Abstract: A system (100) for monitoring a field (20) under a body of water, wherein the system (100) comprises a reference station (112) and a plurality of permanent seafloor sensors (120, 121). Each permanent seafloor sensor (120, 121) is fixed relative to a seafloor (2) on or at the field (20). The seafloor sensor (120, 121) further has a nearby survey station (111) sufficiently distant to ensure that a movable sensor (122) visiting the nearby survey station (111) does not disturb measurements from the permanent seafloor sensor (120). The distance is sufficiently close to ensure that the offset (?p, ?g) from a value provided by the permanent seafloor sensor (120) is constant or can be modelled, e.g. to account for changes in the pressure/depth relation due to changes in water density. Each seafloor sensor is associated with a unique drift function d(t) at least comprising a drift rate (a).

Abstract: A device (110) for performing measurements on a seabed (3), comprises a chamber (111) containing a sensor (120) and a fluid (115) at a constant temperature and at an ambient pressure. This removes the need for calibration in large ranges of both pressure and temperature. In addition, this eliminates the need to wait until the sensor (120) has achieved ambient temperature, and thereby achieves a desired accuracy of the recordings from the sensor while decreasing the operation time. The device preferably comprises an insulating layer (113), an internal temperature stabilising device (130) and a circulating device (131) to ensure a constant temperature and low temperature gradients within the chamber (111). The pressure within chamber (111) may be equalised to ambient pressure by a pressure inlet (112).

Abstract: A device (110) for performing measurements on a seabed (3), comprises a chamber (111) containing a sensor (120) and a fluid (115) at a constant temperature and at an ambient pressure. This removes the need for calibration in large ranges of both pressure and temperature. In addition, this eliminates the need to wait until the sensor (120) has achieved ambient temperature, and thereby achieves a desired accuracy of the recordings from the sensor while decreasing the operation time. The device preferably comprises an insulating layer (113), an internal temperature stabilising device (130) and a circulating device (131) to ensure a constant temperature and low temperature gradients within the chamber (111). The pressure within chamber (111) may be equalised to ambient pressure by a pressure inlet (112).

Abstract: A system (400) for processing microseismic data comprises an array (330) of seismic sensors (331, 332) at known locations, means (331, 332; 410) for enhancing SNR in a seismic signal output from a seismic sensor, means (331, 332; 410) for detecting a microseismic event in the seismic signal and inverting means (410) for adapting a rock physical model (255) to microseismic data that are acquired at least partially from the seismic signal representing a microseismic event. The rock physical model comprises a set of spatial volume elements mapping a set of physical volume elements (320) within a volume (300) to be monitored, wherein each spatial volume element comprises attributes for the position and extension of the physical volume element (320), a velocity and an attenuation. Data of various kinds, e.g. pore geometry, and from numerous sources, e.g. laboratory measurements, can be incorporated in the rock physical model (255).

Abstract: A system (100) for monitoring a subterranean structure comprises an array (10) with n acoustic sensors capable of detecting P-waves and/or S-waves from the subterranean structure and a central controller (120) for receiving a signal (X) from the sensors. The system further comprises a lookup table (20) comprising a pre-computed travel time curve (24) expressed as relative arrival times of a signal from a location (Lm) to each of the sensors (1-n); a comparison unit for comparing the received signal (X) with the pre-computed travel time curve (24), and means for raising an alarm if the received signal (X) matches the precomputed travel time curve (24). Preferably, the alarm is raised if a computed semblance value (26, 27) exceeds a predefined threshold. The system may monitor several locations (Lm) in parallel using a fraction of the computer resources and time required by prior art techniques.

Abstract: A method for measuring subsidence and/or uprise on a field, comprises the steps of: deploying at least one cable on a solid surface; collecting inline tilt data from numerous tilt sensors deployed along each cable (100); and performing a statistical analysis on the tilt data to determine changes in curvature on the solid surface. Preferably, the statistical method involves computing a cumulative inline and/or cross-line tilt, whereby random errors cancel and systematic changes add. In addition, regression and/or interpolation may provide a quantitative estimate of curvature etc.

Abstract: A system (100) for monitoring a subterranean structure comprises an array (10) with n acoustic sensors capable of detecting P-waves and/or S-waves from the subterranean structure and a central controller (120) for receiving a signal (X) from the sensors. The system further comprises a lookup table (20) comprising a pre-computed travel time curve (24) expressed as relative arrival times of a signal from a location (Lm) to each of the sensors (1?n); a comparison unit for comparing the received signal (X) with the pre-computed travel time curve (24), and means for raising an alarm if the received signal (X) matches the precomputed travel time curve (24). Preferably, the alarm is raised if a computed semblance value (26, 27) exceeds a predefined threshold. The system may monitor several locations (Lm) in parallel using a fraction of the computer resources and time required by prior art techniques.

Abstract: A system (400) for processing microseismic data comprises an array (330) of seismic sensors (331, 330 332) at known locations, means (331, 332; 410) for enhancing SNR in a seismic signal output from a seismic sensor, means (331, 332; 410) for detecting a microseismic event in the seismic signal and inverting means (410) for adapting a rock physical model (255) to microseismic data that are acquired at least partially from the seismic signal representing a microseismic event. The rock physical model comprises a set of spatial volume elements mapping a set of physical volume elements (320) within a volume (300) to be monitored, wherein each spatial volume element comprises attributes for the position and extension of the physical volume element (320), a velocity and an attenuation. Data of various kinds, e.g. pore geometry, and from numerous sources, e.g. laboratory measurements, can be incorporated in the rock physical model (255).