WO2006131745A2 - Procede de profilage sismique vertical - Google Patents

Procede de profilage sismique vertical Download PDF

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Publication number
WO2006131745A2
WO2006131745A2 PCT/GB2006/002108 GB2006002108W WO2006131745A2 WO 2006131745 A2 WO2006131745 A2 WO 2006131745A2 GB 2006002108 W GB2006002108 W GB 2006002108W WO 2006131745 A2 WO2006131745 A2 WO 2006131745A2
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WO
WIPO (PCT)
Prior art keywords
location
source
signature
downhole
seismic
Prior art date
Application number
PCT/GB2006/002108
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English (en)
Other versions
WO2006131745A3 (fr
Inventor
Stephen Mclaughlin
Antoni Marjan Ziolkowski
Brendan Michael Walsh
Original Assignee
The University Court Of The University Of Edinburgh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The University Court Of The University Of Edinburgh filed Critical The University Court Of The University Of Edinburgh
Publication of WO2006131745A2 publication Critical patent/WO2006131745A2/fr
Publication of WO2006131745A3 publication Critical patent/WO2006131745A3/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
    • G01V1/40—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging
    • G01V1/42—Seismology; Seismic or acoustic prospecting or detecting specially adapted for well-logging using generators in one well and receivers elsewhere or vice versa

