National Institute of Oceanography (Council of scientific and Industrial Research)
Dona Paula, Goa – 403 004
ORV SAGAR NIDHI
Cruise Report: SN-21
12 Jan-1 Feb, 2009
Acquisition of Geophysical Data and seabed samples for gas hydrates studies
Chief Scientist: T. Ramprasad
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Project Title: Studies on gas hydrate exploration and technology development for its exploitation
Funding agency:
Ministry of Earth Sciences Government of India
through
National Institute of Ocean Technology, Chennai (Autonomous Institution under MoES)
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Participants:
1. Sh. T. Ramprasad Sci. F
2. Dr. S. M. Karisiddaiah Sci. F 3. Dr. P. Dewangan Sci. C 4. Sh. Gavin Walkar T.O. C 5. Sh. W. Fernandes JTA 6. Sh. G. Sri Ram PA II 7. Sh. S. Vijayan PA I
8. Sh. F. K. Badesab PA I 9. Sh. P. B. Ramamurthy PA I 10. Ms. A. N. Usapkar PA II 11. Ms. E. R. Ramya PA II
12. Sh. R. Murali Krishna Central University Hyderabad
13. Sh. M. Dayalan Norinco Tech. 14. Sh E. James Norinco Tech.
Ship’s complement:
1. Capt. Advani Shyam G. MASTER
2. Sh. Rangaraja Satishraja C/OFF 3. Sh. Venkatarangan Bharani 2/OFF 4. Sh. Mishra Rajesh 2/OFF
5. Sh. N. Subba Rao C/ENG 6. Sh. Penumatch Sridhar 2/ENG 7. Sh. Gaikwad Ramdas Namdev E/O 1 8. Sh. Manimozhi Amarnath E/O 2 9. Sh. Lionel Morais Kingsly 3/E 10. Sh. Giridharan Narendra AB 1
11. Sh. Harmanjit Singh AB 2 12. Sh. Paramasivan Aravind AB 3 13. Sh. Singarayen Sudeesh OS 1 14. Sh. Singh Birendra Kumar OS 2 15. Sh. Ganapathy Arumugam OLR 1 16. Sh. Sangaiah Sivakumar OLR 2 17. Sh. Bappaithotty Abeed Hussain CH.CK
18. Sh. Ingh Raman 2nd/CK 19. Sh. Mohammad Tasleem GS 1 20. Sh. Arun Sankar GS 2 21. Sh. Tandel Miteshkumar . V GS 3
22. Sh. Yadav Gautam GS 4 23. Dr. K. Balasubramaniyam Owner Doctor
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Itinerary of the vessel: Boarded the vessel 10:01.2009 17:30 hrs Installation of Sparker system 11.01.2009 19:00 hrs Departure from Chennai port 12.01.2009 16:30 hrs Arrival in survey area 14.01.2009 12:00 hrs Departure from the survey area 30.01.2009 19:30 hrs Arrival at Chennai port 01.02.2009 10:00 hrs
Equipment brought from NIO:
Instrument Status
1. Trimble GPS Receiver Model 4000SE brought from NIO
The Navigational Positioning System is working satisfactorily
2. Geo-Spark 800-tip Sparker Working satisfactorily
3. Geo-Resources Sparker Cable winch
Working satisfactorily
4. 10 KJ Sparker power supply Working satisfactorily
5. OYO Geo Space Thermal Plotter GS612
Working satisfactorily.
6. Geo-Trace 2 High Resolution Sparker Data acquisition system
Working satisfactorily.
