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WO2018130272A1 - Procédé de détermination rapide de l'emplacement d'un événement d'émission acoustique dans un milieu vti/tti - Google Patents

Procédé de détermination rapide de l'emplacement d'un événement d'émission acoustique dans un milieu vti/tti Download PDF

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Publication number
WO2018130272A1
WO2018130272A1 PCT/EP2017/050446 EP2017050446W WO2018130272A1 WO 2018130272 A1 WO2018130272 A1 WO 2018130272A1 EP 2017050446 W EP2017050446 W EP 2017050446W WO 2018130272 A1 WO2018130272 A1 WO 2018130272A1
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WIPO (PCT)
Prior art keywords
event
symmetry axis
waves
acoustic emission
hypocenter
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PCT/EP2017/050446
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English (en)
Inventor
Jakob B.U. Haldorsen
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Read As
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Priority to PCT/EP2017/050446 priority Critical patent/WO2018130272A1/fr
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Classifications

    • 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
    • G01V1/288—Event detection in seismic signals, e.g. microseismics
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/10—Aspects of acoustic signal generation or detection
    • G01V2210/12—Signal generation
    • G01V2210/123—Passive source, e.g. microseismics
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/10—Aspects of acoustic signal generation or detection
    • G01V2210/14—Signal detection
    • G01V2210/142—Receiver location
    • G01V2210/1425—Land surface
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/60—Analysis
    • G01V2210/64—Geostructures, e.g. in 3D data cubes
    • G01V2210/646—Fractures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V2210/00—Details of seismic processing or analysis
    • G01V2210/60—Analysis
    • G01V2210/65—Source localisation, e.g. faults, hypocenters or reservoirs