Definitions

  • This invention relates to a method of vertical seismic profiling (VSP).
  • a better solution is to build the receivers into the bottom hole assembly BHA and to develop a robust algorithm that can pick the first breaks with high accuracy within such a noisy environment.
  • the current state of the art is Schlumberger's SeismicVision tool (Esmersoy, C. et al., 2005, Seismic MWD: The Leading Edge, Vol. 24, Issue 1, pp56-62, January 2005) which can apparently pick the first breaks downhole and transmit them to the surface. This tool however can only operate during pauses in drilling. This is because of the high noise levels associated with circulation and rotation of the bit.
  • FBP First Break Picking
  • the present invention provides a method of vertical seismic profiling, according to,, claim 1.
  • Preferred or optional features of the invention are defined in the dependent claims.
  • deconvolution By deconvolution, the long oscillatory airgun signature is compressed to a compact zero- phase wavelet with low side lobe energy. This has the effect of shifting the first break from the first departure point of the wavelet to the peak. Since the peak is well above the noise it is much easier to pick automatically simply by finding the maximum point in an appropriately sized window, as is done in trough-to-trough picking. Deconvolution to zero phase also improves the resolution as the zero phase wavelet is the shortest possible wavelet for a given bandwidth (Berkhout, A. J., 1977, Least-squares inverse filtering and wavelet deconvolution, Geophysics, 42, 1369-1383). Brief Description of the Drawings
  • Figure 1 shows a near field source signature recorded near an airgun array
  • Figure 2 shows the signature of Figure 1 with the sea surface ghost removed, as well as the computed far field signature
  • Figure 3 shows the virtual source method of calculating the distance R travelled by a reflected wave, with the source at a depth D;
  • Figure 4 shows raw data recorded downhole.
  • Figure 5 shows an example of source and receiver configurations for the method of the present invention.
  • the present invention is described with reference to an air gun source.
  • the method described herein may be used with other types of seismic sources including impulsive sources and vibratory sources.
  • Commonly used impulsive sources include explosives and sparkers.
  • Commonly used vibratory sources include land vibrators and marine vibrators.
  • ⁇ what the wavelet looks like in the near field.
  • We can suggest a quality factor for this result by looking at the ratio of adjacent peaks, for example if there is a lot of noise or the deconvolution is poor, the adjacent peaks will be of similar size to the first break. In this case the energy would be spread over a few points in the detection time window, giving a poor quality factor; when the deconvolution works well the energy will be maximised at the first break peak, giving a good quality factor.
  • the far-field signature differs from the near-field signature in the relative amplitudes of the direct arrival and the arrival reflected from the sea surface.
  • the direct arrival shown in Figure 1 has a much higher amplitude than the reflected arrival.
  • the path lengths of the direct and reflected waves are similar, because both signals are attenuated by similar amounts due to spherical divergence, and the amplitude of the direct wave matches the amplitude of the reflected wave.
  • the shape of the signal does not change significantly with increasing distance. This is only true if the source array has little or no directivity, which is the case for the small arrays used in normal VSP surveys.
  • the next step is to design an optimum deconvolution filter to compress it to a zero-phase wavelet.
  • the zero-phase wavelet needs to have an amplitude spectrum similar to that of the original signature. This ensures that the increase in resolution is obtained without a decrease in signal-to-noise ratio.
  • the gun signatures may change significantly. For example, one gun might drop out of the array or the array may be moved.
  • One method of communicating this change to the downhole tool is to have a library of signatures downhole with the same library uphole. The measured signature is compared uphole to the library signature in use downhole. When the RMS error between the signatures is over 5% the next best signature is found uphole and then a pulse is sent • downhole to tell the tool to use the corresponding signature. This method is only as good as the signature library; and a decision needs to be made on the extent of the library based on actual field experience of the variability of the airgun signature, field conditions, and the amount of storage available downhole.
  • a better option is to compute the shaping filter uphole for every shot and transmit the filter coefficients downhole. By doing this we can account for and remove any type of signature variation and ensure we get the best results every time.
  • the resulting filter can then be convolved with the data to compress the signature and simultaneously make it zero phase.
  • the measured near-field source signature consists of two components: a direct wave, which travels directly from the source, and a wave reflected from the sea surface as shown in Figure 5. We require to compute the far-field signature.
  • V p (t) is the recorded time signal
  • h is the sensitivity of the hydrophone
  • r is the distance between hydrophone and the centre of the air gun bubble
  • R is the distance between the hydrophone and the centre of the virtual bubble
  • s(t) is the source time function.
  • Equation 3.1 for the pressure at a time t anywhere in the water is the ghost; we can obtain the source time function by transforming to the frequency domain and rearranging:
  • F ⁇ ) S( ⁇ ) — exp(z ' ⁇ — ) exp(z ' ⁇ )— — ) (3.3) r f c R f c
  • F( ⁇ ) is the Fourier transform of the far-field signature
  • R f is the distance from the virtual source to the point in the far field.
  • the far-field signature fit is obtained by transforming F( ⁇ ) back to the time domain.
