Abstract: An articulated downhole surveying instrument and method for measuring parameters of a wellbore includes one or more laterally flexible coupling sections. The laterally flexible coupling sections are rigid in axial tension and axial compression, and are smaller in cross-section than the surveying instrument housing. A separate housing is used for each component of the surveying instrument, and each component housing is interconnected with the laterally flexible coupling. One or more flexible spacer bars are also provided. The spacer bars and coupling sections enable the assembly to be passed through a short-radius angle wellbore with greatly reduced risk of sticking or hanging up.

Abstract: A well jar has telescoping inner and outer elements having a torque transmitting connection therebetween. An intermediate member is rotatably mounted relative to the telescoping elements and is affixed in a longitudinal direction to one of the telescoping elements. A releasable latch is connected between the intermediate member and one of the telescoping elements. The intermediate member is rotatable relative to the telescoping elements upon a predetermined minimum longitudinal force applied between the telescoping elements. The rotation causes a release of the latch and movement of the telescoping elements to an impact of coacting impact faces on the telescoping elements. An improvement involves a time delay section connected between the intermediate member and at least one of the telescoping elements for restraining such relative rotation for a preselected time interval of application of at least such minimum longitudinal force.