The oil created the mycosynth. The mycosynth created New Phyrexia.

Mycosynth Wellspring

When this artifact enters or is put into a graveyard from the battlefield, you may search your library for a basic land card, reveal it, put it into your hand, then shuffle.

The mycosynth created the groove. The groove created the party.

Secret Lair Drop

The Brothers' War Commander

When Mycosynth Wellspring enters the battlefield or is put into a graveyard from the battlefield, you may search your library for a basic land card, reveal it, put it into your hand, then shuffle.

Commander 2021

Commander Anthology Volume II

When Mycosynth Wellspring enters the battlefield or is put into a graveyard from the battlefield, you may search your library for a basic land card, reveal it, put it into your hand, then shuffle your library.

The ability will trigger when Mycosynth Wellspring is put into a graveyard from the battlefield, even if the ability that triggered when it entered hasn't resolved yet.