WO2002023222A1 - Conditions de mise en images par ponderation et illumination de donnees sismiques de migration - Google Patents

Conditions de mise en images par ponderation et illumination de donnees sismiques de migration Download PDF

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Publication number
WO2002023222A1
WO2002023222A1 PCT/US2001/028744 US0128744W WO0223222A1 WO 2002023222 A1 WO2002023222 A1 WO 2002023222A1 US 0128744 W US0128744 W US 0128744W WO 0223222 A1 WO0223222 A1 WO 0223222A1
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WIPO (PCT)
Prior art keywords
image
generating
shots
subsurface
frequency band
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PCT/US2001/028744
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English (en)
Inventor
Zheng-Zheng Zhou
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Nutec Sciences, Inc.
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Priority to AU2001292663A priority Critical patent/AU2001292663A1/en
Publication of WO2002023222A1 publication Critical patent/WO2002023222A1/fr

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V1/00—Seismology; Seismic or acoustic prospecting or detecting
    • G01V1/28—Processing seismic data, e.g. for interpretation or for event detection

Definitions

  • Each one of the shots may generate over one thousand traces, a trace being defined as the data recorded by a single receiver from a single shot. Given the large number of shots and receivers involved in a typical project, a massive amount of data may be collected. The data recorded by the receivers is processed to produce an image of the geological subsurface of the earth.
  • the data recorded by each receiver is a time series representing reflections from the subsurface caused by the explosive source at the surface of the Earth. This time series is known as a trace.
  • the behavior of these traces is governed by the wave equation. It is known that, by using the redundancy that is built into the method of data acquisition, the wave equation can be used to predict the speed at which the sound waves propagate through the Earth's surface.
  • the wave equation predicts the dissipation of energy as a function of the known velocities of geological formations in the x, y, and z directions as the waves propagate through the Earth. After a large amount of data, in the form of seismic traces, is collected, it is processed.
  • a stacking process may be performed in which traces are summed together into a three dimensional array of numbers comprising the amplitudes of reflected seismic waves recorded over a period of time.
  • the stacked data can be migrated.
  • Data migration is the reconstruction of an image or map of the Earth's subsurface from the seismic data in the time domain as recorded by the seismic receivers at the Earth's surface. Data migration converts the data from the time domain to space or image-point domain. The data that exists in the time domain is mispositioned both laterally and vertically. Migration converts these mispositioned data to data representing lateral and depth positions of geological structures.
  • An example of seismic record migration is described in U.S. Patent No.
  • Acoustic illumination is the ability of a particular shot to transmit acoustic energy to a particular subsurface point. The greater the amount of energy that passes through a particular subsurface point, the greater the illumination of the subsurface point. Resolving or accurately identifying the geology of a particular subsurface point is directly related to the ability of the shot to illuminate the area of the subsurface point. If a point in the subsurface is highly illuminated, it is more likely that the seismic survey will lead to the correct evaluation of the geology of the point in the subsurface. Conversely, if a point in the subsurface is poorly illuminated by a seismic shot, it is less likely that the seismic survey will lead to the correct evaluation of the geology the point in the subsurface.
  • the migration of shot-gathered pre-stack traces on the basis of the wave equation involves the separate downward continuation of the up and down going wave field to the depth level of interest.
  • An imaging condition is applied at each depth level to construct the migrated image at each depth level.
  • the application of the imaging condition includes a computational cost that is relatively small when compared to the computational cost associated with performing the downward continuation function to both the up going and down going wave fields. Despite the relative size of computational cost, the choice of an imaging condition can have an appreciable effect on the migration product.
  • the amplitude of the incident and reflected waves is a function of both location or position r and frequency ⁇ . i the approximated value in the right side of the dynamic imaging condition of Equation 1, the value ⁇ is a non-negative real number added to the denominator for numerical stability.
  • the dynamic or deconvolution imaging condition includes the correct formula to remove at least theoretically all of the amplitude effects introduced by wave propagation and to deconvolve the source wavelet signature from the reflected wave, yielding the true amplitude reflectivity for the entire subsurface.
