DOWNHOLE COMPUTING SYSTEM AND METHOD FOR PRECISE REAL-TIME COMPUTATION OF DEPTH TRACKING, TRUE VERTICAL DEPTH, AND RATE OF PENETRATION

An apparatus and method for estimating measured depth, rate of penetration, and true vertical depth of a drill bit and bottom hole assembly in a borehole using multiple longitudinally separated sensors for detecting properties of the borehole or formation and an orientation sensor. The multiple sensors may be paired with each pair of sensors including a first sensor and a second sensor. The sensors within a pair may be of the same of different types. The rate of penetration can be determined by comparing trends derived from data gathered by the longitudinally separated sensors and the time at which each records specific features of the formation or borehole. Multi-sensor fusion may be employed to enhance the accuracy of the orientation estimation. Combined with orientation information, a known longitudinal separation, and a measured depth, the true vertical depth can be determined without input from the surface.