Definitions

  • the invention relates to the field of seismic prospecting, and more particularly concerns a method for fast determination of the hypocenter of an acoustic emission event for a vertical or tilted transverse isotropic (VTI/TTI) by means of micro- seismic monitoring.
  • VTI/TTI vertical or tilted transverse isotropic
  • Micro-seismic monitoring may be used for estimating the size and orientation of induced fractures in formations.
  • the main objective is to analyze data related to micro-seismic events. This includes their locations and the mechanisms associated with their generation.
  • Micro-seismic activity can be detected by placing an array of geophones in a wellbore. By mapping the location of any small seismic events associated with a fracture, the approximate geometry of the fracture can be decided.
  • VTI Vertical Transverse Isotropic
  • Tilted Transverse Isotropic (TTI) formation With the anisotropy of a VTI symmetric formation, where the velocities are invariant under lateral translation, ray bending will be entirely in a vertical plane, i.e. the sagittal plane of source/receiver. This also applies to a formation where the axis of symmetry is not vertical, i.e. the symmetry axis is tilted away from the vertical axis. This is called a Tilted Transverse Isotropic (TTI) formation.
  • TTI Transverse Isotropic
  • the ray bending is all in a plane along the tilted symmetry axis and consequently, all rays project to straight lines in a plane perpendicular to this tilted symmetry axis, i.e. similar to the horizontal plane for a VTI formation.
  • the difference between a VTI and TTI formations is only in the orientation of the symmetry axis.
  • the transform from one to the other can be achieved with a rotation of the coordinate system, i.e., orienting the axis of symmetry along the z (or
  • the two elastic waves used for estimating the location, i.e. the hypocenter, of micro-seismic events are of two types: compressional waves (P waves), that have associated particle movement along the ray of propagation, and shear waves that have associated particle movement polarized in a direction perpendicular to the ray of propagation.
  • P waves compressional waves
  • shear waves that have associated particle movement polarized in a direction perpendicular to the ray of propagation.
  • shear waves For a VTI medium, one also normally separate the shear waves into two categories: horizontal shear waves (Sh waves) that have associated particle movement polarized in the horizontal plane and perpendicular to the ray of propagation, and vertical shear waves (Sv waves) that have associated particle movement in a vertical plane, perpendicular to the ray of propagation.
  • the P and Sv waves will both maintain their polarization vector in the same vertical (sagittal) plane containing both the source and receiver locations, the Sh waves will be polarized perpendicular to this plane.
  • READ previously introduced a unique approach in handling micro-seismic data processing, ref. Haldorsen, J.B. U., N.J. Brooks, M. Milenkovic, 2013, Locating microseismic sources using migration-based deconvolution: Geophysics, 78, 5, pp. KS73-KS84.
  • the former least-squares inversion approach that is over 100 years old has many flaws and limitations when applied to oil fields and geothermal micro- seismic data.
  • READ takes a staged approach that treats full waveform micro- seismic data.
  • a proprietary de-noising method can also be applied for increasing the signal-to-noise ratio.
  • the event epicenter can nevertheless be found by a least-squares intersection of the planes parallel to the symmetry axis through the receiver location, containing either the particle movement polarization vector of the compressional or a Sv shear wave, or perpendicular to the particle movement polarization vector of a Sh shear wave generated by the micro-seismic event.
  • the location of a seismic event away from the epicenter can be found by a ID migration along a single line through the event epicenter along the symmetry axis.
  • each of the two sets of possible sagittal planes will contain three planes, one through each receiver.
  • Each pair of planes within each of the two sets of planes will intersect along lines parallel to the symmetry axis, each set thus defining three parallel lines. These three parallel lines will coincide, within the measurement uncertainty, for the correct choice of sagittal planes, and be statistically distinct for the erroneous choice.
  • the correct identification of the wave modes as either shear or compressional can be made based on the closeness of the intersections of the associated sagittal planes.
  • the present invention is defined by a method for fast determination of the location of a hypocenter of an acoustic emission event for a Vertical or Tilted Transverse Isotropic formation, each having a symmetry axis, by means of at least three receivers comprising the following steps: spreading the receivers out perpendicular to a symmetry axis for wave velocities;
  • independent source/receiver sagittal planes as planes parallel to said symmetry axis that include the location of the receiver
  • an event epicenter as a single point where all the sagittal planes intersect with a plane perpendicular to the symmetry axis, and where said point represents a projection of the event hypocenter, and estimating the true hypocenter for an acoustic emission event from the epicenter by a ID migration along a single line through the event epicenter along the symmetry axis.
  • Figure 1 shows multiple seismic events within the same time window
  • Figure 2 shows an extracted event of the energy on each of the three components across an entire array consisting of 12 three-component receivers
  • Figure 3 shows azimuth angles for each receiver
  • Figure 4 shows the same event as in figure 3 after rotating the sagittal plane
  • Figure 5a - 5c shows back-projection of the recorded data
  • Figure 6 shows a plotting of the energy-weighted correlation function
  • Figure 7 shows the epicenter defined by intersecting straight lines
  • Figure 8 shows the sum of the squares of the distance from a point in the surface horizontal plane to all of the straight lines in the figure 7, and
  • Figure 9 shows a single trace giving a well-focused location directly below the event epicenter.
  • the invention concerns a method for fast determination of the hypocenter for an acoustic-emission event for a VTI or a TTI formation.
  • a wave mode separation technique to point the incoming compressional energy in the plane of the micro-seismic source is used.
  • the second and third components search for the Sv and Sh (vertical and horizontal shear waves) and align themselves accordingly.
  • Each X, Y, Z component is rotated to a new P, Sv, Sh system.
  • No hodograms or time picks are used.
  • Haldorsen et al. 2013 apply a proprietary deconvolution operator,
  • compressional wave to create a shear wave origin time relative to P.
  • the de-convolved time series should have a maximum at the relative time equal to zero.
  • the de-convolution algorithm used by Haldorsen et al. 2013, called semblance-weighted deconvolution or energy-weighted correlation is designed to minimize noise and improve event location accuracy.
  • the energy-weighted correlation is applied with a simultaneous back projection in order to map a recorded event - either to all possible locations in the 3D image space, or along a vertical plane already determined during the wave- mode separation process.
  • VTI and TTI formations are only in the orientation of the symmetry axis.
  • the transform from one to the other can be achieved with a rotation of the coordinate system, orienting the axis of symmetry along a vertical axis.
