American Oil and Gas Reporter - July 2019 - 70
SpecialReport: Reservoir Characterization
FWI Images Complex Subsalt Features
By Zhigang Zhang,
Jiawei Mei,
Feng Lin,
Rongxin Huang
and Ping Wang
HOUSTON-Full waveform inversion
(FWI) goes beyond refraction and reflection tomography techniques that use
only the travel-time kinematics of the
seismic data by incorporating more information provided by the amplitude and
phase of the seismic waveform.
The result is a high-resolution velocity
model that can be used to resolve complex
geological features, improve reservoir
imaging and identify potential geohazards.
The highly detailed models also can be
input directly to pore pressure prediction
flows, time-lapse monitoring and reservoir
characterization analysis.
Subsurface images derived from FWIbased modeling provide interpreters with a
much higher degree of confidence with respect to reservoir delineation and subsequent
well planning. However, using FWI to
update velocity models that contain complex
salt bodies with high velocity contrasts has
been a challenge. It is even harder if largescale salt geometry errors are part of the
starting velocity model for FWI.
At the BP-operated Atlantis Field in
the Gulf of Mexico's subsalt Miocene
play, FWI recently was applied to wideoffset ocean-bottom node (OBN) 3-D
data acquired with a usable low-frequency
signal down to 1.6 hertz. The unmodified
FWI velocity model was then used to reverse-time migrate the seismic data. According to a paper presented by BP at the
Society of Exploration Geophysicists'
2017 Annual Meeting, the FWI-based
velocity model generated "some of the
best subsalt images ever seen at Atlantis
and clearly revealed several major interpretation errors in the legacy salt model"
(SEG 17738630, "Salt Model Building
at Atlantis with Full Waveform Inversion,"
by Xukai Shen, Imtiaz Ahmed, Andrew
Brenders, Joe Dellinger, John Etgen and
Scott Michell).
The Atlantis Field FWI work stressed
the importance of low frequencies, full
azimuths and long offsets of the OBN
data. Encouraged by the success at Atlantis,
some aspects of FWI algorithms have
been revisited to minimize the cycleskipping and amplitude discrepancy issues
that are common in the presence of salt
and salt misinterpretations. The newly
developed FWI algorithm, called "timelag FWI" uses travel-time misfit measured
in frequency-dependent time windows as
the FWI cost function. It is devised to
minimize the negative impact from the
amplitude discrepancy and cycle skipping
between the recorded data and modeled
synthetic data.
Furthermore, time-lag FWI uses a
cross-correlation coefficient between
recorded data and synthetic data as a
weight function in gradient computation
to promote higher quality travel-time
measurements. The effectiveness of this
approach has been demonstrated using a
full-azimuth streamer dataset in a field
with complex shallow salt bodies in the
Keathley Canyon area in the Central Gulf
of Mexico.
Salt Model Building
Building an accurate salt velocity
model is a critical step in subsalt imaging.
Standard practice for salt model building
is to use tomography, sometimes combined
with shallow diving-wave FWI, to first
build the best possible sediment velocity
model. Then, a sediment-flood migration
FIGURE 1
Full-Azimuth Towed Streamer Dataset in Keathley Canyon Study Area
A
70 THE AMERICAN OIL & GAS REPORTER
B
C
is used for top-of-salt (TOS) interpretation,
followed by a salt-flood migration for
base-of-salt (BOS) interpretation. In the
next step, a number of salt scenario tests
usually are required to resolve the salt
geometry, especially for complex areas.
This procedure is not only labor-intensive
and time-consuming, but it is also prone
to human misinterpretation.
FWI is considered the most promising
data-driven tool to automatically build
velocity models by iteratively minimizing
the difference between recorded data and
modeled synthetic data. Many successful
examples have been reported using FWI
to update shallow sediments, gas pockets
and mud volcanoes. However, FWI had
not been used successfully to update salt
structures until the Atlantis Field project
using low-frequency, full-azimuth and
long-offset OBN data.
Two major issues that cause FWI to
fail are cycle skipping and amplitude discrepancies between synthetic data and
recorded data, particularly when there are
sharp contrasts and large-scale
geobodies/salt bodies in the model. When
phases, or travel-time differences, between
synthetic and recorded data are large, the
oscillatory pattern of the seismic signals
introduces local minima. FWI may attempt
to fit the synthetic data to a wrong cycle
in the recorded data. In addition, the amplitude distribution of recorded seismic
data is usually very different from that of
synthetics. If this difference is not appropriately addressed, it will be interpreted
as velocity error by FWI, which leads the
inversion to erroneous velocity models.