  • reflectivity is a measure of the ratio of the amplitudes of the reconstructed reflected wave and the reconstructed incident wave as measured at a single subsurface point at a single time. Summing the real parts of the ratio of the amplitudes of the incident and reflected waves across frequency ⁇ ensures that there is no time lag between the incident and reflected wave for a given subsurface point.
  • Equation 1 provides only a partial image of the subsurface.
  • data from several shots must be aggregated.
  • a common approach is to add all of the partial single-shot images and divide the total by the total number of partial images. Alternatively, the images within a range can be summed and the result divided by the number of shots within the range, as shown in Equation 2:
  • the imaging condition is the source of most of the noise.
  • Equations 1 and 2 yield inaccurate image values that are based, in part, on shot sources and receiver locations that are located too great a distance from the region of the subsurface being summed in Equation 1.
  • the unreliability and inaccuracy of these image values is enhanced by the structure of Equation 1, where the amplitude of the down going wave is in the denominator of the Equation 1.
  • a strategy for reducing the errors introduced by the summation of shots in Equations 1 and 2 is to apply a weighting factor to the shot under analysis in the summation so that the partial images are weighted prior to being summed.
  • a purely geometric weighting system might involve assigning a weight of a 1 or a weight of a 0 to a shot depending on whether the shot is within a predefined range relative to the subsurface region or point under analysis.
  • Equation (3) the structure of Equations 1 and 2, in which the placement of the amplitude of the down going wave field in the denominator of the equation, has the effect of amplifying noising or inaccurate signals to the detriment of the summation.
  • the correlation imaging condition [Claerbout] involves omitting the denominator of Equation 1.
  • the imaging condition as shown below in Equations 3 and 4, does not have the effect of boosting the inaccurate, high error regions in the partial images for each shot.
  • Equations 3 and 4 The effect of Equations 3 and 4 is that the contribution of the partial image of each shot is effectively windowed or restricted to a narrow region around the shot. Taking a product of the amplitude of the incident and reflected waves, rather than a division of the incident and reflected waves, is an improvement over the dynamic imaging condition in that neither the amplitude of the up going wave or the down going wave appears in the denominator.
  • the correlation imaging condition generates images that are substantially cleaner than the dynamic imaging condition.
  • the relative success of the correlation imaging condition as compared to the dynamic imaging condition in reducing noise in the final product confirms that noise is introduced as a function of the imaging condition, rather than as a function of the process of applying a downward continuation function to the incident and reflected waves.
  • the reflectivity in the regions of poor illumination is influenced at each step by the poor illumination of the region under analysis.
  • This double-attenuation effect introduces an uncertainty that compromises one of the advantages of wave equation migration, as compared to Kirchoff migration, i.e., the high reliability of the amplitude determined by a wave equation migration as a measure of the subsurface reflectivity distribution.
  • the dynamic imaging condition can be said to remove the attenuation even for regions of poor illumination, albeit at the cost of introducing strong noise.
  • the images produced by Equations 3 and 4 often have amplitudes that decrease rapidly with depth, necessitating the application of spherical divergence compensation before or after migration. Applying spherical divergence compensation before migration will alter the dynamics of the input data, whereas applying spherical divergence compensation after migration will likely fail to capture many of the details and nuances of the wave dynamics under analysis.
  • a method for applying an imaging condition to migrated seismic data is provided that eliminates or reduces disadvantages or problems associated with prior image generation techniques.
  • the present invention involves the use of an imaging technique for seismic data in which migrated data is imaged by the correlation imaging condition and the application of a normalization factor.
  • the correlation imaging condition can be applied by summing, across a range of frequencies and a selection of a set of shots, the real part of the product of the down going and up going waves.
  • the normalization factor that is applied to the result of the correlation imaging condition is the sum, across the frequency band and the set of shots, of the squared amplitudes of the down going waves.
  • the illumination weighting condition of the present invention is advantageous in that it introduces a weighting factor to an imaging condition without introducing attenuation errors into the imaging process.
  • the weighting factor of the present invention is also accurate in that it does not depend upon the crude selection of shots within a predefined range.
  • Another advantage of the imaging condition of the present invention is the correction of the tendency of the correlation imaging condition to introduce a double-attenuation effect. By placing the square of the amplitudes of the down going waves in the denominator of the imaging condition, the illumination weighted imaging condition is better able to account for areas that are poorly illuminated because of the subsurface geology.
