Ppt

1. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Three Point problems
23 April 2010

2. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Varying contact orientation
Figure: Planar contacts crossing same landscape

3. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem

4. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem

5. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem

6. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem

7. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem

8. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem

9. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Units repeat in E-W direction. Why?

10. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Apparent thickness of units (as seen on map surface)
depends on dip angle and slope of topography.

11. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Which is on top: Formation A or Formation B?

12. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Where is the top of Formation B (B-C contact)?

13. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Dipping Bed (unit of interest)

14. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Distance along which borehole is expected to pass
thorough the unit - inversely, calculate true thickness based on
exploratory boreholes

15. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem

16. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: True and Vertical thickness are related by cos (dip angle)

17. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Find thickness of unit B by finding top and bottom of unit
at same x-y position

18. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: elevation of A-B contact @ x-y position of B-C contact =
1000m

19. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: elevation of A-B contact @ x-y position of B-C contact =
1000m
tan(11) · 750m = 150m

20. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: true thickness of tabular unit is measured perpendicular to
contacts
cos (dip angle) = true thickness / vertical thickness
(250m) · cos(11) = true thickness
= 245 m

21. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: What if you have 3 points of known x-y-z position, but no
2 points at same elevation?

22. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Construct a gradient between highest and lowest points
(orientation is arbitrary- not dip angle!

23. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Set up similar triangles to find point along line connecting
highest and lowest, where elevation = middle point

24. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Measure distance x from reference point - construct point
@ elevation of middle point.

25. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Strike line connects 2 points of equal elevation. Dip is
perpendicular - then proceed as for yesterday’s problem.

26. Three Point
problems
Outline
Outcrop Patterns:
Strike and Dip 2
Unit Thickness
Three-point problem
Figure: Conclusions: Outcrop pattern seen on this map is due to
planar beds dipping 11West, intersecting with a curved, irregular
topographic surface.