Apparatus and method for determining drilling fluid acoustic properties

A logging while drilling tool comprising:

• a substantially cylindrical logging while drilling tool body including at least one stabilizer;
• first and second longitudinally spaced nuclear density sensors deployed on the stabilizer;
• first and second radially offset standoff sensors deployed on the tool body;
• each of the standoff sensors configured to (i) transmit an ultrasonic pressure pulse into a borehole and (ii) receive a reflected waveform;
• and
• a controller including instructions for determining at least one of (i) a drilling fluid acoustic velocity and (ii) a drilling fluid attenuation coefficient from the reflected waveforms received at the first and second standoff sensors.

A method for determining an acoustic velocity of drilling fluid in a borehole, the method comprising:

• (a) transmitting first and second acoustic signals in a borehole utilizing corresponding first and second radially offset transducers;
• (b) receiving first and second reflected signals at the corresponding first and second transducers from corresponding first and second acoustic signals transmitted in (a);
• (c) determining a time delay between a predetermined wellbore reflection component of the corresponding first and second reflected signals received in (b);
• and
• (d) processing the time delay determined in (c) to determine the acoustic velocity of the drilling fluid.

A method for determining an attenuation coefficient of drilling fluid in a borehole, the method comprising:

• (a) transmitting first and second acoustic signals in a borehole utilizing corresponding first and second radially offset transducers;
• (b) receiving first and second reflected signals at the corresponding first and second transducers from corresponding first and second acoustic signals transmitted in (a);
• (c) determining an amplitude of a first predetermined component of each of the corresponding first and second reflected signals received in (b);
• and
• (d) processing the amplitudes determined in (c) to determine the attenuation coefficient of the drilling fluid.

A method for determining an acoustic velocity and an attenuation coefficient of drilling fluid in a borehole, the method comprising:

• (a) transmitting first and second acoustic signals in a borehole utilizing corresponding first and second radially offset transducers;
• (b) receiving first and second reflected signals at the corresponding first and second transducers from the corresponding first and second acoustic signals transmitted in (a);
• (c) determining a time delay between a predetermined wellbore reflection component of the corresponding first and second reflected signals received in (b);
• (d) determining an amplitude of the predetermined wellbore reflection components of the corresponding first and second reflected signals received in (b);
• and
• (e) processing the time delay and the amplitudes determined in (c) and (d) to determine the acoustic velocity and the attenuation coefficient of the drilling fluid.

A method for estimating a local roughness of a subterranean borehole wall, the method comprising:

• (a) transmitting first and second acoustic signals in a borehole utilizing corresponding first and second radially offset transducers;
• (b) receiving first and second reflected signals at the corresponding first and second transducers from corresponding first and second acoustic signals transmitted in (a);
• (c) determining a transit time delay between wellbore reflection components of the first and second reflected signals received in (b);
• (d) repeating (a), (b), and (c) a plurality of times;
• and
• (e) processing the time delays determined in (c) to determine a time delay deviation, the time delay deviation being a measure of the borehole roughness such that increasing deviations indicate increasing roughness values.