scholarly journals The Use of Core & Log Anisotropy Parameters into Seismic Data Processing: A Case Study of Deep-Water Reservoir

2021 ◽  
Vol 873 (1) ◽  
pp. 012038
Author(s):  
Madaniya Oktariena ◽  
Wahyu Triyoso ◽  
Dona Sita Ambarsari ◽  
Sigit Sukmono ◽  
Erlangga Septama ◽  
...  
Keyword(s):  
Seismic Velocity ◽  
Transverse Isotropy ◽  
Anisotropy Parameter ◽  
Water Reservoir ◽  
Velocity Analysis ◽  
Subsurface Imaging ◽  
Sonic Log ◽  
Anisotropy Parameters ◽  
Vertical Transverse Isotropy

Abstract The seismic far-offset data plays important role in seismic subsurface imaging and reservoir parameters derivation, however, it is often distorted by the hockey stick effect due to improper correction of the Vertical Transverse Isotropy (VTI) during the seismic velocity analysis. The anisotropy parameter η is needed to properly correct the VTI effect. The anisotropy parameters of ε and δ obtained from log and core measurements, can be used to estimate the η values, however, the upscaling effects due to the different frequencies of the wave sources used in the measurements must be carefully taken into account. The objective is to get better understanding on the proper uses of anisotropy parameters in the the velocity analysis of deepwater seismic gather data. To achieve the objective, the anisotropy parameters from ultrasonic core measurements and dipole sonic log were used to model the seismic CDP gathers. The upscaling effects is reflected by the big difference of measured anisotropy values, in which the core measurement value is about 40 times higher than the log measurement value. The CDP gathers modelling results show that, due to the upscaling effect, the log and core-based models show significant differences of far-offset amplitude and hockey sticks responses. The differences can be minimized by scaling-down the log anisotropy values to core anisotropy values by using equations established from core – log anisotropy values cross-plot. The study emphasizes the importances of integrating anisotropy parameters from core and log data to minimize the upscaling effect to get the best η for the VTI correction in seismic velocity analysis.

Velocity-independent τ-p moveout in a horizontally layered VTI medium

Geophysics ◽  
2011 ◽  
Vol 76 (4) ◽  
pp. U45-U57 ◽  
Author(s):  
Lorenzo Casasanta ◽  
Sergey Fomel
Keyword(s):  
Seismic Velocity ◽  
Transverse Isotropy ◽  
Anisotropy Parameter ◽  
Complete Information ◽  
Velocity Model ◽  
Natural Domain ◽  
Taylor Series Expansions ◽  
Vertical Transverse Isotropy ◽  
Vti Media ◽  
And Inversion

Local slopes of seismic events carry complete information about the structure of the subsurface. This information is sufficient for accomplishing all time-domain imaging tasks, without the need to estimate or know the seismic velocity model. A velocity-independent [Formula: see text] imaging approach has been developed to perform moveout correction in horizontally layered vertical-transverse-isotropy (VTI) media. The effective and interval anisotropic parameters are transformed into data attributes through the use of slopes and become directly mappable to the zero-slope traveltime. The [Formula: see text] transform is the natural domain for anisotropy parameter estimation in layered media because the phase velocity is given explicitly in terms of [Formula: see text]. Therefore, the [Formula: see text] transform permits reflection-traveltime modeling and inversion that are simpler than traditional methods, which are based on Taylor-series expansions of traveltime in the t-x domain. Synthetic and field data tests demonstrate the practical effectiveness of the [Formula: see text] method.

Seismic velocity analysis case study: Geostatistical contributions

1985 ◽  
Author(s):  
T. K. Young ◽  
A. J. Davis ◽  
D. R. Palmore ◽  
D. H. Thorson
Keyword(s):  
Seismic Velocity ◽  
Velocity Analysis

Anisotropy correction for deviated‐well sonic logs: Application to seismic well tie

Geophysics ◽  
2003 ◽  
Vol 68 (2) ◽  
pp. 464-471 ◽  
Author(s):  
Brian E. Hornby ◽  
John M. Howie ◽  
Donald W. Ince
Keyword(s):  
Group Velocity ◽  
Anisotropy Parameter ◽  
Compressional Wave ◽  
P Wave ◽  
Wave Group ◽  
Sonic Log ◽  
Velocity Surface ◽  
Anisotropy Parameters ◽  
Sonic Logs ◽  
Shale Anisotropy

