# Seismic attribute analysis and its application to mapping folds and fractures

vii Table of Contents Acknowledgments ............................................................................................................ iv

Table of Contents ............................................................................................................ vii

List of Figures ................................................................................................................... ix

Abstract .......................................................................................................................... xvii

Chapter 1 Motivation and Objectives ............................................................................. 1

Chapter 2 Introduction..................................................................................................... 3

Chapter 3 Theory and Methodology ............................................................................... 5

Structural dip, amplitude gradient, and curvature – A 360 o perspective ........................ 5

Curvature......................................................................................................................... 7

Geometric description ................................................................................................. 7

Mathematical description ............................................................................................ 8

Shape index and curvedness ........................................................................................... 9

Curvature Lineaments – Multi-attribute displays and rose diagrams ........................... 10

Summary ....................................................................................................................... 11

List of Figures ............................................................................................................... 12

References ..................................................................................................................... 19

Chapter 4 Attributes applied to the Cuu Long Basin, Vietnam ................................. 21

Description .................................................................................................................... 21

Enhanced seismic data processing and interpretation for fractured basement in the Cuu Long basin, Vietnam ..................................................................................................... 22

Chapter 5 Attributes applied to the Chicontepec basin, Mexico ................................ 45

Description .................................................................................................................... 45

Attribute-aided interpretation of complex structures, an example from the Chicontepec basin, Mexico ................................................................................................................ 46

Chapter 6 Use of seismic attributes in structural interpretation ............................... 76

Summary ....................................................................................................................... 76

Attribute Illumination of basement faults, Cuu Long Basin, Vietnam ......................... 78

Attribute illumination of basement faults, examples from Cuu Long Basin basement, Vietnam and the Midcontinent, USA............................................................................ 83

Curvature lineaments and multi-attribute display of full-stack PP, SS, and acoustic impedance seismic data – Diamond-M field, West Texas ............................................ 93

Coherence and volumetric curvature and their spatial relationship to faults and folds, an example from Chicontepec basin, Mexico ............................................................... 98

Using 3D rose diagrams for correlation of seismic fracture lineaments with similar lineaments from attributes and well log data .............................................................. 103

Multi-attribute display and rose diagrams for interpretation of seismic fracture lineaments, example from the Cuu Long Basin, Vietnam .......................................... 108

viii Using automatically generated 3D rose diagrams for correlation of seismic fracture lineaments with similar lineaments from attributes and well log data ........................ 112

Chapter 7 Conclusions .................................................................................................. 118

Appendix ........................................................................................................................ 119

Overview ..................................................................................................................... 119

Master Graphic User Interface (GUI): aaspi_util ....................................................... 122

AASPI seismic attribute GUIs and computing programs ........................................... 124

