Optoplan and StatoilHydro have together developed new technology for seismic reservoir monitoring. Fibre-optic seismic sensors are permanently installed in the seabed for cost-effective monitoring of the oil production.
Fibre optic sensors (4C OBS)
Seismic reservoir monitoring is normally done by comparing the results of high fidelity offshore 3D seismic reflection surveys re-run several years apart over the same area. The technique is known as 4D or time-lapse seismic, where time is the fourth dimension.
Differences are interpreted in terms of fluid or pressure changes caused by reservoir production, while areas showing little or no change may suggest the location of remaining reserves.
A better way of doing this is to deploy four component (4C) seismic sensors directly on the seabed. The advantages of Ocean Bottom Seismic (OBS) are better data resolution and the direct recording of both shear and pressure wave information.
OBS also facilitates continuous, rather than intermittent, monitoring as part of an e-field/integrated management concept.
StatoilHydro and Optoplan AS are aiming to introduce the next generation, consisting of fibre optic 4C-OBS sensors linked to a remote control room via a fibre optic telemetry network.
The sensors and cables were tested in Trondheimsfjorden in early 2006, and an offshore field tests was completed in the summer. A cable fitted with sensors was deployed at 300-metre depth.
The tests were a success and clear the way for real-time optical geophysical reservoir monitoring throughout the life of a field.
Besides having "4D data on demand", such a system promises to
- halve the price of its present state of the art counterparts
- largely remove the risk of failure by using fibre optic rather than electronic sensors and cables
- generate data whose quality is on a par with the very best.
