Rotational alignment method and apparatus for tubing conveyed perforating guns

Claim 1

Well perforating apparatus for use with a tubular conduit extending from the well head to a point above the casing zone to be perforated, said conduit being capable of carrying fluid, comprising: an axially concentric perforating gun assembly including a plurality of angularly and axially spaced explosive charge containers; the angular spacing of said containers being 120 degrees and said containers being aligned in three axially extending rows; a swivel unit connecting said perforating gun assembly to the end of the tubular conduit, said swivel unit comprising an annular thrust bearing thereby permitting rotation of said perforating assembly relative to the conduit; and an axially extending narrow rib on the exterior of said perforating gun assembly aligned with and overlying a portion of one said row of containers, the containers overlaid by said rib being blank, which shifts the center of gravity to cause said perforating gun assembly to gravitationally rotate in any non-vertical section of the well casing to position said rib in engagement with the upper wall portion of the non-vertical casing section; said rib being angularly positioned relative to all the explosive charge containers so that no explosive charge is directed vertically upward.