher. This reflects the potential advantages of fiber detectors in deep target imaging and shallow high-resolution stratigraphic characterization.

Field A is a carbonate field in Sarawak, Malaysia which was completed through a number of overburden sands (F, SB3.4 and H sands). Most of the wells experienced sustained annulus pressure from the start of production. A comprehensive surveillance plan has been put in place to establish the risk of operating these wells and monitor for potential escalation of the leak and its sources.

A periodic DAS and DTS data acquisition on fibers has been chosen as one of the surveillance methodologies. This is complemented with annular investigation and gas isotopes analysis for further validation.

We see repeatability between the conventional noise logging to the fiber optics DAS data within the 10–20Hz frequency window, where indications of leaks are observed from ∼2000 ft upwards (F sands). However, at the deeper sands, some signs of fluid movements were only detected on DAS data.

This surveillance strategy, in combination with the safeguards in place are key in safely operating the wells with sustained annulus pressure since 2019. Distributed acoustic and temperature sensing on fiber optics has been successful in characterizing the source of the leak path, despite the low rates (low frequency) nature of the leak.

Historically, hydraulic fracture stimulation has relied on surface-based pressure gauges for quality control, a known limitation that often results in suboptimal treatments. Operations rarely include downhole gauges, high-frequency pressure monitoring, or microseismic services to monitor fluid entry points and estimate stimulated rock volume. Recently, low- and high-frequency acoustic data from fiber-optic (FO) cables have emerged as valuable tools, providing enhanced precision and real-time insights. This approach aims to improve the understanding of slurry distribution, fracture dynamics, and real-time optimization in multi-stage hydraulic fracturing by leveraging advancements in FO data acquisition and fracture modeling.

This innovative workflow utilizes particulate diverters, dynamically generates pumping schedules for each cluster, and integrates them with a hydraulic fracturing simulator, replacing traditional rate-splitting methods. This methodology visualizes fracture evolution over space and time, detects discrepancies between designed and actual fracture parameters, and optimizes cluster efficiency and fracture coverage across the reservoir’s net pay thickness or lateral.

The integration of fiber-optic data acquisition with real-time monitoring and multi-physics hydraulic fracturing simulators enhances monitoring accuracy and enables the optimization of hydraulic stimulation operations. The workflow identifies discrepancies between design parameters and actual outcomes, allowing real-time adjustments to improve efficiency and achieve desired stimulation performance. The proposed workflow applies to both fracturing and refracturing operations, supporting real-time and post-job analysis. By enabling detailed real-time data processing, it bridges traditional and advanced hydraulic fracturing techniques, offering a novel approach to treatment optimization. It addresses technologies such as diversion optimization, proppant suspension with degradable fibers, stage isolation correction, and flow conformance in unconventional reservoirs. By replacing rate-splitting with real-time measured data, it leverages fiber-optic technologies and stimulation models for greater accuracy. It integrates with fiber-optic methods like microseismic monitoring, strain monitoring, and seismic surveys, using the same monitoring device to deliver several complementary answer products.