  • the term horizontal plane should be replaced by a term describing a plane perpendicular to the axis of symmetry
  • the term vertical plane should be replaced by term describing a plane along this axis.
  • the source/receiver sagittal plane as being along the axis of symmetry
  • the event epicenter as the projection of the event location on a plane perpendicular to the axis of symmetry. The simplest way to implement this is by first rotating the coordinate axes such that the rotated vertical axis falls along the axis of symmetry.
  • FIG. 1 shows multiple events within the same time window, ref. step 1 above.
  • An event detector is used to extract events for the next step.
  • the figure shows the vertical components (Z), followed by two sets of horizontal components (X, Y) recorded for a number of typical events.
  • Figure 2 shows an extracted event of the energy on each of the three components across an entire array of 12 three-component receivers, and where this is in coordinates pointing to the directions Up, East and North, ref. step 2 above.
  • Figure 3 shows the azimuth angles that each of the receivers needs to be rotated to have the second component pointing along the source/receiver sagittal plane.
  • all receivers agree that the source is at an azimuth angle of 57 degrees clockwise from East. This direction defines a source/receiver sagittal plane common to all receivers, with the source located in this plane, ref. step 3 above.
  • Figure 4 shows the same event after rotation to have the P and S wave components in the sagittal plane through the source and the receiver.
  • a third wave mode, probably a transverse shear is visible on the third component.
  • Figures 5a to 5c shows back-projection of the recorded data, based on polarization, the geometry and the velocities, for finding the P and S source signatures for events that possibly could have been generated at any point in the 3D image space. For this, one would preferably use the azimuth calculated above with 2D migration in the source/receiver sagittal plane. A full 3D migration approach to solve this estimation problem is also available.
  • Figure 5a shows the estimated P signature.
  • Figure 5b shows the S signature that conceivably could have been generated at a specific point in this plane. To accept that there is an event at that point, they require the two signatures to be coherent (similar in waveform) and synchronous. A measure of these two conditions being satisfied is the proprietary energy- weighted correlation function shown in Figure 5c.
  • the ray bending is still entirely in the source-receiver sagittal plane, but the sagittal plane is different for each receiver.
  • the sagittal planes are purely vertical, they will each intersect with the horizontal plane along straight lines. These straight lines will intersect at a single point, which is the surface projection of the event location, i.e. the epicenter of the event.
  • the ray bending will be entirely in a vertical plane, i.e. the source/receiver sagittal plane.
  • Figure 7 illustrates this principle.
  • the figure is based on real data recorded by three- component receivers distributed along the "double ⁇ " structure in the middle of the figure.
  • the straight lines are lines along the horizontal vectors formed by the two horizontal components of the data. These straight lines represent the projections on to a horizontal plane of all rays. Based on these straight lines, the event epicenter can be estimated determined by their closest interception.
  • the present invention is defined by a method for fast determination of the location of the hypocenter for an acoustic emission event for a Vertical or Tilted Transverse Isotropic formation (VTI, TTI), each having a symmetry axis, by means of at least three receivers.
  • the method comprises several steps.
  • the first step is spreading the receivers out perpendicular to a symmetry axis for wave velocities.
  • the next step is defining independent source/receiver sagittal planes as the planes to said symmetry axis that include the location of the receiver and either the particle movement polarization vector of compressional waves (P waves) or vertical shear waves (Sv waves) generated by the acoustic emission event,
  • P waves particle movement polarization vector of compressional waves
  • Sv waves vertical shear waves
  • the event epicenter can be found from the intersection of the straight lines along the compressional polarization in the plane perpendicular to the symmetry axis, or along directions perpendicular to the shear polarization in the plane perpendicular to the symmetry axis.
  • the next step is defining an event epicenter as a single point where all the sagittal planes intersect with a plane perpendicular to the symmetry axis, and where said point represents a projection of the event hypocenter.
  • the sagittal plane in rotated to appear as a VTI sagittal plane prior to the next estimating step.
  • the single point representing a projection of the event hypocenter is defined from the intersection of straight lines in the horizontal plane directed along the observed polarization of compressional waves in the plane perpendicular to the symmetry axis.
  • the single point representing a projection of the event hypocenter is defined from the intersection of straight lines along directions perpendicular to the polarization of shear waves in the plane perpendicular to the symmetry axis.
  • the location of the event away from the epicenter can be found by a ID migration along a single line through the event epicenter along the symmetry axis.
  • the last step of the inventive method is estimating the true hypocenter for an acoustic emission event from the epicenter by a ID migration along a single line through the event epicenter along the symmetry axis.
  • Figure 8 shows the sum of the squares of the distance from a point in the surface horizontal plane to all of the straight lines in the figure 7. This sum of squares has a well-defined minimum, which is the least-squares VTI solution to the event epicenter.
  • Figure 9 shows an example of doing this to create a single trace giving a well- focused location directly below the event epicenter.
  • the processing used is equivalent to the processing that gave the 2D image in the sagittal plane, described above with the processing used for a vertical array.
  • One difference is that for a vertical array the migration needed to be 2D, whereas we now only need a ID image in the depth direction, as the event epicenter is already known.
  • Another difference is that only P waves were used for this image, with the accuracy in the depth estimate essentially coming from the curvature for the P wave front, as measured over the aperture of the receiver array.
  • each receiver can be seen to be associated with its own source/receiver sagittal plane.
  • this sagittal plane is defined as the plane that includes both the receiver and the source locations, and is parallel to the axis of symmetry.
  • the sagittal planes are all vertical.
  • the sagittal planes will appear as vertical after an appropriate TTI-to-VTI rotation.
  • any source/receiver pair any ray bending between the source and the receiver will be entirely within its individual sagittal plane. All sagittal planes are independent.
  • Any axis of symmetry for anisotropy in geological formations are related to layering and stress applied to the formation.
  • the main layering is horizontal and the main stresses in a geological formation is vertical, giving, predominantly, the vertical axis as the axis of symmetry.
  • Higher-order symmetries like orthorhombic or triclinic symmetries, may be introduced by vertical or sub-vertical fractures or horizontally applied stress, resulting in, e.g., shear velocities that vary with azimuth.

