News Column

Patent Application Titled "Seismic Sensor Devices" Published Online

June 3, 2014



By a News Reporter-Staff News Editor at Information Technology Newsweekly -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventors MUIJZERT, EVERHARD JOHAN (GIRTON, GB); MARTIN, JAMES EDWARD (COTTENHAM, GB), filed on January 16, 2014, was made available online on May 22, 2014.

The assignee for this patent application is Westerngeco L.l.c.

Reporters obtained the following quote from the background information supplied by the inventors: "The invention relates to sensor devices.

"Seismic data are typically gathered during a survey using an array of detectors. In the case of marine surveys, hydrophones measure pressure fluctuations in the water caused by incoming seismic waves. Geophones measure vector quantities such as displacement, velocity or acceleration. In the case of marine surveying, a plurality of cables or streamers, which are spaced apart typically by about 100 metres, are towed behind a boat. Each cable has detectors spaced along the cable at intervals. In the case of land surveys, a geophone array is laid out on the ground with the geophones in an approximate grid formation. The detector array detects seismic signals from reverberations of a signal from a seismic source, such as an airgun for marine surveys. In Ocean Bottom (OBC or OBS) acquisition, a detector array is fixed on the sea bed. In this case, the source may be an airgun mounted on a boat.

"The differences between the different types of surveying are considerable, mainly of the different propagation characteristics of different physical environments. Different problems exist, and have different effects to mitigate, in different surveying environments. For instance, marine surveys involve very significant reflections at the sea bed, where there is a large difference between the acoustic velocities either side of the boundary. Land surveys are subjected to unwanted propagation, including shear waves (also known as S-waves) and Love waves, which are not experienced in marine surveying. As such, different hardware and different data processing techniques are used in the different surveying environments.

"There are four main wave types detected by land survey sensors. These are S-waves, Love waves, P-waves (also known as primary waves, because they are the first detected after an earthquake) and Rayleigh waves. Rayleigh and Love waves are horizontally-propagating surface waves, whereas S-waves and P-waves propagate through bodies and thus are of most interest to seismological surveyors. P-waves are compressional waves, Rayleigh waves have a complex motion involving compressional modes and S-waves and Love waves have no compressional component.

"Rayleigh and Love waves are together termed 'ground-roll.' These waves are generally considered to be noise and obscure to some degree reflections from boundaries in the geology being surveyed. As such, the removal of the effects of ground-roll from land surveying data is of considerable interest. Various techniques have been developed that reduce the amplitude of the ground-roll and thus enhance the reflections.

"A commonly used technique involves deployment of dense field arrays or single sensors of vertical component geophones. Ground-roll is attenuated using dip or velocity filters in further data processing. In order to avoid spatial aliasing, this technique requires at least two geophones per lowest wavelength inline, i.e. in the source receiver direction. Side scattering of the seismic energy can be reduced using two-dimensional array of geophones. Ideally such an array has similar sampling intervals both inline and transverse to the seismic source.

"When data from three-component geophones is available, polarisation filtering can be applied. Polarisation filtering identifies the Rayleigh wave part of the ground-roll from the 90 degree phase-shift between its horizontal and vertical component, thereby allowing it to be removed by data processing. Polarisation filtering has been discussed by Kragh and Peardon, 1995, 'Ground roll and polarisation,' First Break, 13, 9, pages 369-378, ISSN (printed): 0263-5046 and more recently has been promoted by Kappius and Crewe, 2002, 'Adaptive Vector Filters for Ground Roll Reduction,' CSEG Geophysics, available at the time of writing at http://www.cseg.ca/conferences/2002/2002abstracts/Kappius_R_Adaptive_Vect- or_Filters_for_Ground_Roll_Reduction_.pdf. An omniphone is a device with horizontal and vertical geophones and a signal processing unit that applies a polarisation filter to the data before output, as is discussed by Lawton, D. C. and M. B. Bertam, 1991, available at the time of writing at http://www.crewes.org/Reports/1991/1991-01.pdf.

"Since the slowly propagating ground-roll is locally attenuated, the minimum required spatial sampling depends on the fast seismic reflection. As such, a survey carried out in this way typically requires relatively few geophone stations. However, polarisation filtering techniques do not work well in areas with a complicated near surface as they do not take into account the scattered Love waves present on the horizontal component data."

