Processing of directional survey data recorded during rotational drilling
Method for obtaining a directional survey in a rotating downhole component include acquiring and generating, while rotating, sets of raw data having 3-axis magnetic field data and 3-axis gravity field data. A set of rotationally-invariant data is obtained for each of the sets of raw data to generate a first number of sets of rotationally-invariant data. An earth property value is calculated from each of the sets. An accuracy indicator is estimated for each of the sets using a respective earth property value, an earth property reference value, and an error model, to generate a plurality of accuracy indicators. A set of mean values is determined using the plurality of sets of rotationally-invariant data using a second number of sets of rotationally-invariant data of the plurality of sets of rotationally-invariant data. The directional survey is estimated and used to control the downhole component.
1 . A method for obtaining a directional survey in a rotating downhole component, the method comprising:
rotating the downhole component in a wellbore with a rotational speed, the downhole component comprising a processor, a magnetic field sensor, and a gravity field sensor;
acquiring, while rotating the downhole component, raw data comprising magnetic field data from the magnetic field sensor and gravity field data from the gravity field sensor, to generate a plurality of sets of raw data, wherein each of the sets of raw data comprises 3-axis magnetic field data and 3-axis gravity field data;
determining, in the downhole component, a set of rotationally-invariant data for each of the sets of raw data of the plurality of sets of raw data to generate a plurality of sets of rotationally-invariant data, the plurality of sets of rotationally-invariant data having a first number of sets;
calculating, in the downhole component, an earth property value from each of the sets of rotationally-invariant data of the plurality of sets of rotationally-invariant data;
estimating, in the downhole component, an accuracy indicator for each of the sets of rotationally-invariant data of the plurality of sets of rotationally-invariant data using a respective earth property value associated with each of the sets of rotationally-invariant data, an earth property reference value, and an error model, to generate a plurality of accuracy indicators;
identifying a second number of sets from the plurality of sets of rotationally invariant data, using the accuracy indicator, wherein the second number of sets is smaller than the first number of sets;
determining, in the downhole component, a set of mean values using the identified second number of sets of the plurality of sets of rotationally-invariant data;
estimating the directional survey using the set of mean values; and
controlling the downhole component using the directional survey.
2 . The method of claim 1 , wherein the plurality of sets of raw data is acquired within a time interval using a sample rate, wherein the sample rate is larger than or equal to 50 samples per second.
3 . The method of claim 2 , wherein the time interval is between 1 s and 100 s.
4 . The method of claim 2 , further comprising estimating the rotational speed of the downhole component using at least a portion of the sets of raw data of the plurality of sets of raw data acquired within the time interval.
5 . The method of claim 1 , wherein the earth property value is at least one of a total gravity field value, a total magnetic field value, and a magnetic dip value.
6 . The method of claim 5 , wherein the estimating the accuracy indicator comprises calculating a difference between the calculated earth property value and the earth property reference value.
7 . The method of claim 6 , wherein the estimation of the accuracy indicator comprises a minimum rotational speed and the determining the set of mean values comprises discarding at least one set of rotationally-invariant data of the plurality of sets of rotationally-invariant data based on the rotational speed of the downhole component being below a minimum rotational speed.
8 . The method of claim 1 , wherein the controlling the downhole component comprises transmitting the set of mean values to a surface location and to operate the downhole component based on the transmitted set of mean values.
9 . The method of claim 8 , further comprising:
determining a flag, wherein the flag comprises an indicator of the second number of sets; and
transmitting the flag to the surface location.
10 . The method of claim 9 , wherein the flag is a ratio of the second number of sets and the first number of sets.
11 . The method of claim 8 , further comprising determining a flag, wherein the flag comprises at least one of an indicator of the rotational speed of the rotating downhole component and an indicator of a vibration level of the downhole component.
12 . The method of claim 1 , wherein the error model comprises a calibration parameter for at least one of the magnetic field sensor and the gravity field sensor.
13 . The method of claim 12 , wherein the error model provides an error expectation value, the error expectation value related to errors based on at least one of the rotational speed of the downhole component and a vibration level of the downhole component in the wellbore.
14 . The method of claim 12 , wherein the error model includes a weighting function.
15 . The method of claim 1 , wherein the directional survey is estimated downhole in the downhole component while the downhole component is rotating, and the controlling the downhole component is performed by the processor in the downhole component using the directional survey.
16 . The method of claim 15 , wherein the controlling the downhole component is performed automatically without input from a human operator.
17 . The method of claim 1 , wherein the directional survey includes at least one of an azimuth and an inclination.
18 . A system obtaining a directional survey comprising:
a downhole component configured to be rotated in a wellbore with a rotational speed, the downhole component comprising a processor, a magnetic field sensor, and a gravity field sensor;
wherein, while rotating, the system is configured to:
acquire raw data comprising magnetic field data from the magnetic field sensor and gravity field data from the gravity field sensor, to generate a plurality of sets of raw data, wherein each of the sets of raw data comprises 3-axis magnetic field data and 3-axis gravity field data;
determine, in the downhole component, a set of rotationally-invariant data for each of the sets of raw data of the plurality of sets of raw data to generate a plurality of sets of rotationally-invariant data, the plurality of sets of rotationally-invariant data having a first number of sets;
calculate, in the downhole component, an earth property value from each of the sets of rotationally-invariant data of the plurality of sets of rotationally-invariant data;
estimate, in the downhole component, an accuracy indicator for each of the sets of rotationally-invariant data of the plurality of sets of rotationally-invariant data using a respective earth property value associated with each of the sets of rotationally-invariant data, an earth property reference value, and an error model, to generate a plurality of accuracy indicators;
identify a second number of sets from the plurality of sets of rotationally invariant data, using the accuracy indicator, wherein the second number of sets is smaller than the first number of sets;
determine, in the downhole component, a set of mean values using the identified second number of sets of the plurality of sets of rotationally-invariant data;
estimate the directional survey using the set of mean values; and
control the downhole component using the directional survey.
19 . The method of claim 7 , wherein the error model is specific to the downhole component.
20 . The method of claim 7 , wherein the accuracy indicator is determined for each set of rotationally-invariant data of the plurality of sets of rotationally-invariant data.