Many methods have been proposed to
solve cycle-skipping and amplitude discrepancy issues. The travel-time difference
of seismic signals is more linearly related
to the velocity error than the waveform
difference, and any discrepancies in the
amplitude difference are inconsequential.
Alternatively, synthetic and recorded data
can be brought in phase by applying a
matching filter to one of the two datasets.
New FWI Algorithm
The time-lag FWI algorithm integrates
a travel-time cost function with a frequency-dependent time window for travel-time measurements and a cross-correlation coefficient-based weight function
to promote travel-time measurements of
high quality. As demonstrated on a full-
American Oil and Gas Reporter - July 2019
Table of Contents for the Digital Edition of American Oil and Gas Reporter - July 2019
Contents
American Oil and Gas Reporter - July 2019 - Intro
American Oil and Gas Reporter - July 2019 - 1
American Oil and Gas Reporter - July 2019 - 2
American Oil and Gas Reporter - July 2019 - Contents
American Oil and Gas Reporter - July 2019 - 4
American Oil and Gas Reporter - July 2019 - 5
American Oil and Gas Reporter - July 2019 - 6
American Oil and Gas Reporter - July 2019 - 7
American Oil and Gas Reporter - July 2019 - 8
American Oil and Gas Reporter - July 2019 - 9
American Oil and Gas Reporter - July 2019 - 10
American Oil and Gas Reporter - July 2019 - 11
American Oil and Gas Reporter - July 2019 - 12
American Oil and Gas Reporter - July 2019 - 13
American Oil and Gas Reporter - July 2019 - 14
American Oil and Gas Reporter - July 2019 - 15
American Oil and Gas Reporter - July 2019 - 16
American Oil and Gas Reporter - July 2019 - 17
American Oil and Gas Reporter - July 2019 - 18
American Oil and Gas Reporter - July 2019 - 19
American Oil and Gas Reporter - July 2019 - 20
American Oil and Gas Reporter - July 2019 - 21
American Oil and Gas Reporter - July 2019 - 22
American Oil and Gas Reporter - July 2019 - 23
American Oil and Gas Reporter - July 2019 - 24
American Oil and Gas Reporter - July 2019 - 25
American Oil and Gas Reporter - July 2019 - 26
American Oil and Gas Reporter - July 2019 - 27
American Oil and Gas Reporter - July 2019 - 28
American Oil and Gas Reporter - July 2019 - 29
American Oil and Gas Reporter - July 2019 - 30
American Oil and Gas Reporter - July 2019 - 31
American Oil and Gas Reporter - July 2019 - 32
American Oil and Gas Reporter - July 2019 - 33
American Oil and Gas Reporter - July 2019 - 34
American Oil and Gas Reporter - July 2019 - 35
American Oil and Gas Reporter - July 2019 - 36
American Oil and Gas Reporter - July 2019 - 37
American Oil and Gas Reporter - July 2019 - 38
American Oil and Gas Reporter - July 2019 - 39
American Oil and Gas Reporter - July 2019 - 40
American Oil and Gas Reporter - July 2019 - 41
American Oil and Gas Reporter - July 2019 - 42
American Oil and Gas Reporter - July 2019 - 43
American Oil and Gas Reporter - July 2019 - 44
American Oil and Gas Reporter - July 2019 - 45
American Oil and Gas Reporter - July 2019 - 46
American Oil and Gas Reporter - July 2019 - 47
American Oil and Gas Reporter - July 2019 - 48
American Oil and Gas Reporter - July 2019 - 49
American Oil and Gas Reporter - July 2019 - 50
American Oil and Gas Reporter - July 2019 - 51
American Oil and Gas Reporter - July 2019 - 52
American Oil and Gas Reporter - July 2019 - 53
American Oil and Gas Reporter - July 2019 - 54
American Oil and Gas Reporter - July 2019 - 55
