Abstract: A method and system for reducing error contributions to gyroscopic measurements is provided. The method includes receiving a plurality of signals indicative of at least one component of the Earth's rotation substantially perpendicular to a portion of a wellbore and a component of the Earth's rotation substantially parallel to the portion of the wellbore. The plurality of signals is generated by one or more gyroscopic sensors within the portion of the wellbore. The method further includes calculating, using the plurality of signals and using one or more signals indicative of the Earth's rotation rate and one or more signals indicative of the latitude of the one or more gyroscopic sensors within the portion of the wellbore, a mass unbalance offset for the one or more gyroscopic sensors.

Abstract: An apparatus and method for measuring depth, velocity, or both depth and velocity of instrumentation along a wellbore is provided. The apparatus includes a downhole portion movable within the wellbore in a direction generally parallel to the wellbore. The apparatus further includes a first acceleration sensor that generates a first signal indicative of a first acceleration. The apparatus further includes a second acceleration sensor that generates a second signal indicative of a second acceleration. The apparatus further includes a bend sensor generating a third signal indicative of an amount of bend of at least a portion of the downhole portion.

Abstract: An apparatus for initializing a tool configured to be moved along a wellbore includes at least one directional reference system configured to provide data indicative of an orientation of the at least one directional reference system with respect to a reference direction. The apparatus further includes a mounting portion configured to be mechanically coupled to the tool such that the tool has a predetermined orientation with respect to the at least one directional reference system.

Abstract: A method and an apparatus are provided for determining an orientation of a tool with respect to a reference direction. At least one first signal is indicative of an orientation of a directional reference system with respect to the reference direction. The directional reference system is positioned spaced from the tool. At least one second signal is indicative of a relative orientation of the tool with respect to the directional reference system. The orientation of the tool at the first position is determined in response at least in part to the at least one first signal and the at least one second signal.