The Grid calculator creates a new property of a 3D grid from the properties that grid already contains. The expression is evaluated cell by cell, so it is a quick way to derive a property such as net-to-gross, a saturation or a permeability estimate from properties that were upscaled or modelled earlier. It works on both S-Grids and tetrahedral grids.

Opening the calculator

In the Data Manager expand 3D Grids, right-click the grid you want to work on and choose Open grid calculator at the end of the grid context menu. The same tool is listed as Grid calculator in the Actions panel; opened from there it works on the current grid.

The grid must already contain at least one property. If its Properties folder is empty, g-Space reports that the grid has no properties and that a property has to be added or upscaled first.

Writing the expression

The name of the result and the formula are typed together in the Expression field, in the form name = expression. The part before the equals sign becomes the name of the new grid property, and the part after it is the formula, written with the names of the properties in that grid.

The main controls are:

• Property and Paste — select one of the grid properties and click Paste to insert its name into the expression at the cursor.
• Algebra, Logic and Trig tabs and the Keypad — insert mathematical functions, operators and digits. U inserts the undefined value and C clears the expression.
• Angle mode (Rad, Deg, Grad) — sets how trigonometric functions interpret angle values.

Refer to Trace headers math for a description of the available mathematical functions.

The Expression field is a drop-down that remembers the last five expressions applied in this calculator, so a previous calculation can be reused without retyping it. The history is kept separately for each project, and the Grid calculator keeps its own list, so it does not share expressions with the other calculators.

Running the calculation

Click ENTER to run the calculation. If the name in front of the equals sign is missing, g-Space reports that the output name is not specified. If the grid already contains a property with that name, you are asked whether to replace it. Closing the window without clicking ENTER leaves the grid unchanged.

The result is stored as a property of the same grid and appears under its Properties folder in the Data Manager, ready to display or to use as the input of a further calculation. A cell is left undefined where every property used in the expression is undefined, and where the formula does not produce a valid number.