North Sea reservoir description: Benefits of an elastic migration/inversion applied to multicomponent vertical seismic profile data

Geophysics ◽  
1990 ◽  
Vol 55 (2) ◽  
pp. 209-217 ◽  
Author(s):  
W. B. Beydoun ◽  
M. Mendes ◽  
J. Blanco ◽  
A. Tarantola
Keyword(s):  
North Sea ◽  
Confidence Region ◽  
Seismic Profile ◽  
Background Model ◽  
Quality Data ◽  
S Wave ◽  
Ray Method ◽  
Target Zone ◽  
The North ◽  
Paraxial Ray

A linearized elastic migration/inversion (M/I) technique is applied to multicomponent offset VSP data collected in the North Sea. High‐resolution elastic images of the target zone (P- and S-wave velocities and density) are obtained from upgoing P-P and P-S wave fields. These M/I images are an approximate representation of rapid variations of subsurface parameters. Three image confidence criteria provide a measure of uncertainty in the interpretation. VSP-CDP transform maps assisted in the definition of the confidence region in M/I images. M/I was helpful in delineating the Brent reservoir, and detecting a twofault system. Preliminary interpretation indicates an increase in Poisson’s ratio at the top of the reservoir. Surface data were not able to image this target due to strong multiples at the Cretaceous base. This is the first time elastic depth images have been obtained from M/I of offset VSP field data. Generally, image artifacts depend on the following conditions: (1) good quality data with satisfactory coverage of the target zone; (2) accurate, amplitude‐preserving data preprocessing techniques for filtering out “unwanted” waves; and (3) an elastic background model which adequately represents the main subsurface features. Our M/I approach is flexible, since it can be used with single or multicomponent prestack data P-P, P-S, S-P, and S-S scattered waves simultaneously, an arbitrary acquisition geometry, and a two‐dimensional heterogeneous background model. Computational efficiency results from concentrating the inversion on a target zone and using the paraxial ray method to compute ray‐approximate Green’s functions.

Shear‐wave velocity and density estimation from PS-wave AVO analysis: Application to an OBS dataset from the North Sea

Geophysics ◽  
2000 ◽  
Vol 65 (5) ◽  
pp. 1446-1454 ◽  
Author(s):  
Side Jin ◽  
G. Cambois ◽  
C. Vuillermoz
Keyword(s):  
Wave Velocity ◽  
North Sea ◽  
Random Noise ◽  
P Wave ◽  
S Wave ◽  
Data Set ◽  
Avo Analysis ◽  
The North ◽  
Avo Inversion ◽  
The North Sea

S-wave velocity and density information is crucial for hydrocarbon detection, because they help in the discrimination of pore filling fluids. Unfortunately, these two parameters cannot be accurately resolved from conventional P-wave marine data. Recent developments in ocean‐bottom seismic (OBS) technology make it possible to acquire high quality S-wave data in marine environments. The use of (S)-waves for amplitude variation with offset (AVO) analysis can give better estimates of S-wave velocity and density contrasts. Like P-wave AVO, S-wave AVO is sensitive to various types of noise. We investigate numerically and analytically the sensitivity of AVO inversion to random noise and errors in angles of incidence. Synthetic examples show that random noise and angle errors can strongly bias the parameter estimation. The use of singular value decomposition offers a simple stabilization scheme to solve for the elastic parameters. The AVO inversion is applied to an OBS data set from the North Sea. Special prestack processing techniques are required for the success of S-wave AVO inversion. The derived S-wave velocity and density contrasts help in detecting the fluid contacts and delineating the extent of the reservoir sand.

Data-driven adaptive decomposition of multicomponent seabed seismic recordings: Application to shallow-water data from the North Sea

Geophysics ◽  
2007 ◽  
Vol 72 (6) ◽  
pp. V133-V142 ◽  
Author(s):  
Remco Muijs ◽  
Johan O. A. Robertsson ◽  
Klaus Holliger
Keyword(s):  
North Sea ◽  
Decomposition Method ◽  
Data Driven ◽  
Full Potential ◽  
S Wave ◽  
Data Set ◽  
The North ◽  
Decomposition Procedure ◽  
The North Sea

