IMN/NSE/NE-2015-220 - DMON 2015.28 (April 2015)
IFREMER SEISMIC DEVICES UPGRADE PROJECT
This document presents Ifremer seismic devices upgrade project and gives some details about
the equipment availability for the forthcoming scientific cruises. The following points are
addressed:
1.
2.
3.
4.
5.
Introduction
Description of Ifremer seismic devices available until 2014
Presentation of Ifremer seismic devices upgrade project
Project organization and schedule
Availability of Ifremer seismic devices
1. Introduction
Marine seismic devices involve an acoustic source (high pressure air compressors and
airguns) and a set of pressure sensors (hydrophones) distributed along cables towed by a
survey vessel. These cables, called seismic streamers, have a diameter of about 60mm and can
be up to several kilometers long (maximum length of about 14km). The seismic source
generates an acoustic wave that propagates in the seawater and in the subsurface. At each
interface between two successive sediment layers, one part of the incident wave energy is
reflected toward the surface and the other part is transmitted to the deeper layers. The
reflected signals are received by the seismic streamer hydrophones, then recorded.
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Seismic devices are complex systems whose main components are presented in the following
drawing.
Seismic devices are widely used to explore the oceanic crust for depths between several
meters to several kilometers. The use of these devices has contributed to a large number of
fundamental discoveries in earth sciences. Seismic imaging is especially useful to study plate
tectonics, mechanisms of continental breakup and margin formation, relief erosion or
sediment basins segmentation. Seismic imaging is also essential for the understanding of
subduction zones and for earthquake hazard assessment, which may have an impact on
densely populated coastal area. Seismic imaging is also a fundamental tool for mineral
resources exploration. Finally, seismic imaging is a dedicated toll to study the subsurface
fluid related processes, which are key phenomena affecting the global ocean carbon budget
and the seabed properties.
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2. Description of Ifremer seismic devices available until 2014
Until 2014, Ifremer main seismic devices were:
-
SMT: muli-channel seismic (streamer length: 4500m, seismic source made of 18 Ggun
and Bolt airguns).
SISRAP: high speed seismic (streamer length: 300m, acquisition speed 8-10 knots,
seismic source made of 2 GI airguns).
HR 2D-3D: high resolution seismic (streamer length: 450m or 2 x 300m, seismic
source made of 1 to 6 mini-GI airguns).
Part
Description
Streamer
Technology
Active part length
Number of traces
and distance between
traces
Acquisition
SMT
HR2D
300 m
24 tr x 12,5 m
(25 m between
streamers)
ECOS (GENAVIR)
Navigation system
Sercel Seal 408XL
Compressor
Airguns
Integration
SISRAP
Sercel, fluid streamers (isopar oil)
450 m
2x300 m
72 tr x 6,25 m
2 x 48 tr x 6,25 m
4500 m
360 tr x 12,5 m
Acquisition
Source
HR3D
Overall volume
3
3
3
3
1200 m /h
300 m /h
300 m /h
300 m /h
18 Bolt / Ggun
aiguns
Sparker or
1 to 6 mini-GI
2 to 6 mini-GI
2 GI
12 containers 20"
2 containers 10"
4 containers 10"
2 winches
4 containers 10"
1 winch
4-5 knots
4-5 knots
8-10 knots
~150 tons
Survey
Acquisition speed
Specifications
Frequency
5-50 Hz
40-250 Hz
10-100 Hz
Investigation depth
~5000 m
~500 m
~1000 m
~10 m
2-5 m
~5 m
1999
2001
2004
Resolution
Development year
A few photographs of the old seismic devices are presented below:
SMT streamer with a bird.
SMT tail buoy.
HR seismic source.
SISRAP streamer on a winch.
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Seismic surveys studied areas spread from coastal zones to deep sea areas and the scientific
requirement in term of resolution and investigation depth in sediment can be very various. As
the main features of Ifremer seismic devices complete each other, the seismic device
configuration can be chosen according to the specific objectives of each scientific cruise.
Ifremer seismic devices have been developed in 1999 (SMT), 2001 (HR) and 2004 (SISRAP).
These devices are integrated in standard 10 or 20-feet containers and can be implemented on
several research vessels from Ifremer or other institutes. For example, the SMT seismic
device (Ifremer largest device) is integrated in twelve 20-feet containers and its total weight is
about 150 tons.
