Grid Math Examples

Example #1: Subtracting Two Time Grids

  1. Give your new horizon grid a name by clicking on ‘HzMath01’ under Target Grid (New) and entering a new name. In our example we'll use grid3.
  2. Select the Equation for Time check box, on the right side of the equals mark.
  3. Double click on the T[x] of the one of the grids you wish to use. In our example we'll use grid1.
  4. Type <+> on your keyboard.
  5. Double click on the T[x] of the grid. In our example we'll use grid2.
  6. The time equation should now read: grid3 = T[grid1] - T[grid2].
  7. Click <Execute>.

Example #2: REP Function

Use the REP function to create a new grid based on a test of the values in an existing grid. We will provide a range of numbers. If the values on the test grid are inside this range we will keep them, if they are outside the range we will replace them with 0. Even though we are working with an amplitude grid, we will still need to fill the time portion of the database, so we will enter a time equation as well as the amplitude equation we are interested in.

  1. Give your new grid a name by clicking on HzMath01 under Target Grid (New) and entering a new name. In our example well use finalgrid.
  2. Select the Equation for Time check box on the right side of the equals mark
  3. Use the keypad at the right of the dialog to enter 1000. (We are doing this to satisfy the database requirement that every grid entry must have a time component.)
  4. Change the Math for Time Only entry to read Creates Seismic Amplitude.
  5. To post well tops with the resulting grid you must associate a Reference Horizon.
  6. Click into the bottom equation box on the right side of the equals mark.
  7. Click the REP button on the keypad.
  8. "REP()" is entered on the right side of the equation.

You will see that your cursor is blinking inside the parenthesis. We will enter the parameters for the function between these parenthesis. Each of the parameters in the function will be separated by commas.

REP Parameters

  1. Double click on the A[x] for the grid you wish to test. The grid name is entered into the equation, For this example we will use A[Pearl].
  2. Use the keypad or your keyboard to enter a minimum test limit and the maximum limit. For this example we will use 0 for the minimum limit and 32767 as the maximum. If a value in the Pearl amplitude grid, A[Pearl], is greater than 0 and less than 32767 it will pass the test.
  3. Enter a constant or a source grid for the value to write to the result grid if A[Pearl] passes the test (is inside).
  4. Enter a constant or source grid for the value to write to the result grid if A[Pearl] fails the test (is outside).

In this example, we want to use the positive amplitudes in our grid but we want to set all negative amplitudes to 0. So we will enter A[Pearl] followed by a comma and 0.

The equation in the bottom box will look like this:

finalgrid = REP(A[Pearl],0,32767,A[Pearl],0)

The instruction to WinPICS can be paraphrased as the following: If the amplitude of the Pearl Amplitude grid is between 0 and 32767, write that amplitude to the output grid. If the value is not between 0 and 32767 then write 0 instead.

What do you want to do?