METHOD OF MONITORING A FLUID AND USE OF A TRACER FOR MONITORING A FLUID

Abstract

A method of monitoring a fluid is described comprising introducing a luminescent nanoparticle into the fluid; removing a fluid sample from the fluid; adding a reagent to the fluid sample to vary the luminescence behaviour of the luminescent nanoparticles and/or of other luminescent species present in the fluid; analysing the luminescence of the modified fluid sample to determine an amount of the nanoparticle present therein. A use of a tracer based on these principles is also described.

Claims

1. (canceled)

2. A method of monitoring a parameter of a hydrocarbon well, pipeline or formation, the method comprising: introducing a plurality of luminescent nanoparticles as a tracer into the hydrocarbon well, pipeline or formation; producing an aqueous fluid from the hydrocarbon well, pipeline or formation, the aqueous fluid comprising water soluble organic species which are naturally fluorescent and the luminescent nanoparticles; removing a fluid sample from the aqueous fluid; adding a reagent to the fluid sample to vary the luminescence behaviour of the luminescent nanoparticles or of the water soluble species present in the fluid, wherein the reagent is selected to act either to suppress the luminescence of the water soluble organic species or to increase the luminescence of the luminescent nanoparticles to enable better resolution of the luminescence of the luminescent nanoparticles from background luminescence of the water soluble organic species; analysing the luminescence of the modified fluid sample to determine an amount of the nanoparticle present therein; and monitoring a parameter of the hydrocarbon well, pipeline or formation based on the determined mount of nanoparticles present in the modified fluid sample, wherein the parameter being monitored is the flow of water through or from the hydrocarbon well, pipeline or formation.

3. (canceled)

4. A method according to claim 1, wherein the aqueous fluid comprises produced water from which the oil phase has been largely removed.

5. (canceled)

6. A method according to claim 1 comprising adding the reagent at least to vary the luminescence of the luminescent nanoparticles.

7. A method according to claim 3 comprising selecting a combination of luminescent nanoparticles and reagent that are known to interact together in aqueous solution such that the luminescence behaviour of the luminescent nanoparticles varies in the presence of the reagent.

8. A method according to claim 1, wherein the reagent is selected to change a condition parameter of the fluid, the said condition parameter being one the variation of which is known to cause a variation in luminescence of the luminescent nanoparticles or of the water soluble organic species present in the fluid.

9. A method according to claim 5 comprising the additional step of measuring a condition parameter of the fluid sample before adding the reagent, and subsequently adding the reagent to change the condition parameter.

10. A method according to claim 5, wherein the condition parameter is the pH of the aqueous fluid.

11. (canceled)

12. (canceled)

13. (canceled)

14. A method according to claim 1, wherein the luminescent nanoparticles are selected to have a surface functionality modified such as to cause the nanoparticle to exhibit a luminescence response that varies with varying pH.

15. A method according to claim 8, wherein the surface of the luminescent nanoparticles comprises one or more functional groups that act in aqueous solution as proton donors or proton acceptors.

16. A method according to claim 8, wherein the surface of the luminescent nanoparticles comprises one or more functional groups selected from: carboxyl, carbonyl, sulfonyl, hydroxyl, thiol, amine, amide, imide, and combinations and derivatives of the same.

17. A method according to claim 1, wherein the luminescent nanoparticles comprise carbon-based nanoparticles.

18. A method according to claim 1, wherein the luminescent nanoparticles are doped.

19. A method according to claim 1, wherein the luminescent nanoparticles are water-dispersible.

20. (canceled)

21. A method according to claim 1, wherein at least a part of the surface of the luminescent nanoparticles comprises hydrophilic groups, for example selected from one or more of: amine groups, hydroxyl groups, carbonyl groups.

