DETECTION OF PRODUCTION FLUID ADDITIVES USING SPIKING

Abstract

A method of detecting production fluid additives in a fluid conducting and containment system when the additive is below its effective dose. The method includes adding an additional surfactant containing chemical to a fluid until the point of micelle formation in order to determine the amount of additive in a system when it is below its effective dose.

Claims

1. A method of detecting production fluid additives in a fluid conducting and containment system comprising: a) taking a sample of a production fluid comprising an additive from the system; b) adding an optical marker and detecting an optical signal from a marker solution in the presence of micelles; c) if no micelles are detected, adding an additional micelle forming surfactant-containing chemical to the sample before, at the same time as, or after the marker solution until a micelle-related signal is generated; and d) determining the amount of additive in the sample as a function of the additional micelle forming surfactant-containing chemical added to the sample.

2. The method according to claim 1, wherein the additive is a corrosion inhibitor.

3. The method according to claim 1, further comprising the step of determining the critical micelle concentration for the additive being added to the system prior to step a).

4. The method according to claim 1, further comprising the step of diluting the sample prior to step a).

5. The method according to claim 1, wherein the additional micelle forming surfactant-containing chemical added to the sample is the additive in step a).

6. The method according claim 1, wherein the fluid conducting and containment system is a system used to screen, test, produce and process oil and gas, and their products.

7. The method according claim 1, wherein micelle formation is measured using laser diffraction, interferometry or imaging, spectroscopic means, hyperspectral imaging or flow cytometry.

8. The method according claim 1, wherein the fluid comprises one or more of water, oil, solids, gas, liquefied gas and/or emulsions.

9. The method according claim 1, wherein sampling is performed at one or more locations in the system.

10. The method according claim 1, further comprising the step of preparing at least one control sample.

11. The method according to claim 10, wherein salt is added to at least one of the control samples in order to assess the ionic strength of the sample.

12. The method according to claim 10, wherein an additional micelle-forming chemical is added to at least one of the control samples in order to assess if the sample contains a component that prevents the formation of micelles.

13. A kit for performing the method of claim 1 comprising: at least one marker solution containing an optically detectable marker.

14. The kit according to claim 13, further comprising: positive and negative controls.

15. The kit according to claim 13, further comprising: reference standards.

16. The kit according to claim 13, further comprising: a means to measure transmission of samples.

17. The kit according to claim 13, further comprising: a means to measure pH of samples.

18. The kit according to claim 13, further comprising: a means to filter samples.

19. The kit according to claim 13, further comprising: a means to centrifuge samples.

20. The kit according to claim 13, further comprising: instructions for performing the method.

21. The kit according to claim 13, further comprising: a micelle forming surfactant-containing chemical.

Description

[0039] The invention will be further described with reference to the drawings and figures, in which:

[0040] FIG. 1 shows a graph of optical signal intensity verses the amount of additive added to two field samples between 0-200 ppm; and

[0041] FIG. 2 shows a graph of optical signal intensity after adding micelle forming surfactant to samples containing corrosion inhibitor to enable micelle detection at the critical micelle concentration.

EXPERIMENT A: ADDING SURFACTANT CHEMICAL TO FIELD SAMPLES TO ENABLE MICELLE DETECTION

[0042] The following experiments were conducted on-site at an oil and gas processing facility. Spiking in 25 ppm of surfactant chemical, used to mitigate corrosion, into Field Sample A (110 ppm dose rate) resulted in a strong micelle signal, indicating the chemical was present in the spiked sample at a concentration above the CMC (FIG. 1). When the dose was lowered to 90 ppm no micelles were detected in Field Sample B. Spiking 25 ppm into Field Sample B, showed a signal around the CMC, while spiking in 50 ppm resulted in a chemical concentration in the spiked sample B above the CMC (FIG. 1). A dose of around 110-135 ppm would be expected to result in the presence of chemical above the CMC for this area of the system. As the dosage of chemical into the system was reduced the amount of chemical required to be added to the sample to detect micelles was increased.

