Accuracies in the 4D gravity and seafloor deformation data

OCTIO Environmental's surveys for measuring 4D gravity and vertical seafloor deformation make use of patented methods and technologies, that provide world-best accuracies in gravity changes and vertical seafloor deformation monitoring.

This accuracy in 4D gravity is of just a few microgals, which represents a billionth of the normal gravity field on the Earth surface, or the gravitational field caused by a normal person at a distance of half a meter. More importantly, such an accuracy in gravity provides sub-meter sensitivity to the displacement of fluid interfaces in the subsurface.

OCTIO Environmental's technology is the only one in the market providing field-wide seafloor subsidence monitoring with subcetimeter accuracy. The method is free from drift, and the accuracy itself is directly measured by using reference positions.

OCTIO Environmental's survey method

Gravity and seafloor deformation data are acquired simultaneously in combined surveys. A sensor frame containing three relative gravimeters and three pressure sensors is used for the measurements. To obtain the measured accuracies in 4D gravity correction for vertical seafloor deformation is key.

Seafloor deformation data can also be acquired alone in dedicated surveys. The principal measurement is then pressure and these surveys are available with a more compact instrumentation and at reduced operational cost.

The gravity and pressure data are collected at stations distributed at the seafloor both above and surrounding the survey region of interest. The latter ones are used to provide in-situ calibration and a means to directly measuring the accuracy of the measurements. The stations are defined by semi-permanent concrete platforms that are placed at the seafloor. The role of the platforms is to guarantee time-lapse repeatability on the locations of the measurements.

During a survey, a vessel is positioned sequentially above the stations, and a remotely operated vehicle deploys the sensor frame to perform the measurements on top of each of them. The duration of a survey is typically a few weeks depending on the size of the survey region.

Tide gauges are deployed during the whole survey to correct raw pressure and gravity measurements for tides and other oceanographic effects.

OCTIO Environmental's instrumentation

OCTIO Environmental uses the best gravimeters, pressure sensors and tide gauges in the market. That is made possible by collaboration with respectively Scintrex, Paroscientific and Aanderaa.

OCTIO Environmental's integrated instrumentation features all the elements required for a cost-efficient, high data quality application:

  • Automatization of the operation of the gravimeter
  • Stabilization of sensor environment
  • Real-time quality control of acquired data
  • Continuous R&D to provide cost reductions and to meet particular project requirements

Applications of gravimetry and subsidence montoring

Vertical seafloor deformation monitoring

OCTIO Environmental provides a unique surveying technology that gives regional seafloor subsidence measurements with an accuracy of a few millimeters.

4D GRAVITY AT THE SEAFLOOR

OCTIO Environmental provides a unique surveying technology that gives 4D gravity measurements at the seafloor with an accuracy orders of magnitude better than what can be obtained by ship or airborne gravity measurements.

CO2 SEQUESTRATION MONITORING

OCTIO Environmental's technologies are suited and have been successfully used in CO2 sequestration projects.