Methods of evaluating rock properties while drilling using downhole acoustic sensors and a downhole broadband transmitting system

1. A method of analyzing properties of rock in a formation in real-time during drilling, the method comprising the steps of:

sending sampling commands to a surface data acquisition unit in communication with a downhole data interface through a surface data interface and a communication medium extending between the surface data interface and the downhole data interface, the downhole data interface operably coupled to a plurality of acoustic sensors carried by a downhole sensor assembly;

receiving, by a computer, digitized raw acoustic sensor data from the surface data acquisition unit, the digitized raw acoustic sensor data representing an acoustic signal generated real-time as a result of rotational contact of a drill bit with rock during drilling;

transforming the digitized raw acoustic sensor data into the frequency domain;

filtering the transformed data; and

performing, by the computer, the following processing steps in real-time during rotational contact of a drill bit with rock during drilling:

deriving a plurality of acoustic characteristics from the filtered data, the plurality of acoustic characteristics including mean frequency and normalized deviation of frequency,

comparing the mean frequency and the normalized deviation of frequency for the rock undergoing drilling with mean frequency and normalized deviation of frequency for a plurality of rock samples having different lithologies; and

identifying lithology type of the rock undergoing drilling responsive to the step of comparing;

deriving petrophysical properties from the filtered data utilizing a petrophysical properties evaluation algorithm employable to predict one or more petrophysical properties of rock undergoing drilling;

providing the one or more petrophysical properties of rock undergoing drilling or the lithology type of the rock undergoing drilling to a driller to assist in drilling operations.

2. The method as defined in claim 1 , wherein the mean frequency and normalized deviation of frequency are examined together as part of the step of comparing to thereby determine an amount of correlation of the acoustic characteristics associated with the rock undergoing drilling and the acoustic characteristics associated with the rock samples.

3. The method as defined in claim 1 ,

wherein the step of comparing further includes employing mean amplitude, normalized deviation of amplitude, and apparent power as part of the comparison to further enhance accuracy of the lithology determination; and

wherein the mean frequency and the mean amplitude are examined together to determine an amount of correlation of the acoustic characteristics associated with the rock undergoing drilling and the acoustic characteristics associated with the rock samples.

4. The method as defined in claim 1 , wherein the one or more petrophysical properties comprise: lithology type, porosity, water saturation, and permeability of rock undergoing drilling.

5. The method as defined in claim 1 , wherein the one or more petrophysical properties comprise: presence of hydrocarbons in rock undergoing drilling when existing and presence of fractures in the rock undergoing drilling when existing.

6. The method as defined in claim 1 ,

wherein the plurality of acoustic characteristics further include mean amplitude, normalized deviation of amplitude, and apparent power;

wherein the processing steps comprise deriving the plurality of acoustic characteristics from the filtered data; and

wherein the method further comprises the steps of:

comparing the mean frequency, the normalized deviation of frequency, the mean amplitude, and the normalized deviation of amplitude, and the apparent power for the rock undergoing drilling with mean frequency, normalized deviation of frequency, mean amplitude, normalized deviation of amplitude, and apparent power for a plurality of rock samples having different known lithologies to thereby determine an amount of correlation of the acoustic characteristics associated with the rock undergoing drilling and the acoustic characteristics associated with the rock samples, and

determining a location of a formation boundary encountered during drilling responsive to the step of comparing.

7. The method as defined in claim 1 , wherein the processing steps comprise deriving the petrophysical properties from the filtered data utilizing a petrophysical properties evaluation algorithm, wherein the petrophysical properties evaluation algorithm is a bit-specific petrophysical properties evaluation algorithm, the method further comprising the steps of:

collecting petrophysical properties data describing one or more petrophysical properties of rock contained in a data set and correspondent acoustic data for a preselected type of drill bit;

processing the collected acoustic data to produce filtered Fast Fourier Transform data;

determining one or more relationships between features of the filtered Fast Fourier Transform data and correspondent one or more petrophysical properties of rock for each type of drill bit; and

coding the determined relationships into computer program code defining the petrophysical properties evaluation algorithm; and

wherein the step of deriving the petrophysical properties includes employing the petrophysical properties evaluation algorithm to predict one or more petrophysical properties of the rock undergoing drilling real-time responsive to filtered data associated with the digitized raw acoustic sensor data produced in response to the drilling.

