Tapered Mutes for Survey Boundaries

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Tapered Mutes for Survey Boundaries

We sometimes encounter low fold data at the edge of surveys. The low fold reduces the stack quality in an area extending inward from the survey boundary with increasing depth or time. 

The Volume Sculpting process is perfect for excluding entire traces based on horizons or polygons… But how do we mute the edges of a stack at varying depths?

This workflow creates a muting horizon that extends inward from the survey edge with depth. Everything below the horizon will be muted. In the low fold area near the edge of the survey, the horizon is shallow. Where the quality is good, the horizon must be deeper than the data.

Let’s confirm the quality by looking at some time slices.

As expected, the attenuation at the deepest slice extends the greatest distance from the boundary. Let's get started.

Define the Mute Boundaries with Polygons

Create a polygon around the data area.

  1. In the Map View, view a slice of the data.
  2. Right-click on the map and choose Create New Polygon.
  3. Draw around the edge of the volume.
  4. Name it “Volume Boundary”.

Next, create a polygon that surrounds the data to preserve: the good-quality, high-fold data. This will be the inner edge of the taper. 

  1. In the map view, view a deep time slice near the bottom of the data.
  2. Draw a polygon around the good quality data.
  3. Name it “Taper Inner Edge”.

Next, create the outer edge of the taper in the same way. Name it “Taper Outer Edge”

You should have three polygons displayed on the map.

Create the Muting Surface

Time to create the muting horizon. Anything deeper than this horizon will be clipped by the mute.

Create the base:

  1. In the Map > Operations tab, choose Create Constant Horizon
  2. Enter a value deeper than the maximum trace length, in our case, that’s 4000ms.
  3. Choose the “Taper Inner Edge” polygon
  4. Click Calculate then choose Create.
    • This creates the horizon: “4,000 ms X/Y”.

Now create the top.

This is the time that the muting will start.

  1. In the Map > Operations tab, choose Create Constant Horizon
    • Enter 0 ms
  2. This starts the mute at the top of the trace.
  3. Choose the “Volume Boundary” polygon
  4. Click “Calculate”, then choose Create.
    • This creates the horizon: “0 ms X/Y”.

And erase within the “Taper Outer Edge”:

  1. In the Map > Operations tab, choose Erase
  2. Choose the “Taper Outer Edge” polygon.
  3. Click “Erase inside”.

Merge the two horizons:

We'll use a little horizon math:

  1. In the Map > Operations tab, choose Horizon Maths
  2. Add the two horizons constant horizons. 
  3. Use the formula: merge (h1, h2)
  4. Click Calculate and choose Create.

Use interpolation to smoothly ramp between the two values:

  1. In the Map View, select the “Merge” result horizon.
  2. Choose the operation Interpolate/Extrapolate.
  3. Click Interpolate then Replace This Horizon.
  4. In the horizon tab, rename the “Math: merge…” horizon to “TWT Varying Mute”

Looks good! Remember that you can build custom mutes with different start and end times by using different values when creating the constant horizons. 

Applying the Mute

Finally, apply the mute to the stack using a process:

  1. In the Process tab, add a Volume Sculpt process.
  2. Name it: “Muted-Stack”
  3. At Volume, choose the volume to mute
  4. At Bottom Horizon, select the “TWT Varying Mute”

Take a look at a section to see where the mute will be applied.

Now you've got a nice sculpted volume with the low fold edges removed. 

We have used this workflow to build a custom, spatially varying, "muting surface". Use the same approach to generate any map that smoothly varies spatially between two inputs. It's a handy technique to have in your analytical bag-of-tricks!

Enjoy Insight!

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