ix List of Figures Theory and Methodology……………………………………………………………….5 Figure 1: Mathematical definition of a dipping surface. By convention, n = unit vector normal to the surface; a = unit vector dip along the surface; θ = dip magnitude; ψ = dip azimuth; ξ = strike; θ x = the apparent dip in the xz plane; and θ y = the apparent dip in the yz plane (modified after Chopra and Marfurt 2007)............................................................................ 12 Figure 2: Outcrop of fracture granite basement in Phan Thiet, Vietnam. The exfoliation fracture surface (rectangle) is represented by the strike ξ in E-W direction, dipping θ into the direction of unit vector dip a (image courtesy of PetroVietnam). ......................................... 12 Figure 3: A schematic diagram showing a 2D estimate of coherence. The high coherence response represents a seismic reflector (modified after Marfurt et al. 1998). ....................... 13 Figure 4: A schematic diagram showing a 3D search-based estimate of coherence, in which p x indicates the inline and p y the crossline components of vector time dip (modified after Marfurt et al. 1998). .............................................................................................................. 13 Figure 5: A schematic diagram showing the calculation of seismic reflector dip. θ x = the apparent dip magnitude in the x direction. p x = the inline components of vector time dip. v = average time to depth conversion velocity. ........................................................................................ 14 Figure 6: Processing workflow to generate directional attributes. (a) Generating directional dip or amplitude energy gradient attribute from seismic amplitude. (b) Generating Euler curvature attributes from inline and crossline dip attributes. ................................................................ 14 Figure 7: Folding surface, Lago Argentino .................................................................................... 15 Figure 8: Definition of curvature. For a particular point P on a curve, green arrows indicate normal vectors, n, to the curve. Ĳ is the vector tangent to the curve at point P. Curvature is defined in terms of the radius of the circle tangent to the curve at the analysis point. Anticlinal features have positive curvature (k 2D >0), and synclinal features have negative curvature (k 2D <0). Planar features (dipping or horizontal) have zero curvature (k 2D =0) (modified after Roberts, 2001). ............................................................................................. 15 Figure 9: A quadratic surface with the normal, n, defined at point P. The circle tangent to the surface whose radius is minimum defines the magnitude of the maximum curvature, |k max |Ł1/R min (in blue). For a quadratic surface, the plane perpendicular to that containing the previously defined blue circle will contain one whose radius is maximum, which defines the magnitude of the minimum curvature, |k min |Ł1/R max (in red). Graphically, the sign of the curvature will be negative if it defines a concave surface and positive if it defines a convex surface. For seismic interpretation, we typically define anticlinal surfaces as being convex up, such that k max has a negative sign and k min has a positive sign in this image. .................. 16 Figure 10: The definition of 3D quadratic shapes expressed as a function of the most-positive principal curvature, k 1 , and the most-negative principal curvature, k 2 . By definition, k 1 k 2 . Thus, if both k 1 and k 2 are less than zero, we have a bowl; if both are greater than zero, we have a dome; and if both are equal to zero, we have a plane. ............................................... 16 Figure 11: Example of shape index modulated by curvedness. Chicontepec, Mexico. ................. 17 Figure 12: Example of ridge curvedness and the azimuth of minimum curvature composite image, DiamondM, Texas. ................................................................................................................ 17 Figure 13: G function of shape components (al-Dossary and Marfurt, 2006) ............................... 18 Figure 14: Example of 3D rose diagrams on time structure map, DiamondM, Texas. .................. 18 Attributes applied to the Cuu Long Basin, Vietnam………………………………...21

x Figure 1: Cuu Long basin in the Southeast Continental shell of Vietnam (image courtesy of PetroVietnam). ...................................................................................................................... 36 Figure 2: Geological cross section, Cuu Long basin. .................................................................... 37 Figure 3: Seismic cross section showing fractures and faults inside granite basement, generated during rifting of the basin. ..................................................................................................... 37 Figure 4: Seismic model representing fractured basement in Cuu Long Basin. ............................ 38 Figure 5: Modeled gather (a) before and (b) after application of parabolic Radon filter. ............. 38 Figure 6: Time-migrated seismic section showing the basement (a) before and (b) after re- processing with Radon and Ĳ-p filters applied. ...................................................................... 39 Figure 7: Comparison of (a) Kirchhoff depth migration and (b) controlled beam migration on depth slice at z=3100m. Line AA’ shown in Figure 8. While the lateral resolution is slightly lower, the controlled beam migration much better indicates the fractures. ........................... 40 Figure 8: Comparison of (a) Kirchhoff depth migration and (b) controlled beam migration on a vertical seismic section. Yellow line indicates location of depth slice displayed in Figure 7. ............................................................................................................................................... 41 Figure 9: Mathematical, geologic, and seismic nomenclature used in defining reflector dip. By convention, n = unit vector normal to the reflector; a = unit vector dip along the reflector; θ = dip magnitude; ψ = dip azimuth; ξ = strike; θ x = the apparent dip in the xz plane; and θ y = the apparent dip in the yz plane (after Chopra and Marfurt 2007). ....................................... 42 Figure 10: Vertical seismic section showing top of basement and interpreted faults. Depth slices shown in Figure 11-13 are indicated in green and yellow lines. ........................................... 42 Figure 11: Depth slices at z=2850 m through apparent dip, p ψ , computed at apparent direction ψ=0 O , 30 O , 60 O , 90 O , 120 O , and 150 O from North. White arrows indicate lineaments were interpreted as main NE-SW faults running along basement top. Red and yellow arrows indicate faults and fractures within basement. ...................................................................... 43 Figure 12: Depth slices at z=3100 m through apparent dip, p ψ , computed at apparent direction ψ=0 O and 60 O from North. .................................................................................................... 43 Figure 13: Depth slices at z=3100 m through apparent amplitude gradients, gψ, computed at apparent direction ψ=0 O , 30 O , 60 O , 90 O , 120 O , and 150 O from North. White arrows indicate lineaments were interpreted as main NE-SW faults running along basement top. Red and yellow arrows indicate faults and fractures within basement. ............................................... 44 Attributes applied to the Chicontepec Basin, Mecico………………………………...45 Figure 1. Definition of curvature. For a particular point P on a curve. Green arrows indicate normal vectors, n, to the curve. Ĳ is the vector tangent to the curve at point P. Curvature is defined in terms of the radius of the circle tangent to the curve at the analysis point. Anticlinal features have positive curvature (k 2D >0), and synclinal features have negative curvature (k 2D <0). Planar features (dipping or horizontal) have zero curvature (k 2D =0). (Modified after Roberts, 2001). ............................................................................................. 63 Figure 2. (a) A quadratic surface with the normal, n, defined at point P. (b) The circle tangent to the surface whose radius is minimum defines the magnitude of the maximum curvature, |k max |Ł1/R min (in blue). For a quadratic surface, the plane perpendicular to that containing the previously defined blue circle will contain one whose radius is maximum, which defines the magnitude of the minimum curvature, |k min |Ł1/R max (in red). Graphically, the sign of the curvature will be negative if it defines a concave surface and positive if it defines a convex surface. For seismic interpretation, we typically define anticlinal surfaces as being convex up, such that k max has a negative sign and k min has a positive sign in this image. .................. 63 Figure 3. Lateral displacement of most-positive (k pos ) and most-negative curvature (k neg ) anomalies, correlating the crest and trough of the folded structure from what we denote as

