Method and apparatus for the downhole in-situ determination of the speed of sound in a formation fluid
An apparatus and a method for measuring a speed of sound in a fluid in a well bore may include a frame adapted to receive the fluid there through are provided. The apparatus includes an acoustic source mounted on the frame; an acoustic detector to measure a signal propagating through the fluid, the acoustic detector disposed proximate the frame at a known distance from the acoustic source; and a test circuit adapted to synchronize the acoustic detector with a signal propagating through the frame. A method to determine physical properties of a fluid in a geological formation including a shear wave anisotropy in the geological formation and the formation composition using the fluid density and the fluid speed of sound is also provided.
1. An apparatus for measuring a speed of sound in a fluid in a well bore, the apparatus comprising:
a frame adapted to receive the fluid therethrough;
an acoustic source mounted on the frame and configured to generate one or more acoustic impulses;
an accelerometer configured to detect movement of the frame caused by the generated one or more acoustic impulses and determine a time at which the impulses arrive at the accelerometer, the accelerometer disposed proximate the frame at a known distance from the acoustic source; and
processing circuitry coupled to the acoustic source and accelerometer to perform operations comprising:
providing, at a first time, an acoustic impulse to a first predetermined location of the frame having a hollow core at least partially filled with a fluid;
detecting, at a second predetermined location, a first arrival time of the acoustic impulse propagated along the frame;
detecting, at the second predetermined location, a second arrival time of the acoustic impulse propagated along the fluid; and
determining a speed of sound in the fluid using a time interval between the first and second arrival times.
2. The apparatus of claim 1 wherein the accelerometer comprises an optical mechanism.
3. The apparatus of claim 1 wherein the accelerometer comprises an electro-mechanical transducer.
4. The apparatus of any one of claims 1 through 3 wherein the acoustic source comprises a coil circuit and a magnet.
5. The apparatus of any one of claims 1 through 3 wherein the accelerometer is synchronized with the acoustic source so that the accelerometer detects the time at which the signal arrives, at a detection time, the one or more signals produced at an initial time by the acoustic source.
6. The apparatus of any one of claims 1 through 3 wherein the frame includes a first end portion and a second end portion each having more mass and a different geometry than a middle portion of the frame.
7. The apparatus of any one of claims 1 through 3 wherein the accelerometer comprises two accelerometers placed at a known distance from one another.
8. The apparatus of any one of claims 1 through 3 wherein the acoustic source comprises an electromagnetic hammer.
9. The apparatus of claim 1 wherein the acoustic source comprises an electro-mechanic transducer.
10. The apparatus of claim 9 wherein the electro-mechanic transducer comprises a piezoelectric material.
11. The apparatus of any one of claims 1 through 3 wherein the frame is made of a material selected from the group consisting of a metal, a glass, and a ceramic material.
12. A method to determine fluid speed of sound comprising:
providing an acoustic impulse to a first location of a sensor frame having a hollow core at least partially filled with a fluid;
detecting, at a second location, a first arrival time of the acoustic impulse propagated along the sensor frame;
detecting, at the second location, a second arrival time of the acoustic impulse propagated along the fluid; and
determining a fluid speed of sound using the first arrival time and the second arrival time.
13. The method of claim 12 wherein determining a fluid speed of sound comprises determining a distance between the first location and the second location.
14. The method of claim 12 or 13 further comprising:
detecting, at an echo time, an acoustic echo from the acoustic impulse at the first location;
determining the speed of the acoustic impulse using the second time and the echo time;
determining a speed of the acoustic echo; and
comparing the speed of the acoustic impulse to the speed of the acoustic echo to determine a fluid flow rate.
15. The method of claim 12 , wherein determining the fluid speed of sound further comprises utilizing a known speed of sound of the frame.
16. The apparatus of claim 1 , wherein determining the fluid speed of sound further comprises:
determining a distance between the first and second predetermined location; and
utilizing the determined distance and a known speed of sound of the frame to determine the fluid speed of sound.