  • Another advantage of the present invention is that the normalization factor of the imaging condition is calculated from the downward continued source wave field. As a result, the normalization factor or the illumination pattern can be obtained at little additional computation cost.
  • the illumination pattern is advantageous in that it can be used as a tool in both the analysis of subsurface geology and the design of seismic surveys.
  • the illumination pattern can be generated from a knowledge of the location of shots by means of a downward continuation function.
  • Figure 1 is a velocity model for a vertical section of the earth's subsurface
  • Figure 2 is an illumination pattern for the vertical section of Figure 1
  • Figure 3 is a seismic image produced by the weighted illumination imaging condition.
  • the imaging condition of the present invention involves the benefits of the high signal to noise ratio of the correlation imaging condition and the more physical dynamics of the dynamic imaging condition.
  • the partial images from each shot are weighted prior to summation of the final image.
  • the dynamic imaging condition has been modified to include a weighting condition W, which is applied for each shot k, frequency ⁇ , and location r .
  • Equation 6 shown below, a normalization factor is introduced to account for the weighting condition.
  • the crude aperture condition that was formerly employed as a proxy for a weighting condition in the dynamic imaging condition has been replaced by the weighting conditions of Equation 5 and Equation 6.
  • the weighting condition is chosen so that the weighting condition accurately reflects the resolving power of each shot.
  • the ability of a shot to resolve the subsurface at a given point is directly related to the ability of the shot to illuminate or transmit acoustic energy to the subsurface point in question.
  • One weight function that may be used with the illumination condition of the present invention is a measure of the down going energy at the subsurface point under analysis.
  • the weighting function of the down going energy is shown in Equation 7: W k ( ⁇ , r) - d k * ( ⁇ , r) • d k ( ⁇ , r) Equation (7)
  • Equation 8 the weighted illumination imaging condition I w is evaluated for each location r for the entire seismic survey as a function of the sum of the products of the amplitude of the down going wave and the up going wave for all shots across all frequencies divided by the sum of the square of the amplitude of the down going wave for all shots across all frequencies.
  • the denominator of Equation 8 is the sum of the total down going energy of all of the shots of the seismic experiment. If the partial illumination pattern, L, for each shot k is:
  • the full illumination pattern is:
  • a velocity model for a vertical section of the earth's subsurface is shown in Figure 1.
  • the illumination pattern of Figure 2 is generated by a series of evenly spaced shots fired from across the surface of the earth. Blue colors represent low intensity, and red colors represent high intensity.
  • a Kirchoff migration method can be used to migrate the recorded seismic data, while the downward continuation illumination modeling technique disclosed herein can be used to produce the illumination pattern of the subsurface.
  • This illumination pattern can then be used as an aid in the analysis of the Kirchoff-migrated image by illustrating regions of high and low illumination, a crucial piece of information that is not provided by Kirchoff migration.
  • the determination of an illumination pattern may also be employed as a standalone tool in the design stage of a seismic survey.
  • the illumination pattern L ( r ) can be generated through a series of downward continuation steps on the collected data.
  • the illumination pattern such as the illumination pattern of Figure 2
  • the illumination pattern can be used during the design stage of a seismic survey to evaluate the illumination characteristics of the subsurface. Knowledge that an area of poor illumination exists in the area under analysis may allow the seismic survey to be conducted with a variety of shots to pennit the greatest illumination of the these regions.
  • an illumination pattern can demonstrate areas of poor illumination prior to the actual survey, allowing the seismic surveyor to modify his survey techniques to better illuminate areas of the subsurface that have a tendency to be poorly illuminated. This technique of generating an illumination pattern may also be used as an aid in evaluating the accuracy of images generated through any migration technique.
  • a computation may be conducted in which a compact wavelet, such as a mathematical spike, is used to approximate a shot.
  • the wavelet serves as the initial condition of the downward going wave.
  • an illumination pattern of the subsurface can be generated.
  • the illumination pattern for such a single shot k is shown in Equation 9, and, in the case of multiple shots, the summed illumination pattern is shown in Equation 10.
  • the frequency band for calculating the illumination pattern can be smaller than the frequency band used for data migration.
  • the illumination pattern L of Equation 9 is not a function that is influenced by high frequencies, the function will not show aliasing effects even when sampled at relatively large depth steps.