Borehole sonic logs acquired in deviated wells penetrating the HRZ and Colville shales in the Niakuk field in Alaska's North Slope are seen to be significantly faster than vertical well logs. These differences are attributed to shale anisotropy. An iterative inversion scheme was created to invert for shale anisotropy parameters using multiple wells penetrating shale sections at different angles. The inversion involves fitting the sonic log data at a range of borehole angles to the compressional wave group velocity surface. The result is an estimate of the anisotropy parameters (ε and δ) and the vertical P‐wave velocity. The results show that the shales are strongly anisotropic, with compressional‐wave anisotropy (Thomsen's parameter ε) on the order of 40% and the anisotropy parameter δ (relates vertical velocity to short‐offset NMO velocity) around 10%. This large anisotropy can affect seismic imaging, AVO, and time–depth calculations. A procedure was created to estimate the anisotropy‐corrected vertical sonic logs from sonic data recorded in a deviated well. The inputs are well deviation, P‐wave sonic log, volume of shale or gamma ray data, and anisotropy parameters for rock with 100% shale volume. With these inputs the compressional‐wave group velocity surface is computed and the equivalent vertical P‐wave sonic log is output. The equivalent vertical sonic log can then be used for standard seismic applications using isotropic velocity assumptions. The application was applied to a well deviated at approximately 67°. Shale anisotropy parameters were taken from the sonic log inversion, and an anisotropy‐corrected sonic log was produced. Seismic well ties were attempted using both the recorded logs and the anisotropy‐corrected logs, with the result that the well tie using the measured logs was poor while a tie using the anisotropy‐corrected logs was good.

The measurement of weak anisotropy with the generalized reciprocal method

Geophysics ◽  
2000 ◽  
Vol 65 (5) ◽  
pp. 1583-1591 ◽  
Author(s):  
Derecke Palmer
Keyword(s):  
Phase Velocity ◽  
Critical Angle ◽  
Seismic Velocity ◽  
Anisotropy Parameter ◽  
Anisotropy Factor ◽  
Weak Anisotropy ◽  
Refraction Tomography ◽  
Anisotropy Parameters ◽  
Reciprocal Method ◽  
Refraction Data

Anisotropy parameters can be determined from seismic refraction data using the generalized reciprocal method (GRM) for a layer in which the velocity can be described with the Crampin approximation for transverse isotropy. The parameters are the standard anisotropy factor, which is the horizontal velocity divided by the vertical velocity, and a second poorly determined parameter which, for weak anisotropy, is approximated by a linear relationship with the anisotropy factor. Although only one anisotropy parameter is effectively determined, the second parameter is essential to ensure that the anisotropy does not degenerate to the elliptical condition which is indeterminate using the approach described in this paper. The anisotropy factor is taken as the value for which the phase velocity at the critical angle given by the Crampin equation is equal to the average velocity computed with the optimum XY value obtained from a GRM analysis of the refraction data. The anisotropy parameters can be used to improve the estimate of the refractor velocity, which can exhibit marked dip effects when the overlying layer is anisotropic. In a model study, depths computed with the phase velocity at the critical angle are within 3% of the true values, whereas those calculated with the horizontal phase velocity (which assumes isotropy) are greater than the true depths by about 25%. Anisotropy illustrates the pitfalls of model‐based inversion strategies, which seek agreement between the travetime data and the computed response of the model. With anisotropic layers, the traveltime data provide the seismic velocity in the overlying layer in the horizontal direction, whereas the seismic velocity near the critical angle is required for depth computations. If anisotropy is applicable, then the GRM using the methods described in this paper is able to provide a good starting model for other approaches, such as refraction tomography.

scholarly journals Velocity-independent estimation of kinematic attributes in vertical transverse isotropy media using local slopes and predictive painting