7. Geo Sense 24 element Streamer Working satisfactorily
8. Geo Sense 8 element Streamer Working satisfactorily
9. The post processing system for processing the high resolution sparker system
Working satisfactorily
10. Vanveen Grab Working satisfactorily 11. Chain Back Dredge Working satisfactorily 12. Magnetometer Not Operated
Onboard equipment used:
Instrument Status
1. Trimble DSM™ 232 GPS Receiver
Working satisfactorily
2. CTD Rosette, SVP and Water sampling
Rosette Not working; SVP is working; Nansen Bottles were used with messengers for water sampling (only 3 messengers available on board)
3. SeaBat 7111Shallow Water Multibeam Echosounder System
A few of the exterior beams are found to be erroneous. The swath coverage is about 4 times the depth of operation. The acquired data exhibits a systematic latency. It appears the system needs calibration at various depths.
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4. SeaBat 7150 Deep Sea
Multibeam Echosounder System
Majority of exterior beams are erroneous. The resulting swath is less than the twice the depth of operation whereas the system manual depicts that the swath coverage could be upto 5.5 times the depth of operation. The data acquired by the system could not be effectively used to prepare accurate bathymetry contour map. The system perhaps needs calibration to acquire bathymetry data at its fullest capability.
5. INNOMAR Technologies Sub-Bottom Profiler
Working satisfactorily to a large extent, except for the few places when the depth exceeded the 1000m isobath. However, the system worked fine even at water depths beyond 1800m, although the drop-keel was not lowed for deeper depth data acquisition.
6. Deep Sea Winch with Kevlar Aramide Rope.
Working satisfactorily. The heaving was very slow. Status is as below.
7. Deck Machinery: A-Frame, Heavy duty crane
Working satisfactorily.
Introduction
Presence of gas hydrate deposits in marine sediments has been inferred mainly from the appearance of an anomalous reflection pattern in the seismic reflection records, commonly referred as a bottom simulating reflection (BSR). Other proxies such as gas escape features (pockmarks, vents, blanking zones, wipeouts, mud diapirs, and cold seeps etc) in the surface and subsurface sedimentary layers and geochemical anomalies (sulfate and chloride anomalies) are in general carried out as the supporting evidences to infer the presence of gas/gas hydrates.
Under the national auspicious NGHP program the prestigious drillship JOIDES Resolution of IODP has been chartered in 2006 to acquire core samples from the subsurface depths in Kerala-Konkan basin along the West Coast , Krishna Godavari and Mahanadi basins in the East Coast and in Andaman Sea. The drilling results reveal the presence of massive zones of gas hydrates occurring in fractured clay in few locations of KG Basin. The Drilling results also indicate that the gas hydrates formation in KG Basin is very discrete and not a continuous formation. To understand various geological, geochemical and microbilogical proxies related to gas hydrates, long sediment cores (~15-50mbsf) have been acquired onboard M/V Marion Dufresne. The existing geophysical, geochemical and geological data is inadequate to estimate the areal extent of the gas hydrates deposits in Krishna-Godavari and Mahanadi basins. The high-resolution seismic data in
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the region would help in providing additional tools to study the lateral and vertical extent of the gas hydrates deposits.
Objective of the survey: To acquire high resolution digital seismic, Sub-bottom Profiler (SBP) and
multibeam bathymetry data onboard ORV Sagar Nidhi in Krishna-Godavari offshore Basin, Bay of Bengal, Central East coast of India. The cruise is aimed at acquiring the above geophysical data for gas hydrates studies for the project “Studies on gas hydrate exploration and technology development for its exploitation” under the Ministry of Earth Sciences, Government of India.
The original plan includes the acquisition of similar data in Mahanadi Offshore Basin if the time permits. Alternately, magnetometer was also installed onboard the vessel to acquire magnetic data in the event of the sparker system failure to acquire quality seismic data.
The survey was carried out in between latitudes 15°40’ and 16°25’, and
longitudes 81° 30’ and 82° 30’. The survey (track map enclosed) is divided mainly into five categories:
1. Acquisition of multibeam data in the northern sector of the survey area
along 26 coast parallel lines spaced at variable distance accounting for the varying swath coverage with depth.