American Oil and Gas Reporter - July 2019 - 56
American Oil and Gas Reporter - July 2019 - 57
American Oil and Gas Reporter - July 2019 - 58
American Oil and Gas Reporter - July 2019 - 59
American Oil and Gas Reporter - July 2019 - 60
American Oil and Gas Reporter - July 2019 - 61
American Oil and Gas Reporter - July 2019 - 62
American Oil and Gas Reporter - July 2019 - 63
American Oil and Gas Reporter - July 2019 - 64
American Oil and Gas Reporter - July 2019 - 65
American Oil and Gas Reporter - July 2019 - 66
American Oil and Gas Reporter - July 2019 - 67
American Oil and Gas Reporter - July 2019 - 68
American Oil and Gas Reporter - July 2019 - 69
American Oil and Gas Reporter - July 2019 - 70
American Oil and Gas Reporter - July 2019 - 71
American Oil and Gas Reporter - July 2019 - 72
American Oil and Gas Reporter - July 2019 - 73
American Oil and Gas Reporter - July 2019 - 74
American Oil and Gas Reporter - July 2019 - 75
American Oil and Gas Reporter - July 2019 - 76
American Oil and Gas Reporter - July 2019 - 77
American Oil and Gas Reporter - July 2019 - 78
American Oil and Gas Reporter - July 2019 - 79
American Oil and Gas Reporter - July 2019 - 80
American Oil and Gas Reporter - July 2019 - 81
American Oil and Gas Reporter - July 2019 - 82
American Oil and Gas Reporter - July 2019 - 83
American Oil and Gas Reporter - July 2019 - 84
American Oil and Gas Reporter - July 2019 - 85
American Oil and Gas Reporter - July 2019 - 86
American Oil and Gas Reporter - July 2019 - 87
American Oil and Gas Reporter - July 2019 - 88
American Oil and Gas Reporter - July 2019 - 89
American Oil and Gas Reporter - July 2019 - 90
American Oil and Gas Reporter - July 2019 - 91
American Oil and Gas Reporter - July 2019 - 92
American Oil and Gas Reporter - July 2019 - 93
American Oil and Gas Reporter - July 2019 - 94
American Oil and Gas Reporter - July 2019 - 95
American Oil and Gas Reporter - July 2019 - 96
American Oil and Gas Reporter - July 2019 - 97
American Oil and Gas Reporter - July 2019 - 98
American Oil and Gas Reporter - July 2019 - 99
American Oil and Gas Reporter - July 2019 - 100
American Oil and Gas Reporter - July 2019 - 101
American Oil and Gas Reporter - July 2019 - 102
American Oil and Gas Reporter - July 2019 - 103
American Oil and Gas Reporter - July 2019 - 104
American Oil and Gas Reporter - July 2019 - 105
American Oil and Gas Reporter - July 2019 - 106
American Oil and Gas Reporter - July 2019 - 107
American Oil and Gas Reporter - July 2019 - 108
American Oil and Gas Reporter - July 2019 - 109
American Oil and Gas Reporter - July 2019 - 110
American Oil and Gas Reporter - July 2019 - 111
American Oil and Gas Reporter - July 2019 - 112
American Oil and Gas Reporter - July 2019 - 113
American Oil and Gas Reporter - July 2019 - 114
American Oil and Gas Reporter - July 2019 - 115
American Oil and Gas Reporter - July 2019 - 116
American Oil and Gas Reporter - July 2019 - 117
American Oil and Gas Reporter - July 2019 - 118
American Oil and Gas Reporter - July 2019 - 119
American Oil and Gas Reporter - July 2019 - 120
American Oil and Gas Reporter - July 2019 - 121
American Oil and Gas Reporter - July 2019 - 122
American Oil and Gas Reporter - July 2019 - 123
American Oil and Gas Reporter - July 2019 - 124
https://www.nxtbook.com/nxtbooks/aogr/202407
https://www.nxtbook.com/nxtbooks/aogr/202406
https://www.nxtbook.com/nxtbooks/aogr/202405
https://www.nxtbook.com/nxtbooks/aogr/202404
https://www.nxtbook.com/nxtbooks/aogr/202403