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. U73-U85 ◽  
Author(s):  
M. Javad Khoshnavaz ◽  
Andrej Bóna ◽  
Milovan Urosevic
Keyword(s):  
Model Building ◽  
Seismic Velocity ◽  
Transverse Isotropy ◽  
Velocity Model ◽  
Velocity Estimation ◽  
Computational Time ◽  
Sufficient Information ◽  
Zero Offset ◽  
Vertical Transverse Isotropy ◽  
Vti Media

Agood seismic velocity model is required for many routine seismic imaging techniques. Velocity model building from seismic data is often labor intensive and time consuming. The process becomes more complicated by taking nonhyperbolic traveltime estimations into account. An alternative to the conventional time-domain imaging algorithms is to use techniques based on the local event slopes, which contain sufficient information about the traveltime moveout for velocity estimation and characterization of the subsurface geologic structures. Given the local slopes, there is no need for a prior knowledge of a velocity model. That is why the term “velocity independent” is commonly used for such techniques. We improved upon and simplified the previous versions of velocity-independent nonhyperbolic approximations for horizontally layered vertical transverse isotropy (VTI) media by removing one order of differentiation with respect to offset from the imaging kinematic attributes. These kinematic attributes are derived in terms of the local event slopes and zero-offset two-way traveltime (TWTT). We proposed the use of predictive painting, which keeps all the attributes curvature independent, to estimate the zero-offset TWTT. The theoretical contents and performance of the proposed approach were evaluated on synthetic and field data examples. We also studied the accuracy of moveout attributes for shifted hyperbola, rational, three-parameter, and acceleration approximations on a synthetic example. Our results show that regardless of the approximation types, NMO velocity estimate has higher accuracy than the nonhyperbolicity attribute. Computational time and accuracy of the inversion of kinematic attributes in VTI media using our approach were compared with routine/conventional multiparameter semblance inversion and with the previous velocity-independent inversion techniques.

scholarly journals Estimasi Parameter Koreksi Anisotropi Seismik Melalui Pendekatan Nonhyperbolic Moveout Pada Gather Konvensional, DMO, dan CRS

2019 ◽  
Vol 15 (1) ◽  
pp. 15
Author(s):  
Julius Febriardi ◽  
Wahyu Triyoso
Keyword(s):  
Transverse Isotropy ◽  
Velocity Analysis ◽  
Hockey Stick ◽  
Common Reflection Surface ◽  
Vertical Transverse Isotropy

Sifat anisotropi pada suatu medium menyebabkan adanya perbedaan kecepatan rambat gelombang berdasarkan arah rambatnya. Medium bersifat transvere isotropy memiliki nilai kecepatan yang berbeda ke arah lateral dan vertikal. Medium bersifat vertical transverse isotropy (VTI) memiliki kecepatan lateral yang lebih besar daripada kecepatan vertikal. Perbedaan ini menyebabkan timbulnya efek hockey stick, terutama pada offset jauh. Karena informasi pada offset jauh amat penting, maka efek ini perlu dikoreksi terlebih dahulu sebelum melanjutkan ke tahapan pemrosesan data selanjutnya. Untuk mendapat pemahaman yang lebih baik, maka dibuat model sintetik VTI yang diproses menggunakan normal moveout (NMO), dip moveout (DMO) dan common reflection surface (CRS). Untuk menghilangkan efek dipping dan agar didapatkan hasil velocity analysis yang baik, DMO dan CRS dilakukan. Pilihan ini atas pertimbangan bahwa metode DMO dapat menghilangkan sifat dip- dependent pada gather seismik, dan analisis kecepatan paling mudah dilakukan pada metode CRS. Hasil perbandingan metode DMO dan CRS menunjukkan bahwa CRS menunjukkan S/N ratio yang lebih baik dan memiliki ketidakpastian yang lebih kecil dalam analisis kecepatan yang berpengaruh langsung dalam estimasi parameter koreksi anisotropi. Nilai parameter koreksi anisotropi diestimasi pada CDP yang ditentukan menggunakan pendekatan nonhyperbolic moveout. Nilai rata-rata yang diperoleh pada masing-masing metode menunjukkan hasil yang berbeda. Nilai ηeff yang paling mendekati nilai η model adalah pada metode DMO dan CRS.

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