2. Acquisition of multibeam data along four coast parallel lines in the central part of the survey area covering toe-thrust and mud diapir region
3. Acquisition of high-resolution digital sparker data in the planned entire region covering the JOIDES Resolution Drill sites and long core locations raised onboard Marion Dufresene consisting of total 27 coast perpendicular and 4 coast parallel tracks.
4. Sub Bottom Profiler data along with the multibeam/sparker track lines. 5. Sampling by Grabs (15 nos.) and Dredging (1 no.) in the mud-diapir
and known gas hydrates locations.
Description of the equipment used in the cruise
1. Positioning System
The positions for the underway geophysical data during survey have been obtained from two independent GPS systems: a) Trimble DSM 232 GPS receiver installed onboard ORV Sagar Nidhi, b) Trimble GPS Receiver Model 4000SE brought from NIO. The later was mainly used for interfacing the navigation data to the high resolution sparker data acquisition system through a RS232 9-pin connecter, as there is no such interface available in the Lab 1 (or the sampling lab) where it has been placed.
A brief description of the GPS systems is given below:
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a) Trimble DSM 232 GPS receiver on board ORV Sagar Nidhi
The DSM 232 GPS receiver is an innovative modular GPS receiver for dynamic applications. Scalable accuracy levels enable to choose from SBAS (Satellite Based Augmentation System), Beacon, OmniSTAR-VBS/XP/HP, and RTK (Real-Time Kinematic) differential correction sources. The DSM 232 GPS receiver can provide the level of accuracy needed for any operation. The Navigational position available from this system has been mainly used by the SeaBat 7111 Shallow water Multibeam Echosounder System, SeaBat 7150 Deep Water Multibeam Echosounder System,INNOMAR Technologies Sub-Bottom Profiler, the general navigation of the vessel and for the sampling operations.
b) Trimble GPS Receiver Model 4000SE brought from NIO There is no RS232 9-pin connectivity for navigational position in the
starboard sampling laboratory or Lab 1 to interface with the Geo-Trace 2 high-resolution sparker data acquisition system. A GPS repeater is available in the laboratory Lab 1, but there is no way a RS232 (9 pin) connectivity could be tapped. An alternate possibility is to lay a cable from the bridge to the laboratory. Instead a Trimble GPS positioning system brought from NIO was used for obtaining the position of the vessel and to interface with the Geo-Trace 2 acquisition PC. The antenna was installed on the railing in the middle of the Boat deck, which is also approximately lying in the middle of the ship’s length and breadth. Initially, the GPS receiver could not start as the connecter was shorting. An innovative connector has been prepared by Sh. Gavin Walker, which has solved the problem.
A NMEA-102 output was taken from the receiver and interfaced to the
seismic data acquisition system via serial 9-pin connection. The GPS system worked satisfactorily through out the cruise and the data output from GPS receiver was consistent.
2. High Resolution Sparker System
The high resolution sparker system consists of the following major components:
a. High Voltage Pulsed power supply housed in a container b. 800 tip Geo-Spark 800 c. Sparker winch with high voltage cable (50m) d. A high voltage deck cable (50m) e. Geo-Sense 8/24 element streamer f. Geo-Trace 2 Acquisition System g. Post processing computer with Geo-Trace Software
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a. High Voltage Pulsed power supply
The high voltage pulsed power supply consists of a low voltage controller unit operating on 230 V input and high voltage pulsed power generator which requires ship’s 3 phase 380 V power input. As the ship’s 3 phase supply is of 415V, a voltage stabilizer (step-down transformer) has been used to feed 3 phase 380V with high voltage pulsed power generator. The HV power generator with five capacitor banks which can be included or excluded for generation of high voltage depending on the requirement. The HV power generator is capable of generating upto -5600V with respect to ground and 10KJ of power. The high voltage power supply is housed in a container with an air conditioner to control the temperature rise while the high voltage is generated.