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Abstract

L'invention concerne un procédé de détermination rapide de l'emplacement d'un hypocentre d'un événement d'émission acoustique pour une formation isotrope transversale verticale ou inclinée, ayant chacun un axe de symétrie, au moyen d'au moins trois récepteurs comprenant l'étalement des récepteurs hors perpendiculaire à un axe de symétrie pour des vitesses d'onde; la définition de plans sagittal source/récepteur indépendants sous forme de plans parallèles audit axe de symétrie qui comprennent l'emplacement du récepteur et soit le vecteur de polarisation de mouvement de particule d'ondes de compression (ondes P) soit les ondes de cisaillement vertical (ondes Sv) produites par l'événement d'émission acoustique, soit les plans perpendiculaires au vecteur de polarisation de mouvement de particule d'une onde de cisaillement horizontal (onde Sh) produite par l'événement d'émission acoustique; la définition d'un épicentre d'événement sous forme de point unique où tous les plans sagittaux coupent un plan perpendiculaire à l'axe de symétrie, et où ledit point représente une projection de l'hypocentre d'événement, et l'estimation du véritable hypocentre pour un événement d'émission acoustique à partir de l'épicentre par une migration 1D le long d'une ligne unique par l'intermédiaire de l'épicentre d'événement le long de l'axe de symétrie.
PCT/EP2017/050446 2017-01-11 2017-01-11 Procédé de détermination rapide de l'emplacement d'un événement d'émission acoustique dans un milieu vti/tti WO2018130272A1 (fr)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110398540A (zh) * 2019-08-26 2019-11-01 中南大学 未知波速体系下声发射源线性定位方法和系统
CN112014883A (zh) * 2020-09-08 2020-12-01 中南大学 一种基于Log-Cosh函数的微震震源定位方法、系统、装置及可读存储介质

