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 record-breaking data quality in surveys in 2019 .

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.

Accuracy in the measurement of seafloor subsidence

OCTIO'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.

Applications of gravimetry and subsidence montoring

Detect undepleted compartments
Map and quantify aquifer influx
Update hydrocarbon volumes

Detect undepleted compartments
Time window for drilling of infill wells
Provide installation safety

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