The container is kept on board the vessel over the wooden deck with a
view that it may generate spark with metal deck in case of ungrounded current is remaining. The container frame is grounded by lowering a copper wire in to the water on port side of the ship to remove any surges that may have caused due to the generation of high voltage. It was tied with a nylon rope to the aft of the ship with additional weight ensured the wire remained in the water even while the ship roll.
b. Geo-Spark 800 c. Sparker winch with high voltage cable (50m) d. A high voltage deck cable (50m)
The Geo-Spark 800 is a steel frame consisting of 8 strips fitted with 100
tips of electrodes each. The sparker is designed such that the sparker frame acts as the earth (Positive earth Pole, PeP) and the electrodes as –ve pole. The –ve voltage is connected to the 800 tips in parallel that is divided in equal proportions. The advantage of the sparker is that the sparker tips (electrodes) wear minimally as the frame itself acts as the anode. To avoid the frame wearing, 8 zinc anodes are mounted on the sparker frame which serves as positive earth pole.
The sparker frame is connected to a 2 “ high voltage multi core cable
through a connecter which is capable of dragging the sparker at the sea surface. However, the sparker is lowered and dragged with a help of a rope through the A-frame of the survey vessel. The high voltage sparker winch is fitted with axial connectors to connect the high voltage deck cable for the high voltage power. The high voltage deck cable draws power from the High Voltage Pulsed Power supply.
e. Geo-Sense 8/24 element streamer
The Geo-Sense single channel streamers (8 elements or 24 elements)
are specially designed for high frequency spectrum emitted by the Geo-Spark source. The molded pre-amp is located in a stainless steel container at the head of the streamer, just behind the Kevlar reinforced PU tow lead. The pre-amp is powered by the top-end interface box, which conditions the signal
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output to the digital recorder. The top-end interface box integrates 1) a low-noise power supply (12 V DC) for the streamer pre-amp, 2) an external amplifier (up to 20 dB) and 3) selectable analogue low-cut filter (up to 80Hz) to eliminate swell induced low-frequency noise.
f. Geo-Trace 2 Acquisition System
The Geo-Trace 2 Acquisition System consists of analogue interface with
an A/D converter. The Geo-Sense Streamer (8/24) towed at the aft at a minimum distance away from the survey vessel to avoid ship’s noise which acquires the seismic signal in the form of electrical signal. This signal is fed to the analogue interface and then converted to digital form. Thus each seismic trace is stored as a digital signal in Geo-Trace native format on the hard disk.
h. Post processing computer with Geo-Trace Software
The data was filtered using band-pass filter and swell filter. The data is
then converted to SEGY format so that the data could be read on ProMAX or Seismic Unix.
3. SeaBat 7111 Shallow Water Multibeam System
The SeaBat 7111 is a 100 kHz multibeam echosounder system. This system illuminates a 150° sector to a range of 5-1000 meters from the Sonar Array.
Technical Specifications Depth Rating: 100 - 1000 meters Frequency: 100 kHz Horizontal Beam Width: 1.8° at the center beam Vertical Beam Width: 1.5°, 3.0°, 4.5°, or 6.0° (Operator selected) No. of Horizontal Beams: 201 Range Resolution: 0.5 m (at all ranges) Ping Rates: Up to 20 pings per second. Sector Coverage: 150°
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4. SeaBat 7150 Deep Sea Multibeam System The SeaBat 7150 system is a 12 and/or 24 kHz Full Ocean Depth Multibeam Echosounder (MBES) System that measures bottom depth across up to a 150° swath perpendicular to a vessel's track. The SeaBat 7150 is hull mounted. The SeaBat 7150 generates up to 256 equally spaced (or 880 equidistant) bathymetry soundings per ping and broadcasts from the 7-P Sonar Processor to the data acquisition software, where they are corrected for mechanical offsets, motion, heading, refraction, tide or depth and position. (To perform these corrections, the appropriate sensors are interfaced to the data acquisition software). The SeaBat 7150 is available in several modular configurations, depending on the requirements for survey depth and resolution.