https://www.nxtbook.com/nxtbooks/aogr/202402
https://www.nxtbook.com/nxtbooks/aogr/202401
https://www.nxtbook.com/nxtbooks/aogr/202312
https://www.nxtbook.com/nxtbooks/aogr/202311
https://www.nxtbook.com/nxtbooks/aogr/pbios_202310
https://www.nxtbook.com/nxtbooks/aogr/202309
https://www.nxtbook.com/nxtbooks/aogr/202308
https://www.nxtbook.com/nxtbooks/aogr/202307
https://www.nxtbook.com/nxtbooks/aogr/202306
https://www.nxtbook.com/nxtbooks/aogr/202305
https://www.nxtbook.com/nxtbooks/aogr/202304
https://www.nxtbook.com/nxtbooks/aogr/202303
https://www.nxtbook.com/nxtbooks/aogr/202302
https://www.nxtbook.com/nxtbooks/aogr/202301
https://www.nxtbook.com/nxtbooks/aogr/202212
https://www.nxtbook.com/nxtbooks/aogr/202211
https://www.nxtbook.com/nxtbooks/aogr/202210
https://www.nxtbook.com/nxtbooks/aogr/202209
https://www.nxtbook.com/nxtbooks/aogr/202208
https://www.nxtbook.com/nxtbooks/aogr/202207
https://www.nxtbook.com/nxtbooks/aogr/202206
https://www.nxtbook.com/nxtbooks/aogr/202205
https://www.nxtbook.com/nxtbooks/aogr/202204
https://www.nxtbook.com/nxtbooks/aogr/202203
https://www.nxtbook.com/nxtbooks/aogr/202202
https://www.nxtbook.com/nxtbooks/aogr/202201
https://www.nxtbook.com/nxtbooks/aogr/202112
https://www.nxtbook.com/nxtbooks/aogr/202111
https://www.nxtbook.com/nxtbooks/aogr/pbios_202110
https://www.nxtbook.com/nxtbooks/aogr/202109
https://www.nxtbook.com/nxtbooks/aogr/202108
https://www.nxtbook.com/nxtbooks/aogr/202107
https://www.nxtbook.com/nxtbooks/aogr/202106
https://www.nxtbook.com/nxtbooks/aogr/202105
https://www.nxtbook.com/nxtbooks/aogr/202104
https://www.nxtbook.com/nxtbooks/aogr/202103
https://www.nxtbook.com/nxtbooks/aogr/202102
https://www.nxtbook.com/nxtbooks/aogr/202101
https://www.nxtbook.com/nxtbooks/aogr/202012
https://www.nxtbook.com/nxtbooks/aogr/202011
https://www.nxtbook.com/nxtbooks/aogr/202010
https://www.nxtbook.com/nxtbooks/aogr/202009
https://www.nxtbook.com/nxtbooks/aogr/202008
https://www.nxtbook.com/nxtbooks/aogr/202007
https://www.nxtbook.com/nxtbooks/aogr/202006
https://www.nxtbook.com/nxtbooks/aogr/202005
https://www.nxtbook.com/nxtbooks/aogr/202004
https://www.nxtbook.com/nxtbooks/aogr/202003
https://www.nxtbook.com/nxtbooks/aogr/202002
https://www.nxtbook.com/nxtbooks/aogr/202001
https://www.nxtbook.com/nxtbooks/aogr/201912
https://www.nxtbook.com/nxtbooks/aogr/201911
https://www.nxtbook.com/nxtbooks/aogr/201910
https://www.nxtbook.com/nxtbooks/aogr/201909
https://www.nxtbook.com/nxtbooks/aogr/201908
https://www.nxtbook.com/nxtbooks/aogr/201907
https://www.nxtbook.com/nxtbooks/aogr/201906
https://www.nxtbook.com/nxtbooks/aogr/201905
https://www.nxtbook.com/nxtbooks/aogr/201904
https://www.nxtbook.com/nxtbooks/aogr/201903
https://www.nxtbook.com/nxtbooks/aogr/201902
https://www.nxtbook.com/nxtbooks/aogr/201901
https://www.nxtbook.com/nxtbooks/aogr/201812
https://www.nxtbook.com/nxtbooks/aogr/201811
https://www.nxtbook.com/nxtbooks/aogr/201810
https://www.nxtbook.com/nxtbooks/aogr/pbios_201810
https://www.nxtbook.com/nxtbooks/aogr/201809
https://www.nxtbook.com/nxtbooks/aogr/201808
https://www.nxtbook.com/nxtbooks/aogr/201807
https://www.nxtbook.com/nxtbooks/aogr/201806
https://www.nxtbook.com/nxtbooks/aogr/201805
https://www.nxtbook.com/nxtbooks/aogr/201804
https://www.nxtbook.com/nxtbooks/aogr/201803
https://www.nxtbook.com/nxtbooks/aogr/201802
https://www.nxtbook.com/nxtbooks/aogr/201801
https://www.nxtbook.com/nxtbooks/aogr/201712
