A Deterministic Evaluation of eismic Fidelity using Velocity Modeling ...

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inline direction and crossline direction (Figure 60). From these histograms, I determined the parameters for migration. Output parameters were also set based on acquisition, a 0 - 180° radius was set because of the radial acquisition. The software vendor provided me with suggestions to improved efficiency. 4.4 Migration Results I compared the results from the initial sediment model migration to the PSTM seismic volume. Improved resolution was apparent in the PSDM especially in imaging the salt flanks (Figure 61). I imaged the salt flanks with more detail, and coherent events were maintained deeper into the survey (Figure 62). One of the benchmarks I used to assess the value of this method was the ability to image small compartmentalized reservoirs. In the PSTM volume fault compartments that had been interpreted using log data were not imaged, but in the initial PSDM faults are more focused and smaller faults can be interpreted that were not imaged in the PSTM volume. Differences in the two volumes are apparent in the portion of the survey where small, compartmentalized fault blocks were interpreted using well logs but not imaged in the PSTM (Figure 63). I was able to interpret fault blocks in this portion of the survey, identified by the missing section in the Anahuac picks on the well logs, with the well-based PSDM (Figure 64). Comparing the well-based and prestack time migrated velocity model PSDM I can identify several differences. The same events are at different depths, the prestack time migrated velocity model PSDM data places events at about 200 feet shallower, indicating a slower model, or a faster well-based model. Fault planes are more coherent in the well- 80
ased data, indicating higher fidelity because seismic events are in their proper x, y, and z space. A section perpendicular to the traverse in Figure 65 also images fault planes that are more coherent in the well-based section. Another interesting observation is the event that intersects the Anahuac well pick when followed eastward merges into an event that is salt on the PSTM (Figure 65). Observing the depth sections of both velocity models also provides differences in the data set for comparison (Figure 66). Imaging of faults and the salt are more coherent in the depth slice from the well-based PSDM than from that of the prestack time migrated velocity model PSDM. Another illustration of the improved fidelity provided by the PSDM is from the drilling of a bright spot interpreted with the PSTM (Figure 67) near the salt flank. A comparison of the PSDM from both the well-based velocity model and the prestack time migrated velocity model show that there is no bright spot. Analysis of the PSDM shows that there is salt at that location, although the impedance contrast is not as great as it is shallower (Figure 68). There are two issues in the differences of the PSTM and the PSDM that further demonstrate the improvements in imaging provided by the well-based PSDM. The first is the bright spot that appears in the PSTM but is not in the PSDM. An explanation for this is that incorrect modeling of velocities close to the salt flank resulted in constructive interference of noise. This explanation is appealing because of the close proximity to the salt and the inherent difficulty of imaging salt flanks with PSTM. Both of the PSDM seismic volumes do not image a bright spot demonstrating the ability of PSDM to image in areas of strong lateral velocity changes. The second issue is the 81
Page 1 and 2:
Chapter 1 Introduction 1.1 Summary
Page 3 and 4:
1.2.1 Geology Vinton Dome is a pier
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layer in land data that in extreme
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logs as being an effective approach
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Chapter 2 Geology of Vinton Dome 2.
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The Gulf of Mexico Basin contains U
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developed from repetitive episodes
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of the upper Frio. Overlying the lo
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structures form by the differential
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Dividing the Gulf of Mexico Basin i
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2.6 Geologic Modeling Historically,
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2.6.1 Vinton Geology Analysis of se
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surface and a number of small subma
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established the Mississippi delta a
Page 29 and 30: Figure 2. Outline of the extents of
Page 31 and 32: Figure 6. Salt sediment contacts us
Page 33 and 34: Figure 10. Fault pattern representa
Page 35 and 36: Figure 14. Stratigraphic column of
Page 37 and 38: Top Hackberry Sand Hackberry Base N
Page 39 and 40: Figure 18. Structure map contoured
Page 41 and 42: Gyroidina scalata Outer shelf Gyroi
Page 43 and 44: Upper Frio Sands A Sand base B Sand
Page 45 and 46: Top Anahuac Middle Shelf Heterosteg
Page 47 and 48: Miocene sands Figure 27. Spontaneou
Page 49 and 50: Vinton Dome Figure 30. Late Miocene
Page 51 and 52: 3.1 Introduction Chapter 3 Processi
Page 53 and 54: 3.3 Processing My primary objective
Page 55 and 56: 38-42). For QC I would brute stack
Page 57 and 58: Another significant issue was to id
Page 59 and 60: Table 2 Final processing flow Input
Page 61 and 62: Number of stacked traces 12.5km 12.
Page 63 and 64: TWT seconds a 12.5km TWT seconds b
Page 65 and 66: TWT seconds 12.5km Figure 38. Brute
Page 71 and 72: Chapter 4 Velocity Modeling and Pre
Page 73 and 74: quality motivated a reassessment of
Page 75 and 76: The layer-based approach is much mo
Page 77 and 78: of seismically derived velocities.
Page 79: To test differences between seismic
Page 83 and 84: 4.5 Conclusions and Discussion I co
Page 85 and 86: By using sonic logs the velocities
Page 87 and 88: Figure 50. Velocity cube of the sed
Page 89 and 90: Velocity in ft/sec Figure 52. Prest
Page 91 and 92: Depth in kilo-feet a. b. Figure 56.
Page 93 and 94: Figure 59. Graphic user interface s
Page 95 and 96: Truncation of sediment onto salt a
Page 97 and 98: s 1 s 1 S e C 0 1 O W 34 M M 0 C a
Page 99 and 100: Prestack time migrated velocity mod
Page 101 and 102: Salt on PSTM Prestack time migrated
Page 103 and 104: Time in seconds Bright spot 12.5km
Page 105 and 106: PSTM prestack time well-based migra
Page 107 and 108: attributes also provided me with an
Page 109 and 110: types of coherence. The first type
Page 111 and 112: comparisons, those at the same dept
Page 113 and 114: Identifying reduced fidelity in the
Page 115 and 116: Faults Channel Figure 72. PSTM cohe
Page 117 and 118: Depth slice of coherence cube from
Page 119 and 120: Compartmentalized faults 5895 feet
Page 121 and 122: Well-based PSDM - faults traced fro
Page 123 and 124: Channel Radial faults 3985 feet a C
Page 125 and 126: Well-based PSDM Prestack time migra
Page 127 and 128: Well-based PSDM Faults imaged with
Page 129 and 130: structure and they must complement
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Imaged poorly was a fault identifie
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interpretation of the high angle gr
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Inline 1391 well-based PSDM Inline
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Figure 83. Interpretation showing t
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Channel nnen a Channel b Figure 85.
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yet there are several issues regard
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7.2.3 Attributes I used attributes
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seismic data provided a more detail
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educed the noise in the field data
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PSDM data to evaluate velocity mode
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10, Society of Exploration Geophysi
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Marfurt, K. J., Kirlin, R. L., Farm
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