Bottom hole survey apparatus

Abstract

A bottom hole survey apparatus is characterized by a survey instrument having a reference line therein, the instrument being receivable by the engagement of flanges provided along the instrument into keyways provided on the interior of a non-magnetic instrument barrel. When engaged, the reference line of the survey instrument is disposed in a predetermined angular relation with respect to the barrel. The barrel has means provided on the exterior thereof for receiving a visual sighting element thereon, the sighting element being in a predetermined angular relationship with respect to the reference line. At least one non-magnetic spacer element is connectable to the barrel, the spacer element being provided with an adapter having a T-shaped head thereon which is received within a corresponding T-shaped groove provided at the lower end of the instrument. A mule shoe element having a slot therein is adjustably connectable to the lower end of the spacer, the mule shoe slot being adapted to receive a second visual sighting element such that when the sighting elements are aligned the reference line within the instrument is within a predetermined axial alignment with the mule shoe slot. A torque transmitting sub element including a plurality of axially spaced arrays of circumferentially disposed ridges engageable with an array of circumferentially disposed grooves may be connected between the spacer and the mule shoe.