Life of Field Seismic at Ekofisk - Utilizing 4D Seismic for Evaluating Well Target

Lyngnes, B.; Landa, H.; Ringen, K.; Haller, N.

doi:10.3997/2214-4609.20130848

Cited by 7 publications

(5 citation statements)

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“…The high velocities in the center of the array coincide with a production‐induced subsidence bowl. Rapid pressure depletion in the early phase of production and weakening due to subsequent water injection caused more than 9 m of seafloor subsidence over the Ekofisk field [ Hermansen et al , ; Lyngnes et al , ]. The fast directions of anisotropy form a large ring surrounding the platform.…”

Section: Near‐surface Anistropic Phase Velocities At Ekofisk Field Nmentioning

confidence: 99%

Elliptical‐anisotropic eikonal phase velocity tomography

Ridder

Biondi

Nichols

2015

Geophysical Research Letters

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We formulated an anisotropic eikonal tomography approach for phase velocities based on a two‐dimensional elliptical‐anisotropic wave equation. We can fit the parameters of the ellipse directly from measured first‐order traveltime surface gradients and constrain these parameters to vary smoothly over space. The method is applied to Scholte waves in virtual seismic sources from stations in the Life of Field Seismic Ocean Bottom Cable array installed over the Ekofisk field. The fast directions of the azimuthally anisotropic Scholte wave velocities form a large circular pattern over the Ekofisk field. This pattern dominates the Scholte wave phase velocities at Ekofisk between 0.7 and 1.1 Hz. It results from the overburden stress state and from seafloor subsidence induced by decades of hydrocarbon extraction.

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Section: Near‐surface Anistropic Phase Velocities At Ekofisk Field Nmentioning

confidence: 99%

Elliptical‐anisotropic eikonal phase velocity tomography

Ridder

Biondi

Nichols

2015

Geophysical Research Letters

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“…Rapid pressure depletion in the early phase of production and weakening due to subsequent water injection caused more than 9 m of seafloor subsidence over the Ekofisk field (Hermansen et al, 1997;Lyngnes et al, 2013). Since 2010, Ekofisk field has had a Life of Field Seismic (LoFS) 4C optical sensor array of ocean-bottom cables (OBCs) buried approximately 2 m into the sand of the seafloor (Eriksrud, 2010).…”

Section: Introductionmentioning

confidence: 97%

Ambient seismic noise tomography at Ekofisk

Ridder

Biondi

2015

GEOPHYSICS

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We have studied an approximately 40-hr recording from the Life of Field Seismic array installed over Ekofisk field to assess whether the recorded ambient seismic energy was suitable for passive seismic surface-wave interferometry. Passive seismic interferometry aims to retrieve virtual seismic sources by crosscorrelation. We have found that the noise recorded by the pressure sensors between 0.4 and 1.4 Hz consisted predominantly of Scholte-wave microseism energy. The noise incidence directions have an almost uniform distribution over the azimuth, enabling the synthesis of nearly symmetric estimated Green's functions between all stations in the array that formed virtual seismic sources. These sources were dominated by Scholte waves traveling along the seafloor, and we sought to determine which features in the subsurface can be imaged by straight-ray group-velocity tomography. We located a high-velocity anomaly in the center of Ekofisk's production-induced subsidence bowl, surrounded by lower velocities. This pattern seemed to result from production-induced seafloor subsidence that altered the near-surface shear strengths. A dispersion analysis showed that the Scholtewave virtual seismic source exhibited an approximate penetration depth to 600 m below the seafloor. These results are significant because they demonstrated that recordings made at the oceanbottom cable array at Ekofisk field in the absence of seismic shooting can be used to image and monitor the near surface.

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“…Ekofisk field is one of the largest hydrocarbon fields in the North Sea, it was Norway's first producing field in 1971 (Van den Bark & Thomas, 1979) and has a projected lifespan exceeding year 2050. Rapid pressure depletion in the early phase of production and weakening due to subsequent water injection caused more than 9 m of seafloor subsidence over the Ekofisk field (Herwanger & Horne, 2009;Lyngnes et al, 2013). The subsidence is known to dominate the pattern in the anisotropic Scholte wave phase velocities in the near-surface (Kazinnik et al, 2014;De Ridder et al, 2015).…”

Section: Anisotropic Seismic Gradiometry 21 4 Field Data Example At Ementioning

confidence: 99%

Seismic Gradiometry using Ambient Seismic Noise in an Anisotropic Earth

Ridder¹,

Curtis

2017

Geophysical Journal International

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We introduce a wavefield gradiometry technique to estimate both isotropic and anisotropic local medium characteristics from short recordings of seismic signals by inverting a wave equation. The method exploits the information in the spatial gradients of a seismic wavefield that are calculated using dense deployments of seismic arrays. The application of the method uses the surface wave energy in the ambient seismic field. To estimate isotropic and anisotropic medium properties we invert an elliptically anisotropic wave equation. The spatial derivatives of the recorded wavefield are evaluated by calculating finite di↵erences over nearby recordings, which introduces a systematic anisotropic error. A two step approach corrects this error: finite di↵erence stencils are first calibrated, then the output of the wave-equation inversion is corrected using the linearized impulse response to the inverted velocity anomaly. We test the procedure on ambient seismic noise recorded in a large and dense ocean bottom cable array installed over Ekofisk field. The estimated azimuthal anisotropy forms a circular geometry around the production-induced subsidence bowl. This conforms with results from studies employing controlled sources, and with 2 S.A.L. de Ridder and A. Curtis interferometry correlating long records of seismic noise. Yet in this example, the results where obtained using only a few minutes of ambient seismic noise.

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Life of Field Seismic at Ekofisk - Utilizing 4D Seismic for Evaluating Well Target

Cited by 7 publications

References 0 publications

Elliptical‐anisotropic eikonal phase velocity tomography

Elliptical‐anisotropic eikonal phase velocity tomography

Ambient seismic noise tomography at Ekofisk

Seismic Gradiometry using Ambient Seismic Noise in an Anisotropic Earth

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