Borehole survey method and apparatus for drilling substantially horizontal boreholes
AssigneeKerr-McGee Corporation
InventorLarry S. Trowsdale
Life of this patent
Estimating the term…
Abstract
A borehole survey method and apparatus for use in drilling substantially horizontal boreholes through a mineral deposit wherein a dip accelerometer, a roll accelerometer assembly and a fluxgate are disposed near the drill bit, which is mounted on a bent sub, and connected to a surface computation and display unit by a cable which extends through the drill string. The dip angle of the borehole near the drill bit, the azimuth of the borehole near the drill bit and the roll angle or orientation of the bent sub are measured and selectively displayed at the surface while the drill string is in the borehole for utilization in guiding the drill bit through the mineral deposit along a predetermined path.
Claims32
An apparatus adapted for drilling substantially horizontal boreholes through an earth formation, comprising:
- a drill bit;
- a drill motor operatively connected to the drill bit for driving the drill bit to form the borehole through the earth formation;
- a probe housing, the drill motor and the drill bit being connected to one end of the probe housing;
- a probe supported within the probe housing and disposed near the drill bit;
- means for measuring the components of the earth's magnetic field along a preselected "x" axis extending perpendicularly to the axial centerline of the probe and along a "z" axis extending along the axial centerline of the probe and providing an output indication of the azimuth of the borehole from the "z" component of the earth's magnetic field and the "x" component of the earth's magnetic field when the "x" axis is disposed in a horizontal plane, comprising:
- a fluxgate supported in the probe for measuring the component of the earth's magnetic field strength along the "x" axis and providing a first output signal proportional to the measured component of the earth's magnetic field strength generally along the "x" axis, and for measuring a component of the earth's magnetic field strength generally along the "z" axis and providing a second output signal proportional to the measured component of the earth's magnetic field strength generally along the "z" axis;
- an angle converter receiving the first and second output signals provided by the fluxgate and providing an output signal proportional to an angle whose tangent is the quotient of the first and second output signals provided by the fluxgate, the angle converter output signal being proportional to the azimuth of the probe housing;
- and
- means for receiving the output signal provided by the angle converter and providing an output indication of the azimuth of the probe housing.
A borehole survey apparatus adapted for use in drilling boreholes, comprising:
- a fluxgate supportable within the borehole for measuring a component of the earth's magnetic field strength measured along an "x" axis extending perpendicularly to the axial centerline of the borehole and providing a first output signal proportional to the measured component of the earth's magnetic field strength generally along the "x" axis, and for measuring a component of the earth's magnetic field strength generally along a "z" axis which extends generally along the axial centerline of the probe and providing a second output signal proportional to the measured component of the earth's magnetic field strength generally along the "z" axis;
- and
- means for receiving the fluxgate first and second output signals and providing an output indication of the azimuth of the borehole at a position near the location of the fluxgate in reasponse to the first and second output signals when the "x" axis is disposed in a horizontal plane, comprising:
- an angle converter receiving the first and second output signals provided by the fluxgate and providing an output signal proportional to an angle whose tangent is the quotient of the first and second output signals provided by the fluxgate, the angle converter output signal being proportional to the azimuth of the probe housing;
- and
- means for receiving the output signal provided by the angle converter and providing an output indication of the azimuth of the probe housing.
A method for indicating parameters of a substantially horizontal borehole formed through an earth formation, comprising the steps of:
- measuring a component of the earth's magnetic field strength measured along a "z" axis which extends generally along the axial centerline of the borehole;
- providing an output signal proportional to the measured component of the earth's magnetic field strength generally along the "z" axis;
- measuring a component of the earth's magnetic field strength measured along an "x" axis which extends perpendicular to the "z" axis and which extends in a generally horizontal direction;
- providing an output signal proportional to the measured component of the earth's magnetic field strength generally along the "x" axis;
- and
- receiving the output signals proportional to the measured components of the earth's magnetic field strength generally along the "x" and the "z" axes and providing an output indication of the azimuth in response to the received output signals.
The method of claim 30 wherein the step of receiving the output signals proportional to the measured components of the earth's magnetic field strength generally along the "x"0 and the "z" axes is defined further as providing an output signal indicative of an angle whose tangent is the ratio of the input signals.
Dependencies are inferred from the claim text.