Methods for evaluating rock properties while drilling using drilling rig-mounted acoustic sensors

A method of identifying rock properties in real-time during drilling, the method comprising the steps of:

• providing an acoustic signal recording and transmitting system including an acoustic sensor;
• connecting the acoustic sensor to one or more of the following:
• (i) a drive shaft of a drill rig, the drive shaft having a plurality of extensions and (ii) an extension of the plurality of extensions of the drive shaft, the drive shaft connected to a drill string, a drill bit connected to the downhole end of the drill string;
• operably coupling a computer to one or more components of the acoustic signal recording and transmitting system to establish communications therebetween;
• receiving an acoustic sensor data signal from the acoustic signal recording and transmitting system by the computer, the acoustic sensor data signal representing an acoustic signal generated real-time by the acoustic sensor as a result of rotational contact of the drill bit with rock during drilling;
• deriving a plurality of acoustic characteristics from the acoustic sensor data signal, the plurality of acoustic characteristics including mean frequency, normalized deviation of frequency, mean amplitude, normalized deviation of amplitude, and apparent power;
• and
• correlating the mean frequency, the normalized deviation of frequency, mean amplitude, the normalized deviation of amplitude, and apparent power with the same types of the acoustic characteristics of a rock sample of known lithology type to identify, in real-time, one or more of the following:
• (i) the lithology type, and (ii) one or more petrophysical properties of the rock engaged by the drill bit during drilling operations, the steps of receiving, deriving, and correlating performed substantially continuously during drill bit steering.

A method of identifying rock properties in real-time during drilling, the method comprising the steps of:

• providing an acoustic signal recording and transmitting system including an acoustic sensor;
• connecting the acoustic sensor to one or more of the following:
• (i) a drive shaft of a drill rig, the drive shaft having a plurality of extensions and (ii) an extension of the plurality of extensions of the drive shaft, the drive shaft connected to a drill string, a drill bit connected to the downhole end of the drill string;
• operably coupling a computer to one or more components of the acoustic signal recording and transmitting system to establish communications therebetween;
• receiving an acoustic sensor data signal from the acoustic signal recording and transmitting system by the computer, the acoustic sensor data signal representing an acoustic signal generated real-time by the acoustic sensor as a result of rotational contact of the drill bit with rock during drilling;
• deriving a petrophysical properties evaluation algorithm to predict one or more petrophysical properties of rock engaged by the drill bit during drilling operations and encoding the derived petrophysical properties evaluation algorithm into a subroutine for a petrophysical properties analyzing program, the petrophysical properties evaluation algorithm including the steps of:
• transforming acoustic signal data using a Fast Fourier Transformation thereby to convert the acoustic signal data to frequency domain data, and
• filtering the frequency domain data to remove frequency domain data produced from sources other than rock engaged by the drill bit during drilling operations thereby to create filtered data;
• and
• deriving a plurality of acoustic characteristics from the filtered data, the plurality of acoustic characteristics including mean frequency, mean amplitude, normalized deviation of frequency, normalized deviation of amplitude, and apparent power, and
• correlating the mean frequency, the mean amplitude, the normalized deviation of frequency, the normalized deviation of amplitude, and the apparent power with the same types of the acoustic characteristics of a rock sample of a known lithology type to identify, in real-time, one or more of the following:
• the lithology type and the one or more petrophysical properties of the rock engaged by the drill bit during drilling operations;
• and
• employing the encoded petrophysical properties evaluation algorithm to predict the one or more petrophysical properties of rock engaged by the drill bit during drilling operations from the acoustic data contained within the acoustic sensor data signal.