Apparatus for establishing electrical contact with the casing in a wellbore

Claim 1

Well logging apparatus comprising suspension means for insertion into a well casing, a plurality of electrical contact apparatus carried by said suspension means, each electrical contact apparatus comprising shaft means, flexible support means having first and second ends, a rotatable cutting and electrical contact means intermediate the support means first end and the support means second end, first retaining means fixedly attaching the support means first end to the shaft means and having no moving parts, second retaining means fixedly attached to the shaft means, engaging means attached to the support means second end for slidably engaging the shaft means, biasing means having a first end restrained by the second retaining means and having a second end contacting the engaging means for biasing the engaging means toward the first retaining means to cause the flexible support means to flex to move said rotatable cutting and electrical contact means outwardly from the shaft means, insulation means electrically insulating each electrical contact apparatus from the rest, electrical circuit means connecting said electrical contact means in series including from one rotatable cutting and electrical contact means in one electrical contact apparatus through a portion of said well casing to an adjacent rotatable cutting and electrical contact means in a separate electrical contact apparatus, and electrical equipment means operatively connected to said electrical circuit means for registering the electrical potential of the portion of the well casing included in said series connection.