Other

Ola Eiken

Mark A Zumberge

John G Hildebrand

The invention is a method for monitoring subsidence of the sea-bed ( ) of a survey area ( ) caused by compaction of an underground hydrocarbon reservoir ( ), and comprises the following steps: Conducting at least two series (S , . . . ,S , . . . ,S ) of time-indexed depth measurements ( ), with separation in time &Dgr; between the measurement series characteristic of a significantly detectable long-term change of seafloor elevation due to compaction to take place in the reservoir. Measurements are time-indexed and corrected for tidal depth variations. Depth measurements ( ) are conducted on survey stations ( ) arranged on benchmarks ( ) which have settled in the locally consolidated seabed ( ). To handle short-term depth variations several stationary time-indexed short-time local reference depth measurement series ( ) are conducted at short-term local reference stations ( ) at benchmarks ( ) during each separate measurement series (S ). The reference depth measurement series ( ) are continuous for correcting each depth measurement ( ) for short-time tidal depth variations occuring during each separate measurement series (S ). To monitor compaction or seafloor subsidence during the series of measurements, the depth measurements ( ) are conducted relative to a depth measurement ( ) during each series (S) at reference station ( ) arranged on the seabed ( ) at a distance from the reservoir ( ) being sufficiently far to be unaffected by long-term effects taking place due to compaction in reservoir ( ).

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Trondheim, Norway

Ola Eiken