[0043] Experiment B. Adding chemical to samples to demonstrate the impact fluid changes can have on the CMC

[0044] 50 mL of brine was added to a 100 mL volumetric flask which was then placed on a balance and weighed. 100 L of a commercially available formulated corrosion inhibitor (Aliphatic amine derivative) was added to the flask and the flask re-weighed to determine the mass of inhibitor added. The contents were gently swirled to ensure mixing without foam generation, the volume was adjusted to the graduated mark with the relevant brine, the flask capped and inverted carefully (10 times) to ensure homogeneity of the prepared 1,000 ppm solution. Each of the inhibitor-salt solutions were homogenous, with no droplet precipitation or haze observed at the time of use. The 1,000 ppm inhibitor solution was diluted with further diluent brine to give final concentrations of inhibitor. To 1980 L of the inhibitor brine solution was added 20 L of optical marker (Nile Red) through a positive displacement pipette. The cuvette was capped securely and inverted gently (5 times) to ensure homogeneity of solution but without causing the mixture to foam. Fluorescence readings were taken immediately upon complete mixing. The concentration of brine had a significant impact on critical micelle concentration:

[0045] 40,000 ppm chloride ion (CaCl.sub.2). CMC 41 ppm

[0046] 20,000 ppm chloride ion (CaCl.sub.2), CMC 51 ppm

[0047] In field fluids, the amount of micelle-forming surfactant that may be required to be added to a sample to form micelles will vary. This will reflect changes in the field fluids and micelles can help capture information on the influence of such changes on corrosion inhibitor effectiveness or availability.

[0048] 22 produced fluids were centrifuged prior to use (6000 rpm for 1 hour). After centrifugation, 10 mL of supernatant from each fluid was transferred to a glass vial and 50 L of 10,000 ppm Myristyltrimethylammonium bromide (micelle forming surfactant; MTAB) was added. This gave a 50 ppm MTAB solution for each of the produced fluids. The spiked samples were mixed well by inversion and then allowed to settle for ca 1 hour. After 1 hour, 5 mL of each spiked fluid was transferred to separate glass vialseach containing 0.29 g of NaCl. This amount of NaCl gave a 1 M NaCl brine, assuming no other salts were present in the produced fluid. The samples were mixed gently until all the salt dissolved and then left to settle for ca 1 hour. The 50 ppm spikes, with and without salt, were subsampled for analysis by mixing 2 mL of sample with 20 L of optical marker (Nile Red) and fluorescence determined, see FIG. 2.

[0049] For many samples micelle-related signal was very low, until the salt concentration was increasedB, E, F, O, P, X. Oil and gas field fluids can vary significantly: this might be in terms of water cut, salinity, production chemicals, type of hydrocarbon or solids. These differences can impact the critical micelle concentration which will be reflected in the amount of chemical required to be added to a sample before micelles are observed.

[0050] Experiment C: Adding micelle forming surfactant to samples containing corrosion inhibitor to enable micelle detection at the critical micelle concentration

[0051] The critical micelle concentration of a commercially available formulated corrosion inhibitor, whose primary ingredients were tall oil fatty acids and thioglycolic acid, was determined to be 25-30 ppm in 1M NaCl.

[0052] Solutions of 0, 5, 10, 15 and 20 ppm were prepared and then spiked with various amounts of the corrosion inhibitor until the CMC was reached. This was recorded compared to the CMC as originally determined. As shown in Table 1, all samples showed a good match i.e. the amount of chemical added plus the original concentration in the sample equalled the CMC determined for the chemical at the outset.

TABLE-US-00001 TABLE 1 Spike Calcu- Base conc. Total lated Differ- conc. for micelle conc. CMC ence (ppm) (ppm) (ppm) (ppm) (ppm) 0 22 22 25 to 30 3 5 21 26 25 to 30 In range 10 15 25 25 to 30 In range 15 15 30 25 to 30 In range 20 4 24 25 to 30 1

[0053] The invention relates to the issue of how to determine the amount of a production fluid additive if it is in a system below the effective dose. The effective, or optimal, dose is an amount of additive at which the critical micelle concentration is reached. For example, if it is known or has been determined that the critical micelle concentration for an additive is 100 ppm, then knowing that 10 ppm needs to be added to a sample to form micelles means that the sample is at 90 ppm. The spiked chemical may be added to the aqueous or hydrocarbon phase of a sample. This is to best mimic partitioning and behaviour in the systems.

[0054] The approach described here may also be applied to understand the impact system changes have on chemical availability. For example, an operator believes solids are going to be produced and questions if the chemical additive will adsorb to them. A sample from the system is taken and it is determined if micelles are present, and if not, how much additive is needed to be added to form them. Solids are added to another sample and additive added in order to determine if more chemical, which would indicate loss of chemical to the solids surface, is required. The same could be done for other potential system changes, such as water cut, hydrocarbon type, production chemicals and brine strength.

[0055] Additive micelles may be detected in a number of ways. For example, an imaging approach may be used. Micelles are, by definition, not truly water-soluble and exist as dispersed liquid particles. It is therefore possible to observe corrosion inhibitor micelles by optical means. If large enough (i.e. greater than the Abbe limit of about 0.5 m) then conventional microscopic imaging is possible and the images can be analysed using particle analysis software. Other optical means may also be used depending on the properties of the micelles.

