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Monitoring of Offshore Reservoirs Using 4D Gravimetry at the Seafloor - State of the ArtNormal access

Authors: H. Ruiz, R. Agersborg, L.T. Hille, M. Lien, J.E. Lindgård and M. Vatshelle
Event name: 77th EAGE Conference and Exhibition 2015
Session: Permanent Reservoir Monitoring
Publication date: 01 June 2015
DOI: 10.3997/2214-4609.201412551
Organisations: EAGE
Language: English
Info: Extended abstract, PDF ( 1.27Mb )
Price: € 20

Summary:
Seafloor time-lapse gravity and subsidence data provide a measurement of the density distribution within the reservoir. This independent source of information complements the inputs from seismic and electromagnetic techniques to effectively constrain the reservoir models. 4D gravity is especially fitted for monitoring contacts between fluids with relatively large density contrast, like gas-water, gas-oil, or CO2-water in injection sites. The precision of seafloor gravity measurements has dramatically improved in the last two decades to the level of 2 µGal. This is orders of magnitude better than in other gravimetric techniques, with the additional advantage of measurements being taken closer to the source. This has established gravity as a mature and cost-efficient monitoring technique. In the example of localizing a raising gas-water contact, the attainable precision translates into sub-meter sensitivity in the height of the contact. The value of gravity and subsidence data has become evident in many gas production and sequestration fields in the last decade. This paper reviews a few of those cases, and presents the recent advances in the technology. In addition, the range of applicability in terms of reservoir properties and the lateral resolution that can be attained are discussed.


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