8. The method as defined in claim 7 , wherein the collected petrophysical properties data describes petrophysical properties of a plurality of samples taken from the formation undergoing drilling operations.

9. The method as defined in claim 1 , wherein the processing steps comprise deriving the petrophysical properties from the filtered data utilizing a petrophysical properties evaluation algorithm, wherein the petrophysical properties evaluation algorithm is a bit-independent petrophysical properties evaluation algorithm, the method further comprising the steps of:

collecting petrophysical properties data describing one or more petrophysical properties of rock and correspondent acoustic data for a plurality of different types of drill bits;

processing the collected acoustic data to produce filtered Fast Fourier Transform data;

determining bit-type independent features of the filtered Fast Fourier Transform data;

determining one or more relationships between the bit-type independent features of the filtered Fast Fourier Transform data and correspondent one or more petrophysical properties of the rock; and

coding the determined relationships into computer program code defining the petrophysical properties evaluation algorithm; and

wherein the step of deriving the petrophysical properties includes employing the petrophysical properties evaluation algorithm to predict one or more petrophysical properties of the rock undergoing drilling real-time responsive to filtered data associated with the digitized raw acoustic sensor data produced in response to the drilling.

10. The method as defined in claim 9 , wherein the collected petrophysical properties data describes petrophysical properties of a plurality of samples taken from the formation undergoing drilling operations.

11. A method of analyzing properties of rock in a formation in real-time during drilling, the method comprising the steps of:

receiving, by a computer, raw acoustic sensor data from a surface data acquisition unit in communication with a downhole data interface through a surface data interface and a communication medium extending between the surface data interface and the downhole data interface, the downhole data interface operably coupled to a plurality of acoustic sensors; and

performing, by the computer, the following processing steps in real-time during rotational contact of a drill bit with rock during drilling:

deriving a plurality of acoustic characteristics from the raw acoustic sensor data, the plurality of acoustic characteristics including mean frequency, normalized deviation of frequency, mean amplitude, normalized deviation of amplitude, and apparent power, and

deriving petrophysical properties from the raw acoustic sensor data utilizing a petrophysical properties evaluation algorithm employable to predict one or more petrophysical properties of rock undergoing drillings

providing the one or more petrophysical properties of rock undergoing drilling to a driller to assist in drilling operations.

12. The method as defined in claim 11 , further comprising the steps of sending sampling commands to the surface data acquisition unit, and deriving a frequency distribution of the acoustic data from the raw acoustic sensor data, the step of deriving a frequency distribution comprising the steps of:

transforming the raw acoustic sensor data into the frequency domain; and

filtering the transformed data.

13. The method as defined in claim 11 , wherein the processing steps comprise deriving the plurality of acoustic characteristics from the raw acoustic sensor data, the method further comprising the steps of:

comparing the mean frequency, the normalized deviation of frequency, the mean amplitude, the normalized deviation of amplitude, and the apparent power for the rock undergoing drilling with mean frequency, normalized deviation of frequency, mean amplitude, normalized deviation of amplitude, and apparent power for a plurality of rock samples having different known lithologies, the mean frequency and normalized deviation of frequency being examined together and the mean frequency and the mean amplitude being examined together to determine an amount of correlation of the acoustic characteristics associated with the rock undergoing drilling and the acoustic characteristics associated with the rock samples, the step of comparing being performed substantially continuously during drill bit steering; and

performing one or more of the following responsive to the step of comparing:

identifying lithology type of the rock undergoing drilling, and

determining a location of a formation boundary encountered during drilling.

