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

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effects of geology such as the impact of the inclination of strata on the velocity model is one area of future work. An explanation for the success of using a well-based velocity model for the PSDM is that sonic log velocities in dipping strata sample the horizontal velocity. My study has provided a benchmark for seismic data, especially land data acquired over piercement salt domes and provides an opportunity to use data from this study to further the understanding of the geology of Vinton Dome and the surrounding areas. Details regarding structure and salt tectonics integrated along with the stratigraphy will yield greater precision. Building on the initial improvements in the geologic model of Vinton Dome will lead to a fuller understanding of geology. 7.4 Conclusions and Discussion PSDM are not common to 3-D land surface seismic data, there are several reasons for this some I have mentioned. A motivation for this study was to apply the current state-of-the art technology to data over a mature oil field. The goal of this study was to improve the spatial fidelity of seismic imaging through a deterministic evaluation of surface seismic data with velocity modeling and attribute analysis. To achieve the goal and fulfill the motivations behind the study current methods had to be either modified or replaced. Identification of areas needing improvement required an assessment of current methods and testing. Testing allowed for data to be pre-migration processed in a manner that 146
educed the noise in the field data and provided a high enough signal-to-noise ratio that made them suitable for PSDM. 3-D surface seismic land data contain noise that is not as common in 3-D marine data. 3- D surface seismic land data noise is one of the principle issues to address to accurately model sediment velocities for a PSDM. Errors incorporated into an initial, sediment velocity model will propagate throughout the iterative PSDM process resulting in spurious data. At best, non-unique solutions result from the resolution of noise issues through processing in 3-D surface seismic land data. Non-uniqueness was a motivation for using a non-seismic method, specifically sonic logs, to model initial sediment velocities. Comparing PSDM volumes generated from a well-log velocity model to a traditional seismically derived velocity model demonstrates the improvements that result from the well-log velocity modeling method. I based comparisons on analysis of CIGs and an innovative use of coherence attributes as a QC tool. Steeply dipping beds tend to diminish the accuracy of a PSTM as demonstrated in this study. To overcome the effects of steeply dipping beds and lateral velocity changes induced by salt, data are PSDM. Using geologic horizons from the PSTM domain and integrating them with depth interval velocities from sonic logs the two domains are merged. Using an accurate velocity to convert time picked horizons to depth allows the horizons to be accurately spaced from each other. By extrapolating the velocities vertically between each horizon, I was able to insert a smooth and accurate velocity 147
Page 1 and 2:
Chapter 1 Introduction 1.1 Summary
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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
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Figure 2. Outline of the extents of
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Figure 6. Salt sediment contacts us
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Figure 10. Fault pattern representa
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Figure 14. Stratigraphic column of
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Top Hackberry Sand Hackberry Base N
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Figure 18. Structure map contoured
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Gyroidina scalata Outer shelf Gyroi
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Upper Frio Sands A Sand base B Sand
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Top Anahuac Middle Shelf Heterosteg
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Miocene sands Figure 27. Spontaneou
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Vinton Dome Figure 30. Late Miocene
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3.1 Introduction Chapter 3 Processi
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3.3 Processing My primary objective
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38-42). For QC I would brute stack
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Another significant issue was to id
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Table 2 Final processing flow Input
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Number of stacked traces 12.5km 12.
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TWT seconds a 12.5km TWT seconds b
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TWT seconds 12.5km Figure 38. Brute
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Chapter 4 Velocity Modeling and Pre
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quality motivated a reassessment of
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The layer-based approach is much mo
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of seismically derived velocities.
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To test differences between seismic
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ased data, indicating higher fideli
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4.5 Conclusions and Discussion I co
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By using sonic logs the velocities
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Figure 50. Velocity cube of the sed
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Velocity in ft/sec Figure 52. Prest
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Depth in kilo-feet a. b. Figure 56.
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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
Page 131 and 132: Imaged poorly was a fault identifie
Page 133 and 134: interpretation of the high angle gr
Page 135 and 136: Inline 1391 well-based PSDM Inline
Page 137 and 138: Figure 83. Interpretation showing t
Page 139 and 140: Channel nnen a Channel b Figure 85.
Page 141 and 142: yet there are several issues regard
Page 143 and 144: 7.2.3 Attributes I used attributes
Page 145: seismic data provided a more detail
Page 149 and 150: PSDM data to evaluate velocity mode
Page 151 and 152: 10, Society of Exploration Geophysi
Page 153 and 154: Marfurt, K. J., Kirlin, R. L., Farm
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