xi the most-positive and most-negative principal curvature anomalies (k 1 and k 2 ) which correlate to the more geologically relevant anticlinal and synclinal fold axes. For this image with approximately 2D symmetry in the vertical plane, the anomalies for k max would be identical in location and sign for those of k 1 and k 2 , such that the major anomalies could be efficiently mapped using a single (rather than two) attributes. ............................................. 64 Figure 4. Normal faults expressing different mechanisms: (a) a fault showing simple displacement with no drag, that would result in a coherence anomaly, but exhibiting no change in dip and hence no volumetric curvature anomalies, (b) a fault with drag on both sides exhibiting no coherence anomalies, but a most-positive principal curvature anomaly on the footwall (in red) and a most-negative principal curvature anomaly on the hanging wall (in blue), and (c) a growth fault with syntectonic deposition, which would exhibit both a coherence anomaly and a most-positive principal curvature anomaly over the roll-over anticline (in red). ................................................................................................................... 65 Figure 5. A vertical slice along y=-30 m, of the 3D derivative operator s (a) /x, (b) /y, and (c) /t applied to the inline and crossline components of dip used in volumetric curvature computation for data sampled at ¨x=30 m, ¨y=30 m, and ¨t=2 ms. The operator /t is computed from /z using a constant reference velocity. The value of /y along y=0 is identically zero. ..................................................................................................................... 66 Figure 6. (a) Representative seismic amplitude vertical and time slice. On the same slices, I co- render (b) shape index modulated by curvedness with (c) seismic amplitude and (d) coherence. The seismic amplitude is set to be 50% transparent. White arrows indicate faults, blue arrows indicate valleys, and yellow arrows indicate ridge features. (e) 2D color table used in shape index modulated by curvedness, and color legend for coherence and seismic amplitude. ................................................................................................................. 67 Figure 7. Location of Chicontepec basin, Mexico. (After Salvador, 1991). .................................. 68 Figure 8. Most-positive curvature anomalies (yellow) co-rendered with most-positive principal curvature anomalies (red). Note how the anomalies are aligned in the western, flatter part of the image. .............................................................................................................................. 69 Figure 9. (a) A cartoon of a fold. Anticlinal feature with most-positive principal curvature anomalies, k 1 , in red, delineating the anticline’s hinge line, and most-negative principal curvature anomalies, k 2 , in blue, corresponding to the synclinal axes of the fold. There are no significant coherence anomalies. (b) Representative vertical slice through the seismic amplitude volume showing a fold. (c) Seismic amplitude co-rendered with most-positive and most-negative principal curvatures. (d) 3D view of a vertical and time slice through the amplitude data co-rendered with most-positive and most-negative principal curvature. (e) The shape index modulated by curvedness, co-rendered with seismic amplitude. 2D color legend same as Figure 6e. ..................................................................................................... 70 Figure 10. (a) Cartoon of a pop-up structure showing two faults giving rise to coherence (green) anomalies separating most-positive principal curvature (red), and most-negative principal curvature (blue) anomalies. (b) Vertical section through the seismic amplitude data showing a pop-up block. (c) Seismic amplitude co-rendered with most-positive and most-negative principal curvatures and coherence. (d) 3D view of a vertical and time slice through the amplitude data co-rendered with most-positive and most-negative principal curvature and coherence. (e) The shape index modulated by curvedness, co-rendered with coherence and seismic amplitude. 2D color legend same as Figure 6e. ....................................................... 71 Figure 11. (a) Cartoon of a graben structure showing two faults giving rise to coherence (green) anomalies separating most-positive principal curvature (red), and most-negative principal curvature (blue) anomalies. (b) Vertical section through the seismic amplitude data showing graben. (c) Seismic amplitude co-rendered with most-positive and most-negative principal curvatures and coherence. (d) 3D view of a vertical and time slice through the amplitude data co-rendered with most-positive and most-negative principal curvature and coherence.

