18 Subsurface Mapping
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Transcript of 18 Subsurface Mapping
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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