Geol 755: Basin Analysis Geophysics Week 3. Structural Interpretation Fault Recognition & Mapping Interpretation Procedures

Transcription

1 April 23 Two Options for ExxonMobil Class Welcome/Introductions 3:00 Welcome/Introductions 3:00 Lecture 2 Basics of Prospecting 3:15 Lecture 2 Basics of Prospecting 3:15 Exercise 3 Play Adequacy 3:35 Exercise 3 Play Adequacy 3:50 Lecture 5 Basics of the Seismic Method 4:30 Break 4:10 Lecture 10 - Structural Analysis 4:20 Break for Light Supper 5:00 Exercise 10a - Mapping Faults 5:30 Lecture 11 Stratigraphic Analysis (part 1) 6:10 Exercise 11a Interpreting Seismic Sequences 6:50 Exercise 17 Carbonate Exploration Problem 7:45 Lecture 10 - Structural Analysis 5:00 Break for Light Supper 5:00 Exercise 10a - Interpreting Faults 6:00 Lecture 11 Stratigraphic Analysis 6:35 BREAK 7:10 Exercise 11a Interpreting Seismic Sequences 7:20 Questions & Answers 8:20 Q&A 8:50 ADJOURN 8:30 ADJOURN 9:00 Geol 755: Basin Analysis Geophysics Week 3 Direct Contouring and the Importance of the Strike Perspective The horizontal (time or depth) section plays a unique role:. John N. Louie, Presenter It shows the true strike of a reflector; The inline and crossline vertical sections usually show apparent dip. Structural Interpretation Fault Recognition & Mapping Interpretation Procedures 1

2 Direct Contouring and the Importance of the Strike Perspective Direct Contouring and the Importance of the Strike Perspective Structural contours follow strike on horizontal sections. Dip generally <45, so fewer horizontal than vertical sections are needed to cover a reflector. Structure that is obvious in horizontal section can be very subtle in vertical section. Direct Contouring and the Importance of the Strike Perspective Direct Contouring and the Importance of the Strike Perspective Have to decide which color to draw contours around; Have to appreciate the structure to know top from base. Progressive direct contouring- around red. 2

3 Direct Contouring and the Importance of the Strike Perspective Fault Recognition and Mapping Event width on a horizontal section decreases with: Increasing dip; Increasing frequency. Fault Recognition and Mapping Tracing event strikes on horiz. horiz. sections is a huge advantage of 3D over 2D. Since we can interpret horiz. horiz. event terminations on the horiz. horiz. sections, we find many more faults with 3D. Fault Recognition and Mapping This Gulf of Thailand vertical section shows faults clearly. Pick faults in horizontal and vertical sections. 3

4 Fault Recognition and Mapping Fault Recognition and Mapping Since event strikes are parallel to the faults, the horiz. horiz. section doesn doesn t show faults well. The coherence seismic attribute will allow fault mapping. Why the different widths at the bottom of 2260 ms? Fault Recognition and Mapping Where there is a significant angle between event and fault strike, terminations align and faults are easy to map. Section shows prominent and subtle faults as well as culminations and lateral changes in event character. Picking the faults in horiz. horiz. section will help map the fault network. Interpretation in the Vicinity of Salt Special Gulf of Mexico Concentric Circle Shoot shows radial faulting around a salt diapir. diapir. 4

5 Interpretation in the Vicinity of Salt Ring-syncline events near diapir are narrow, steep-dipping. Interpretation in the Vicinity of Salt To image steep-dipping reservoirs sealed by a salt diapir: diapir: Interpretation in the Vicinity of Salt Shoot the survey in the strike direction of the radially dipping reservoir beds. Reservoir is clearer in cross-line section (lower) than in-line section (upper). Composite Displays Horizontal above vertical composites Circular structure is a syncline Example of subsalt imaging achieved through 3D PreStack Depth Migration (PSDM). Also needed in Nevada to image geothermal reservoirs subbasin. 5

6 Composite Displays Veritcal above horizontal composite Composite Displays Composite Displays Composite Displays Chair composite Cube composite- two faces are distorted Multiple composite by Louie from degroot degroot s Norway data Shows 3D geometry of a growth fault 6

7 Interpretation Procedures (1) 1. Preview of data on composite displays and movies. 2. Horizon identification at wells. Assessment of data phase and polarity. 3. Recognition of major faults on widely-spaced vertical sections. 4. Map fault framework by tying together with horizontal sections. Pick seed points for autotracking on faults & horizon contours 5. Initial horizon control using vertical and horizontal sections. Horizontal sections provide efficiency of coverage. 6. Automatic spatial tracking to complete horizon on every point, within each fault block interpreted. Autotracking provides precision picking. Get to this point as quickly as possible. Interpretation Procedures (2) 7. Scrutiny of intermediate horizon products for new features and for validation of tracking: Color-posted time structure (including lineations of untracked points) Color-posted horizon slice (for lineations and patterns in amplitude) High spatial frequency residual Dip magnitude and azimuth, difference, edge detection and illumination 8. Revision of horizons and faults, and rerun of autotracking. 9. Final time structure maps and horizon slices with chosen amounts of gridding or smoothing. 10. Isochron, isopach and depth maps. 11. Detailed stratigraphic and reservoir studies. Interpretation Procedures poor data or unconformity tracking Interpretation Procedures Confidence of horizon tracking 7

8 Interpretation Capabilities Automatic and manual tracking of horizons on vertical and horizontal sections; Automatic spatial horizon tracking and editing through a 3-D data volume; Correlation of vertical sections with well data; Extraction, storing and manipulation of seismic amplitudes; Manipulation of maps; Flexible use of color; and, Extraction and use of seismic attributes. Understand the phase of data before embarking on the mainstream interpretation, Use horizontal sections to full advantage; benefit from the efficiency of strike, Study only as many vertical and horizontal sections as is necessary to provide initial input control for automatic spatial tracking, Use intermediate horizon products to full advantage for refining the interpretation, Do not smooth any map or map-style product until degree of smoothing required can be judged intelligently, and Engage in stratigraphic and reservoir studies in order to get the most out of the data. Advantages and Disadvantages of Different Displays Interpretation Principles Top: dual-polarity variable area Middle: color-coded amplitude Bottom: color-coded phase Advantages and Disadvantages of Different Displays Color coding of amplitude and phase 8

9 Advantages and Disadvantages of Different Displays Advantages and Disadvantages of Different Displays Track the peaks along the zero-phase color contour, or Color zero phase specially Subtle Structural Features Peak and trough phase colors superimposed on amplitude colors for easy picking Time-structure map (right) with subtle fault identified in many contiguous horizontal sections (left). Subtle Structural Features (l) Devonian Impact structure w/ central-peak uplift (r) Joint pattern, North Sea 9

10 Visualization and Autotracking 3D scene combines horizons (color-coded for amplitude or time) with fault surfaces surfaces a geologic hypothesis Visualization and Autotracking Time-structure map of an automatically tracked horizon. Visualization and Autotracking Time-structure map of an automatically tracked horizon. With lineations of depth points not picked. Could be subtle faults, dip, facies changes, channels channels Taken From: Alistair R. Brown, AAPG Memoir 42, Interpretation of Three 10