Patent ID: 7028409
Filing Date: 2006-04-18
Classification: G01V

Abstract:
1. A method for computing the differential azimuth between two sets of spaced-apart gravity component measurement devices in a borehole, subject to the constraint that there is no net rotation about the borehole axis between the two sets of gravity component measuring devices having outputs, comprising the steps of: a) modeling the relationship of the sensitive axes of a first set of said gravity component measurement devices to an earth fixed coordinate set in terms of an inclination rotation angle, alpha, from the vertical and an orthogonal highside rotation angle, beta, about said borehole longitudinal axis, b) modeling the relationship of the sensitive axes of a second set of said gravity component measurement devices to said sensitive axes of said first set of gravity measurement devices in terms of a rotation angle, tau, a bend direction angle, about said borehole axis, and another rotation angle, kappa, a bend magnitude angle, about an axis that is perpendicular to said borehole axis and defined by the bend direction angle tau and a last rotation angle that is the negative of said first rotation angle tau about the said borehole axis, c) forming equations relating said rotation angles alpha, beta, gamma and delta to the outputs of said gravity measuring devices, d) solving said equations to derive the values representative of all of said rotation angles, using measured values of said outputs from said first and second sets of gravity component measuring devices, and e) computing from said values of said rotation angles the direction cosines of the borehole axis of said second set of gravity component measurement devices to an assumed initial reference set of horizontal axes and from said direction cosines computing the differential azimuth angle between said first set and said second sets of gravity measuring devices.