22. A method according to claim 1, wherein the luminescent nanoparticles are fluorescent nanoparticles.

23. (canceled)

24. (canceled)

25. (canceled)

26. (canceled)

27. (canceled)

28. (canceled)

Description

DESCRIPTION OF THE DRAWINGS

[0080] Embodiments of the present invention will now be described, by way of example, and not in any limitative sense, with reference to the accompanying drawings, of which:

[0081] FIG. 1 shows the typical fluorescence intensity response spectrum of produced water;

[0082] FIG. 2 shows a measured fluorescence intensity response spectrum of a known fluorescent carbon-based nanoparticle suitable for use in the method of the invention;

[0083] FIG. 3 show the difference of the fluorescence intensity response of the fluorescent carbon-based nanoparticle of FIG. 2 in a solution where the pH of the solution is approximately 4 and 9

[0084] FIG. 4 shows the variation of the peak height of the fluorescent carbon-based nanoparticle of FIG. 2 plotted against pH where the pH of the solution varies over a range from approximately 4 to 9;

[0085] FIG. 5 shows an example use of such a carbon-based nanoparticle as a tracer in a method of monitoring a hydrocarbon reservoir;

[0086] FIG. 6 shows the effect of cysteine on the fluorescence properties of nanoparticles;

[0087] FIG. 7 shows the effect of L-ascorbic acid on the fluorescence properties of nanoparticles.

DETAILED DESCRIPTION

Effect of pH on Fluorescent Properties of Nanoparticles

[0088] In an example of the method of the invention, fluorescent carbon-based nanoparticles are used as tracers which exhibit a fluorescence that varies with pH, and most particularly that exhibit a fluorescence that may be enhanced at a known excitation energy at a known pH, and a reagent is added to vary the pH and produce such an effect.

[0089] FIGS. 1 and 2 show respectively an intensity spectrum for a sample of produced water and a comparable spectrum for a known fluorescent carbon-based nanoparticle, each with normalized peak height, to illustrate the problem of background fluorescence.

[0090] FIG. 1 shows a sample of produced water from which at least 99% of the oil phase has been removed. Even so, there is strong fluorescence from organics which have distributed into and for example dissolved in the produced water phase. The peak region of fluorescence is in particular found to occur at shorter wavelengths in the visible spectrum. Only limited fluorescence is exhibited above 500 nm, even less above 550 nm, and almost none beyond 600 nm.

[0091] In FIG. 2 a comparable spectrum is shown for a known fluorescent carbon-based nanoparticle having a peak fluorescence intensity at the blue end of the visible spectrum. As can be seen, this exhibits strong fluorescence in the blue/cyan end of the spectrum, with most fluorescence occurring in the range 450-520 nm.

[0092] It can be seen that a major part of the intensity of the background fluorescence overlaps with the peak fluorescence intensity of the fluorescent carbon-based nanoparticles.

[0093] Any method that could help distinguish these responses, for example by enhancing the fluorescence response of the fluorescent carbon-based nanoparticle so as to reduce the background effect, is likely to be advantageous.

[0094] FIG. 3 show the difference of the fluorescence intensity response of the fluorescent carbon-based nanoparticle of FIG. 2 in a deionized water solution where the pH of the solution is respectively approximately 4 (broken line) and 9 (solid line).

[0095] In FIG. 4, a measured fluorescence intensity peak height for the fluorescent carbon-based nanoparticle of FIG. 2 in deionized water solution is plotted against pH of that solution where the pH of the solution varies over a range from approximately 4 to 9.

[0096] The pH of the solution is varied by adding a suitable reagent to the solution. In the example given a buffer solution was used. In practical systems in the field a more powerful reagent such as NaOH may be preferred.

[0097] It can be seen that enhanced fluorescence intensity is obtained as the pH of the solution increases. The two figures show that it is possible over this range to increase the peak height by a factor of two or more by modifying the pH over the range from approximately 4 to approximately 9.

[0098] To be applicable to the invention it might be preferable that the luminescence and in the example case fluorescence of a nanoparticle tracer is at least 10% higher at the modified pH than at the unmodified pH. It follows that preferably the nanoparticle is selected to exhibit a variable luminescence and for example fluorescence response with pH that varies from a lower level of fluorescence intensity to a higher level of fluorescence intensity at least 10% higher than the said lower level of fluorescence intensity across a pH range that represents a range that can be practically modified by addition of a suitable reagent. Where the fluid is produced water from a hydrocarbon well, such a range might be for example across a pH of 5 to 9.

[0099] It can be seen that across this range in the example embodiment the fluorescence intensity varies by about a factor of two. Moreover, the carbon-based nanoparticles are found to remain chemically stable across this range. Such a combination of variation in fluorescence with chemical stability makes the carbon-based nanoparticles admirably suited for application in the method of the invention. Other nanoparticles exhibiting a similar luminescence variation across a similar pH range with good chemical stability across the range will be likely to be similarly useful for application in the method of the invention.