xii (e) The shape index modulated by curvedness, co-rendered with coherence and seismic amplitude. 2D color legend same as Figure 6e. .................................................................... 72 Figure 12. Seismic artifacts due to shallow volcanic and low fold giving rise to curvature and coherence anomalies. ............................................................................................................ 73 Figure 13. (a) Time-structure map of the top-Cretaceous horizon. (b) Horizon slice through coherence along the top-Cretaceous co-rendered with corresponding most-positive and most-negative principal curvature slices. (c) Horizon slice through coherence along the top- Cretaceous co-rendered with the shape-index modulated by curvedness slice. 2D color legend same as Figure 6e. ..................................................................................................... 74 Figure 14. (a) Time slice at 1.5s at the approximate top Cretaceous level though seismic amplitude, co-rendered with corresponding most-positive and most-negative principal curvature slices. (b) Time slice at 1.5s at the approximate top Cretaceous level though coherence along the top-Cretaceous co-rendered with the shape-index modulated by curvedness slice. 2D color legend same as Figure 6e. ......................................................... 75 Attribute Illumination of basement faults, Cuu Long Basin, Vietnam……………...78 Figure 1: Mathematical, geologic, and seismic nomenclature used in defining reflector dip. By convention, n = unit vector normal to the reflector; a = unit vector dip along the reflector; θ = dip magnitude; ψ = dip azimuth; ξ = strike; θx = the apparent dip in the xz plane; and θy = the apparent dip in the yz plane. (after Chopra and Marfurt 2007) ....................................... 78 Figure 2: Seismic section on (a) apparent dip depth slice and (b) amplitude gradient. The white arrows show location where the attributes help interpreting fault features ........................... 79 Figure 3: Depth slices at z=2750 m through apparent dip, p ψ , computed at ψ=0 O , 30 O , 60 O , 90 O , 120 O , and 150 O. from North. Block white arrows indicate lineaments that we interpret to be associated with faults and fractures. Several meandering channel segments can be seen in the sedimentary section to the SE. ........................................................................................ 80 Figure 4: Depth slices at z=2750 m through apparent amplitude gradients, g ψ , computed at ψ=0 O , 30 O , 60 O , 90 O , 120 O , and 150 O. from North. Block white arrows indicate lineaments that we interpret to be associated with faults and fractures. Several meandering channel segments can be seen in the sedimentary section to the SE. ................................................. 81 Figure 5: Depth slices at z=2750 m through (a) maximum curvature (b) minimum curvatures and (c) azimuth of minimum curvature. ....................................................................................... 81 Attribute illumination of basement faults, examples from Cuu Long Basin basement, Vietnam and the Midcontinent, USA……………………………………...83 Figure 1: Mathematical, geologic, and seismic nomenclature used in defining reflector dip. By convention, n = unit vector normal to the reflector; a = unit vector dip along the reflector; θ = dip magnitude; ψ = dip azimuth; ξ = strike; θ x = the apparent dip in the xz plane; and θ y = the apparent dip in the yz plane. (after Chopra and Marfurt 2007) ....................................... 83 Figure 2: An illustrated definition of 2D curvature. Concave downward features have a positive value while concave upward features have a negative value. ............................................... 84 Figure 3: Seismic section on (a) negative curvature and (b) positive curvature depth slice. The arrows show location where the attributes help interpreting fault features ........................... 85 Figure 4: Depth slices at z=2750 m through apparent dip, p ψ , computed at ψ=0 O , 30 O , 60 O , 90 O , 120 O , and 150 O. from North. Block white arrows indicate lineaments that we interpret to be associated with faults and fractures. Several meandering channel segments can be seen in the sedimentary section to the SE. Cuu Long basin .............................................................. 87

