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Complex Plan Example Feature of Plan Plus Plan 2002 computes volumes from multiple hills by combining contours of equal height together to form a single hill and then compute the volume from combined contours. For example suppose a contour map has a 0', 10', two 20', and two 30' contours (a map with 2 hills). The areas of the two 20' contours are added together to form one 20' contour and the areas of the two 30' contours are added together to form one 30' contour. The volume is then computed from the 0', 10', combined 20', and combined 30' contours. This is the standard method of computing volumes in the oil industry. A more accurate method of computing the volume is to compute a volume for each hill and then add the volumes together. Plan Plus contains these calculations in the Complex Plan portion of the program. The difference in volumes between Plan and Complex Plan usually varies less and 5% and is dependent on the complexity of the map and the frequency of the contours. Another technique for computing volume is the Vertical Slice Method. The Vertical Slice Method computes volumes of vertical rings of the isopach map. In the vertical slice method the area of the higher contour is subtracted from the area of the lower contour and multiplied by the average thickness. In the Trapezoid method the areas of the lower contour and upper contour are averaged and then multiplied by the difference in thicknesses (horizontal slices). Below is an multiple hill example with the different volumetric methods. The map has three hills with contours up to 70'.
The Plan program adds contours together and computes volume. The trapezoid method computes a volume of 53,908 ac-ft and the pyramid method 53,586 ac-ft.
In Plan Plus, the Complex Plan computes the volume of each hill separately and adds the volumes of the hills. Complex Plan computed a modified trapezoid volume of 53,427 ac-ft a difference of 500 ac-ft or 1%. The Vertical Slice Method also computed a volume of 53,427 ac-ft.
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