[0100] In practical use, the carbon-based nanoparticles are introduced as an aqueous tracer for example using a familiar technique into a hydrocarbon well, pipeline or formation; an aqueous produced fluid is obtained from the hydrocarbon well, pipeline or formation into which a proportion of the tracer has passed; a sample is taken, NaOH or another reagent with similar effects is added to modify the pH of the sample; and the modified sample is then analysed for the presence of the carbon-based nanoparticle.

[0101] The fluorescence intensity of the carbon-based nanoparticles in the sample is increased. The effect of the fluorescence attributable to the carbon-based nanoparticle tracer in the sample is enhanced relative to the background fluorescence attributable to residual organics. It becomes easier to distinguish the fluorescence of the tracer and the fluorescence of the residual organics. The effectiveness of the tracer is increased.

[0102] FIG. 5 provides a simple schematic of a method of monitoring a hydrocarbon reservoir 110 using such a tracer. The method comprises introducing a tracer 114 into the reservoir 110, producing fluid from the reservoir 110 and detecting the tracer 114 in the fluid so as to monitor the reservoir 110. In this example, the tracer 114 is introduced into the reservoir 110 in a release system 111. The tracer could also be injected (for example as in a water-flood application) or be there before production (for example in a hydraulic fracturing operation). The tracer 114 is released from the release system 111 and carried by the production flow 112 of the reservoir fluids to the surface where it is first treated as above to modify the pH and enhance the fluorescence effect and then detected using a suitable known apparatus and method. The reservoir 110 includes a surface facility 115 and a pH modification and a fluorescence detection apparatus is installed and the method carried out at the surface facility 115. Preferably the analysis is carried out on-line in real time.

Example Carbon Nanoparticle Synthesis Method

[0103] 30 mL of glutathione in formamide (10% w/v) was added to a sealed microwave reactor (100 mL in volume) and irradiated to maintain a temperature of 180° C. for 30 minutes. Once cooled the reaction product was added to acetone (60 mL) and cooled to 0° C. for 1 h. The mixture was then centrifugated at 10k RCF (relative centrifugal force) for 20 minutes. The liquid phase was discarded. Acetone (60 mL) was then added to the precipitated product followed by centrifugation at 10k RCF for 20 minutes. The precipitated product was then dispersed in deionised water (100 mL) and filtered through a 100 nm polyether sulfone filter.

Effect of Cysteine on the Fluorescence Properties of Nanoparticlees

[0104] Two 10 mL solutions of carbon nanoparticle material were prepared in water. To the first solution, 0.3 g of L-cysteine was added. The solution was magnetically stirred at room temperature for 1 hour and was then filtered through a 100 nm polyether sulfone filter. The second solution was retained as a control.

[0105] FIG. 6 shows the emission intensity of the cysteine treated product versus the control solution. As can be seen from the graph, emission intensity is significantly increased by cysteine compared to the control solution. This mechanism is distinct from the previous pH change mechanism.

Effect of L-Ascorbic Acid on the Fluorescence Properties of Nanoparticles

[0106] A stock solution of carbon nanoparticle material in water was prepared (Control). Further solutions were prepared as follows.

[0107] To 10 mL of the stock solution, 2M hydrochloric was added to change the pH to 4-5 (Acidified(HCl)).

[0108] To 10 mL of the stock solution, 0.3 g L-ascorbic acid was added, and the solution magnetically stirred for 30 minutes. The pH of this solution was 4-5 (Acidified(Ascorbic acid)).

[0109] FIG. 7 shows the emission intensity of the control and the two treated product solutions. As can be seen from the graph, ascorbic acid causes an increase in emission intensity between 600 and 700 nm compared to the control. However, this effect is not related to the pH change resulting from addition of the ascorbic acid. Causing a corresponding pH change using hydrochloric acid results in a decrease in emission intensity between 600 and 700 nm compared to the control. This is consistent with the graph shown in FIG. 4 which indicates a decrease in emission with a decrease in pH. As such, the increase in emission intensity with addition of ascorbic acid in this example is due to another mechanism distinct from pH change.

CONCLUSIONS

[0110] It is apparent that there are several different reagents and mechanisms which can be used to vary the luminescence behaviour of luminescent nanoparticles and/or of other luminescent species present in a fluid sample in order to more readily detect the luminescent nanoparticles in a fluid sample and determine the amount of nanoparticles present. While this invention has been particularly shown and described with reference to certain embodiments, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appended claims.