Comparison of borehole seismic recordings from Distributed Acoustic Sensing and conventional 3C geophones: a VSP experiment at the PITOP testing site (OGS-ECCSEL)

Distributed Acoustic Sensing (DAS) based on fibre-optic technology is increasingly used in seismic monitoring and subsurface imaging, thanks to its dense spatial sampling, robustness, and operational flexibility. Despite its growing adoption, a detailed comparison with conventional borehole seismic sensors under controlled conditions remains essential to better understand the respective strengths, limitations, and complementarities of the two technologies.

This study presents a controlled Vertical Seismic Profiling (VSP) experiment carried out in the PITOP2 well at the PITOP geophysical testing site¹, operated by OGS and part of the ECCSEL-ERIC facilities². The experiment was performed within a Transnational Access framework funded by the Geo-INQUIRE project³. The acquisition was specifically designed to compare the seismic response of a non-permanent deployment of a borehole DAS fibre-optic cable with that of a co-located cemented array of three-component borehole geophones.

The seismic source consisted of a Vibroseis Minivib operating in P-mode, with three surface energization points located at offsets of 25, 50, and 75 m from the well. The DAS measurements were acquired using two different interrogators (Silixa iDAS and Carina®), enabling the assessment of DAS response consistency across interrogation systems. The borehole DAS cable and the Carina® interrogator were purchased thanks to PNRR ITINERIS⁴ funding.

The experiment benefits from the well-characterized subsurface conditions and permanent infrastructure available at PITOP, minimizing geological uncertainties and allowing the focus to be placed on instrumental and acquisition-related effects.

The results of this study enabled to draw technical and scientific evaluations on the experimental design, acquisition parameters and comparison strategy, outlining the analysis of waveform characteristics, frequency content, signal-to-noise ratio, and depth-dependent response.

All datasets of this experiment are openly available in SEG-Y format through the PITOP data portal¹, in compliance with FAIR data principles, supporting transparency, reproducibility, and reuse by the scientific and industrial communities

The experiment builds upon previous geophysical investigations conducted at PITOP, as summarized in the recent publication “Geophysical exploration case histories at the PITOP geophysical test site – A key facility in the ECCSEL-ERIC consortium”⁵, further demonstrating the role of PITOP as a reference facility for testing emerging seismic technologies.

Acknowledgements:

Geo-INQUIRE is funded by the European Commission under project number 101058518 within the HORIZON-INFRA-2021-SERV-01 call.

ECCSEL ERIC was established by the European Commission implementing decision of 9 June 2017 (EU) 2017/996.

References:

• OGS PITOP website: pitop.ogs.it - Transnational Access, SeisDAS Project 2025, EXP1, DOI: 10.13120/0DTM-JX93)
• ECCSEL ERIC PITOP page: https://eccsel.eu/catalogue/facility/?id=126
• Geo-INQUIRE website: https://www.geo-inquire.eu/
• EU - Next Generation EU Mission 4, Component 2 - CUP B53C22002150006 - Project IR0000032 – ITINERIS - Italian Integrated Environmental Research Infrastructures System
• Geophysical exploration case histories at the PITOP geophysical test site – A key facility in the ECCSEL-ERIC consortium: an overview. Bellezza et al., Bulletin of Geophysics and Oceanography, 2025