icroseismic monitoring applied to underground
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natural gas storage
neris assists gas storage operators in all risk expertise phases of the lifecycle of their project,
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from the design of the operation and the preparation of regulatory authorizations to the site clo-
sure and decommissioning. Services include quasi real-time geotechnical and microseismic moni-
toring to control the performance of the host rock. Monitoring solutions set up on two sites, with
different geological contexts and implementation specifications, are described below.
ontext. Underground storage of natural gas in large caverns or reservoirs is a key compo-
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nent of the energy capacity market. It consists in storing the gas produced during low-demand
periods and supplying the market during high-demand periods. This considerably limits risks of disrup-
tion at peak load times. Considering the field and regulatory constraints, microseismic monitoring tech-
nique is set up to meet specific objectives.
he first site consists of a 100.000 m3 cavern mined in a
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160 m deep limestone layer, South of France. Microseis-
mic monitoring is designed to fulfill two safety requirements:
first, to control the overall stability of the storage cavern also in
case of a regional natural seismic event and second, to detect
local roof falls that could impact the artificial water curtain sys-
tem located a few meters above.
he operator required to progressively upgrade a pre-
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existing monitoring solution. Besides many improvements,
Ineris updated the acquisition unit, allowing a drastic decrease
in artefact triggering. Then gradual replacement of the pre-
existing downhole probes, suffering from interferences along
their cables, by SYTMIS probes equipped with built-in
amplifiers, considerably enhanced the signal-to-noise ratio and
the processing of the waveforms. Testing of the system was
done thanks to large block falls on surface.
eismic files are automatically transmitted to Ineris data
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center to be processed, classified and made available
through e.cenaris web-monitoring platform. A specific proce-
dure is used to trigger an alarm if necessary.
Installation of a downhole SYTMIS
3-component retrievable microseismic
probe.
INERIS ■ Parc technologique ALATA ■ BP n°2 ■ 60550 Verneuil-en-Halatte ■ France
Phone: +33 (0)3 44 55 66 77 website: www.ineris.fr
he second site is situated in a moderate seismical-
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ly active zone in South Europe. It comprises
several large salt-leaching caverns located below a
1000 m thick impermeable caprock. Ineris realized the
design, installation and calibration of a modular micro-
seismic monitoring network. Retrievable self-
anchoring 3-component SYTMIS seismic probes were
installed in deep boreholes in order to pass through
the altered and attenuating first geological layers and
to ensure good coupling with the surrounding rock for
better detection. Smart-dual-mode
(continuous and
triggering) acquisition units were implemented on
each distant platform, covering a 2 km2 area, and con-
nected to a pre-existent LAN for automated real-time
transmission and remote management through
e.cenaris also. Here calibration was done with surface
blasts.
Top View of Site 2 - the salt caverns are projected
on the ground surface.
Results. Both monitoring systems and
dataset have been managed for several
years now.
n Site
1, seismic files are artefacts
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generated by the surface anthropogenic
activity. Typical waveforms are documented
and easily classified. Any microseismic data
following a detected regional seismic event
in a 24 h range is examined with details as a
potential rupture in the roof of the caverns.
n Site 2, a few events of low magnitude
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ranging from
-0.5 to
1 are recorded
3D location of microseismic events recorded on Site 2
each month. 3D location is precise enough
deep storage salt caverns.
to assign events to a given cavern with an
accuracy of a few ten meters in XY plane.
Here microseismic activity analysis revealed to be mainly related to caving processes associated to
an additional cavern under development. No microseismic event has ever been detected in the higher
part of the roof close to the caprock, proving the integrity of the geosystem.
essons learned. Underground gas storage industry needs advanced monitoring solu-
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tions that provide the control of the performance of the underground facilities, that is stability of
the caverns and integrity of the host rock. Over the past years, microseismic monitoring has proven
successful as an efficient non-invasive technique to detect and to locate local failures, yielding im-
portant information to all involved parties. Technological progress makes it possible not only to steadi-
ly improve the resolution inside the rock mass response but also to lower efforts in time-consuming
data analysis while allowing faster result sharing thanks to the internet.
INERIS ■ Parc technologique ALATA ■ BP n°2 ■ 60550 Verneuil-en-Halatte ■ France
Phone: +33 (0)3 44 55 66 77 website: www.ineris.fr