Method and apparatus for determining inclination angle of a borehole while drilling

• US 5,128,867 A
• Filed: 09/19/1990
• Issued: 07/07/1992
• Est. Priority Date: 11/22/1988
• Status: Expired due to Term

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Teleco Oilfield Services, Inc. (Baker Hughes Company)
• Inventors: Helm, Walter A.
• Primary Examiner(s): Shaw, Dale M.
• Assistant Examiner(s): BODENDORF, ANDREW
• Application Number:
  US07/586,754
• Time in Patent Office: 657 Days
• Field of Search: 364/422, 33/302, 33/304, 33/312, 33/313
• US Class Current: 702/9
• CPC Class Codes: E21B 47/022 of the borehole, e.g. using geomagnetism

Abstract

A method and apparatus is presented for determining the inclination angle of a borehole being drilled, the data for determining the inclination angle being obtained while the drillstring is rotating.

Claims

1. A method for determining the inclination angle of a borehole being drilled by instruments contained downhole in a tool in a drillstring, including the steps of:

rotating the drillstring;

sensing with accelerometer means while the drillstring is rotating instantaneous acceleration components of gx or gy and gz at a location of the tool wherein the component gz is along an axis of the drillstring and the components gx and gy are orthogonal to gz;

determining a rotation rate of the drillstring, said rotation rate being independent of said sensed instantaneous acceleration components;

determining inclination angle INC from at least one of the equivalent relationships ##EQU14## where Gx=a magnitude of a first discrete fourier transform coefficient of gx;

Gy=a magnitude of a first discrete fourier transform coefficient of gy; and

Gz=a time average of gz.

2. The method of claim 1 including the step of:

##EQU15## .

3. The method of claim 1 wherein said sensing step includes sensing a preselected number of samples and wherein said drillstring is rotated a preselected number of rotations and including the step of:

determining Gz from the equation ##EQU16## where K=said preselected number of drillstring rotations;

N=said preselected number of samples taken in one rotation; and

Tm=period for the m'"'"'th tool rotation.

4. An apparatus for determining the inclination angle of a borehole being drilled by instruments contained downhole in a tool in a drillstring, including:

means for rotating the drillstring;

accelerometer means for sensing while the drillstring is rotating instantaneous acceleration components of gx or gy and gz at a location of the tool wherein the component gz is along an axis of the drillstring and the components gx and gy are orthogonal to gz;

means for determining a rotation rate of the drillstring, said rotation rate being independent of said sensed instantaneous acceleration components;

means for determining inclination angle INC from at least one of the equivalent relationships ##EQU17## where Gx=a magnitude of a first discrete fourier transform coefficient of gx;

Gy=a magnitude of a first discrete fourier transform coefficient of gy; and

Gz=a time average of gz.

5. The apparatus of claim 4 including:

means for determining |Gx| from the equation ##EQU18## .

6. The apparatus of claim 4 wherein said accelerometer means senses a preselected number of samples and wherein said drillstring is rotated a preselected number of rotations and including:

##EQU19## where Tm=period for the m'"'"'th tool rotation.

N=said preselected number of samples taken in one rotation; and

K=said preselected number of drillstring rotations.