Method for determining borehole direction

Claim 1

A method for determining the direction of a borehole during drilling of the borehole using a drill string by using a triaxial accelerometer/magnetometer package arranged in the drill string, the method comprising the steps of: measuring, during drilling gravity acceleration components g x , g y , g z of the gravity acceleration vector g at a plurality of locations within the borehole where each location within the borehole is l i where i are consecutive positive integers; determining inclination angle θ and highside angle φ of the borehole at each of locations within the borehole based on the gravity acceleration components; measuring, during drilling at each of the locations within the borehole, magnetic field components B x , B y , B z of the total magnetic field B; and determining azimuth angle ψ at each of the locations within the borehole wherein azimuth angles ψ are calculated in accordance with B.sub.i =[φ.sub.i ].sup.T [θ.sub.i ].sup.T {[ψ.sub.i ].sup.T B.sub.e }+B.sub.p where i=is a positive integer each corresponding to a measurement location, B e is the local earth magnetic field, B p is the magnetic field perturbating B e , and [ ] T indicates "Transpose" matrices for coordinate transformations from the NEV-system to the XYZ-system under Euler-angles φ, θ, and ψ, and x, y and z are vector components in a Cartesian XYZ-coordinate system fixed to the package during the drilling, and ψ, θ and φ are angles defining rotations between said XYZ-system and a Cartesian NEV-coordinate system, with N the magnetic north direction, V the vertical g-direction, and E the magnetic east or magnetic west direction.

Claim 2

A method for determining the direction of a borehole during drilling of the borehole using a drill string by using a triaxial accelerometer/magnetometer package arranged in the drill string, the method comprising the steps of: measuring, during drilling gravity acceleration components g x , g y , g z of the gravity acceleration vector g at a plurality of locations within the borehole where each location within the borehole is l i where i are consecutive positive integers; determining inclination angle θ and highside angle φ of the borehole at each of locations within the borehole based on the gravity acceleration components; measuring, during drilling at each of the locations within the borehole, magnetic field components B x , B y , B z of the total magnetic field B; and determining azimuth angle ψ at each of the locations within the borehole wherein azimuth angles ψ are calculated in accordance with B.sub.i =[φ.sub.i ].sup.T [θ.sub.i ].sup.T {[ψ.sub.i ].sup.T B.sub.e }+B.sub.p where i=is a positive integer each corresponding to a measurement location, B e is the local earth magnetic field, B p is the magnetic field perturbating B e , and [ ] T indicates "Transpose" matrices for coordinate transformations from the NEV-system to the XYZ-system under Euler-angles φ, θ, and ψ, and x, y and z are vector components in a Cartesian XYZ-coordinate system fixed to the package during the drilling, and ψ, θ and φ are angles defining rotations between said XYZ-system and a Cartesian NEV-coordinate system, with N the magnetic north direction, V the vertical g-direction, and E the magnetic east or magnetic west direction.