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INPUT   DATA

♥ EXAMPLE Of Input/Output

Title

Xmin		ft
Ymin		ft
Xmax		ft
Ymax		ft

Name of Z property
Unit of Z

#	X	Y	Z	Location
	(ft)	(ft)	(Z unit)	ID
1	Xmin	Ymin
2	Xmin	Ymax
3	Xmax	Ymin
4	Xmax	Ymax
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

MAP   CONTROLS

True Aspect Ratio ?	Yes No
Show Input Z-Values ?	Yes No
Show Location ID's ?	Yes No

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OUTPUT   :   CONTOUR GRAPH

Areal Contouring

A contour map or contour surface is a 2-dimensional representation of a 3-dimensional phenomenon or surface. Contouring geological properties like tops, porosity, pressure requires interpolation between data at random observation points (called control points e.g. well locations), to produce a continuous surface defined at all possible positions in the map. X,Y coordinates represents the areal coordinates and Z is property values.

The gridding method implemented here is based on the nearest neighbour search (four points, preferably one per quadrant) coupled with inverse distance squared weighting. This is one of the most widely used contouring algorithms.

A 50x50 grid mesh is thrown over the area of interest, and the value at each grid node is estimated as follows:

For the node P, let the four closest control points have values Z₁, Z₂, Z₃, Z₄, and d₁, d₂, d₃, d₄ are their distances from P. Then:

This equation is modified slightly for special cases like nodes on the boundary of the area of interest. Also when a node is within 20 feet of a control point, the node is assigned the control point's Z-value.

Tips

    ◊ Use link EXAMPLE Of Input/Output  to demo data entry expectations and results; you may edit & use it as starting point
    ◊ If the required Java plug-in not installed on your computer, an auto-download of this plug-in will be initiated before the plot is displayed.

The user must first define the rectagular Area of Interest, by entering the X,Y values of its four corners. To prevent spurious extrapolation, estimates of Z values must also be supplied at these four corners. Thereafter, the user can supply as many (X,Y,Z) control points as desired up to a mazimum of 20. Z values can be positive and/or negative numbers.

Location IDentities: These are labels for the observation/measurement points, usually well sequence numbers. They are an optional input. User must supply unique integers between 1 and 999 or leave blank.

Map Controls: Three "Yes/No" switches can be selected to indicate whether or not to:
- honour True Aspect Ratio,
- post the location ID's on the the map, and/or
- post the control points' values on the map.

Contour Initiation: When the Calculate button is pressed, a series of data validation takes place and if successful, a Raster and Line contour plot is created, along with a Colorkey. Ten uniform contour levels spanning the Z range, is the default.

Control points can be added or removed, and map controls can be changed at any time, and the plotting process repeated by pressing "Calculate".

Some on-the-fly modifications can be made.

Zooming: To zoom on a region of the display press left mouse button and drag the mouse to define a rectangular region. To reset zoom press "Ctrl" (control) key and left mouse button at same time. The spatial time axes auto scale when zooming, and may change its "style" to improve readability.

Moving Text: The Title and Property labels can be selected by clicking the left mouse button on the label. A red rectangle will indicate the label has been selected. You may then use the mouse to drag the rectangle to a new location. Once the mouse button is released the label will be drawn at the new location.

Edit Contour Style: With this button, you will be able to select from three contour displays (i.e. Raster (grid-filled), Contour lines, and their combination). You can also pick your own choice of contour levels, delete contour levels, change contour line attributes, etc

PRINTING/PLOTTING

Printing can be accomplished in a MS Window's environment as follows:
- Display the map & mapkey fully in your browser, and hit the Print Screen key to copy the screen image to your Clipboard.
- Paste this image on a Windows application like Word.
- Select and Edit this image using the Picture Cropping facility to trim out the unwanted screen edges.
- Resize proportionately from the centre outwards by using Ctrl+Shift and dragging a corner sizing handle.
- Then use the regular print facility of the Windows application.

LIMITATIONS: Current version does not support faults.

BIBLIOGRAPHY

• Robinson, J.E.; Computer Applications In Petroleum Geology; Publ. by Hutchinson Ross Publ. Co., New York, 1982.
• Denbo D., & National Oceanic and Atmospheric Administration, USA; Scientific Graphics Toolkit; 2001.