  • the aim of the signature deconvolution is to convert the far-field signature f(t) into the shortest possible wavelet with the same bandwidth, that is, to a zero phase wavelet (Berkhout, 1977, supra). This has the effect of moving the first break to the peak of the first arrival, rather than the first departure from zero, thus making it easier to detect in the presence of noise.
  • the filter which converts the far-field signature to the zero phase wavelet, is convolved with the data recorded for that signature; this has the effect of making all the wavelets in the data zero phase. For a perfect deconvolution all events other than noise would be zero phase wavelets therefore maximising the resolution; the noise could be reduced later by stacking.
  • the tool's only telemetry is low bandwidth mud pulse (10 bits/s), it has to be able to function with very little instruction from the surface.
  • the tool In order to perform the deconvolution and the first break picking, the tool needs to know what the source signature is and the source and receiver geometry. This should vary by only a few cm once the equipment is deployed.
  • the coordinates can easily be transmitted downhole before drilling or firing begins, and if for any reason the array moves then the coordinate can be retransmitted, for example while the guns are warming up.
  • the source signature presents a problem: it is possible to produce a very repeatable source signature once the guns are warmed up, but with small arrays the signature can vary. Large towed arrays are much more repeatable but are only employed for large-scale surface surveys with hydrophone streamers.
  • the signature is measured uphole by use of a near field hydrophone. The extrapolation to the far field and the computation of the deconvolution filter can all be done uphole, the filter coefficients can then be sent by mud pulse downhole, where the tool can use them to deconvolve the data. In this way all shot-to-shot variations can be removed.
  • the uphole and downhole clocks should be synchronized and should not drift outside a predefined range.
  • An atomic clock such as that disclosed in DiFoggio et al. (US-A- 6837105) may be used.
  • the problem then becomes one of starting downhole recording at the right time, and one solution is to keep the time between airgun shots almost constant.
  • the tool should be continually listening and deconvolving, the first break picker should also run continually. While the array is not firing there could be some noise peaks that appear and the tool should not misinterpret these as first breaks.
  • the key is to make sure the tool only starts recording and transmitting data when these first break peaks recur at a constant time interval (in practice there would be some error bounds, eg. +/- 100ms).
  • a method would be as follows: The downhole tool is told to start recording and, deconvolving data, at the same time the guns uphole start firing. The tool downhole records a continuous record which is deconvolved using the filter coefficients that are sent down to it. Next the first break routine looks for maxima or minima in the data (depending on the polarity convention), and sends the absolute times of these events uphole. (Note: the time origin of the data is the same as the uphole clock, not the time at which the tool starts recording).
  • the tool treats these as a signature and knows to start recording. It can then send the first break times uphole along with a quality factor, derived from the ratio of the first break peaks to adjacent noise peaks and the time interval between the first breaks. Once these times are received and the quality factor is high then we need to obtain the transit time for the direct waves.
  • each first break time will be close to a particular shot time, and the first breaks should be separated by the firing delay of the airguns; a very accurate record of the firing times, for example from a zero field time break sensor, then permits a simple subtraction of the absolute firing time from the corresponding absolute first break time to leave the relative transit time of the wave, i.e. the first break.
  • the accuracy of the first break time is related to how accurately the time between shots is known.
  • FIG. 5 an example is shown of source and receiver configurations for the method of the present invention.
  • a drillbit 50 near the bottom of a borehole 26'.
  • the drillbit is part of a bottomhole assembly (BHA) conveyed into the wellbore on a drilling tubular such as a drillstring or coiled tubing.
  • BHA bottomhole assembly
  • a surface seismic source is denoted by S and a reference receiver near the surface is denoted by R.
  • a downhole receiver is denoted by 53, while 55 shows an exemplary raypath for seismic waves originating at the source S and received by the receiver 53.
  • the receiver 53 is usually in a fixed relation to the drillbit in the BHA.
  • a raypath 55' from the source S to another position 53' near the bottom of the borehole.
  • This other position 53' could correspond to a second receiver in one embodiment of the invention wherein a plurality of seismic receivers are used downhole.
  • the position 53' corresponds to another position of the receiver 53 when the drillbit and the BHA are at a different depth.
  • Raypaths 55 and 55' are shown as curved. This ray-bending commonly happens due to the fact that the velocity of propagation of seismic waves in the earth generally increases with depth. Also shown in Fig. 5 is a reflected ray 61 corresponding to seismic waves that have been produced by the source, reflected by an interface such as 63, and received by the receiver at 53.
  • the processing of the data may be accomplished by a downhole processor.
  • the data recorded downhole may be either telemetered uphole or stored on a suitable memory device for subsequent retrieval and processing by a surface processor or a processor at a remote location.
  • wireline or MWD (measurement while drilling) implementations are possible.
  • the downhole apparatus includes a logging string that includes a processor and a downhole receiver conveyed on a wireline.
  • Implicit in the control and processing of the data is the use of a computer program implemented on a suitable machine readable medium that enables the processor to perform the control and processing.
  • the machine readable medium may include ROMs, EPROMs, EAROMs, Flash Memories and Optical disks.

