1. Subsurface Mapping
Introduction

2. Introduction
Objectives of subsurface mapping
Methods
Before you start

3. Objectives Most of the Earth’s structure and stratigraphy are hidden
Structure/stratigraphy may host features of economic or academic importance
Need to be able to map/interpret the subsurface

4. Objectives Petroleum industry Mining Groundwater
Explore for and develop oil and natural gas reserves
Mining
Explore for and develop minerals and other economic deposits
Groundwater
Explore for and develop groundwater

5. Objectives Waste disposal Geotechnical engineering Academic studies
Find suitable repositories for waste
Environmental remediation
Geotechnical engineering
Locate and map the distribution of layers with specific properties
Academic studies
Structure, stratigraphy
Etc.

6. Objectives This course: focus on petroleum Why?
Methods applicable to other fields
Best datasets

7. Objectives
Develop the most reasonable subsurface interpretation(s) for the area being studied, even in areas where the data are sparse or absent
Integration of different types of data
Interpretations used to direct future exploration & development

8. Methods Wireline logs Core, cuttings (“samples”)
Seismic data (2-D, 3-D)
Potential field data (gravity, aeromag)
Ground-penetrating radar
Engineering data (fluids, pressures, etc.)
Previous reports
Etc.

13. Geophysical logs used in groundwater studies

14. Geotechnical borehole logs

17. Tail buoy
Streamer
Air Guns
Marine seismic vessels typically tow arrays of air guns and streamers containing hydrophones a few meters below the surface of the water.

18. Messinian Salt – Mediterranean Sea
Courtesy TGS-Nopec

19. Vibroseis Operations - Algeria
Courtesy François Gauthier

20. Mapping Faults Using Dip Panels in Thrust Regimes
Waiting on 84wy314
* Dip panels are areas of continuous, (near) parallel dip
* 'Smooth' changes in dip usually indicate axial planes
* Discordant dip panels show fault locations
* No data areas are usaully POORLY IMAGED steep dips, not faults
Courtesy Anadarko

21. Slicing and Dicing to Extract Geologic Information
Seismic Cube
Timeslices

22. Methods Previous reports Paper copies of data (analog)
Digital data: computer-based interpretations

25. Methods
Caveat: Without understanding what you’re doing, you’ll get a wrong answer.
Working with computers, you’ll get a wrong answer at light speed (but it may be good-looking!).

26. Methods
Interpretations (maps, etc.) are working hypotheses, never “final”
May need to update, revise as new data become available
Easier with digital data
Applies to ANY branch of (Earth) Science!!!

27. Collect Data
Collect Data
Interpret Data
Interpret Data
Drill
Drill

29. Before you start… Need clear definition of objectives
Structure? Stratigraphy? Exploration? Development? Etc.
Without knowing where you’re going, you’re unlikely to get there…

30. Before you start…
Need good understanding of structural geology, stratigraphy and other related fields
The more geology one knows, the more reasonable the resulting interpretation
Need good understanding of physical basis for any geophysical methods being used

32. Prestack Depth Migration Example
Subsalt – Offshore GOM

34. Before you start… Use correct mapping techniques and methods
Prepare reasonable subsurface maps and cross-sections
“Maps and cross-sections are the primary vehicles used to organize, interpret and present available subsurface information”
Digital products (e.g., volumes) becoming more common

37. Geocellular model:
Each cube is assigned initial properties (porosity, permeability, fluid saturation etc.)

38. 3D display of georeferenced scanned images of collar locations, geological cross-sections, integrated with drillholes displaying assay concentrations, and magnetic and gravity modeled bodies.

39. Before you start… Need to define fault behaviour in 3-D
Faults may have important affects on location, movement of fluids
Show location of faults on maps, but also map fault surfaces
May need to do structural reconstruction to validate accuracy of fault interpretations

40. A 2-D expression of a fault

41. Faults are 3-D features
Twiss and Moores, 1992

42. Fault visualization (Hart et al., 2001)

43. Fault visualization (Sagan and Hart, in press)

44. Courtesy Midland Valley

45. Before you start…
All subsurface data need to be used to develop a reasonable and accurate subsurface interpretation
Geologic (including paleontologic), geophysical, engineering
Attention to resolution, accuracy of each type
Integration of different types of data results in more robust interpretation

46. Before you start… Need to document the work done.
Lots of data likely to be collected and/or generated – document in a format that may be referenced, used, revised
People working on project may change, may want to “revisit” work many years after it is done
Electronic media (PowerPoint files, hypertext documents, etc.) good vehicles – especially when working with digital data

47. Really great stuff Fred, but how did you generate it?
Ummm….
Really great stuff Fred, but how did you generate it?

48. Summary
Subsurface mapping of important economic & fundamental importance
Push towards digital, computer-based interpretation
Need to understand fundamentals – geology, geophysics
Integration of different types of data results in more robust interpretation