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Geol 472Subsurface Mapping

Representing a 3D surface on a map

Movie

The arrow points at

A. A ridge.

B. A valley.

What is a contour line?

Describethe

structure

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Simple Contouring Rules

A contour line separates points that are higherfrom points that are lower

Contour lines cannot cross

Contour lines cannot merge

Contour lines must close on themselves orextend to the edge of the map

Contour interval must remain constant for theentire map

How do you make a contour map?

A contour lines separate points thatare higher from points that are lower

Space the contours between all theknow points

Honor all the data

Contour this data using 25m intervalDatum =0 m

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10m contour spacing

Problem: How to interpolatebetween the known points?

100

125

150

175

Methods of interpolation

Least squares

Tangential

Spline

Weighted average

Minimum curvature

Polynomial

Hyperbolic

Kriging

Trend surface Etc., etc., etc.!

a. Inverse distance

b. Kriging

c. Minumumcurvature

d. Triangulation

e. Polynomialregressiona.

c.

b.

e.d.

Advantages of Hand Contouring

Allows you to impart your geologicknowledge to the interpretation

Advantages of Computer Contouring

Objective and unbiased

Easily updated

Ready for subsequent processing

Only practical way if you have 1000s of datapoints

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Depth Structure Maps

Sea level

-152 (302)

-362 (502)

-385 (525)

-211(356)

Land surface

Dealing with multiple layersIsopachmapsPlot the elevation difference between two maps

Pennsylvanian Top

1800

1500

1800

1700

Mississippian

Pennsylvanian-Mississippian Isopach

500

600

300

400

800

700

Pennsylvanian plus Isopach

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What about mapping other parameters?

Extensive Surfaces:

Tops and Bottoms of formations

Isopachs

Fault surfaces

Fluid contacts, i.e. Gas-Oil, Water-Oil

Intensive Surfaces:

Porosities

Fluid Saturations

Ash content

BTU

What about Unconformities?

Unconformity Surface Top of Layer A

Base of Layer A Isopachof Layer A

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Which well would encounter the thickestsand?

Types of fault

Contouring Faulted Surfaces Faults break the continuity of a surface

Faulted structure contour map

Faulted surfaces

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Making a map of a faulted structure

1. Contour the surface without faults

2. Contour the fault plane

3. Find the intersection of the two maps

4. Correct the contours for the verticalseparation across the fault

5. Clean up

Faulted structure contour map

Faults from well data

Reverse Faults Reverse Faulting Example

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UNION OOLITE THRUST MODEL WITH FRACTURE SWARMUNION OOLITE THRUST MODEL WITH FRACTURE SWARM

(after Nelson, 2001)no scale

UNION OOLITE

DEPI #5639 (047DEPI #5639 (047--055055--00226) Gamma Ray log00226) Gamma Ray log

UNION OOLITE(Hanging wall)

UNION OOLITE(Foot wall)

100

PILOT KNOBTHRUST FAULT

228 vertical displacement

CrossCross--section Asection A --AA

A A

0

-500

-1000

-1500

PILOT KNOB

ARISTA

NW SE

Scale:500

500

5645

5644

5639

5646

3035

12715

12896

12366

5234

447

3093

UNION

PICKAWAY

DENMAR

LITTLELIME

PRICE

Where is thehighest point in the

structure in this

depth map?

A.

B.

C.

D.

E.

AD

C

B

E