xiii Figure 5: Depth slices at z=2750 m through apparent amplitude gradients, g ψ , computed at ψ=0 O , 30 O , 60 O , 90 O , 120 O , and 150 O. from North. Block white arrows indicate lineaments that we interpret to be associated with faults and fractures. Several meandering channel segments can be seen in the sedimentary section to the SE. Cuu Long basin....................................... 88 Figure 6: (a) Depth slices at z=2750 m through apparent dip, p ψ , computed at ψ=0 O from North. (b) Major fault frequency detected in direction ψ=0 O . Mean direction of faults detected in this case is about 74 0 . Cuu Long basin .................................................................................. 88 Figure 7: (a) Depth slices at z=2750 m through apparent dip, p ψ , computed at ψ=90 O from North. (b) Major fault frequency detected in direction ψ=90 O . Mean direction of faults detected in this case is about 161 0 . Cuu Long basin ................................................................................ 89 Figure 8: (a) Depth slices at z=2750 m through apparent amplitude gradients, p ψ , computed at ψ=0 O from North. (b) Major fault frequency detected in direction ψ=0 O . Mean direction of faults detected in this case is about 69 0 . Cuu Long basin ...................................................... 89 Figure 9: (a) Depth slices at z=2750 m through apparent amplitude gradients, p ψ , computed at ψ=90 O from North. (b) Major fault frequency detected in direction ψ=90 O . Mean direction of faults detected in this case is about 157 0 . Cuu Long basin ............................................... 89 Figure 10: Depth slices at z=2750 m through (a) seismic, (b) variance, (c) positive curvature, and (d) negative curvature – Cuu Long basin .............................................................................. 90 Figure 11: Seismic section on (a) negative curvature and (b) positive curvature time slice. The arrows show location where the attributes aided fault interpretation - Osage county ......... 90 Figure 12: Time slices at z=700ms through (a) seismic, (b) variance, (c) negative curvature, and (d) positive curvature. Osage county ..................................................................................... 91 Figure 13: Time slices at z=630 ms through (a) seismic, (b) variance, (c) negative curvature, and (d) positive curvature. Osage county ..................................................................................... 91 Figure 14: Time slices at 700ms through (a) inline amplitude gradient, (b) crossline amplitude gradient and Time slices at 630ms through (a) inline amplitude gradient, (b) crossline amplitude gradient. Osage county ......................................................................................... 92 Curvature lineaments and multi-attribute display of full-stack PP, SS, and acoustic impedance seismic data – Diamond-M field, West Texas…………………...……….93 Figure 1: Location of study area, Midland basin, Texas. (after WorldOil.com) ........................... 93 Figure 2: An illustrated definition of 3D curvature. Synclinal features have negative curvature and anticlinal features have positive curvature. (After Lisle, 1994). .................................... 93 Figure 3: 2D multi-attribute display. The ridge component of curvedness is plotted against lightness and modulates the azimuth of minimum curvatures, ȥ min , plotted against hue. ..... 93 Figure 4: (a) Multi-attribute display of the azimuth of minimum-curvature, ȥ min , modulated by the ridge component of curvedness and (b) the corresponding rose diagrams. .......................... 94 Figure 5: Time structure map coresponding to top of Pennsivanian age Canyon Reef formation, interpreted from the PP seismic data. .................................................................................... 94 Figure 6: PP data at time slice t=935ms just below the top of the Canyon Reef Fm through (a) most-positive and (b) most- negative curvature volumes. (c) Multi-attribute display using transparency to show anomalous features seen in (a) and (b) on top of the seismic amplitude time slice. (d) Multi-attribute ridge-ȥ min , display described in Figure 3 overlain by rose diagrams (in white). .............................................................................................................. 95 Figure 7: SS data at time slice t=1871ms (just below the top of the Canyon Reef Fm and equivalent to 935ms in PP data) through Reef Fm through (a) most-positive and (b) most- negative curvature volumes. (c) Multi-attribute display using transparency to show anomalous features seen in (a) and (b) on top of the seismic amplitude time slice. (d) Multi- attribute ridge-ȥ min , display overlain by rose diagrams (in white). ....................................... 96

