Schlumberger Technology Corporation

Ichiro Shirasaka

Jean-Michel Hache

Wayne J Phillips

Mauricio Tejada

Kirby G Schrader

A borehole survey method is provided for processing continuous measurements of the earth's magnetic and gravitational fields obtained while drilling a borehole. The present invention improves borehole acquisition of targeted geological structures by substantially reducing continuous measurement errors attributable to noise, shock and vibrations from turning the drill bit against rock.

Borehole survey method utilizing continuous measurements

The invention is, in its various aspects, a method and apparatus useful for strapdown inertial navigation and surveying in a borehole. The method comprises maneuvering a probe including three vibrating mass, Coriolis effect gyroscopes in a borehole and initializing the probe's attitude in the borehole within the probe's frame of reference. Three orthogonal, incremental rotation angles and three orthogonal, incremental velocities are determined for the probe within the probe's frame of reference. The incremental rotation angles are determined from the gyroscopes. The method then translates the three incremental velocities from the probe's frame of reference into the inertial frame of reference using the three incremental rotation angles. Next, a velocity vector in a local-vertical, wander-azimuth frame of reference is determined from the translated incremental velocities. A velocity error observation is then obtained. A system error is then estimated from the velocity vector and the velocity error observation. The system error is then fed back into the inertial navigation system for use in refining the method. In as second aspect, the invention is a strapdown, inertial measurement unit. The inertial measurement unit includes a housing, three accelerometers, and three vibrating mass, Coriolis effect gyroscopes. The three accelerometers are mounted within the housing. The three vibrating mass, Coriolis effect are rigidly mounted within the housing.

Method and apparatus for borehole surveying

A method for calculating a gyroscope survey is disclosed. The method includes measuring outputs of gyroscopes and accelerometers in a survey instrument. An instrument rotational movement is determined from the outputs of the gyroscopes. If the rotational movement exceeds a predetermined threshold, an instrument attitude is calculated from the gyroscope measurements, using the most recent alignment measurement to initialize the attitude measurement. Instrument alignment is calculated from the output of the accelerometers and gyroscopes when the threshold is not exceeded. In one embodiment, alignment is calculated using Kalman filtering. In a particular application, azimuth and inclination of a wellbore are determined at selected positions from the alignment and/or attitude measurements. The wellbore azimuth and inclination are used in one embodiment to calculate the wellbore trajectory along its length.

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Sugar Land, TX, United States of America

Ichiro Shirasaka