https://www.nxtbook.com/nxtbooks/aogr/201711
https://www.nxtbook.com/nxtbooks/aogr/201710
https://www.nxtbook.com/nxtbooks/aogr/201709
https://www.nxtbook.com/nxtbooks/aogr/201708
https://www.nxtbook.com/nxtbooks/aogr/201707
https://www.nxtbook.com/nxtbooks/aogr/201706
https://www.nxtbook.com/nxtbooks/aogr/201705
https://www.nxtbook.com/nxtbooks/aogr/201704
https://www.nxtbook.com/nxtbooks/aogr/201703
https://www.nxtbook.com/nxtbooks/aogr/201702
https://www.nxtbook.com/nxtbooks/aogr/201701
https://www.nxtbook.com/nxtbooks/aogr/201612
https://www.nxtbook.com/nxtbooks/aogr/201611
https://www.nxtbook.com/nxtbooks/aogr/201610
https://www.nxtbook.com/nxtbooks/aogr/pbios2016_programguide
https://www.nxtbook.com/nxtbooks/aogr/201609
https://www.nxtbook.com/nxtbooks/aogr/201608
https://www.nxtbook.com/nxtbooks/aogr/201607
https://www.nxtbook.com/nxtbooks/aogr/201606
https://www.nxtbook.com/nxtbooks/aogr/201605
https://www.nxtbook.com/nxtbooks/aogr/201604
https://www.nxtbook.com/nxtbooks/aogr/201603
https://www.nxtbook.com/nxtbooks/aogr/201602
https://www.nxtbook.com/nxtbooks/aogr/201601
https://www.nxtbook.com/nxtbooks/aogr/201512
https://www.nxtbook.com/nxtbooks/aogr/201511
https://www.nxtbook.com/nxtbooks/aogr/201510
https://www.nxtbook.com/nxtbooks/aogr/201509
https://www.nxtbook.com/nxtbooks/aogr/201508
https://www.nxtbook.com/nxtbooks/aogr/201507
https://www.nxtbook.com/nxtbooks/aogr/201506
https://www.nxtbook.com/nxtbooks/aogr/201505
https://www.nxtbook.com/nxtbooks/aogr/201504
https://www.nxtbook.com/nxtbooks/aogr/201503
https://www.nxtbook.com/nxtbooks/aogr/201502
https://www.nxtbook.com/nxtbooks/aogr/201501
https://www.nxtbook.com/nxtbooks/aogr/201412
https://www.nxtbook.com/nxtbooks/aogr/201411
https://www.nxtbook.com/nxtbooks/aogr/201410
https://www.nxtbook.com/nxtbooks/aogr/201409
https://www.nxtbook.com/nxtbooks/aogr/pbios2014_programguide
https://www.nxtbook.com/nxtbooks/aogr/201408
https://www.nxtbook.com/nxtbooks/aogr/201407
https://www.nxtbook.com/nxtbooks/aogr/201406
https://www.nxtbook.com/nxtbooks/aogr/201405
https://www.nxtbook.com/nxtbooks/aogr/201404
https://www.nxtbook.com/nxtbooks/aogr/201403
https://www.nxtbook.com/nxtbooks/aogr/201402
https://www.nxtbook.com/nxtbooks/aogr/201401
https://www.nxtbook.com/nxtbooks/aogr/201312
https://www.nxtbook.com/nxtbooks/aogr/201311
https://www.nxtbook.com/nxtbooks/aogr/201310
https://www.nxtbook.com/nxtbooks/aogr/201309
https://www.nxtbook.com/nxtbooks/aogr/201308
https://www.nxtbook.com/nxtbooks/aogr/201307
https://www.nxtbook.com/nxtbooks/aogr/201306
https://www.nxtbook.com/nxtbooks/aogr/201305
https://www.nxtbook.com/nxtbooks/aogr/201304
https://www.nxtbook.com/nxtbooks/aogr/201303
https://www.nxtbook.com/nxtbooks/aogr/201302
https://www.nxtbook.com/nxtbooks/aogr/201301
https://www.nxtbook.com/nxtbooks/aogr/201212
https://www.nxtbook.com/nxtbooks/aogr/201211
https://www.nxtbook.com/nxtbooks/aogr/201210
https://www.nxtbook.com/nxtbooks/aogr/201209
https://www.nxtbook.com/nxtbooks/aogr/2012_pbios
https://www.nxtbook.com/nxtbooks/aogr/201208
https://www.nxtbook.com/nxtbooks/aogr/201207
https://www.nxtbook.com/nxtbooks/aogr/201206
https://www.nxtbook.com/nxtbooks/aogr/201205
https://www.nxtbook.com/nxtbooks/aogr/201204
https://www.nxtbook.com/nxtbooks/aogr/201203
https://www.nxtbook.com/nxtbooks/aogr/201202
https://www.nxtbook.com/nxtbooks/aogr/201201
https://www.nxtbook.com/nxtbooks/demo/aogr_clone
https://www.nxtbook.com/nxtbooks/aogr/201112
https://www.nxtbookmedia.com