xiv Figure 8: Acoustic Impedance data at time slice t=935ms just below the top of the Canyon Reef Fm through (a) most-positive and (b) most- negative curvature volumes. (c) Multi-attribute display using transparency to show anomalous features seen in (a) and (b) on top of the seismic amplitude time slice. (d) Multi-attribute ridge-ȥ min , display overlain by rose diagrams (in white). .............................................................................................................. 96 Multi-attribute display and rose diagrams for interpretation of seismic fracture lineaments, example from the Cuu Long Basin, Vietnam…………………………...98 Figure 1: An illustrated definition of 3D curvature. Synclinal features have negative curvature and anticlinal features have positive curvature ..................................................................... 98 Figure 2: Most-positive and most-negative curvatures (Modified from Lisle, 1994) .................... 98 Figure 3: Illustration of fold with positive and negative curvature. ............................................... 98 Figure 4: An illustration of normal faults with positive and negative curvature: (a) simple displacement with no drag, (b) fault with drag on one side, (c) fault with drag on two sides, and (d) fault with syntectonic depositions. ............................................................................ 99 Figure 5: Ant-tracking on most-positive curvature (red, with blue arrow) and on new defined maximum curvature (pink, with pink arrow). ....................................................................... 99 Figure 6: Anticlinal feature. Minumum curvature features (blue) delineate the two limbs of the fold, while maximum curvature (red) delineate the axial plane.. There are no significant coherence anomalies. .......................................................................................................... 100 Figure 7: Intepreted faults (yellow) on a pop-up feature bound by coherence (green), maximum curvature (red), minimum curvature (blue) anomalies. ....................................................... 100 Figure 8: Interpreted faults (yellow) and intervening graben delineated by maximum curvature (red) and minimum curvature and coherence (green). ....................................................... 100 Figure 9: A representative seismic line with (a) interpreted faults, (b) coherence, (c) co-rendered ant-tracked maximum curvature, minimum curvature and coherence with the vertical seismic line, and (d) with an itersecting time slice as well. Intepreted faults (yellow) on a pop-up feature bound by coherence (green), maximum curvature (red), minimum curvature (blue) anomalies. ................................................................................................................. 101 Figure 10: Interpreted faults (yellow) and intervening graben delineated by maximum curvature (red) and minimum curvature and coherence (green): (a) seismic line with interpreted fault (b) coherence, c) ant-tracked maximum curvature, minimum curvature and coherence on seismic line, d) their horizontally extend. ........................................................................... 101 Using 3D rose diagrams for correlation of seismic fracture lineaments with similar lineaments from attributes and well log data …………………………………….....103 Figure 1. Lineaments on most-positive curvature horizon slice manually-interpreted as yellow line segments and transformed into a rose diagram shown in the inset.(After Chopra and Marfurt, 2007b). .................................................................................................................. 105 Figure 2. Strat-slice from coherence volume displayed at a marker horizon and merged with 3D rose diagrams (in red) generated with a search radius of 600 m. In (a) the rose diagrams were generated with the ridge attribute and in (b) the roses were generated with the valley attribute. Notice that there are slight differences in their amplitudes but the orientations seem to be close. ................................................................................................................. 105 Figure 3. Strat-slice from coherence volume displayed at a marker horizon and merged with 3D rose diagrams (in red) generated with a search radius of (a) 300m, (b) 600 m, and (c ) 100m. In all cases the valley attribute was used besides the azimuth of minimum curvature. Notice that this choice will depend to a large extent on the features on the horizon or time slices being viewed. ...................................................................................................................... 105