# Spatially blend partially overlapping volumes - alternate workflow

An alternate workflow for spatially blending velocity volumes when one volume does not completely enclose the other. To find out how to spatially blend two volumes where one does enclose the other see our manual page *Spatially merge two volumes smoothly*.

This approach uses manual polygon interpretation to create a map template containing values between 0 and 1 which defines the blend zone. This blend zone template is used to control the contribution from each volume at each location, using volume maths to give a final merged volume.

First, we need two input volumes that exist on the same survey. If you have two 3D volumes on different surveys, you can *export* one of your volumes to the other survey. DUG-Insight will automatically expand the survey to include the new volume extents.

Input volumes composed of 2D data must be interpolated/extrapolated first, using the *Volume Interpolation/Extrapolation process* to create two 3D volumes on the same survey.

Using the *Volume Combine process* to simply join the two volumes results in a visible boundary between these different volumes. Not ideal.

The sharp transition between the volumes can be reduced by using a blend zone template to combine the volumes instead.

## Create a horizon template using polygons

To create the horizon template, digitize polygons that cover the area of interest for both volumes. Pick another polygon which marks the limit of the blend zone where the 2 volumes overlap.

- Create 2 new polygons to cover each volume AOI (see
*Creating a Polygon*). - Create a polygon for your transition zone (see
*Creating a Polygon*).

i. Use polygons created in step 1

ii. Select both polygons in the polygon tab of the control menu and right click

iii. Select ‘create polygon from’ and choose ‘intersection of shapes’

iv. Use this polygon for your blend zone or, if desired, manually edit it to your desired area

v. Build a new polygon covering the total area of both volumes by using the 'union of shapes' option for the

two polygons outlining your volumes.

When finished there should be 2 polygons marking the input volume edges, a 3rd polygon defining an overlap zone where you want to blend the two volumes, and a 4th polygon outlining the entire area covered by both volumes. Both input volumes must completely cover your blending zone.

- Go to
**Map View > Operations tab > Create a Constant horizon**a.**Horizon**set value 1.

b.**Output Grid**select polygon defining one of you volumes (example below volume 1).

c. Click**Calculate**and**Create New horizon**.

- Create a hole in the constant horizon using the blend zone polygon.
- Go to
**Map View > Operations > Erase**.

a.**Polygon Erase:**blend zone polygon.

b. Erase inside polygon button.

- Repeat steps 3, 4, and 5, this time creating a constant horizon with the value 0. Set the Output grid area to the polygon defining the other volume (this example: Volume 2).

Now to create the horizon template.

- Use
*Horizon Maths*operation and add the previously created horizons.

a.**Inputs:**h1 = 0ms horizon, h2 = 1ms constant horizons

b. Merge the constant horizons together by using formula:**merge (h1, h2)**.

c. Click**Calculate**and**Create New horizon**.

- Interpolate empty space between values 0 and 1 using
*Interpolate/Extrapolate*operation.

a. Go to**Horizon operation >Interpolate/Extrapolate**.

b. Limit interpolation using polygon which covers entire area of both volumes.

## Combine the velocities

- Create a
*Volume Maths*process

a.**Input volumes:**v1 = Volume 1, v2 = Volume 2.

b.**Input horizons:**h1 = template horizon created.

c. Merge two volumes based on horizon template using the formula:**merge (v1 * h1 + (1 - h1) * v2, v2, v1)**.

- QC the results.

a. Adjust polygon sizes as required to increase or decrease the blend zone.

(Optionally) use the *volume smoothing process* on the final results to give a seamless transition.