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "According to the invention, there is provided a sensor device adapted to be installed at a land-air interface, the sensor device comprising: a fluid-filled housing; and a sensor arrangement supported within the housing and coupled directly to the fluid so as to detect movement thereof.

"Sensor devices according to the invention can remove the effects of ground-roll at the sensor location, avoiding the need to remove the effects by data processing.

"The sensor device may be adapted to be installed at a land-air interface by comprising a coupling device located at a lower part of the housing. Alternatively or in addition, the sensor device may be adapted to be installed at a land-air interface by comprising a level oriented in common with a sensor of the sensor arrangement.

"The sensor arrangement may comprise a hydrophone and be absent of geophones and accelerometers.

"The sensor arrangement may comprise three hydrophones arranged generally horizontally and in different orientations to one another.

"The sensor arrangement may comprise a hydrophone and one or more geophones or accelerometers. Alternatively, the sensor arrangement may be absent of a hydrophone and comprise two or more geophones or accelerometers. In either case, the sensor arrangement may comprise two geophones or accelerometers arranged generally horizontally and in different orientations to one another. In this device, the sensor arrangement may include a vertically aligned geophone or accelerometer and a horizontally aligned geophone or accelerometer. The sensor arrangement may include two horizontally aligned geophones or accelerometers aligned orthogonally to one another.

"The sensor device as claimed in any preceding claim may comprise a mechanical decoupling arrangement for mechanically decoupling one or more sensors of the sensor arrangement from the housing. The mechanical decoupling arrangement may comprise a spring and dashpot arrangement. In the case of an acceleration cancelling hydrophone, no mechanical decoupling is needed.

"Installations constructed using sensor devices according to the invention also can achieve a given quality of data with significantly fewer sensor devices than the corresponding prior art installations. In particular, installations can require half the number of sensor devices in a given dimension, resulting in a 50% reduction in sensor device numbers for a one dimensional array and a 75% reduction for a two dimensional array.

"A second aspect of the invention provided a seismic sensor installation comprising a sensor device installed at a land-air boundary, wherein the sensor device comprises: a fluid-filled housing; and a sensor arrangement supported within the housing and coupled directly to the fluid as to detect movement thereof.

"The sensor device may be installed on top of a land surface at the land-air boundary. Alternatively it may be partially buried in a land surface at the land-air boundary, or provided in a borehole.

"The installation may comprise a coupling device located at a lower part of the housing. The installation may comprise a level oriented in common with a sensor of the sensor arrangement.

"The installation may comprise a one dimensional array of sensor devices installed at the land-air boundary. Alternatively it may comprise a two dimensional array of sensor devices installed at the land-air boundary.

"A third aspect of the invention provides a seismic sensor installation comprising plural sensor devices installed at a land-air boundary, wherein the installation comprises plural sensor devices absent of hydrophones and, adjacent an obstacle, plural sensor devices comprising: a fluid-filled housing; and a hydrophone and one or more geophones or accelerometers supported within the housing and coupled directly to the fluid as to detect movement thereof.

"Installations according the invention also can achieve a given quality of data with significantly fewer sensor devices than the corresponding prior art installations. In particular, installations can require half the number of sensor devices in a given dimension, resulting in a 50% reduction in sensor device numbers for a one dimensional array and a 75% reduction for a two dimensional array.

BRIEF DESCRIPTION OF THE DRAWINGS

"Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings of which:

"FIGS. 1 and 3 to 12 are schematic illustrations respectively of first to eleventh embodied sensor devices;

"FIGS. 2a to 2d are charts of sensor outputs when the FIG. 1 sensor device is exposed to different types of wave;

"FIGS. 13 to 16 are schematic illustrations of embodied installations incorporating a sensor device of one of FIGS. 1 and 3 to 12;

"FIGS. 17a and 18a are schematic illustrations of prior art deployments of sensor devices; and

"FIGS. 17b to 17d and 18b to 18e are schematic illustrations of embodied deployments of sensor devices.

"In the drawings, like reference numerals denote like elements."

For more information, see this patent application: MUIJZERT, EVERHARD JOHAN; MARTIN, JAMES EDWARD. Seismic Sensor Devices. Filed January 16, 2014 and posted May 22, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4030&p=81&f=G&l=50&d=PG01&S1=20140515.PD.&OS=PD/20140515&RS=PD/20140515

Keywords for this news article include: Westerngeco L.l.c, Information Technology, Information and Data Processing.

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Source: Information Technology Newsweekly


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