Technical Specification Overview
Sonar Operating Frequency
12 kHz 24 kHz
Across-Track Beam Width at nadir beam*
3x3 Array: 4° 3x3 Array: 2°
6x6 Array: 2° 6x6 Array: 1° 12x12 Array: 1° 12x12 Array: 0.5°
Along-Track Beam Width
Same as above Same as above
Number of Across-TrackBeams
256 256
Swath Coverage Up to 150° with maximum swath width** of approximately 5.5 times the water depth.
Depth (typical) 100 - 12800 meters 100 - 6400 meters
Ping Rate Up to 15 pings per second Pulse Length 0.5 - 20 ms 0.5 - 20 ms Bottom Detection Resolution
100-200 m: 12 cm 100-400 m: 12 cm 400-600 m: 25 cm 600-800 m: 25 cm 800-1200 m: 50 cm 1200-1600 m: 50 cm
1600-2400 m: 1 m 2400-4800 m: 1 m 3200+ m: 2 m 6400+ m: 2 mers
12 kHz Option 24 kHz * Assuming a 1° system, as the beams radiate away from the nadir, their width will increase to 2.0° at ±60° from nadir, and 2.9° at ±70° from nadir.
** Swath width decreases from maximum as a function of depth
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5. INNOMAR Technologies Sub-Bottom Profiler The technical parameters of the SES-2000 deep sub-bottom profiler are summarized in the following table. Water depth range 5 …6000 m
Vertical resolution up to 15 cm Penetration depth up to 150 m (depending on sediment
type) Accuracy of the depth measurement 0.15 m + 0.02% of the water depth
Primary transmitter frequency ca. 35 kHz Secondary transmitter frequency 2, 3, 4, 5, 6, 7 kHz
Transmitter pulse length 0.25 … 3.7 ms Source level > 244 dB/µPa re 1m Repetition rate up to 30 s-1
Beam width (-3 dB) ±1.5° @ 2 … 7 kHz
Heave / Roll compensation yes Transducer dimensions / weight ca. 80 cm × 75 cm × 15 cm / ca. 204 kg
System unit dimensions / weight 2 × (52 cm × 44 cm × 40 cm) / ca. 115 kg
The SES-2000 deep system is fitted with a transducer for both, HF (35kHz) and LF (2–7kHz) operation. For easy handling the transducer array is divided into three sections, see figure below.
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Transducer Array of SES-2000 deep consisting of 3 sections (left) and mounted into a supporting structure (right, in board the German research vessel R/V Merian)
The transducer cable has a sea water resistant polyurethane sheet and is attached unsolvable to the transducer (cable diameter: 20mm; minimum recommended bend radius: static: 100mm, dynamic: 200mm).
There is a system software, called “SES for Windows” (or SESWIN for short), is used with the SES-2000 system to manage the system’s on-line operation, data acquisition as well as data replay. This software is pre-installed on the built-in control PC of the SES-2000 system. To ensure proper operation of the system the settings of the BIOS and the Windows OS and any other software packages and device drivers are not changed.
6. Deep Sea Winch with Kevlar Aramide Rope. The Deep Sea Winch with Kevlar Aramide Rope along with the A-Frame at the aft of the vessel was used for sediment sampling by the Vanveen grab from the seafloor at 15 locations in the survey area. Later, a modified Chain Bag Dredge fitted with a fine net to collect objects bigger than 1” diameter. The winch performed well until the dredge operation. During the 1st dredge operation, the heaving speed of the winch has been reduced to 10m/min while the actual capacity of the winch is 60m/min. The ship’s engineers had a look into the operation of the Winch and found that the rope is misaligned at the Storage winch section. The traction winch was not taking the load, According to the engineers, the traction winch does not take load when there is slack on
The sketch on the right shows dimensions of the transducer connector that is fixed unsolvable at the cable end (diameter 55mm; length 76mm). It could be offered to mount the connectors after transducer installation (charged additional).