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  • Engineering & Computer Science (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Acoustics & Sound (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Geophysics (AREA)
  • Geophysics And Detection Of Objects (AREA)

Abstract

L'invention concerne des conditions de mise en images de données sismiques de migration dans lesquelles un facteur de pondération est appliqué aux conditions de mise en images par corrélation. Le facteur de pondération comprend le carré des amplitudes de l'onde descendante ajouté sur une gamme de fréquences et une sélection de tirs du relevé sismique.
PCT/US2001/028744 2000-09-15 2001-09-12 Conditions de mise en images par ponderation et illumination de donnees sismiques de migration WO2002023222A1 (fr)

Priority Applications (1)

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AU2001292663A AU2001292663A1 (en) 2000-09-15 2001-09-12 Illumination weighted imaging condition for migrated seismic data

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US66272900A 2000-09-15 2000-09-15
US09/662,729 2000-09-15

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9025414B2 (en) 2011-05-27 2015-05-05 Conocophillips Company Reciprocal method two-way wave equation targeted data selection for seismic acquisition of complex geologic structures
EP2376947A4 (fr) * 2009-01-19 2015-09-02 Landmark Graphics Corp Acquisition de données et migration par pré-empilement sur la base d'une analyse de visibilité sismique
US9164184B2 (en) 2011-05-27 2015-10-20 Conocophillips Company Reciprocal method two-way wave equation targeted data selection for seismic acquisition of complex geologic structures
EP2697667A4 (fr) * 2011-04-13 2015-10-28 Chevron Usa Inc Compensation stable d'illumination de mesures
US9279896B2 (en) 2011-05-27 2016-03-08 Conocophillips Company Reciprocal method two-way wave equation targeted data selection for improved imaging of complex geologic structures
CN109655879A (zh) * 2017-10-11 2019-04-19 中国石油化工股份有限公司 目的层信噪比一致性能量照明的观测系统优化方法及装置

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4964098A (en) * 1990-03-15 1990-10-16 Exxon Production Research Company Method for seismic trace interpolation

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4964098A (en) * 1990-03-15 1990-10-16 Exxon Production Research Company Method for seismic trace interpolation

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2376947A4 (fr) * 2009-01-19 2015-09-02 Landmark Graphics Corp Acquisition de données et migration par pré-empilement sur la base d'une analyse de visibilité sismique
US9329288B2 (en) 2009-01-19 2016-05-03 Landmark Graphics Corporation Data acquisition and prestack migration based on seismic visibility analysis
EP2697667A4 (fr) * 2011-04-13 2015-10-28 Chevron Usa Inc Compensation stable d'illumination de mesures
US9025414B2 (en) 2011-05-27 2015-05-05 Conocophillips Company Reciprocal method two-way wave equation targeted data selection for seismic acquisition of complex geologic structures
US9116255B2 (en) 2011-05-27 2015-08-25 Conocophillips Company Two-way wave equation targeted data selection for improved imaging of prospects among complex geologic structures
US9164184B2 (en) 2011-05-27 2015-10-20 Conocophillips Company Reciprocal method two-way wave equation targeted data selection for seismic acquisition of complex geologic structures
US9279896B2 (en) 2011-05-27 2016-03-08 Conocophillips Company Reciprocal method two-way wave equation targeted data selection for improved imaging of complex geologic structures
CN109655879A (zh) * 2017-10-11 2019-04-19 中国石油化工股份有限公司 目的层信噪比一致性能量照明的观测系统优化方法及装置

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