Method and apparatus for reservoir characterization using photoacoustic spectroscopy

1. A method for estimating a selected characteristic of a formation fluid, comprising:

obtaining a first fluid sample that includes gas from a first location downhole;

separating at least a portion of the gas from the first fluid sample in a chamber downhole;

supplying laser energy to the gas separated from the first fluid sample to generate photoacoustic waves;

detecting the photoacoustic waves; and

estimating the selected characteristic of the first fluid sample utilizing the detected photoacoustic waves.

2. The method of claim 1 , further comprising:

obtaining a second fluid sample from a second location downhole;

estimating whether the second fluid sample includes the selected characteristic; and

estimating a property of a reservoir from the estimated characteristic of the first fluid sample and the estimated characteristic of the second fluid sample.

3. The method of claim 2 , wherein estimating the property of the reservoir comprises comparing the estimated characteristic of the first fluid sample and the estimated characteristic of the second fluid sample.

4. The method of claim 2 , wherein estimating the characteristic of the first fluid sample and second fluid sample comprises estimating an isotopic ratio.

5. The method of claim 2 , wherein estimating the characteristic of the first fluid sample and the second fluid sample comprises estimating a sample composition.

6. The method of claim 2 , wherein estimating the property of the reservoir comprises comparing phytane and pristine ratios relating to the first and second fluid samples.

7. The method of claim 1 , wherein detecting the photoacoustic waves comprises using a photoacoustic spectrometer or a quartz-enhanced photoacoustic spectrometer.

8. The method of claim 1 , wherein separating gas from the first fluid sample comprises diffusing gas from the first fluid sample into the chamber that is at least partially evacuated.

9. An apparatus for use downhole, comprising:

a probe configured to retrieve a formation fluid;

a chamber configured to receive gas from the retrieved formation fluid;

an energy source configured to induce energy into the gas to generate photoacoustic waves;

a photoacoustic spectrometer configured to estimate a characteristic of the gas from the photoacoustic waves; and

a processor configured to estimate a property of a reservoir utilizing the estimated characteristic of the gas.

10. The apparatus of claim 9 , wherein the photoacoustic spectrometer is a quartz-enhanced photoacoustic spectrometer.

11. The apparatus of claim 9 , wherein the property of the reservoir is compartmentalization and wherein the processor is configured to estimate compartmentalization by comparing the characteristic of gas separated from formation fluids maintained at two separate downhole locations.

12. The apparatus of claim 11 , wherein the processor is further configured to estimate the reservoir compartmentalization by using an isotopic ratio.

13. The apparatus of claim 9 , wherein the energy source is a laser carried by the apparatus and wherein the apparatus further comprises a tuning fork resonator in the chamber configured to detect the photoacoustic waves.

14. The apparatus of claim 9 , wherein the processor is located at one of: (i) in a portion of the apparatus that is configured to be deployed in a wellbore; and (ii) at a surface location.

15. The apparatus of claim 9 , wherein the processor is further configured to compare phytane and pristine ratios to estimate the property of the reservoir.

16. The apparatus of claim 9 , wherein the processor is further configured to estimate composition of the fluid to estimate the property of the reservoir.

17. The apparatus of claim 9 , wherein the processor is further configured to estimate a distinguishing characteristic of the fluid.