14. The method as defined in claim 11 , wherein the processing steps comprise deriving the petrophysical properties from the raw acoustic sensor data utilizing a petrophysical properties evaluation algorithm, wherein the petrophysical properties evaluation algorithm is a bit-specific petrophysical properties evaluation algorithm, the method further comprising the steps of:

collecting petrophysical properties data describing one or more petrophysical properties of rock for a plurality of formation samples and correspondent acoustic data for a preselected type of drill bit;

processing the collected acoustic data to produce filtered Fast Fourier Transform data;

determining one or more relationships between features of the filtered Fast Fourier Transform data and correspondent one or more petrophysical properties of rock describing petrophysical properties of a plurality of formation samples for the preselected type of drill bit; and

coding the determined relationships into computer program code defining the petrophysical properties evaluation algorithm; and

wherein the step of deriving the petrophysical properties includes employing the petrophysical properties evaluation algorithm to predict one or more petrophysical properties of the rock undergoing drilling real-time responsive to filtered data associated with raw acoustic sensor data produced in response to the drilling.

15. The method as defined in claim 11 , wherein the processing steps comprise deriving petrophysical properties from raw acoustic sensor data utilizing a petrophysical properties evaluation algorithm, wherein the petrophysical properties evaluation algorithm is a bit-independent petrophysical properties evaluation algorithm, the method further comprising the steps of:

collecting petrophysical properties data describing one or more petrophysical properties of rock for a plurality of formation samples and correspondent acoustic data for a plurality of different types of drill bits;

processing the collected acoustic data to produce filtered Fast Fourier Transform data;

determining bit-type independent features of the filtered Fast Fourier Transform data;

determining one or more relationships between the bit-type independent features of the filtered Fast Fourier Transform data and correspondent one or more petrophysical properties of the rock; and

coding the determined relationships into computer program code defining the petrophysical properties evaluation algorithm; and

wherein the step of deriving the petrophysical properties includes employing the petrophysical properties evaluation algorithm to predict one or more petrophysical properties of the rock undergoing drilling real-time responsive to filtered data associated with raw acoustic sensor data produced in response to the drilling.

16. A method of analyzing properties of rock in a formation in real-time during drilling, the method comprising the steps of:

receiving, by a computer, raw acoustic sensor data from a surface data acquisition unit in communication with a downhole data interface through a surface data interface and a communication medium extending between the surface data interface and the downhole data interface, the downhole data interface operably coupled to a plurality of acoustic sensors, the raw acoustic sensor data representing an acoustic signal generated real-time as a result of rotational contact of a drill bit with rock during drilling; and

deriving a plurality of acoustic characteristics from the raw acoustic sensor data in real-time during rotational contact of a drill bit with rock during drilling, the plurality of acoustic characteristics including mean frequency and normalized deviation of frequency;

comparing the mean frequency and the normalized deviation of frequency of the rock undergoing drilling with mean frequency and normalized deviation of frequency of a plurality of rock samples having different lithologies, the mean frequency and normalized deviation of frequency being examined together to determine an amount of correlation of the acoustic characteristics associated with the rock undergoing drilling and the acoustic characteristics associated with the rock samples, the step of comparing being performed substantially continuously during drill bit steering; and

performing one or more of the following responsive to the step of comparing:

identifying lithology type of the rock undergoing drilling, and

determining a location of a formation boundary encountered during drilling; and

providing the lithology type of the rock undergoing drilling or the location of the formation boundary to a driller to assist in drilling operations.

17. The method as defined in claim 16 , further comprising the steps of sending sampling commands to the surface data acquisition unit, and deriving a frequency distribution of the acoustic data from the raw acoustic sensor data, the step of deriving a frequency distribution comprising the steps of:

transforming the raw acoustic sensor data into the frequency domain; and

filtering the transformed data.

