Self-calibrated ultrasonic method of in-situ measurement of borehole fluid acoustic properties

A method for determining a borehole fluid property, comprising:

• generating an acoustic signal within a borehole fluid;
• reflecting the acoustic signal from a known object, wherein the known object converts the acoustic signal into a reverberation signal;
• receiving an acoustic return signal from the fluid, the return signal having a received reflection portion and a received reverberation portion;
• and
• analyzing the received reverberation portion to determine the borehole fluid property, the analyzing including:
• obtaining a theoretical reverberation portion, wherein said obtaining includes convolving the received reflection portion with a theoretical reverberation transfer function;
• and
• relating the received reverberation portion and the theoretical reverberation portion to determine the borehole fluid property,
• wherein the theoretical reverberation transfer function has a frequency-domain representation R(w) of:
• R ⁢ ( ω ) = Z m - Z s Z m + Z s + 4 ⁢ Z m ⁢ Z s ⁢ ( Z s - Z m ) ( Z m + Z s ) 3 1 - ( Z s - Z m Z m + Z s ) 2 ⁢ ⅇ - ⅈ2 ⁢ ⁢ ω ⁢ ⁢ C T V s ⁢ ⅇ - ⅈ2 ⁢ ⁢ ω ⁢ ⁢ C T V s ⁢
• where Zm is the impedance of the borehole fluid, Zs is the impedance of the known object, Vs is the speed of sound in the known object, and CT is the thickness of the known object.

A method for determining a borehole fluid property, comprising:

• generating an acoustic signal within a borehole fluid;
• reflecting the acoustic signal from a known object, wherein the known object converts the acoustic signal into a reverberation signal;
• receiving an acoustic return signal from the fluid, the return signal having a received reflection portion and a received reverberation portion;
• and
• analyzing the received reverberation portion to determine the borehole fluid property, the analyzing including:
• obtaining a theoretical reverberation portion, wherein said obtaining includes convolving the received reflection portion with a theoretical reverberation transfer function;
• and
• relating the received reverberation portion and the theoretical reverberation portion to determine the borehole fluid property, wherein said relating includes:
• calculating a sum of amplitudes of the theoretical reverberation portion;
• associating the sum of amplitudes with an impedance used to determine the theoretical transfer function;
• repeating said acts of obtaining, calculating, and associating for a different impedance;
• fitting a curve to the stored sums of amplitudes;
• calculating a sum of amplitudes of the received reverberation portion;
• and determining a curve value corresponding to the sum of amplitudes of the received reverberation portion.

A method for determining a borehole fluid property, comprising:

• generating an acoustic signal within a borehole fluid;
• reflecting the acoustic signal from a known object, wherein the known object converts the acoustic signal into a reverberation signal;
• receiving an acoustic return signal from the fluid, the return signal having a received reflection portion and a received reverberation portion;
• and
• analyzing the received reverberation portion to determine the borehole fluid property, the analyzing including:
• obtaining a theoretical reverberation portion, wherein said obtaining includes convolving the received reflection portion with a theoretical reverberation transfer function;
• and
• relating the received reverberation portion and the theoretical reverberation portion to determine the borehole fluid property, wherein said relating includes:
• determining a difference between the received reverberation portion and the theoretical reverberation portion;
• comparing the difference to an error tolerance;
• and
• if the difference is greater than the error tolerance, adjusting the theoretical reverberation transfer function;
• and
• repeating said acts of obtaining, determining, and comparing until the difference is smaller than the error tolerance.

A method for determining a borehole fluid property, comprising:

• generating an acoustic signal within a borehole fluid;
• reflecting the acoustic signal from a known object, wherein the known object converts the acoustic signal into a reverberation signal;
• receiving an acoustic return signal from the fluid, the return signal having a received reflection portion and a received reverberation portion;
• and
• analyzing the received reverberation portion to determine the borehole fluid property, the analyzing including:
• obtaining a theoretical reverberation portion;
• and
• relating the received reverberation portion and the theoretical reverberation portion to determine the borehole fluid property,
• wherein the known object is a disk having a thickness substantially equal to a half wavelength of the acoustic signal's center frequency.