The figure in the right shows the directivity (beam pattern) of the SES-2000 deep system. There is a very narrow sound beam produced and the LF-directivity shows no side lobes.
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the rope. The Heave compensator section is working well independently, but together with winch it does not seem to correct the slackness of the rope. However, the dredging plan was abandoned until the ship’s engineers trouble shoot the winch. Second phase of dredging was planned on the last day of the voyage. On the assurance that the winch was functional, the dredge was once again lowered to acquire surface samples. The winch problem recurred when the dredge was hauled. The remaining dredge operations were curtailed and the vessel headed for Chennai.
Field preparations
The sparker system could be put in to operation in the survey area after 2 hours of hectic activity of assembling of Geo-Spark 800 sparker frame and the sparker cable winch. The sparker high voltage power supply container was placed on the deck in a place where no hindrance is anticipated. A warning sign of “VERY HIGH VOLTAGE PLEASE DO NOT COME CLOSER” has been displayed to avoid ship’s personnel coming closer to the container, which generates a very high voltage of up to -5600 V.
The streamer cable of Geo-Sense 24 element has been paid out through a
metallic eye fitted to the at the projected end of the 12m long metallic 2” GI pipe to avoid the ship’s steaming noise as well as propeller vibrations. The lead cable of the streamer is connected to the Geo-Trace 2 data acquisition system through an extension cable and battery power pack. While testing, it was observed the streamer was picking up lot of noise and the data could not be acquired for a more than two to three hours. It was then decided that the deck lead and the extension cable was tied to the wooden pillars perched above the side of the ship to avoid induced electric noise generated from the high power ship’s cables. With this measure the streamer sensor noise has been considerably reduced. It is also observed that the Geo-Trace 2 acquisition system is picking up noise from the CTD A-frame and winch controller in the sampling laboratory. The acquisition system was later shifted in to the Lab1 on main deck. With this arrangement, the data recorded was fairly devoid of much noise.
It was observed that the COM1 port gets locked if the RS232 cable is
connected Geo-Trace 2 acquisition system while it is started. The COM2 is reserved by the PCM16 analogue interface. The COM ports of the acquisition system have been clearly marked with a marker pen. The navigation interface to Geo-Trace 2 system should always be COM1 and should not be connected before the PC is started.
Quantum of data Acquired
1. Multibeam bathymetry acquired by SeaBat 7111 system :~836 lkm :~926 km2
2. Multibeam bathymetry acquired by SeaBat 7150 system :~259 lkm :~466 km2
3. Total High Resolution Sparker data :1267 lkm 4. Sub-Bottom Profiler Data :2362 lkm
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5. Sediment Grab Locations : 15 nos 6. Dredge locations : 1 no. (2 operations)
General Observations and Recommendations
1. The seafloor depth and navigation position (with, lat, long, heading/course, speed, way point distance, etc.) repeaters are not available in the working labs. Being a research vessel, it should have this facility as scientists need the position and depth information for cataloging the acquired samples from the sea.
2. The RS232 (9 pin) connectivity of GPS is not available in the labs, which is needed by several data acquisition systems.
3. The SeaBat 7111/7150 Shallow/Deep Sea Multibeam echosounders may need calibration / tuning for improving its capability to acquire full swath coverage, i.e., 5.5 times the depth of operation.
Acknowledgements The chief scientist and the scientific party of the cruise thank Dr. S. Kathiroli, Director NIOT and Dr. D. Rajashekar, the manager VMC, NIOT for providing the ship time, and Sh. N. Ravi, VMC, NIOT for logistic support and every help they rendered. Thanks are also due to Captain Advani Shyam G., his officers, engineer officers and crew for the excellent cooperation extended during the survey for acquisition of scientific data. The catering department of the vessel is thanked for providing good food and hospitality.
