Ask Andy…Remove linear noise using Tau-P domain mute

Can you explain how to effectively remove linear noise using a Tau-P domain mute?

Creating Open Outer Mutes

Tau-P domain muting is a powerful tool for removal of coherent linear noise such as refractions and direct arrivals, allowing for more open outer mutes. Alternatively, if using angle mutes or angle gathers, larger angles as primary energy (often obscured by direct arrivals and refraction energy) is uncovered and can be utilized. In many cases Tau-P domain mutes are the preferred tool as they are considered more AVO friendly than the equivalent FK domain muting.

A more complex problem explained

Picking Tau-P domain mutes is a more complex problem than trying to remove the same linear noise from a shot in the FK domain. Whilst it is relatively simple to interpret an FK Spectra, identify the signal you want to keep and linear noise you wish to remove, Tau-P domain gathers are not so easy to understand.

Below is a shot gather in the Tau-P Domain, with the picked mute displayed. Let’s look at why, in this case, the mutes has been picked as it has:-

Effective Removal of Direct Arrival or Refractions

The main challenge when picking a Tau-P domain mute is effectively removing the direct arrival or refractions whilst preserving the water bottom horizon. This is because they occupy a similar location in the Tau-p domain gather.

In our example, we can see the WB sits inside the dark blue triangle in the top left of the gather from around -1500m/s. Both this and picked mute come quite close to the linear noise we want to remove, so it can be quite easy to remove the WB by accident or be too conservative and leave the unwanted linear noise behind.

Other than the WB. most of the primary energy that you want to preserve sits in the central part of the gather in Tau-P domain, around the zero dip/infinite velocity region.