Our technical solution requires equipment tailored for the task. Click on the images to get more information
An industry standard work class ROV is used, equipped with a dedicated arm supplied by Quad
Permanently deployed monuments on the seafloor serve as foundations for the repeated measurements. These shall be stable over the lifetime of the field production (typically 10-30 years). For the soft clay seafloor conditions often encountered in the North Sea, we have used conical concrete benchmarks. Nearly 500 such stations have been deployed on the seafloor above six fields since 1997.
ROVDOG stands for Remotely Operated Vehicle-deployed Deep Ocean Gravimeter. Quad uses multiple seafloor gravity meters, each also containing a quartz pressure gauge, mounted in a common frame to allow a single deployment to yield several independent measurements of gravity and pressure.
Concrete mats with a podium in the center for the ROVDOG can be used in shallow water where there is risk that erosional currents may wash under the benchmarks. The mats will protect against such erosion.
Stand-alone water pressure recorders are important not only for the subsidence measurements, but also for the ocean tide gravity corrections. Quad uses a variety of sensors and systems. The TG-09 gauges are equipped with an acoustic modem data transmission which allows data downloads during surveys. This improves the quality of the online QC. Another system is TG-11.
Remote operation of the instrument on the seafloor and recording of raw data is controlled by the recording software. No processing is applied before recording, but numerous QC displays allow the operator to detect anomalies and make the necessary actions during data acquisition. Each record is then on-line processed to estimate average values of pressure (depth) and gravity, together with a large number of quality indicators. All measurements go into network adjustment, which includes drift inversion and several QC indicators. Editing and weighting of sensors can also be done. Time-lapse data are visualized. Data from dynamic reservoir models can be imported, and observed and modelled gravity changes and seafloor subsidence can be compared and plotted in map view.