SUB BOTTOM PROFILERS (SBP) - Bentos

1 SUB BOTTOM PROFILERS (SBP) Bentos Servicios y Equipos Marinos Ltda. Avda. Suecia 3005, u oa, Santiago Telephone: (56 2) 296 373 60 Fax: (56 2) 296 373 77 E-mail: A SUB BOTTOM profiler (SBP), WHAT IT IS The seismic profiler consists of a geophysical exploration system based on the seismic principles of vertical reflection and the use of an acoustic wave generating seismic source and one or more receivers of the reflected signal. The SBP obtains recordings of the low frequency acoustic signal reflected by the marine subsoil, thereby enabling the discernment of the interfaces of the different layers or horizons of subsoil materials.

2 Different wave generation and signal processing systems are used depending on the required penetration of the marine sub BOTTOM , bandwidth of operation, spectral resolution and geometry, as well as the absorption of the signal by the aquatic medium and sub BOTTOM being explored. When viewed in terms of the differentiation of the existing types of profiler systems according to the different seismic sources and signal receivers used: The pinger type marine subsoil PROFILERS use ceramic transducers and make it possible to obtain high resolutions with a small amount of output power, achieved by means of the modulation of the signal with CHIRP type signal emitters.

3 The boomer type sources, which are of greater signal power, use electronic condensers to discharge high voltage electricity through a coil that contracts to produce the mechanical wave source. The plasma arc source systems, or sparkers, produce a front of waves of very low frequency by means of the discharge of a voltaic arc. The signal receiver systems, in case of ceramic sources, can be incorporated in the same ceramic transducer emitter array. For boomer or sparker type sources, an array of hydrophones is distributed to receive the signal reflected by the marine sub BOTTOM . THE BOOMER TYPE SBP SYSTEM, HOW IT FUNCTIONS The general principle of functioning of the boomer type SBP system features the emission of sound waves through the boomer plate toward the marine BOTTOM at a characteristic frequency,, with these waves then striking the existing interfaces (water-sediment, sediment-rock and between sediments of different acoustic properties), thereby generating the reflection of the waves back toward the surface at sea level where they are received by a streamer receiver.

4 Unlike the pinger type SBP, the boomer type SBP system requires the deployment of a receiver that is a separate unit from the emission source as shown on the following figure. Power source Boomer plate fitted to catamaran 8-elements single channen streamer CHARACTERISTICS OF THE BOOMER SBP SYSTEM The principal characteristic of the boomer type SBP systems, including the hybrid system that is operated by Bentos , is the generation of a pulse on a broadband spectrum that provides a good compromise between penetration capacity and resolution. This trait makes it possible to reach an energy level of 280 Joules, a penetration depth of up to 150 m when penetrating fine grain sediments ( , clay) and a penetration depth of as much as 25 m when penetrating coarse grain sediments ( , gravel).

5 The boomer plate, model AA200, makes it possible to achieve a vertical resolution of 10 cm in thickness at 200 Joules. In general the boomer systems make it possible to discriminate sedimentary strata of between and 2 m in thickness. CHARACTERISTICS OF THE BOOMER SBP SYSTEM Geophysical descriptions of marine sedimentary strata have a wide range of applications, in which those applications that are most requested include: The determination of the thickness of unconsolidated sedimentary packets (maps of sediment thicknesses), the delineation of the rock stratum (bedrock), support for geotechnical exploration work, the preparation of dredging cost estimates, the detection of buried structures or pipelines, submarine archeology, the detection of deposits of biogas, environmental monitoring and ecological studies, among others.

6 Example of the detection by means of a boomer type SBP system of sets of faults that interrupt the lateral continuity of a stratified sedimentary packet. By estimating the wave propagation velocity the thicknesses in terms of depth in meters are estimated. PRINCIPAL APPLICATIONS OF THE BOOMER SBP Marine soil Bedrock Example of the delineation of bedrock and a stratified sedimentary packet laid down subparallel to the marine soil through use of the boomer type SBP system at Et n, Peru. THE PINGER TYPE SBP, WHAT IT IS The pinger type SBP is a profiler system based on a ceramic transducer as its seismic source, made up of four basic devices: a signal generator transmitter, a transducer (or array of transducers), a receiver and a control and data recording computer.

7 This system can obtain greater resolution than possible when using boomer sources that have lower levels of penetration in the marine sub BOTTOM . Bentos operates a monochannel pinger type system of StrataBox 3510 model made by SyQwest, which operates on two frequencies: 10 kHz (normally with one transducer) and kHz (with an array of four transducers). SyQwest StrataBox 3510 10 khZ 3,5 khZ THE PINGER TYPE SBP, HOW IT FUNCTIONS The general principle of functioning of the pinger type SBP system features the emission of sound waves through the transducer (or array of transducers) toward the marine BOTTOM at a characteristic frequency, with the waves striking the existing interfaces (water-sediment, sediment-rock) thereby producing a wave that is reflected and returns to the transducer.

8 Part of the energy emitted by the transducer is reflected at it passes through the different interfaces of unconsolidated sedimentary strata (Types, I, II, III and ROCK) until the signal becomes attenuated. CHARACTERISTICS OF THE STRATABOX 3510 SBP PINGER SYSTEM The principal characteristic of the pinger type SBP systems is their exploration capacity for discontinuities located down to some tens of meters depth into the marine subsoil, with depth of penetration being variable in accordance with the acoustic nature of the sub BOTTOM , which is generally correlated with sediment grain size.

9 The StrataBox 3510 system achieves nominal discrimination of sedimentary strata 6 cm thick when using one 10 kHz transducer, and with an array of four transducers ( kHz), this system achieves the discrimination of sedimentary strata 15 cm thick. PRINCIPAL PINGER SBP APPLICATIONS The pinger type PROFILERS are used for the preparation of geophysical descriptions of the structure of the marine subsoil in a wide range of applications, including: support for geotechnical exploration work through the delineation of the thickness of unconsolidated sedimentary packets along with the delineation of bedrock, studies of the consolidation of materials for the preparation of dredging cost estimates, the detection of buried objects for submarine archeology work, the detection of deposits of biogas, pipelines and geologic or anthropogenic structures as well as for environmental monitoring and ecological studies.

10 Buried pipeline Example of the detection of a pipeline buried in an unconsolidated sedimentary packet through the use of the StrataBox 3510 system employing an array of four transducers ( kHz). PRINCIPAL APPLICATIONS OF THE PINGER SBP Example of the detection of three shipwrecks partially buried in an unconsolidated sedimentary packet us ing the StrataBox 3510 system with one 10 kHz transducer in the Bah a de Valpara so embayment, Chile. Shipwrecks partially buried PRINCIPAL APPLICATIONS OF THE PINGER SBP Example of the detection of the sediment-rock interface for the purpose of estimating dredging costs in unconsolidated sediments using the StrataBox 3510 system with an array of four transducers operated at kHz.