Genavir is responsible for the seismic devices onboard implementation and is also in charge
of their maintenance. The onboard installation and the unloading of the equipment require
several days (5 & 3 days for the loading onboard & unloading of the SMT device; 2 & 1 days
for the SISRAP or the HR devices). The number of Genavir operators required for the seismic
device implementation varies from 4 persons for the SISRAP device to 10 persons for the
SMT device.
Since 2012, the seismic streamers and associated acquisition systems were obsolete and their
maintenance was no longer possible. There were some spare parts to fix some damages, but it
was no longer possible to be sure that the planned seismic surveys could be carried out
without failure. Moreover, to reach some new objectives, the French scientific community has
required to increase the seismic devices capabilities. The main requirements were to increase
the streamers' length and to better control the transmitted acoustic signals.
Ifremer seismic devices upgrade project was launch at the end of 2013. The objective was to
provide the scientific community with high-performance seismic equipment so that they can
continue and extend their research work in earth sciences.
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3. Presentation of Ifremer seismic devices upgrade project
The aim of Ifremer seismic devices upgrade project is to modernize and to increase the
capabilities of the old seismic devices. The objective is to have two main seismic devices,
SIS 1 and SIS 2, based on solid streamer technology. Thanks to longer streamers, the studied
areas and the investigation depths could be extended. The solid streamer technology, selected
for the whole streamers, will contribute to a more environment-friendly system, with no
hydrocarbon pollution in case of streamer damages. Moreover, this new technology enables to
reach lower noise level and then to get a better seismic data quality.
The main characteristics of the new devices are described below:
-
SIS 1: 2D seismic device with one 6000m long seismic streamer. The seismic source
handling system will be upgraded in order to improve the quality of the transmitted
acoustic signal (better control of the airguns' depth). This new device will replace the
existing SMT device.
-
SIS 2: 3D seismic device with two 600m long seismic streamers (distance between
streamers: 25m). These two streamers will be highly modular in order to be configured
differently according to the scientific objectives and to the operating vessel size (2D or
3D, with streamer length from 150 to 1200m). This new device will replace the
existing SISRAP and HR devices. The seismic sources used with the old SISRAP and
HR devices will be kept with this new SIS 2 seismic device. From this SIS 2 device, it
will be possible to configure two sub-devices at the same time which will make easier
the scientific cruises planning.
SIS 1
Part
Description
Streamer
Technology
Active part length
Number ofe traces
and distance between
traces
Acquisition
SIS2
HR2D
6000 m
960 tr x 6,25 m
Sercel, solid streamers
150 to 1200 m
2 x 600 m
24 à 192 tr x 6,25 m
Navigation system
Compressor
Airguns
Integration
Overall volume
2 x 96 tr x 6,25 m
SISRAP
300 m
48 tr x 6,25 m
(25 m between
streamers)
ECOS (GENAVIR)
Sercel Seal 428
Acquisition
Source
HR3D
3
3
3
3
1200 m /h
300 m /h
300 m /h
300 m /h
18 Bolt / Ggun
airguns
Sparker or
1 to 6 mini-GI
2 to 6 mini-GI
2 GI
12 containers 20"
4 containers 10"
4 containers 10"
2 containers 10"
2 (or 4) winches
2 winches
4-5 knots
4-5 knots
8-10 knots
~150 tons
Survey
Acquisition speed
Specifications
Frequency
5-50 Hz
40-250 Hz
10-100 Hz
Investigation depth
~6000 m
~500 m
~1000 m
2-5 m
~5 m
Resolution
Development year
~10 m
2014-2017
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The main changes concern the seismic streamers, the associated acquisition systems and the
seismic source handling system. These changes will be achieved through:
- The purchase of new digital seismic streamers based on solid technology (SERCEL
Sentinel RD, distance between traces: 6.25m) and the associated acquisition systems
(SERCEL Seal 428).
- The specification and purchase of new seismic streamer winches.
- The development of a new seismic source handling system to better control the
transmitted acoustic signal. The high pressure air compressors and the airguns remain
unchanged.
4. Project organization and schedule
Ifremer seismic devices upgrade project is split in 5 steps, spread over the years 2014-2017.
Thanks to this division in 5 steps, the funding is also spread over 4 years. One constraint for
the project's organization was to make the seismic devices available during all the project
duration and to reduce the seismic equipment downtime. The 5 project's steps are described in
the following paragraphs.
