Apparatus for maintaining clean fluid in a chamber in a subterranean well tool

摘要

A fluid pressure activated firing head for a perforating gun disposed in a subterranean well by a packer is provided with a column of clean fluid overlying and filling the bore of the firing head but communicating with the casing annulus above the set packer. An annular fluid passage extends from the top of the clean fluid column through the set packer and ending in an inverted U-shaped annular passage. A pressure transmitting seal is mounted in the downwardly extending leg of the annular fluid passage to permit the entire fluid passage to be filled with clean fluid of a lighter density than the casing annulus fluids, thus insuring that casing annulus fluid can never enter the interior of the pressure activated firing head.