OCTIO's surveys make use of patented methods and technologies, that provide world-best accuracies in gravity changes and seafloor subsidence.
OCTIO's gWatch instrumentation
In 2018, OCTIO introduced the disruptive gWatch instrumentation. The new equipment is more compact and allows for a more stream-lined operation on smaller and hence cost-efficient vessels.
gWatch has provided
An improved quality in the measurement of gravity makes these benefits available for a wider variety of fields and allows for taking measures aimed at optimizing the production at earlier stages of the hydrocarbon field lifetime.
OCTIO's survey method
Gravity and seafloor subsidence data are acquired simultaneously in combined surveys. A sensor frame containing three relative gravimeters and three pressure sensors is used for the measurements.
Gravity and water pressure are measured at 20 to 120 stations, depending on the field size. 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 20-minute measurements on top of each of them. The duration of a survey ranges from one to five weeks depending on the field size.
Stations are located both above and surrounding the hydrocarbon field. The latter ones are used to provide in-situ calibration and a means to directly measuring the accuracy of the measurements.
Tide gauges are deployed during the whole survey to correct raw pressure and gravity measurements for tides and other oceanographic effects.
Accuracy in the measurement of changes in gravity
The time-lapse sensitivity obtained with the gWatch instrumentation is below one 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 hydrocarbon reservoirs.