Method and apparatus for determining the content of subterranean reservoirs
AssigneeDen Norske Stats Oljeselskap A.S.
InventorsTerje Eidesmo, Svein Ellingsrud, Fan-Nian Kong, Harald Westerdahl, Stale Johansen
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Abstract
A system for determining the nature of a subterranean reservoir 12 whose position and geometry is known from previous seismic surveys. An electromagnetic field 24, 25, 26, 27 is applied by a transmitter 18 on the seabed 14 and detected by antennea 21, 22, 23 also on the seabed 14. The nature of the detected reflected waves 25, 26, 27 is used to determine whether the reservoir 12 contains water or hydrocarbons.
Claims37
A method of determining the nature of a submarine or subterranean reservoir having an electromagnetic characteristic and whose approximate geometry and location are known, which comprises:
- applying a time varying electromagnetic field in the form of a wave to the strata containing the reservoir;
- detecting the electromagnetic wave field response:
- and analysing the effects on the characteristics of the detected field that have been caused by the reservoir, thereby determining the content of the reservoir, based on the analysis, wherein the analysis comprises comparing the electromagnetic characteristic theoretically predicted for the reservoir based on the approximate geometry of the reservoir and based on the reservoir being a water-bearing or hydrocarbon-bearing reservoir to the electromagnetic characteristic for the reservoir that is determined from the detected electromagnetic wave field response of the reservoir, wherein a distance between a transmitter and a receiver is given by the formula 0.5λ≦l≦10λ;
- where λ is the wavelength of the transmission through an overburden and l is the distance between the transmitter and the receiver.
A method of determining the nature of a submarine or subterranean reservoir having an electromagnetic characteristic and whose approximate geometry and location are known, which comprises:
- applying a time varying electromagnetic field to the strata containing the reservoir;
- detecting the electromagnetic wave field response;
- and analyzing the effects on the characteristics of the detected field that have been caused by the reservoir, thereby determining the content of the reservoir, based on the analysis, wherein the analysis comprises comparing the electromagnetic characteristic theoretically predicted for the reservoir based on the approximate geometry of the reservoir and based on the reservoir being a water-bearing or hydrocarbon-bearing reservoir to the electromagnetic characteristic for the reservoir that is determined from the detected electromagnetic wave field response of the reservoir, in which a first transmission by at least one transmitter is made at a first frequency and is received by each receiver in a tuned array of receivers, then a second transmission is made at a second frequency and received by the same tune array of receivers, the receivers being tuned to receive their respective transmission, the at least one transmitter being tuned for optimum transmission.
Dependencies are inferred from the claim text.