Adaptive quality control for monitoring wellbore drilling

A method for monitoring drilling, the method comprising:

• during drilling of a borehole by a drilling system, receiving a first survey from a measurement-while-drilling (MWD) tool, wherein the first survey includes a plurality of measurements of a gravity vector G and a magnetic field vector B;
• using the magnetic field vector, calculating a magnetic dip angle φ;
• generating a first covariant matrix describing the relationship of measurements to expected errors in the measurements, wherein:
• generating the first covariant matrix comprises calculating a plurality of intermediate values based on error estimates for the gravity vector G, the magnetic field vector B, and the magnetic dip angle φ, wherein the error estimates are calculated using a plurality of tool code error coefficients;
• and
• the first covariant matrix comprises a square matrix providing joint variance between the plurality of intermediate values to indicate the relationship of the plurality of measured values to the expected errors in the measured values;
• generating a plurality of residual values corresponding to the plurality of measurements, wherein each residual value comprises a difference between a reference value and a measured value for each of the plurality of measurements;
• responsive to the residual values and the first covariant matrix, computing an error ellipsoid based on the residual values and the first covariant matrix, wherein the error ellipsoid describes the bounds for residual values for the plurality of measurements;
• comparing the first survey with the error ellipsoid to determine if the first survey is within acceptable limits;
• and
• when the first survey is not within acceptable limits, generating a first indication that the drilling should stop.

A system for monitoring drilling, the system comprising:

• a processor;
• a memory coupled to the processor;
• a display device coupled to the processor, wherein the memory comprises instructions executable by the processor for performing the steps of:
• during drilling of a borehole by a drilling system, receiving a first survey from a measurement-while-drilling (MWD) tool, wherein the first survey includes measurements of a gravity vector G and a magnetic field vector B;
• responsive to the magnetic field vector, calculating a magnetic dip angle φ;
• generating a first covariant matrix describing the relationship of a plurality of measured values to a plurality of expected errors in the measured values, wherein:
• generating the first covariant matrix comprises calculating a plurality of intermediate values based on error estimates for the gravity vector G, the magnetic field vector B, and the magnetic dip angle φ, wherein the error estimates are calculated using a plurality of tool code error coefficients;
• and
• the first covariant matrix comprises a square matrix providing joint variance between the plurality of intermediate values to indicate the relationship of the plurality of measured values to the expected errors in the measured values;
• generating residual values corresponding to the measurements as differences between each reference value and each associated measured value for each of the measurements;
• responsive to the residual values and the first covariant matrix, computing a statistical distance associated with the measurements, the statistical distance describing bounds for residual values for the measurements;
• and
• displaying on the display device a comparison of at least a portion of the first survey with the statistical distance to provide a visual indication of whether the first survey is within acceptable limits.