[0056] In one embodiment, a compound capable of associating with a micelle to produce an amplified or detectable signal may be added. For example, a marker solution may be added to the fluid which creates or enhances a detectable property (e.g. fluorescence). The signal is amplified when associated with the micelle relative to the disassociated state and therefore increases the signal to noise ratio resulting in increased overall sensitivity. The alteration in signal might, for example, result from a change in the electronic environment of the marker molecule which varies the molecular dipole moment in the ground and excited states. These differences result in a relative modification of the quantised energy of light absorbed or emitted in spectroscopic processes and so can be measured experimentally, for example through absorption, transmission, fluorescence intensity, fluorescence wavelength, fluorescence polarisation or fluorescence lifetime. Examples of suitable optical markers are meropolymethines, pyridinium-N-phenolate betaines, phenoxazones, N,N-dialkylaminonaphthalenes, N,N-dialkylaminostyrenes, N,N-dialkylaminonitrobenzenes, coumarins, N,N-dialkylindoaniline, vinylquinoliums, arylaminonaphthalene sulfonates and 9-diethylamino-5-benzo[]phenoxazinone (Nile Red).

[0057] Due to these changes being strongly influenced by the polarity of the surrounding matrix, measurement of the light can be a probe for chemical environment. Alternatively, the marker may only be soluble in the micelle and solubility may determine whether a signal is generated or not, in either such case the signal may be colourimetric, absorbance, luminescent or fluorescent. Generally, UV and fluorescence measurements are faster than colourimetric alternatives which require an extraction step.

[0058] Micelles have distinct optical properties of shape and light diffusion, diffraction and reflection which allow them to be discriminated from other particles. Smaller particles may be imaged beyond the diffraction limit using, for example, dark-field imaging and/or Brownian motion analysis.

[0059] Another method that may be used for detecting and analysing the micelles is spectral analysis (spectroscopy). In complex fluids, such as those from oilfield production, there are likely to be a number of components arising from non-corrosion inhibitor origins which must be discriminated against in the analysis. One method of achieving this is by interrogating the analyte with light and recording the resulting spectral properties of the system. In one embodiment this may involve recording the bulk UV, visible or infrared absorption of light at a certain wavelength. The resulting absorption, either with or without the addition of a marker solution, may be indicative of the presence of micelles.

[0060] Alternatively, fluorescence emission, lifetime or polarisation could be used.

[0061] In an expansion on this, spectral resolution can be combined with an imaging system so that each recorded pixel will contain spectral information rather than just intensity. For example, fluorescence imaging can be used to measure the colour of the fluorescence emission, the colour emitted in response to the presence of corrosion inhibitor being different from the colour emitted in response to the presence of, for example, oil, sand or other additives. These methods can be broadly termed as spectral or hyperspectral imaging. In one embodiment, the spectrum imaged may just be a simple recording at three different wavelengths e.g. RGB, or it could include a full spectral scan across e.g. 500-900 nm.

[0062] Diffraction technologies may also be used to detect and monitor the micelles. Systems for measuring nano-particles involving light scattering or diffraction techniques may be used to determine the particle size of the micelles in solution and also the properties of those particles. In its simplest form the diffraction of light resulting from suspended particles in solution can be used to determine the presence, average particle size and the relative distribution of particles in the solution. Addition of supplementary sensing technology such as interferometry, impedance and zeta potential measurements can additionally characterise the system to provide discrimination between micelles and interfering oilfield species.

[0063] Other methods for detecting and monitoring micelle formation are based on particle interrogation and counting systems. For example, flow cytometry is a method of examining and sorting microscopic particles in a fluid. These systems are built to varying specifications and record parameters including particle volume, shape, size etc. They are often also associated with fluorescence detection in microbiological studies and combine this with light scatter analysis in systems such as a Fluorescence-Activated Cell Sorter (FACS). Such a device could be modified to measure micelles in material to provide a rich pool of data. Because micelle detection requires no antibody binding step the analysis would also be much faster than traditional flow cytometry and may be amenable to offshore use.

[0064] Useful information may be obtained from monitoring micelle formation. Indeed, the amount of micelles in the fluid is related to the degree of corrosion inhibition and efficiency of the inhibitor. In addition, analysis of the micelles (e.g. assessment of their number, size and shape) will provide information on the physico-chemical properties of the fluid. As stated above, there is a link between the critical micelle concentration and the optimal corrosion inhibition.