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120051178A1 (en) * 2010-08-30 2012-03-01 Yang Zhang Method for detection of subsurface seismic events in vertically transversely isotropic media

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120051178A1 (en) * 2010-08-30 2012-03-01 Yang Zhang Method for detection of subsurface seismic events in vertically transversely isotropic media

Non-Patent Citations (7)

* Cited by examiner, † Cited by third party
Title
ALKHALIFAH, T.; LARNER, K., MIGRATION ERRORS IN TRANSVERSELY ISOTROPIC MEDIA: GEOPHYSICS, vol. 59, 1994, pages 1405 - 1418
ALKHALIFAH, T.; TSVANKIN, I.: "Velocity analysis for transversely isotropic media", GEOPHYSICS, vol. 60, 1995, pages 1550 - 1566
ANDREW KING ET AL: "Anisotropy Effects on Microseismic Event Location", PURE AND APPLIED GEOPHYSICS ; PAGEOPH, BIRKHÄUSER-VERLAG, BA, vol. 164, no. 11, 3 November 2007 (2007-11-03), pages 2141 - 2156, XP019560424, ISSN: 1420-9136, DOI: 10.1007/S00024-007-0266-8 *
HALDORSEN, J.B. U.,; N.J. BROOKS; M. MILENKOVIC: "Locating microseismic sources using migration-based deconvolution", GEOPHYSICS, vol. 78, no. 5, 2013, pages KS73 - KS84, XP001584714, DOI: doi:10.1190/geo2013-0086.1
JAKOB B U HALDORSEN ET AL: "Locating microseismic sources using migration-based deconvolution", GEOPHYSICS, SOCIETY OF EXPLORATION GEOPHYSICISTS, US, vol. 78, no. 5, 28 August 2013 (2013-08-28), pages ks73 - ks84, XP001584714, ISSN: 0016-8033, [retrieved on 20130828], DOI: 10.1190/GEO2013-0086.1 *
VLADIMIR GRECHKA: "Tilted TI models in surface microseismic monitoring", GEOPHYSICS, vol. 80, no. 6, 22 May 2015 (2015-05-22), US, pages WC11 - WC23, XP055402951, ISSN: 0016-8033, DOI: 10.1190/geo2014-0523.1 *
ZHANG JIANZHONG ET AL: "Velocity modeling and inversion techniques for locating microseismic events in unconventional reservoirs", JOURNAL OF EARTH SCIENCE, CHINA UNIVERSITY OF GEOSCIENCES, HEIDELBERG, vol. 26, no. 4, 25 July 2015 (2015-07-25), pages 495 - 501, XP035519860, ISSN: 1674-487X, [retrieved on 20150725], DOI: 10.1007/S12583-015-0565-4 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110398540A (zh) * 2019-08-26 2019-11-01 中南大学 未知波速体系下声发射源线性定位方法和系统
CN110398540B (zh) * 2019-08-26 2020-08-04 中南大学 未知波速体系下声发射源线性定位方法和系统
CN112014883A (zh) * 2020-09-08 2020-12-01 中南大学 一种基于Log-Cosh函数的微震震源定位方法、系统、装置及可读存储介质
CN112014883B (zh) * 2020-09-08 2021-08-20 中南大学 一种基于Log-Cosh函数的微震震源定位方法、系统、装置及可读存储介质

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