18. The method as defined in claim 16 , wherein the plurality of acoustic characteristics further include mean amplitude, normalized deviation of amplitude, and apparent power, the method further comprising the steps of:

comparing the mean frequency, the normalized deviation of frequency, the mean amplitude, the normalized deviation of amplitude, and the apparent power for the rock undergoing drilling with mean frequency, normalized deviation of frequency, mean amplitude, and normalized deviation of amplitude of a plurality of rock samples having different known lithologies, the mean frequency and normalized deviation of frequency being examined together and the mean frequency and the mean amplitude being examined together to determine an amount of correlation of the acoustic characteristics associated with the rock undergoing drilling and the acoustic characteristics associated with the rock samples, the step of comparing being performed substantially continuously during drill bit steering; and

performing one or more of the following responsive to the step of comparing:

identifying lithology type of the rock undergoing drilling, and

determining a location of a formation boundary encountered during drilling.

19. A method of analyzing properties of rock in a formation in real-time during drilling, the method comprising the steps of:

receiving, by a computer, raw acoustic sensor data from a surface data acquisition unit in communication with a downhole data interface through a surface data interface and a communication medium extending between the surface data interface and the downhole data interface, the raw acoustic sensor data representing an acoustic signal generated real-time as a result of rotational contact of a drill bit with rock during drilling;

deriving petrophysical properties from the raw acoustic sensor data in real-time during rotational contact of a drill bit with rock during drilling utilizing a petrophysical properties evaluation algorithm employable to predict one or more petrophysical properties of rock undergoing drilling;

collecting petrophysical properties data describing one or more petrophysical properties of rocks for a plurality of formation samples and correspondent acoustic data for a preselected type of drill bit;

processing the collected acoustic data to produce filtered Fast Fourier Transform data;

determining one or more relationships between features of the filtered Fast Fourier Transform data and correspondent one or more petrophysical properties of rocks describing petrophysical properties of a plurality of formation samples for the preselected type of drill bit; and

coding the determined relationships into computer program code defining the bit-specific petrophysical properties evaluation algorithm; and

wherein the step of deriving the petrophysical properties includes employing the bit-specific petrophysical properties evaluation algorithm to predict one or more petrophysical properties of the rock undergoing drilling real-time responsive to filtered data associated with raw acoustic sensor data produced in response to the drillings

providing the one or more petrophysical properties of rock undergoing drilling to a driller to assist in drilling operations.

20. A method of analyzing properties of rock in a formation in realtime during drilling, the method comprising the steps of:

receiving, by a computer, raw acoustic sensor data from a surface data acquisition unit in communication with a downhole data interface through a surface data interface and a communication medium extending between the surface data interface and the downhole data interface, the raw acoustic sensor data representing an acoustic signal generated real-time as a result of rotational contact of a drill bit with rock during drilling;

deriving petrophysical properties from the raw acoustic sensor data in real-time during rotational contact of a drill bit with rock during drilling utilizing a petrophysical properties evaluation algorithm employable to predict one or more petrophysical properties of rock undergoing drilling;

collecting petrophysical properties data describing one or more petrophysical properties of rocks for a plurality of formation samples and correspondent acoustic data for a plurality of different types of drill bits;

processing the collected acoustic data to produce filtered Fast Fourier Transform data;

determining bit-type independent features of the filtered Fast Fourier Transform data;

determining one or more relationships between the bit-type independent features of the filtered Fast Fourier Transform data and correspondent one or more petrophysical properties of the rocks; and

coding the determined relationships into computer program code defining the bit-independent petrophysical properties evaluation algorithm; and

wherein the step of deriving the petrophysical properties includes employing the bit-independent petrophysical properties evaluation algorithm to predict one or more petrophysical properties of the rock undergoing drilling real-time responsive to filtered data associated with raw acoustic sensor data produced in response to the drillings

providing the one or more petrophysical properties of rock undergoing drilling to a driller to assist in drilling operations.