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  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Environmental & Geological Engineering (AREA)
  • Geology (AREA)
  • Remote Sensing (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Geophysics (AREA)
  • Geophysics And Detection Of Objects (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Abstract

L'invention concerne un procédé de profilage sismique vertical au cours duquel on active une source (S) sismique en un premier emplacement et on mesure la signature de la source en un champ à proximité de ladite source sismique. Le signal acoustique produit par l'activation de la source (S) sismique est reçu à un emplacement de fond de puits (53) dans un trou de sonde récepteur. On traite le signal reçu au moyen d'un filtre de déconvolution dérivé d'un équivalent de phase nulle de la signature en champ lointain. L'invention concerne enfin un système et un support informatique permettant de réaliser ledit procédé.
PCT/GB2006/002108 2005-06-08 2006-06-08 Procede de profilage sismique vertical WO2006131745A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0511678.5 2005-06-08
GB0511678A GB0511678D0 (en) 2005-06-08 2005-06-08 Vertical seismic profiling method

Publications (2)

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WO2006131745A2 true WO2006131745A2 (fr) 2006-12-14
WO2006131745A3 WO2006131745A3 (fr) 2007-03-08

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WO (1) WO2006131745A2 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7551515B2 (en) * 2005-05-03 2009-06-23 Westerngeco Llc Source signature deconvolution method
US8559267B2 (en) 2006-10-26 2013-10-15 Schlumberger Technology Corporation Methods and apparatus of borehole seismic surveys
WO2015069813A1 (fr) * 2013-11-06 2015-05-14 Westerngeco Llc Chemises de chambre de mise en œuvre de canon à air
FR3035723A1 (fr) * 2015-05-01 2016-11-04 Halliburton Energy Services Inc Estimation de parametre anisotrope a partir de donnees vsp autonomes utilisant une evolution differentielle

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6078868A (en) * 1999-01-21 2000-06-20 Baker Hughes Incorporated Reference signal encoding for seismic while drilling measurement
US20030086335A1 (en) * 2001-11-07 2003-05-08 Charles Naville Method for absolute preserved amplitude processing of seismic well data
WO2004095073A2 (fr) * 2003-04-01 2004-11-04 Exxonmobil Upstream Research Company Source vibratoire haute frequence faconnee

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6078868A (en) * 1999-01-21 2000-06-20 Baker Hughes Incorporated Reference signal encoding for seismic while drilling measurement
US20030086335A1 (en) * 2001-11-07 2003-05-08 Charles Naville Method for absolute preserved amplitude processing of seismic well data
WO2004095073A2 (fr) * 2003-04-01 2004-11-04 Exxonmobil Upstream Research Company Source vibratoire haute frequence faconnee

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
ZIOLKOWSKI A ET AL: "Wavelets, well ties, and the search for subtle stratigraphic traps" GEOPHYSICS SOC. EXPLORATION GEOPHYSICISTS USA, vol. 63, no. 1, January 1998 (1998-01), pages 297-313, XP002401850 ISSN: 0016-8033 *
ZIOLKOWSKI ANTON: "Simplified wavelet estimation using source-signature measurements" LEADING EDGE; LEADING EDGE (TULSA, OK) 2000 SOC OF EXPLORATION GEOPHYSICISTS, TULSA, OK, USA, vol. 19, no. 1, 2000, pages 61-67, XP002401849 *

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7551515B2 (en) * 2005-05-03 2009-06-23 Westerngeco Llc Source signature deconvolution method
US8559267B2 (en) 2006-10-26 2013-10-15 Schlumberger Technology Corporation Methods and apparatus of borehole seismic surveys
WO2015069813A1 (fr) * 2013-11-06 2015-05-14 Westerngeco Llc Chemises de chambre de mise en œuvre de canon à air
US9612349B2 (en) 2013-11-06 2017-04-04 Westerngeco L.L.C. Airgun operating chamber liners
FR3035723A1 (fr) * 2015-05-01 2016-11-04 Halliburton Energy Services Inc Estimation de parametre anisotrope a partir de donnees vsp autonomes utilisant une evolution differentielle
WO2016178654A1 (fr) * 2015-05-01 2016-11-10 Padhi Amit Estimation de paramètres anisotropes à partir de données vsp à déport croissant en utilisant l'évolution différentielle
GB2553438A (en) * 2015-05-01 2018-03-07 Halliburton Energy Services Inc Anisotropic parameter estimation from walkway vsp data using differential evolution

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WO2006131745A3 (fr) 2007-03-08
GB0511678D0 (en) 2005-07-13

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