Gravity for the 5th consecutive timeThe ROV holding the gWatch instrumentation, ready for immersion during the Ormen Lange gravimetry survey in 2018. Photo: OCTIO

Gravity for the 5th consecutive time

Bergen-based OCTIO Gravitude has been awarded a gravimetry survey over the Ormen Lange field.

OCTIO Gravitude will survey the Ormen Lange field during summer 2020. The operation is expected to last for four weeks and will produce measurements of both water depth and gravitational field at the seabed above the gas reservoir.

Using gravimetry for cost-cutting reservoir monitoring.

Seabed gravimetry and subsidence measurements have been acquired every second year at Ormen Lange since 2012.

Gravimetry measurements detect mass changes in the subsurface and thereby provide a picture of how fluids are moving in the reservoir, while seabed subsidence measurements indicate how reservoir rocks are responding to the pressure decrease caused by hydrocarbon production.

These two measurements combined provide valuable insight to improve reservoir management and support efficient hydrocarbon production with reduced cost and environmental impact.

Gravity and subsidence measurement technology have been utilized on ten producing fields on the Norwegian Continental Shelf (NCS), including the Ormen Lange, Midgard, Mikkel, Statfjord and Aasta Hansteen fields.

At Ormen Lange, gravimetry and 4D seismic are combined to provide a complete understanding of the reservoir, and hence to ensure optimal reservoir management.

Gravimetry and subsidence surveys are significantly less expensive than 4D seismic, and the monitoring strategy at Ormen Lange combines two-yearly monitoring with gWatch with less frequent 4D seismic acquisitions.

The Ormen Lange asset is maturing the concept for installing a subsea compression system to further enhance the recovery rates. The gravity and subsidence dataset acquired in 2020 will provide a critical baseline measurement, and the comparison with future gravimetry campaign datasets will provide a valuable insight into reservoir monitoring with compression system and potential to further enhance recovery rates.

For this survey, OCTIO Gravitude will utilize the new gWatch technology, introduced in 2018. gWatch features more efficient operation, lower costs and a largely improved sensitivity when compared with traditional gravimetry instrumentation.

The gWatch instrumentation will be deployed consecutively on a total of 120 subsea measurement locations, by means of a remotely operated vehicle (ROV) supplied by IKM Subsea.

Ormen Lange is the second-largest gas field in Norway. Ormen Lange was discovered in 1997, and the plan for development and operation (PDO) was approved in 2004. Deep water and seabed conditions made the development very challenging and triggered development of new technology. The field has been developed in several phases. The development comprises four 8-slot subsea templates with a total of 24 production wells. Production started in 2007 from two subsea templates in the central part of the field. In 2009 and 2011, two additional templates were installed in the southern and northern parts of the field, respectively. Ormen Lange produces very dry gas and small amounts of condensate from Paleocene sandstone in the Egga Formation. The reservoir lies at a depth of 2,700-2,900 metres below sea level and has excellent quality. License partner companies at the Ormen Lange field are A/S Norske Shell (operator), Petoro AS, Equinor Energy AS, INEOS E&P Norge AS and Vår Energy AS.