Exploiting the full potential of multicomponent seabed seismic recordings requires the decomposition of the recorded data into their upgoing and downgoing P- and S-wave constituents. We present a case study from the North Sea, where a novel adaptive wave-equation-based decomposition method is applied to a 2D data set shot inline with a cable-based seabed seismic acquisition system. The data were recorded in relatively shallow [Formula: see text] water, such that severe interference exists between primary reflections and water-layer multiples. Such conditions represent a challenge for many decomposition methods, because these often require a significant amount of interpretive, user-defined input. Conversely, the adaptive algorithm demonstrated in this study is fully data-driven, requiring as sole input a rough estimate of the water depth. The importance of careful mutual calibration of the sensors is demonstrated by critically assessing the properties of the derived calibration filters and the resulting estimates of the elastic properties of the seabed. To assess the effectiveness of the decomposition procedure, we compare a number of key events identified in the unprocessed data with their equivalents in the decomposed wavefields. The results of this case study show that the noninteractive decomposition method, which was demonstrated on seabed seismic data acquired in deep [Formula: see text] water, can be applied successfully in shallower conditions without further modification.

scholarly journals Ultrasonic and seismic constraints on crystallographic preferred orientations of the Priestley Glacier shear margin, Antarctica

2022 ◽  
Author(s):  
Franz Lutz ◽  
David J. Prior ◽  
Holly Still ◽  
M. Hamish Bowman ◽  
Bia Boucinhas ◽  
...  
Keyword(s):  
Ice Core ◽  
Seismic Profile ◽  
P Wave ◽  
Quality Data ◽  
S Wave ◽  
P Waves ◽  
Velocity Anisotropy ◽  
Wave Data ◽  
Axis Alignment ◽  
Safety Considerations

Abstract. Crystallographic preferred orientations (CPOs) are particularly important in controlling the mechanical properties of glacial shear margins. Logistical and safety considerations often make direct sampling of shear margins difficult and geophysical measurements are commonly used to constrain the CPOs. We present here the first direct comparison of seismic and ultrasonic data with measured CPOs in a polar shear margin. The measured CPO from ice samples from a 58 m deep borehole in the left lateral shear margin of the Priestley Glacier, Antarctica, is dominated by horizontal c-axes aligned sub-perpendicular to flow. A vertical seismic profile experiment with hammer shots up to 50 m away from the borehole, in four different azimuthal directions, shows velocity anisotropy of both P-waves and S-waves. Matching P-wave data to the anisotropy corresponding to CPO models defined by horizontally aligned c-axes gives two possible solutions for c-axis azimuth, one of which matches the c-axis measurements. If both P-wave and S-wave data are used, there is one best fit for azimuth and intensity of c-axis alignment that matches well the measurements. Azimuthal P-wave and S-wave ultrasonic data recorded in the laboratory on the ice core show clear anisotropy that matches that predicted from the CPO of the samples. With good quality data, azimuthal increments of 30° or less will constrain well the orientation and intensity of c-axis alignment. Our experiments provide a good framework for planning seismic surveys aimed at constraining the anisotropy of shear margins.

scholarly journals North Sea Wave Database (NSWD) and the Need for Reliable Resource Data: A 38 Year Database for Metocean and Wave Energy Assessments

Atmosphere ◽  
2019 ◽  
Vol 10 (9) ◽  
pp. 551 ◽  
Author(s):  
George Lavidas ◽  
Henk Polinder
Keyword(s):  
North Sea ◽  
Wave Energy ◽  
Energy Content ◽  
Energy Resource ◽  
Wave Power ◽  
Climatic Data ◽  
S Wave ◽  
North East ◽  
The North ◽  
The North Sea

The study presents a newly generated hindcast database of metocean conditions for the region of the North Sea by parametrising the newly introduced ST6 physics in a nearshore wave model. Exploring and assessing the intricacies in wave generation are vital to produce a reliable hindcast. The new parametrisations perform better, though they have a higher number of tuneable options. Parametrisation of the white capping coefficient within the ST6 package improved performance with significant differences ≈±20–30 cm. The configuration which was selected to build the database shows a good correlation ≈95 % for H m 0, has an overall minimal bias with the majority of locations being slightly over-estimated ±0.5–1 cm. The calibrated model was subsequently used to produce a database for 38 years, analysing and discussing the metocean condition. In terms of wave energy resource, the North Sea has not received attention due to its perceived “lower” resource. However, from analysing the long-term climatic data, it is evident that the level of metocean conditions, and subsequently wave power, can prove beneficial for development. The 95th percentile indicates that the majority of the time H m 0 should be expected at 3.4–5 m, and the wave energy period T e at 5–7 s. Wave power resource exceeds 15 kW/m at locations very close to the coast, and it is uniformly reduced as we move to the Southern parts, near the English Channel, with values there being ≈5 kW/m, with most energetic seas originating from the North East. Results by the analysis show that in the North Sea, conditions are moderate to high, and the wave energy resource, which has been previously overlooked, is high and easily accessible due to the low distance from coasts. The study developed a regional high-fidelity model, analysed metocean parameters and properly assessed the energy content. Although, the database and its results can have multiple usages and benefit other sectors that want to operate in the harsh waters of the North Sea.

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