Step 1: SIS 2, phase 1 (2014-2015)
-
Description: Step 1 corresponds to the purchase of a new 600m long streamer with the
associated 2D acquisition system. This step corresponds to the replacement of the old
SISRAP and HR streamers and to the beginning of the SIS 2 device development.
This new seismic device can be configured either in HR configuration (streamer
length: 600m, streamer depth: 1-4m, acquisition speed: 4-5 knots, seismic source: 1 to
6 mini-GI aiguns) or in SISRAP configuration (streamer length: 300m, streamer
depth: 6-8m, acquisition speed: 8-10 knots, seismic source: 2 GI aiguns).
-
Progress status: The seismic streamer (600m) and the associated acquisition system
have been validated during sea trials on the RV Thalassa (17-24/02/2015). New
winches for the streamer and for the storage of the streamer spare parts will be
delivered in July 2015. New sea trials are planned on the RV Pourquoi pas ? to
validate these new winches (Brest, 2-3/08/2015). This new seismic device will then be
used in HR configuration during the GHASS scientific cruise (September-October
2015) and in SISRAP configuration during the MOZ4 scientific cruise (December
2015).
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Photographs taken during the sea trials on RV Thalassa (February 2015).
Step 2: SIS 1, phase 1 (2014-2015)
-
Description: Step 2 corresponds to the purchase of a new 4500m long streamer with
the associated 2D acquisition system. This step corresponds to the replacement of the
old SMT streamer and to the beginning of the SIS 1 device development.
-
Progress status: The seismic streamer (4500m), the associated acquisition system and
a new winch for the seismic streamer spare parts have been delivered and integrated.
Sea trials are planned on the RV L'Atalante to validate this new seismic device
(Noumea, 25/08-1/09/2015). This new seismic device will then be used during the
TECTA scientific cruise (September-October 2015).
Step 3: SIS 2, phase 2 (2015-2016)
-
Description: Step 3 corresponds to the purchase of a second 600m long streamer with
an associated 3D acquisition system. This step will end the development of the SIS 2
seismic device.
-
Progress status: The delivery of the seismic streamer and of the 3D acquisition system
is planned in December 2015. New winches will be supplied at the beginning of the
year 2016 and sea trials are planned jut after to validate at sea the new seismic device.
This device will be available in 2D configuration from the second semester of 2016.
The implementation of the 3D configuration will require further sea trials (in 2017, the
exact date will be specified later).
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Step 4: SIS 1, phase 2 (2016)
-
Description: Step 4 corresponds to the upgrade of the handling system of the seismic
source associated with the SIS 1 seismic device.
-
Progress status: Two studies are in progress to select several seismic source
configurations and to specify the new airguns handling system. The purchases and
developments corresponding to this step are planned in 2016. Sea trials will be
planned at the end of 2016 to validate the new developments and the new seismic
source will be available from the beginning of the year 2017.
Photographs of the SMT seismic source. Top: 2 compressors, umbilicals, source string integrated in a container.
Bottom: Bolt airguns, boom used to tow one seismic source string.
Step 5: SIS 1, phase 3 (2017)
-
Description: Step 5 corresponds to the purchase of seismic streamer sections to extend
the SIS 1 seismic device to 6000m.
-
Progress status: This step will be confirmed at the beginning of the year 2016. If
confirmed, this step will be carried out in 2017.
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5. Availability of Ifremer seismic devices
The availability of the new SIS 1 and SIS 2 seismic devices during the upgrade project is
described in the following table. From September 2015, the old SMT, HR and SISRAP
seismic devices will no longer be available.
SIS 1
Year
2015
Month
September
October
November
4500 m
+
old SMT source
SIS 2
HR2D
HR3D
SISRAP
150 to 600 m
NO
300 m
December
2016
January
February
March
April
May
June
150 to 1200 m
July
August
September
October
November
December
2017
January
February
March
4500 m
+
new source
April
May
June
July
2 x 600m
August
September
October
November
December
2018
January
February
March
6000 m
(to be confirmed)
+
new source
…
The new SIS 1 et SIS 2 seismic devices could be implemented on the following vessels:
- SIS 1: RV Atalante, Pourquoi pas ? (integration studies have to be conducted for
Marion Dufresne II and Beautemps-Beaupré).
- SIS 2: RV Thalassa, Atalante, Pourquoi pas ?, Suroît, Marion Dufresne II and
Beautemps-Beaupré.
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