Our OPTOWAVE™ multi-component ocean bottom cable (4C OBC) system uses optical sensor technology and is comprised of 4C seismic stations that contain 3 orthogonal accelerometers and a hydrophone, all of which have been developed using optical sensor technology. The system is also made up of fibre optic lead-in cables and a laser interrogation instrumentation system that is placed at the surface, either on a platform, production vessel or other surface facility.

A highly advanced multiplexing technique allows many thousands of sensors to be interrogated by the laser instrumentation through the subsea optical fibre lead-in cable. The subsea components of the system are therefore completely passive with no electronic components whatsoever.

The system provides high-precision seismic measurements together with much lower power consumption, improved reliability and a lower unit cost compared to other technologies. It also provides:

• greatly improved signal-to-noise compared to towed streamer seismic
• a second data set of shear waves that allows for such applications as fracture characterization and imaging below shallow gas
• pin point seismic receiver accuracy that can even allow for individual perforations to be monitored
• time lapse seismic data for the whole life of the field

The use of a permanent multi-component OBC system is widely accepted as an alternative to other marine surface seismic or retrievable OBC acquisition techniques for acquiring 4D data. The enhanced repeatability from survey to survey achievable with a permanently installed system can aid the operating oil companies in modeling the subsurface and the effect of production, thus maximizing the oil recovery rate from the reservoir. The repeat surveys will also be less costly compared with traditional methods as it is only necessary to bring in a single vessel each time to supply the seismic source. It can therefore be the preferred alternative if the economics related to its use over the life of the field are superior.

A 4D seismic survey using the Optowave^TM system permanently installed into the sea floor and connected back to the surface platform.

The introduction of the new Optowave fibre optic permanent OBC system using optical sensing technology is an important breakthrough in many ways, not least that of data quality. The completely passive OBC cable also provides, for example, greater durability and reliability compared with systems that use electronic or moving-coil sensors. This means it will provide 4D for the full production life of a field with much lower maintenance or replacement costs. The fact that it uses only a small number of optical fibres to collect data from many thousands of channels means that manufacturing costs and hence the investment required to purchase a system are much lower. It also means that the system is more compact, lighter and hence easier to install. Optowave is therefore the reliable, cost effective, high quality repeatable 4D seismic system that has been long awaited by producers.

Wavefield Inseis provides a complete permanent 4C OBC reservoir monitoring service from the initial feasibility, through the FEED stage, equipment provision and installation, right through to the repeat data acquisitions and processing.

At the feasibility stage a best-case project timeline and a project risk assessment is delivered. The design phase includes identifying the geophysical objectives and the geological characteristics of the reservoir in order to design the system and define key project elements such as sensor spacing, seismic source characteristics and source effort.
The project must align with previously held knowledge - for example, bringing together field site surveys that highlight existing pipelines, umbilicals and any debris is also a part of the design phase. Obviously, the permanent installation will also be designed to allow for future field infrastructure expansion.

Such detailed engineering design includes assessing how environmental conditions such as 10-year storms or seabed currents impact on equipment design; J-tube pull-in calculations and platform hang-off arrangements; subsea activity schedules including ROV tasking and trenching speeds; back-deck layouts and load testing requirements; task-based risk assessments and contingency planning; detailed procedures and a full suite of engineering drawings.

Presentation

Optowave, the new Wavefield Inseis OBC system uses optical sensing technology and has been designed to be permanently installed on the sea floor.

• Fibre optic permanent 4C4D
• Optowave system background
• Optical seismic sensors
• Optowave 4C4D system field tests
• System manufacturing
• Complete permanent 4C4D provider

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