Source signature repeatability and source array directivity — Measurements from the Valhall 4D survey

Saunders, Mike; Howe, D.; Kommedal, Jan H.

doi:10.1190/1.1839729

Cited by 9 publications

(4 citation statements)

References 4 publications

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“…Examples are differences in the source signature and source positions, changes in the water temperature, random noise in the recording units, coherent noise such as free surface multiples, and changes in the quality factor (damping). Saunders et al (2004) studied differences in source signature from shot to shot and survey to survey at Valhall and concluded that the source signature is sufficiently stable. This is also mentioned by Kommedal et al (2004), which further discuss the non‐repeatability sources of noise, such as noise from rig activity, vessels, and other seismic activities on the field.…”

Section: Discussionmentioning

confidence: 99%

Monitoring overburden layer changes and fault movements from time-lapse seismic data on the Valhall Field

Røste¹,

Landrø²,

Hatchell³

2007

Geophysical Journal International

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S U M M A R YA method developed by Røste et al., which discriminates between layer thickness and velocity changes, is tested on pre-stack time-lapse seismic ocean bottom cable (OBC) data from the Valhall Field. A key parameter in this discrimination process is the dilation factor, α, which is the relative velocity change divided by the relative thickness change within a given layer. The high quality and good repeatability of the OBC data enables us to estimate α with a reasonable accuracy for α-values between 0 and −5. For α-values below −5, complementary information, like for instance geomechanics is required. For the top reservoir horizon we estimate a maximum subsidence of 0.50 m ± 0.29 m and a corresponding velocity decrease for the sequence from the seabed to the top reservoir of 2.0 m s −1 ± 0.40 m s −1 .Time-lapse distortion patterns with characteristic time-shift versus offset signatures are observed. The positions and vertical extents of the distortion zones are determined from ray path considerations and modelling. The distortion zones correlate with buried faults, indicating that a (time-lapse) distortion zone might be produced by a localized slip in a fault zone. We present an extended method which allows for vertical (in addition to lateral) variations in the relative thickness and velocity changes. This method can be viewed as a simplified version of time-lapse tomography, but involving fewer unknown parameters, giving more stability to the estimated changes in thickness and velocity. Using this technique, we are able to estimate α for positions with localized time-lapse distortions.

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Section: Discussionmentioning

confidence: 99%

Monitoring overburden layer changes and fault movements from time-lapse seismic data on the Valhall Field

Røste¹,

Landrø²,

Hatchell³

2007

Geophysical Journal International

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“…In these cases (and in areal WATS and zigzag WATS), it is important that the source wavelet have the same shape and strength in all directions. A nondirectional symmetric source based on the annular port air gun is described by Saunders et al (2004aSaunders et al ( , 2004b.…”

Section: Source Arraymentioning

confidence: 99%

3D Seismic Survey Design, Second edition

Vermeer¹

2012

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“…In order to investigate the effects of a change of firing pressure to the bubble, we perform a convolution test of a far‐field signature with acoustic impedance data from a well log, to create synthetic seismograms with different firing pressures. The far‐field signals were calculated in Nucleus + using an air‐gun array similar to the one used for the Life of Field Seismic Project at the Valhall field (Saunders, Howe and Kommedal 2004). The array is shown in Fig.…”

Section: Effects Of Firing Pressure Changes On Marine Airgun Signaturesmentioning

confidence: 99%

Controlled source strength variation by changing the firing pressure ‐ a sensitivity study for 4D calibration

Barker

Landrø

2012

Geophysical Prospecting

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For a 4D seismic operation to be successful, it is important to know what kind of 4D signal we expect to observe, as well as its magnitude. Normally, in a 4D feasibility study, we use rock physics models to quantify the effect of fluid or pressure changes within the reservoir and calculate the corresponding effects to the seismogram. However, to find if the predicted changes are actually observable at a given field, a dedicated calibration procedure might give valuable insight. One such procedure for marine seismics is to gradually change the source strength by varying the firing pressure in order to detect the sensitivity threshold for a given subsurface reflection. This procedure would be practical and feasible if the change of the source signature changes linearly with the source pressure. However, non‐linear effects will lead to minor changes in the later arrivals of the source signature, the so‐called bubble. By investigating these introduced errors for a reasonable air‐gun array we conclude that the method is still feasible since we find it possible to control and diminish the impact of the introduced errors.

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Source signature repeatability and source array directivity — Measurements from the Valhall 4D survey

Cited by 9 publications

References 4 publications

Monitoring overburden layer changes and fault movements from time-lapse seismic data on the Valhall Field

Monitoring overburden layer changes and fault movements from time-lapse seismic data on the Valhall Field

3D Seismic Survey Design, Second edition

Controlled source strength variation by changing the firing pressure ‐ a sensitivity study for 4D calibration

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